Insufficient observations near the origin of the Kuroshio have led to incomplete understanding of the intraseasonal variability(ISV)of the Kuroshio.Direct measurements of the Kuroshio velocity were performed with an a...Insufficient observations near the origin of the Kuroshio have led to incomplete understanding of the intraseasonal variability(ISV)of the Kuroshio.Direct measurements of the Kuroshio velocity were performed with an array of three profiler moorings(122.7°E,123°E,and 123.3°E)along 18°N from January 2018 to February 2020.The ISV of the Kuroshio at 18°N was investigated based on a combination of mooring observations and global high-resolution HYbrid Coordinate Ocean Model reanalysis data.The estimated time-averaged transport in the upper 350 m across the observation transect was 6.5±2.6 Sv(1.0 Sv=10^(6)m^(3)/s).Two significant ISV peaks at 50-60 and~100 d were recognized in the power spectra of the meridional velocity and transport.Further analysis indicated that the ISV at 50-60 d was caused by westward-propagating eddies at average propagation speed of~13 cm/s and wavelength of~635 km.Another ISV peak at~100 d was mainly caused by northward-propagating eddies generated in the North Equatorial Current region.Further investigation indicated that the ISV of the Kuroshio at 18°N is dominated by meridional transport,rather than by the zonal migration of the Kuroshio main axis.Our findings provide a better understanding of the ISV of the Kuroshio east of Luzon Island.展开更多
This work investigates the boreal-summer intraseasonal variability(ISV)of the precipitation over the lower reaches of the Yangtze River basin(LYRB)during 1979–2016,based on daily Climate Prediction Center global prec...This work investigates the boreal-summer intraseasonal variability(ISV)of the precipitation over the lower reaches of the Yangtze River basin(LYRB)during 1979–2016,based on daily Climate Prediction Center global precipitation data.The ISV of the summer monsoon rainfall over the LYRB is mainly dominated by the lower-frequency 12–20-day variability and the higher-frequency 8–12-day variability.The lower-frequency variability is found to be related to the northwestwardpropagating quasi-biweekly oscillation(QBWO)over the western North Pacific spanning the South China Sea(SCS)and Philippine Sea,while the higher-frequency variability is related to the southeastward propagating midlatitude wave train(MLWT).Moreover,not each active QBWO(MLWT)in the SCS(East Asia)can generate ISV components of the precipitation anomaly over the LYRB.The QBWO can change the rainfall significantly with the modulation of mean state precipitation,while the quasi-11-day mode mainly depends on the intensity of the MLWT rather than the mean precipitation change.These findings should enrich our understanding of the ISV of the East Asian summer monsoon and improve its predictability.展开更多
Using observations and numerical simulations,this study examines the intraseasonal variability of the surface zonal current(u ISV)over the equatorial Indian Ocean,highlighting the seasonal and spatial differences,and ...Using observations and numerical simulations,this study examines the intraseasonal variability of the surface zonal current(u ISV)over the equatorial Indian Ocean,highlighting the seasonal and spatial differences,and the causes of the differences.Large-amplitude u ISV occurs in the eastern basin at around 80°–90°E and near the western boundary at 45°–55°E.In the eastern basin,the u ISV is mainly caused by the atmospheric intraseasonal oscillations(ISOs),which explains 91%of the standard deviation of the total u ISV.Further analysis suggests that it takes less than ten days for the intraseasonal zonal wind stress to generate the u ISV through the directly forced Kelvin and Rossby waves.Driven by the stronger zonal wind stress associated with the Indian summer monsoon ISO(MISO),the eastern u ISV in boreal summer(May to October)is about 1.5 times larger than that in boreal winter(November to April).In the western basin,both the atmospheric ISOs and the oceanic internal instabilities contribute substantially to the u ISV,and induce stronger u ISV in boreal summer.Energy budget analysis suggests that the mean flow converts energy to the intraseasonal current mainly through barotropic instabilities.展开更多
This study investigates the structure and propagation of intraseasonal sea surface temperature（SST） variability in the South China Sea（SCS） on the 30-60-day timescale during boreal summer（May-September）. TRMM-ba...This study investigates the structure and propagation of intraseasonal sea surface temperature（SST） variability in the South China Sea（SCS） on the 30-60-day timescale during boreal summer（May-September）. TRMM-based SST, GODAS oceanic reanalysis and ERA-Interim atmospheric reanalysis datasets from 1998 to 2013 are used to examine quantitatively the atmospheric thermodynamic and oceanic dynamic mechanisms responsible for its formation. Power spectra show that the 30-60-day SST variability is predominant, accounting for 60% of the variance of the 10-90-day variability over most of the SCS. Composite analyses demonstrate that the 30-60-day SST variability is characterized by the alternate occurrence of basin-wide positive and negative SST anomalies in the SCS, with positive（negative） SST anomalies accompanied by anomalous northeasterlies（southwesterlies）. The transition and expansion of SST anomalies are driven by the monsoonal trough-ridge seesaw pattern that migrates northward from the equator to the northern SCS. Quantitative diagnosis of the composite mixed-layer heat budgets shows that, within a strong 30-60-day cycle, the atmospheric thermal forcing is indeed a dominant factor, with the mixed-layer net heat flux（MNHF） contributing around 60% of the total SST tendency, while vertical entrainment contributes more than 30%. However, the entrainment-induced SST tendency is sometimes as large as the MNHF-induced component, implying that ocean processes are sometimes as important as surface fluxes in generating the30-60-day SST variability in the SCS.展开更多
The mean velocity structure and variability of the Kuroshio east of Taiwan,China,were investigated using mooring observations acquired at 23°N/122°E between January 2016 and May 2017.Power spectrum analysis ...The mean velocity structure and variability of the Kuroshio east of Taiwan,China,were investigated using mooring observations acquired at 23°N/122°E between January 2016 and May 2017.Power spectrum analysis reveals marked intraseasonal variability in 70–95 days in the meridional Kuroshio velocity in the upper 800 m.Hybrid Coordinate Ocean Model assimilation data adequately reproduce variations of the Kuroshio.Westward propagating mesoscale eddies that originated from the Subtropical Countercurrent play an important role in intraseasonal variability in the Kuroshio velocity.Cyclonic(anticyclonic)eddies are often associated with negative(positive)sea surface height anomaly,resulting in positive(negative)potential vorticity in the subsurface layer of the eddy center,which decreases(increases)isopycnal slope and then weakens(strengthens)the Kuroshio.When anticyclonic(cyclonic)eddies are active,the Kuroshio axis moves off shore(inshore).Corresponding to the Kuroshio intraseasonal variability(ISV),the variation of the intermediate water salinity also had a signifi cant ISV induced by the mesoscale eddies.展开更多
The modulation of winter intraseasonal variability(ISV)by the Atlantic Multidecadal Oscillation(AMO)is investigated through three sets of reanalysis data and numerical experiments with the NCEP’s atmospheric general ...The modulation of winter intraseasonal variability(ISV)by the Atlantic Multidecadal Oscillation(AMO)is investigated through three sets of reanalysis data and numerical experiments with the NCEP’s atmospheric general circulation model(AGCM).Results show that the positive phase of the AMO tends to intensify ISV activity over the northern Atlantic and shift ISV activity over the Ural Mountains toward the south,causing weakened ISV activity at 200 hPa in the north to the Urals and intensified activity in the south.The modulation of ISV activity by the AMO over the Urals is then explored through comparison of the composite evolution of anomalous ISV cases for the different AMO phases.Fewer ISV cases are found in the AMO positive phase than the negative phase,but no substantial difference in the temporal evolution of anomalous ISV events between the two opposing phases of the AMO.Thus,the AMO exerts its modulation through influencing the occurrence frequency of ISV events,rather than their development or evolution processes.A similar result is seen in the AGCM sensitivity experiments.展开更多
Based on Soil Moisture Active Passive sea surface salinity(SSS)data from April 2015 to August 2020,combined with Objectively Analyzed Air-Sea Heat Flux and other observational data and Hybrid Coordinate Ocean Model(HY...Based on Soil Moisture Active Passive sea surface salinity(SSS)data from April 2015 to August 2020,combined with Objectively Analyzed Air-Sea Heat Flux and other observational data and Hybrid Coordinate Ocean Model(HYCOM)data,this work explores the characteristics and mechanisms of the intraseasonal variability of SSS in the southeastern Arabian Sea(SEAS).The results show that the intraseasonal variability of SSS in the SEAS is very significant,especially the strongest intraseasonal signal in SSS,which is located along the northeast monsoon current(NMC)path south of the Indian Peninsula.There are remarkable seasonal differences in intraseasonal SSS variability,which is very weak in spring and summer and much stronger in autumn and winter.This strong intraseasonal variability in autumn and winter is closely related to the Madden-Julian Oscillation(MJO)event during this period.The northeast wind anomaly in the Bay of Bengal(BOB)associated with the active MJO phase strengthens the East India Coastal Current and NMC and consequently induces more BOB low-salinity water to enter the SEAS,causing strong SSS fluctuations.In addition,MJO-related precipitation further amplifies the intraseasonal variability of SSS in SEAS.Based on budget analysis of the mixed layer salinity using HYCOM data,it is shown that horizontal salinity advection(especially zonal advection)dominates the intraseasonal variability of mixed layer salinity and that surface freshwater flux has a secondary role.展开更多
We investigated the intraseasonal variability of equatorial Pacific subsurface temperature and its relationship with El Nino-Southern Oscillation(ENSO) using Self-Organizing Maps(SOM) analysis.Variation in intraseason...We investigated the intraseasonal variability of equatorial Pacific subsurface temperature and its relationship with El Nino-Southern Oscillation(ENSO) using Self-Organizing Maps(SOM) analysis.Variation in intraseasonal subsurface temperature is mainly found along the thermocline.The SOM patterns concentrate in basin-wide seesaw or sandwich structures along an east-west axis.Both the seesaw and sandwich SOM patterns oscillate with periods of 55 to 90 days,with the sequence of them showing features of equatorial intraseasonal Kelvin wave,and have marked interannual variations in their occurrence frequencies.Further examination shows that the interannual variability of the SOM patterns is closely related to ENSO;and maxima in composite interannual variability of the SOM patterns are located in the central Pacific during CP El Nino and in the eastern Pacific during EP El Nino.The se results imply that some of the ENSO forcing is manife sted through changes in the occurrence frequency of intraseasonal patterns,in which the change of the intraseasonal Kelvin wave plays an important role.展开更多
This study investigates the intraseasonal variability (ISV) of rainfall in Tanzania during the March-April-May (MAM) season, specifically identifying the dominant peaks of ISV in rainfall for that period. The 5-day ru...This study investigates the intraseasonal variability (ISV) of rainfall in Tanzania during the March-April-May (MAM) season, specifically identifying the dominant peaks of ISV in rainfall for that period. The 5-day running mean during the MAM season reveals that Tanzania experienced an irregular pattern of wet and dry days in the year 2022, indicating the presence of ISV that led to fluctuations in weather patterns. Moreover, the study identifies the dominant peak date, where a significant peak was observed in the 10 - 25-day range, showing that ISV exhibits a quasi-biweekly oscillation around 17 days, with composite evolution from day −8 to day +8 after filtering, and day 0 marking peak rainfall. Furthermore, composite atmospheric circulation analysis reveals critical interactions with ISV. Geopotential height wind patterns at 850 hPa indicate that negative/positive geopotential height anomalies over the Western Indian Ocean and Mozambique Channel enhance low-level convergence/divergence of moisture, resulting in wet/dry phase, meanwhile strong positive geopotential height anomalies at 200 hPa are associated with the upper-level divergence that supports peak rainfall (day 0). During Lag −4 to Lag 0, the results revealed dominant negative OLR anomalies (−18 to −20 W/m2) indicating peak dates of ISV of rainfall while the transition to positive OLR anomalies after Lag +2 showed the starting point of a dry phase of ISV. Also, at the initial phase (Lag −8 to Lag −6), weak positive and limited moisture flux anomalies were observed over the region, while in the peak phase (Lag 0), strong positive anomalies dominated, reflecting intense moisture convergence from both the South West Indian Ocean (SWIO) and the Congo Basin, associated with maximum ISV of rainfall activity. After lag 0, transition into the dry phase (Lag +6 to Lag +8), negative anomalies developed as moisture transport diminishes and winds shift, suppressing convergence over Tanzania, leading to the dry phase. The results highlight the significance of integrating ISV patterns into weather forecasting and disaster preparedness to reduce the risks associated with extreme rainfall events like floods and droughts. Additionally, the findings offer valuable insights for managing water resources, planning agriculture, and enhancing climate resilience in areas of Tanzania that depend on rainfall.展开更多
Intraseasonal Oscillation (ISO) which is the eastward-propagating disturbance with a period of 10 - 60 days has been the topic of interest since its discovery by Madden-Julian in 1972. Many researchers have published ...Intraseasonal Oscillation (ISO) which is the eastward-propagating disturbance with a period of 10 - 60 days has been the topic of interest since its discovery by Madden-Julian in 1972. Many researchers have published their work on ISO, yet they all agree that there is no clear understanding of this matter. By using daily observed surface temperature (T2m), this study reveals the presence of significant biweekly ISO over Tanzania, a period shorter than the anticipated Madden-Julian Oscillation (MJO) period of 30 to 60 days. It also reveals significant changes in wind direction when comparing the cold phase to the warm phase, highlighting a distinct atmospheric circulation pattern associated with each phase. Furthermore, the analysis reveals the presence of MJO-like eastward movement of pressure systems in the Subtropical High region, which is associated with this variability. This study presents a new analysis by providing a detailed analysis of the intraseasonal variability (ISV) of temperature over Tanzania, focusing on understanding the 2020 spatial-temporal patterns within the October-November-December (OND) season that may play a role in weather forecasting, agricultural planning, climate adaptation, reducing heat-related illnesses and contributing to the international effort to refine climate models and predictability.展开更多
This study investigates how the El Nino-Southern Oscillation(ENSO)modulates the intraseasonal variability(ISV)of Pacific-Japan(PJ)teleconnection pattern.The PJ index during boreal summer is constructed from the empiri...This study investigates how the El Nino-Southern Oscillation(ENSO)modulates the intraseasonal variability(ISV)of Pacific-Japan(PJ)teleconnection pattern.The PJ index during boreal summer is constructed from the empirical orthogonal function(EOF)of the 850-hPa zonal wind(U850)anomalies.Distinct periods of the PJ index are found during El Nino and La Nina summers.Although ISV of the PJ pattern is significant during 10-25 days for both types of summers,it peaks on Days 30 and 60 in El Nino and La Nina summers respectively.During El Nino summers,the 30-day ISV of PJ pattern is related to the northwestward propagating intraseasonal oscillation(ISO)over the western North Pacific(WNP),which is originated from the tropical Indian Ocean(IO).During La Nina summers,the 60-day ISV of PJ pattern is related to the northeastward propagating ISO from the tropical IO.The low-frequency ISV modes in both El Nino and La Nina summers are closely related to the boreal summer ISO(BSISO),and the high-frequency ISV modes over WNP are related to the quasi-biweekly oscillation.The underlying mechanisms for these different evolutions are also discussed.展开更多
Features of the dominant modes of surface air temperature(SAT)on the intraseasonal timescale over the mid-highlatitude Eurasia(MHE)during boreal summer(June-September)are investigated based on the ERA5 reanalysis data...Features of the dominant modes of surface air temperature(SAT)on the intraseasonal timescale over the mid-highlatitude Eurasia(MHE)during boreal summer(June-September)are investigated based on the ERA5 reanalysis data from 1979 to 2016.The intraseasonal variability(ISV)of SAT over MHE is primarily characterized by an eastward propagation along 60°N,which is found to impact the regional weather in China,including summertime extreme hot and cool events.The forecast skill and potential predictability of the ISV of SAT over MHE are assessed for 5 dynamical models that have participated in the subseasonal-to-seasonal(S2 S)prediction project,by analyzing12 years’(1999-2010)model reforecast/hindcast data.By using the principal component(PC)index of the leading intraseasonal SAT modes as a predictand,we found that the forecast skill for ISV of SAT can reach out to 11-17 days,and the ECMWF model exhibits the best score.All the S2 S models tend to show 1)a relatively higher skill for strong intraseasonal oscillation(ISO)cases,2)a systematic underestimate of the amplitude of the SAT ISV signal,and 3)different skills during different phases of ISO cases.Analysis of potential predictability based on the perfectmodel assumption reveals a 4-6-day skill gap for most models,and the skill gap also varies among different phases of ISO events.The results imply the need for continued development of operational forecasting systems to improve the actual prediction skills for the ISV of SAT over MHE.展开更多
The intraseasonal timescale is critical in Central Africa, because the resources of the region are highly rainfall dependent. In this paper, we use 1DD GPCP rainfall product to investigate the differences in the space...The intraseasonal timescale is critical in Central Africa, because the resources of the region are highly rainfall dependent. In this paper, we use 1DD GPCP rainfall product to investigate the differences in the space-time structures of the 25 - 70-day intraseasonal variability of rainfall, over the Western Central Africa (WCA) and the Eastern Central Africa (ECA), with different climate features. The results of Empirical Orthogonal Functions (EOFs) analysis have shown that the amount of variance explained by the leading EOFs is greater in ECA (58.4%) than in WCA (49.8%). For both WCA and ECA, the power spectra of the Principal Components (PCs) peaked around 40 days, indicating a MJO signal. The seasonality of ISO is evident, but this seasonality is much noticeable in ECA where almost 80% of the total yearly ISO power occurs during November-April season, against only around 60% for WCA. Moreover, the lagged cross correlations computed between WCA and ECA PCs time series showed that most of the WCA PCs led ECA PCs time series with a timescale of 8 - 12 days, revealing that the eastward propagation could potentially be the relationship between WCA and ECA modes. The interannual variations in the ISO activity are weak in WCA, when compared with ECA where the signal exhibits larger interannual variations, quite linked with ENSO.展开更多
Rwanda is a landlocked country in central-eastern Africa.As a country highly dependent on rain-fed agriculture,Rwanda is vulnerable to rainfall variability.Observational data show that there are two rainy seasons in R...Rwanda is a landlocked country in central-eastern Africa.As a country highly dependent on rain-fed agriculture,Rwanda is vulnerable to rainfall variability.Observational data show that there are two rainy seasons in Rwanda,i.e.,the long rainy season and the short rainy season.This study mainly focuses on the dominant intraseasonal rainfall mode during the long rainy season(February-May),and evaluates the forecast skill for the intraseasonal variability(ISV)over Rwanda and its surrounding regions in a state-of-the-art dynamic model.During the long rainy season,observational results reveal that the dominant intraseasonal rainfall mode in Rwanda exhibits a significant variability on the 10-25-day time scale.One-point-correlation analysis further unveils that the 10-25-day intraseasonal rainfall variability in Rwanda co-varies with that in its adjacent areas,indicating that the overall 10-25-day rainfall variability in Rwanda and its adjacent regions(8°S-3°N,29°-37°E)should be considered collectively when studying the dominant intraseasonal rainfall variability in Rwanda.Composite results show that the development of the 10-25-day rainfall variability is associated with the anomalous westerly wind in Rwanda and its surrounding regions,which may trace back to a pair of westward-propagating equatorial Rossby waves.Based on the observational findings,an ISO_rainfall_index and an ISO_wind_index are proposed for quantitatively evaluating the forecast skill.The ECMWF model has a comparable skill in predicting the wind index and the rainfall index,with both indices showing a skill of 18 days.展开更多
Using hindcasts of the Beijing Climate Center Climate System Model, the relationships between interannual variability （IAV） and intraseasonal variability （ISV） of the Asian-western Pacific summer monsoon are diagn...Using hindcasts of the Beijing Climate Center Climate System Model, the relationships between interannual variability （IAV） and intraseasonal variability （ISV） of the Asian-western Pacific summer monsoon are diagnosed. Predictions show reasonable skill with respect to some basic characteristics of the ISV and IAV of the western North Pacific summer monsoon （WNPSM） and the Indian summer monsoon （ISM）. However, the links between the seasonally averaged ISV （SAISV） and seasonal mean of ISM are overestimated by the model. This deficiency may be partially attributable to the overestimated frequency of long breaks and underestimated frequency of long active spells of ISV in normal ISM years, although the model is capable of capturing the impact of ISV on the seasonal mean by its shift in the probability of phases. Furthermore, the interannual relationships of seasonal mean, SAISV, and seasonally averaged long-wave variability （SALWV; i.e., the part with periods longer than the intraseasonal scale） of the WNPSM and ISM with SST and low-level circulation are examined. The observed seasonal mean, SAISV, and SALWV show similar correlation patterns with SST and atmospheric circulation, but with different details. However, the model presents these correlation distributions with unrealistically small differences among different scales, and it somewhat overestimates the teleconnection between monsoon and tropical central-eastern Pacific SST for the ISM, but underestimates it for the WNPSM, the latter of which is partially related to the too-rapid decrease in the impact of E1 Nifio-Southern Oscillation with forecast time in the model.展开更多
The surroundings of the Bay of Bengal(Bo B)suffer a lot from the extreme rainfall events during Indian summer monsoon(ISM).Previous studies have proved that the sea-air interaction is an important factor for the monso...The surroundings of the Bay of Bengal(Bo B)suffer a lot from the extreme rainfall events during Indian summer monsoon(ISM).Previous studies have proved that the sea-air interaction is an important factor for the monsoonal precipitation.Using the 6th Coupled Modol Inter-comparison Project(CMIP6)models,this study examined the biases of surface heat flux,which is the main connection between atmosphere and ocean.Results show that although CMIP6 have a better simulation of intraseasonal sea surface temperature(SST)anomalies over Bo B than the previous ones,the“atmospheric blockage”still delays the response of latent heat flux to the oceanic forcing.Specifically,during the increment of positive latent heat flux in CMIP6,the negative contribution from wind effects covers most of the positive contribution from humidity effects,due to the underestimate of humidity effects.Further diagnostic analysis denote that the surface air humidity has a quarter of a phase ahead of warm SST in observation,but gets wet along with the warm SST accordingly in most CMIP6 models.As a result,the simulated transfer of intraseasonal moisture flux is hindered between ocean and atmosphere.Therefore,as a bridge between both sides,the atmospheric boundary layer is essential for a better sea-air coupled simulation,especially when the atmospheric and the oceanic variabilities involved in a climate model becomes increasingly sophisticated.The surface air humidity and boundary layer processes require more attention as well as better simulations.展开更多
The gridded sea level anomaly（SLA） data-set provided by AVISO is used to track the propagation of intraseasonal Kelvin waves in the Indonesian Throughflow（ITF） region. The large root mean square of intraseasonal S...The gridded sea level anomaly（SLA） data-set provided by AVISO is used to track the propagation of intraseasonal Kelvin waves in the Indonesian Throughflow（ITF） region. The large root mean square of intraseasonal SLA along the Sumatra and Java coast is closely related to the propagation of intraseasonal Kelvin waves that derive from the equatorial Indian Ocean. These Kelvin waves are further found to propagate following different pathways at the Lombok Strait. Pathway A propagates eastward throughout the Sumba Strait and Savu Sea to reach the Ombai Strait. Pathway B penetrates into Lombok and propagates northward to reach the Makassar Strait. Pathway C propagates southeastward along the southwest coast of the Sumba Island. The equatorial Kelvin waves take around 15 days to travel from the equatorial Indian Ocean to Lombok Strait, and around 5 days to penetrate into the Makassar and Ombai straits. The Kelvin wave-induced SLA persists in the ITF region for an additional 5 days and then diminishes subsequently. The phase speeds of these intraseasonal Kelvin waves along Pathways A, B, and C are 1.91–2.86, 1.69, and 1.96 m s^-1,respectively—in agreement with the first two baroclinic modes of Kelvin waves.展开更多
A regional reanalysis product-China Ocean Reanalysis（CORA）-has been developed for the China＇s seas and the adjacent areas. In this study, the intraseasonal variabilities（ISVs） in CORA are assessed by comparing wi...A regional reanalysis product-China Ocean Reanalysis（CORA）-has been developed for the China＇s seas and the adjacent areas. In this study, the intraseasonal variabilities（ISVs） in CORA are assessed by comparing with observations and two other reanalysis products（ECCO2 and SODA）. CORA shows a better performance in capturing the intraseasonal sea surface temperatures（SSTs） and the intraseasonal sea surface heights（SSHs） than ECCO2 and SODA do, probably due to its high resolution, stronger response to the intraseasonal forcing in the atmosphere（especially the Madden-Julian Oscillation）, and more available regional data for assimilation. But at the subsurface, the ISVs in CORA are likely to be weaker than reality, which is probably attributed to rare observational data for assimilation and weak diapycnal eddy diffusivity in the CORA model. According to the comparison results, CORA is a good choice for the study related to variabilities at the surface, but cares have to be taken for the study focusing on the subsurface processes.展开更多
Traditionally,the estimated volume transport of the North Equatorial Current/Undercurrent(NEC/NEUC)is based on geostrophic equations and/or model results;however,direct observational evidence has not been acquired.We ...Traditionally,the estimated volume transport of the North Equatorial Current/Undercurrent(NEC/NEUC)is based on geostrophic equations and/or model results;however,direct observational evidence has not been acquired.We focused on one-year mooring observation data collected along 130°E and calculated the NEC/NEUC volume transport and explore its variability.Results show that the mean NEC and NEUC volume transports calculated from the mean velocity structures in the upper 950 m are 39 Sv and 6 Sv,respectively.Analysis of daily mooring data indicated that the volume transport of the NEC is approximately 52(±14)Sv and the volume transport of the NEUC is approximately 18(±13)Sv.A significant 40-day variation existed for the volume transport of both the NEC and NEUC.Overall,the intraseasonal variability of the NEC is vertically coherent with that of the NEUC.Observations indicated that the NEUC has three cores centered at approximately 8.5°N(~500 m),12.5°N(~700 m),and 17.5°N(~900 m),of which the middle core(12.5°N)is the strongest.The 40-day variability of the NEC and NEUC is related to the variability of local wind stress curl anomalies among various Madden-Julian Oscillation phases.When local wind field generates a negative(positive)wind stress curl anomaly,a weaker NEC(NEUC)and stronger NEUC(NEC)would occur.展开更多
The role of sea surface temperature(SST)variability in the pre-monsoonal(April to July)intraseasonal oscillation(ISO)over the South China Sea(SCS)is investigated using the Community Earth System Model Version 2(CESM2)...The role of sea surface temperature(SST)variability in the pre-monsoonal(April to July)intraseasonal oscillation(ISO)over the South China Sea(SCS)is investigated using the Community Earth System Model Version 2(CESM2).An Atmospheric Model Intercomparison Project(AMIP)simulation forced by daily sea surface temperatures(SSTs)derived from a parallel coupled general circulation model(CGCM)run was compared with observations and the mother coupled simulation.In the coupled model,the SST warming leads the peak convection about 1/4 period as in observations.The paralell uncoupled model fails to simulate this phase relationship,implying the importance of air-sea coupling in reproducing realistic ISO.Due to the near-quadrature phase relationship between SST and precipitation ISOs during the ISO events,it is difficult to distinguish the active/passive role of SST from observations alone.Significant correlation in intraseasonal precipitation between the daily SST-forced AMIP and mother CGCM runs indicates that SST plays a role in driving the atmospheric ISO.展开更多
基金Supported by the National Natural Science Foundation of China(Nos.41976011,42022040)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB42010102)+1 种基金the Shandong Provincial Natural Science Foundation(No.ZR2020JQ18)Shijian HU is a member of the CAS Interdisciplinary Innovation Team(No.JCTD2020-12)。
文摘Insufficient observations near the origin of the Kuroshio have led to incomplete understanding of the intraseasonal variability(ISV)of the Kuroshio.Direct measurements of the Kuroshio velocity were performed with an array of three profiler moorings(122.7°E,123°E,and 123.3°E)along 18°N from January 2018 to February 2020.The ISV of the Kuroshio at 18°N was investigated based on a combination of mooring observations and global high-resolution HYbrid Coordinate Ocean Model reanalysis data.The estimated time-averaged transport in the upper 350 m across the observation transect was 6.5±2.6 Sv(1.0 Sv=10^(6)m^(3)/s).Two significant ISV peaks at 50-60 and~100 d were recognized in the power spectra of the meridional velocity and transport.Further analysis indicated that the ISV at 50-60 d was caused by westward-propagating eddies at average propagation speed of~13 cm/s and wavelength of~635 km.Another ISV peak at~100 d was mainly caused by northward-propagating eddies generated in the North Equatorial Current region.Further investigation indicated that the ISV of the Kuroshio at 18°N is dominated by meridional transport,rather than by the zonal migration of the Kuroshio main axis.Our findings provide a better understanding of the ISV of the Kuroshio east of Luzon Island.
基金This work was supported by the National Natural Science Foundation of China[grant number 41420104002]the Natural Science Foundation of Jiangsu Province[grant numbers BK20150907 and 14KJA170002].
文摘This work investigates the boreal-summer intraseasonal variability(ISV)of the precipitation over the lower reaches of the Yangtze River basin(LYRB)during 1979–2016,based on daily Climate Prediction Center global precipitation data.The ISV of the summer monsoon rainfall over the LYRB is mainly dominated by the lower-frequency 12–20-day variability and the higher-frequency 8–12-day variability.The lower-frequency variability is found to be related to the northwestwardpropagating quasi-biweekly oscillation(QBWO)over the western North Pacific spanning the South China Sea(SCS)and Philippine Sea,while the higher-frequency variability is related to the southeastward propagating midlatitude wave train(MLWT).Moreover,not each active QBWO(MLWT)in the SCS(East Asia)can generate ISV components of the precipitation anomaly over the LYRB.The QBWO can change the rainfall significantly with the modulation of mean state precipitation,while the quasi-11-day mode mainly depends on the intensity of the MLWT rather than the mean precipitation change.These findings should enrich our understanding of the ISV of the East Asian summer monsoon and improve its predictability.
基金The National Natural Science Foundation of China under contract Nos 41822602,41976016 and 4207602the Strategic Priority Research Program of Chinese Academy of Sciences under contract Nos XDB42000000,XDA20060502 and XDA15020901+4 种基金the Guangdong Basic and Applied Basic Research Foundation under contract No.2021A1515011534the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)under contract Nos GML2019ZD0302 and GML2019ZD0306the fund of Innovation Academy of South China Sea Ecology and Environmental Engineering,Chinese Academy of Sciences under contract No.ISEE2021ZD01the fund of State Key Laboratory of Tropical Oceanography under contract No.LTOZZ2002the fund of Youth Innovation Promotion Association of Chinese Academy of Sciences under contract No.Y2021093.
文摘Using observations and numerical simulations,this study examines the intraseasonal variability of the surface zonal current(u ISV)over the equatorial Indian Ocean,highlighting the seasonal and spatial differences,and the causes of the differences.Large-amplitude u ISV occurs in the eastern basin at around 80°–90°E and near the western boundary at 45°–55°E.In the eastern basin,the u ISV is mainly caused by the atmospheric intraseasonal oscillations(ISOs),which explains 91%of the standard deviation of the total u ISV.Further analysis suggests that it takes less than ten days for the intraseasonal zonal wind stress to generate the u ISV through the directly forced Kelvin and Rossby waves.Driven by the stronger zonal wind stress associated with the Indian summer monsoon ISO(MISO),the eastern u ISV in boreal summer(May to October)is about 1.5 times larger than that in boreal winter(November to April).In the western basin,both the atmospheric ISOs and the oceanic internal instabilities contribute substantially to the u ISV,and induce stronger u ISV in boreal summer.Energy budget analysis suggests that the mean flow converts energy to the intraseasonal current mainly through barotropic instabilities.
基金supported by the SOA Program on Global Change and Air–Sea Interactions (Grant No.GASI-IPOVAI03)the National Basic Research Program of China (Grant No.2014CB953902)+1 种基金the Natural Science Foundation of China (Grant Nos.91537103 and 41375087)the Priority Research Program of the Chinese Academy of Sciences (Grant Nos.QYZDY-SSWDQC018 and XDA11010402)
文摘This study investigates the structure and propagation of intraseasonal sea surface temperature（SST） variability in the South China Sea（SCS） on the 30-60-day timescale during boreal summer（May-September）. TRMM-based SST, GODAS oceanic reanalysis and ERA-Interim atmospheric reanalysis datasets from 1998 to 2013 are used to examine quantitatively the atmospheric thermodynamic and oceanic dynamic mechanisms responsible for its formation. Power spectra show that the 30-60-day SST variability is predominant, accounting for 60% of the variance of the 10-90-day variability over most of the SCS. Composite analyses demonstrate that the 30-60-day SST variability is characterized by the alternate occurrence of basin-wide positive and negative SST anomalies in the SCS, with positive（negative） SST anomalies accompanied by anomalous northeasterlies（southwesterlies）. The transition and expansion of SST anomalies are driven by the monsoonal trough-ridge seesaw pattern that migrates northward from the equator to the northern SCS. Quantitative diagnosis of the composite mixed-layer heat budgets shows that, within a strong 30-60-day cycle, the atmospheric thermal forcing is indeed a dominant factor, with the mixed-layer net heat flux（MNHF） contributing around 60% of the total SST tendency, while vertical entrainment contributes more than 30%. However, the entrainment-induced SST tendency is sometimes as large as the MNHF-induced component, implying that ocean processes are sometimes as important as surface fluxes in generating the30-60-day SST variability in the SCS.
基金Supported by the National Key Research and Development Plan(Nos.2017YFC1403401,2016YFC1400505)the Global Climate Changes and Air-sea Interaction Program(Nos.GASI-02-PAC-ST-Wwin,GASIIPOVAI-01-06)+1 种基金the National Natural Science Foundation of China(No.41676005)the NSFC Innovative Group Grant(No.41421005)。
文摘The mean velocity structure and variability of the Kuroshio east of Taiwan,China,were investigated using mooring observations acquired at 23°N/122°E between January 2016 and May 2017.Power spectrum analysis reveals marked intraseasonal variability in 70–95 days in the meridional Kuroshio velocity in the upper 800 m.Hybrid Coordinate Ocean Model assimilation data adequately reproduce variations of the Kuroshio.Westward propagating mesoscale eddies that originated from the Subtropical Countercurrent play an important role in intraseasonal variability in the Kuroshio velocity.Cyclonic(anticyclonic)eddies are often associated with negative(positive)sea surface height anomaly,resulting in positive(negative)potential vorticity in the subsurface layer of the eddy center,which decreases(increases)isopycnal slope and then weakens(strengthens)the Kuroshio.When anticyclonic(cyclonic)eddies are active,the Kuroshio axis moves off shore(inshore).Corresponding to the Kuroshio intraseasonal variability(ISV),the variation of the intermediate water salinity also had a signifi cant ISV induced by the mesoscale eddies.
基金jointly supported by the Strategic Priority Research Program of the Chinese Academy of Sciences[grant number XDA19070401]the National Natural Science Foundation of China[grant numbers 41790473 and41421004]the Fundamental Research Funds for the Central Universities
文摘The modulation of winter intraseasonal variability(ISV)by the Atlantic Multidecadal Oscillation(AMO)is investigated through three sets of reanalysis data and numerical experiments with the NCEP’s atmospheric general circulation model(AGCM).Results show that the positive phase of the AMO tends to intensify ISV activity over the northern Atlantic and shift ISV activity over the Ural Mountains toward the south,causing weakened ISV activity at 200 hPa in the north to the Urals and intensified activity in the south.The modulation of ISV activity by the AMO over the Urals is then explored through comparison of the composite evolution of anomalous ISV cases for the different AMO phases.Fewer ISV cases are found in the AMO positive phase than the negative phase,but no substantial difference in the temporal evolution of anomalous ISV events between the two opposing phases of the AMO.Thus,the AMO exerts its modulation through influencing the occurrence frequency of ISV events,rather than their development or evolution processes.A similar result is seen in the AGCM sensitivity experiments.
基金The National Natural Science Foundation of China under contract No.42130406the Scientific Research Foundation of Third Institute of Oceanography,Ministry of Natural Resources under contract Nos 2022027 and 2018030+1 种基金the Asian Countries Maritime Cooperation Fund under contract No.99950410the Global Change and Air-Sea InteractionⅡunder contract No.GASI-04-WLHY-01.
文摘Based on Soil Moisture Active Passive sea surface salinity(SSS)data from April 2015 to August 2020,combined with Objectively Analyzed Air-Sea Heat Flux and other observational data and Hybrid Coordinate Ocean Model(HYCOM)data,this work explores the characteristics and mechanisms of the intraseasonal variability of SSS in the southeastern Arabian Sea(SEAS).The results show that the intraseasonal variability of SSS in the SEAS is very significant,especially the strongest intraseasonal signal in SSS,which is located along the northeast monsoon current(NMC)path south of the Indian Peninsula.There are remarkable seasonal differences in intraseasonal SSS variability,which is very weak in spring and summer and much stronger in autumn and winter.This strong intraseasonal variability in autumn and winter is closely related to the Madden-Julian Oscillation(MJO)event during this period.The northeast wind anomaly in the Bay of Bengal(BOB)associated with the active MJO phase strengthens the East India Coastal Current and NMC and consequently induces more BOB low-salinity water to enter the SEAS,causing strong SSS fluctuations.In addition,MJO-related precipitation further amplifies the intraseasonal variability of SSS in SEAS.Based on budget analysis of the mixed layer salinity using HYCOM data,it is shown that horizontal salinity advection(especially zonal advection)dominates the intraseasonal variability of mixed layer salinity and that surface freshwater flux has a secondary role.
基金the National Natural Science Foundation of China (NSFC)(Nos.41976027,41976011,41730534,41476017,41576014)the Bureau of International Cooperation Chinese Academy of Sciences (No.132B61KYSB20170005)
文摘We investigated the intraseasonal variability of equatorial Pacific subsurface temperature and its relationship with El Nino-Southern Oscillation(ENSO) using Self-Organizing Maps(SOM) analysis.Variation in intraseasonal subsurface temperature is mainly found along the thermocline.The SOM patterns concentrate in basin-wide seesaw or sandwich structures along an east-west axis.Both the seesaw and sandwich SOM patterns oscillate with periods of 55 to 90 days,with the sequence of them showing features of equatorial intraseasonal Kelvin wave,and have marked interannual variations in their occurrence frequencies.Further examination shows that the interannual variability of the SOM patterns is closely related to ENSO;and maxima in composite interannual variability of the SOM patterns are located in the central Pacific during CP El Nino and in the eastern Pacific during EP El Nino.The se results imply that some of the ENSO forcing is manife sted through changes in the occurrence frequency of intraseasonal patterns,in which the change of the intraseasonal Kelvin wave plays an important role.
文摘This study investigates the intraseasonal variability (ISV) of rainfall in Tanzania during the March-April-May (MAM) season, specifically identifying the dominant peaks of ISV in rainfall for that period. The 5-day running mean during the MAM season reveals that Tanzania experienced an irregular pattern of wet and dry days in the year 2022, indicating the presence of ISV that led to fluctuations in weather patterns. Moreover, the study identifies the dominant peak date, where a significant peak was observed in the 10 - 25-day range, showing that ISV exhibits a quasi-biweekly oscillation around 17 days, with composite evolution from day −8 to day +8 after filtering, and day 0 marking peak rainfall. Furthermore, composite atmospheric circulation analysis reveals critical interactions with ISV. Geopotential height wind patterns at 850 hPa indicate that negative/positive geopotential height anomalies over the Western Indian Ocean and Mozambique Channel enhance low-level convergence/divergence of moisture, resulting in wet/dry phase, meanwhile strong positive geopotential height anomalies at 200 hPa are associated with the upper-level divergence that supports peak rainfall (day 0). During Lag −4 to Lag 0, the results revealed dominant negative OLR anomalies (−18 to −20 W/m2) indicating peak dates of ISV of rainfall while the transition to positive OLR anomalies after Lag +2 showed the starting point of a dry phase of ISV. Also, at the initial phase (Lag −8 to Lag −6), weak positive and limited moisture flux anomalies were observed over the region, while in the peak phase (Lag 0), strong positive anomalies dominated, reflecting intense moisture convergence from both the South West Indian Ocean (SWIO) and the Congo Basin, associated with maximum ISV of rainfall activity. After lag 0, transition into the dry phase (Lag +6 to Lag +8), negative anomalies developed as moisture transport diminishes and winds shift, suppressing convergence over Tanzania, leading to the dry phase. The results highlight the significance of integrating ISV patterns into weather forecasting and disaster preparedness to reduce the risks associated with extreme rainfall events like floods and droughts. Additionally, the findings offer valuable insights for managing water resources, planning agriculture, and enhancing climate resilience in areas of Tanzania that depend on rainfall.
文摘Intraseasonal Oscillation (ISO) which is the eastward-propagating disturbance with a period of 10 - 60 days has been the topic of interest since its discovery by Madden-Julian in 1972. Many researchers have published their work on ISO, yet they all agree that there is no clear understanding of this matter. By using daily observed surface temperature (T2m), this study reveals the presence of significant biweekly ISO over Tanzania, a period shorter than the anticipated Madden-Julian Oscillation (MJO) period of 30 to 60 days. It also reveals significant changes in wind direction when comparing the cold phase to the warm phase, highlighting a distinct atmospheric circulation pattern associated with each phase. Furthermore, the analysis reveals the presence of MJO-like eastward movement of pressure systems in the Subtropical High region, which is associated with this variability. This study presents a new analysis by providing a detailed analysis of the intraseasonal variability (ISV) of temperature over Tanzania, focusing on understanding the 2020 spatial-temporal patterns within the October-November-December (OND) season that may play a role in weather forecasting, agricultural planning, climate adaptation, reducing heat-related illnesses and contributing to the international effort to refine climate models and predictability.
基金Supported by the National Natural Science Foundation of China(41420104002)National Key Research and Development Program of China(2018YFC1505804)。
文摘This study investigates how the El Nino-Southern Oscillation(ENSO)modulates the intraseasonal variability(ISV)of Pacific-Japan(PJ)teleconnection pattern.The PJ index during boreal summer is constructed from the empirical orthogonal function(EOF)of the 850-hPa zonal wind(U850)anomalies.Distinct periods of the PJ index are found during El Nino and La Nina summers.Although ISV of the PJ pattern is significant during 10-25 days for both types of summers,it peaks on Days 30 and 60 in El Nino and La Nina summers respectively.During El Nino summers,the 30-day ISV of PJ pattern is related to the northwestward propagating intraseasonal oscillation(ISO)over the western North Pacific(WNP),which is originated from the tropical Indian Ocean(IO).During La Nina summers,the 60-day ISV of PJ pattern is related to the northeastward propagating ISO from the tropical IO.The low-frequency ISV modes in both El Nino and La Nina summers are closely related to the boreal summer ISO(BSISO),and the high-frequency ISV modes over WNP are related to the quasi-biweekly oscillation.The underlying mechanisms for these different evolutions are also discussed.
基金Supported by the National Key Research and Development Program of China(2018YFC1505803 and 2018YFC1505905)Natural Science Foundation of Jiangsu Province(BK20210660 and BK20191404)National Natural Science Foundation of China(42088101)。
文摘Features of the dominant modes of surface air temperature(SAT)on the intraseasonal timescale over the mid-highlatitude Eurasia(MHE)during boreal summer(June-September)are investigated based on the ERA5 reanalysis data from 1979 to 2016.The intraseasonal variability(ISV)of SAT over MHE is primarily characterized by an eastward propagation along 60°N,which is found to impact the regional weather in China,including summertime extreme hot and cool events.The forecast skill and potential predictability of the ISV of SAT over MHE are assessed for 5 dynamical models that have participated in the subseasonal-to-seasonal(S2 S)prediction project,by analyzing12 years’(1999-2010)model reforecast/hindcast data.By using the principal component(PC)index of the leading intraseasonal SAT modes as a predictand,we found that the forecast skill for ISV of SAT can reach out to 11-17 days,and the ECMWF model exhibits the best score.All the S2 S models tend to show 1)a relatively higher skill for strong intraseasonal oscillation(ISO)cases,2)a systematic underestimate of the amplitude of the SAT ISV signal,and 3)different skills during different phases of ISO cases.Analysis of potential predictability based on the perfectmodel assumption reveals a 4-6-day skill gap for most models,and the skill gap also varies among different phases of ISO events.The results imply the need for continued development of operational forecasting systems to improve the actual prediction skills for the ISV of SAT over MHE.
文摘The intraseasonal timescale is critical in Central Africa, because the resources of the region are highly rainfall dependent. In this paper, we use 1DD GPCP rainfall product to investigate the differences in the space-time structures of the 25 - 70-day intraseasonal variability of rainfall, over the Western Central Africa (WCA) and the Eastern Central Africa (ECA), with different climate features. The results of Empirical Orthogonal Functions (EOFs) analysis have shown that the amount of variance explained by the leading EOFs is greater in ECA (58.4%) than in WCA (49.8%). For both WCA and ECA, the power spectra of the Principal Components (PCs) peaked around 40 days, indicating a MJO signal. The seasonality of ISO is evident, but this seasonality is much noticeable in ECA where almost 80% of the total yearly ISO power occurs during November-April season, against only around 60% for WCA. Moreover, the lagged cross correlations computed between WCA and ECA PCs time series showed that most of the WCA PCs led ECA PCs time series with a timescale of 8 - 12 days, revealing that the eastward propagation could potentially be the relationship between WCA and ECA modes. The interannual variations in the ISO activity are weak in WCA, when compared with ECA where the signal exhibits larger interannual variations, quite linked with ENSO.
基金jointly supported by the National Key Research and Development Program of China[grant number 2019YFC1510004]and the LASG Open Project.
文摘Rwanda is a landlocked country in central-eastern Africa.As a country highly dependent on rain-fed agriculture,Rwanda is vulnerable to rainfall variability.Observational data show that there are two rainy seasons in Rwanda,i.e.,the long rainy season and the short rainy season.This study mainly focuses on the dominant intraseasonal rainfall mode during the long rainy season(February-May),and evaluates the forecast skill for the intraseasonal variability(ISV)over Rwanda and its surrounding regions in a state-of-the-art dynamic model.During the long rainy season,observational results reveal that the dominant intraseasonal rainfall mode in Rwanda exhibits a significant variability on the 10-25-day time scale.One-point-correlation analysis further unveils that the 10-25-day intraseasonal rainfall variability in Rwanda co-varies with that in its adjacent areas,indicating that the overall 10-25-day rainfall variability in Rwanda and its adjacent regions(8°S-3°N,29°-37°E)should be considered collectively when studying the dominant intraseasonal rainfall variability in Rwanda.Composite results show that the development of the 10-25-day rainfall variability is associated with the anomalous westerly wind in Rwanda and its surrounding regions,which may trace back to a pair of westward-propagating equatorial Rossby waves.Based on the observational findings,an ISO_rainfall_index and an ISO_wind_index are proposed for quantitatively evaluating the forecast skill.The ECMWF model has a comparable skill in predicting the wind index and the rainfall index,with both indices showing a skill of 18 days.
基金supported by the National Natural Science Foundation of China (Grant Nos.41305057, 41275076, 41105069, and 41375081)the National Basic Research Program of China (Grant Nos.2010CB951903 and 2014CB953900)the LCS Youth Fund (2014)
文摘Using hindcasts of the Beijing Climate Center Climate System Model, the relationships between interannual variability （IAV） and intraseasonal variability （ISV） of the Asian-western Pacific summer monsoon are diagnosed. Predictions show reasonable skill with respect to some basic characteristics of the ISV and IAV of the western North Pacific summer monsoon （WNPSM） and the Indian summer monsoon （ISM）. However, the links between the seasonally averaged ISV （SAISV） and seasonal mean of ISM are overestimated by the model. This deficiency may be partially attributable to the overestimated frequency of long breaks and underestimated frequency of long active spells of ISV in normal ISM years, although the model is capable of capturing the impact of ISV on the seasonal mean by its shift in the probability of phases. Furthermore, the interannual relationships of seasonal mean, SAISV, and seasonally averaged long-wave variability （SALWV; i.e., the part with periods longer than the intraseasonal scale） of the WNPSM and ISM with SST and low-level circulation are examined. The observed seasonal mean, SAISV, and SALWV show similar correlation patterns with SST and atmospheric circulation, but with different details. However, the model presents these correlation distributions with unrealistically small differences among different scales, and it somewhat overestimates the teleconnection between monsoon and tropical central-eastern Pacific SST for the ISM, but underestimates it for the WNPSM, the latter of which is partially related to the too-rapid decrease in the impact of E1 Nifio-Southern Oscillation with forecast time in the model.
基金The National Natural Science Foundation of China under contract Nos 42076001 and 42106003the Scientific Research Fund of the Second Institute of Oceanography,Ministry of Natural Resources under contract No.JB2206。
文摘The surroundings of the Bay of Bengal(Bo B)suffer a lot from the extreme rainfall events during Indian summer monsoon(ISM).Previous studies have proved that the sea-air interaction is an important factor for the monsoonal precipitation.Using the 6th Coupled Modol Inter-comparison Project(CMIP6)models,this study examined the biases of surface heat flux,which is the main connection between atmosphere and ocean.Results show that although CMIP6 have a better simulation of intraseasonal sea surface temperature(SST)anomalies over Bo B than the previous ones,the“atmospheric blockage”still delays the response of latent heat flux to the oceanic forcing.Specifically,during the increment of positive latent heat flux in CMIP6,the negative contribution from wind effects covers most of the positive contribution from humidity effects,due to the underestimate of humidity effects.Further diagnostic analysis denote that the surface air humidity has a quarter of a phase ahead of warm SST in observation,but gets wet along with the warm SST accordingly in most CMIP6 models.As a result,the simulated transfer of intraseasonal moisture flux is hindered between ocean and atmosphere.Therefore,as a bridge between both sides,the atmospheric boundary layer is essential for a better sea-air coupled simulation,especially when the atmospheric and the oceanic variabilities involved in a climate model becomes increasingly sophisticated.The surface air humidity and boundary layer processes require more attention as well as better simulations.
基金supported by the National Natural Science Foundation of China(NSFC)[grant numbers 41476025,41506036,41306031]NSFC-Shandong Joint Fund for Marine Science Research Centers[grant number U1406404]+1 种基金China Postdoctoral Science Foundation Funded Project[grant number 2014M561883]Postdoctoral Innovation Foundation of Shandong Province[grant number 201403019]
文摘The gridded sea level anomaly（SLA） data-set provided by AVISO is used to track the propagation of intraseasonal Kelvin waves in the Indonesian Throughflow（ITF） region. The large root mean square of intraseasonal SLA along the Sumatra and Java coast is closely related to the propagation of intraseasonal Kelvin waves that derive from the equatorial Indian Ocean. These Kelvin waves are further found to propagate following different pathways at the Lombok Strait. Pathway A propagates eastward throughout the Sumba Strait and Savu Sea to reach the Ombai Strait. Pathway B penetrates into Lombok and propagates northward to reach the Makassar Strait. Pathway C propagates southeastward along the southwest coast of the Sumba Island. The equatorial Kelvin waves take around 15 days to travel from the equatorial Indian Ocean to Lombok Strait, and around 5 days to penetrate into the Makassar and Ombai straits. The Kelvin wave-induced SLA persists in the ITF region for an additional 5 days and then diminishes subsequently. The phase speeds of these intraseasonal Kelvin waves along Pathways A, B, and C are 1.91–2.86, 1.69, and 1.96 m s^-1,respectively—in agreement with the first two baroclinic modes of Kelvin waves.
基金The National Natural Science Foundation of China under contract Nos 41206178,41376034,41276018 and 41321004the Fundamental Research Funds for the Central Universities under contract No.2014B30514+1 种基金the open project supplied by the Key Laboratory of Marine Environmental Information Technology,National Marine Data and Information Service,State Oceanic Administration:Effectiveness on the intraseasonal scale in CORA(2015–2016)the Predictability of Ocean Dynamical System Project under Contract No.151053
文摘A regional reanalysis product-China Ocean Reanalysis（CORA）-has been developed for the China＇s seas and the adjacent areas. In this study, the intraseasonal variabilities（ISVs） in CORA are assessed by comparing with observations and two other reanalysis products（ECCO2 and SODA）. CORA shows a better performance in capturing the intraseasonal sea surface temperatures（SSTs） and the intraseasonal sea surface heights（SSHs） than ECCO2 and SODA do, probably due to its high resolution, stronger response to the intraseasonal forcing in the atmosphere（especially the Madden-Julian Oscillation）, and more available regional data for assimilation. But at the subsurface, the ISVs in CORA are likely to be weaker than reality, which is probably attributed to rare observational data for assimilation and weak diapycnal eddy diffusivity in the CORA model. According to the comparison results, CORA is a good choice for the study related to variabilities at the surface, but cares have to be taken for the study focusing on the subsurface processes.
基金Supported by the National Natural Science Foundation of China(Nos.41576014,41976011)。
文摘Traditionally,the estimated volume transport of the North Equatorial Current/Undercurrent(NEC/NEUC)is based on geostrophic equations and/or model results;however,direct observational evidence has not been acquired.We focused on one-year mooring observation data collected along 130°E and calculated the NEC/NEUC volume transport and explore its variability.Results show that the mean NEC and NEUC volume transports calculated from the mean velocity structures in the upper 950 m are 39 Sv and 6 Sv,respectively.Analysis of daily mooring data indicated that the volume transport of the NEC is approximately 52(±14)Sv and the volume transport of the NEUC is approximately 18(±13)Sv.A significant 40-day variation existed for the volume transport of both the NEC and NEUC.Overall,the intraseasonal variability of the NEC is vertically coherent with that of the NEUC.Observations indicated that the NEUC has three cores centered at approximately 8.5°N(~500 m),12.5°N(~700 m),and 17.5°N(~900 m),of which the middle core(12.5°N)is the strongest.The 40-day variability of the NEC and NEUC is related to the variability of local wind stress curl anomalies among various Madden-Julian Oscillation phases.When local wind field generates a negative(positive)wind stress curl anomaly,a weaker NEC(NEUC)and stronger NEUC(NEC)would occur.
基金Supported by the National Natural Science Foundation of China(No.42090042)the Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(No.2019BT02H594)the Chinese Academy of Sciences(Nos.XDB42010304,133244KYSB20190031,183311KYSB20200015,SCSIO202201)。
文摘The role of sea surface temperature(SST)variability in the pre-monsoonal(April to July)intraseasonal oscillation(ISO)over the South China Sea(SCS)is investigated using the Community Earth System Model Version 2(CESM2).An Atmospheric Model Intercomparison Project(AMIP)simulation forced by daily sea surface temperatures(SSTs)derived from a parallel coupled general circulation model(CGCM)run was compared with observations and the mother coupled simulation.In the coupled model,the SST warming leads the peak convection about 1/4 period as in observations.The paralell uncoupled model fails to simulate this phase relationship,implying the importance of air-sea coupling in reproducing realistic ISO.Due to the near-quadrature phase relationship between SST and precipitation ISOs during the ISO events,it is difficult to distinguish the active/passive role of SST from observations alone.Significant correlation in intraseasonal precipitation between the daily SST-forced AMIP and mother CGCM runs indicates that SST plays a role in driving the atmospheric ISO.
