This paper documents a study to examine the sensitivity to cloud droplet effective radius and liquid water path and the alleviation the energy imbalance at the top of the atmosphere and at the surface in the latest ve...This paper documents a study to examine the sensitivity to cloud droplet effective radius and liquid water path and the alleviation the energy imbalance at the top of the atmosphere and at the surface in the latest version of the Grid-point Atmospheric Model of the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics （LASG）, Institute of Atmospheric Physics （IAP） （GAMIL1.1.0）. Considerable negative biases in all flux components, and thus an energy imbalance, are found in GAMIL1.1.0. In order to alleviate the energy imbalance, two modifications, namely an increase in cloud droplet effective radius and a decrease in cloud liquid water path, have been made to the cloud properties used in GAMIL. With the increased cloud droplet effective radius, the single scattering albedo of clouds is reduced, and thus the reflection of solar radiation into space by clouds is reduced and the net solar radiation flux at the top of the atmosphere is increased. With the reduced cloud optical depth, the net surface shortwave radiation flux is increased, causing a net warming over the land surface. This results in an increase in both sensible and latent heat fluxes over the land regions, which is largely balanced by the increased terrestrial radiation fluxes. Consequently, the energy balance at the top of atmosphere and at the surface is achieved with energy flux components consistent with available satellite observations.展开更多
Arctic clouds strongly influence the regional radiation balance, temperature, melting of sea ice, and freezing of sea water. Despite their importance, there is a lack of systematic and reliabie observations of Arctic ...Arctic clouds strongly influence the regional radiation balance, temperature, melting of sea ice, and freezing of sea water. Despite their importance, there is a lack of systematic and reliabie observations of Arctic clouds. The CloudSat satellite launched in 2006 with a 94GHz Cloud Profiling Radar （CPR） may contribute to close this gap. Here we compare one of the key parameters, the cloud liquid water path （LWP） retrieved from CloudSat observations and from microwave radiometer （MWR） data taken during the ASCOS （Arctic Summer Cloud Ocean Study） cruise of the research vessel Oden from August to September 2008. Over the 45 days of the ASCOS cruise, collocations closer than 3 h and 100 km were found in only 9 d, and collocations closer than 1 h and 30 km in only 2 d. The poor correlations in the scatter plots of the two LWP retrievals can be explained by the patchiness of the cloud cover in these two days （August 5th and September 7th）, as confirmed by coincident MODIS （Moderate-resolution Imaging Spectroradiome- ter） images. The averages of Oden-observed LWP values are systematically higher （40-70 g m-2） than the corresponding CloudSat observations （0-50 g m2）. These are cases of generally low LWP with presumably small droplets, and may be explained by the little sensitivity of the CPR to small droplets or by the surface clutter.展开更多
The Microwave Radiation Imager （MWRI） on board Chinese Fengyun-3 （FY-3） satellites provides measurements at 10.65, 18.7, 23.8, 36.5, and 89.0 GHz with both horizontal and vertical polarization channels. Brightness...The Microwave Radiation Imager （MWRI） on board Chinese Fengyun-3 （FY-3） satellites provides measurements at 10.65, 18.7, 23.8, 36.5, and 89.0 GHz with both horizontal and vertical polarization channels. Brightness temperature measurements of those channels with their central frequencies higher than 19 GHz from satellite-based microwave imager radiometers had traditionally been used to retrieve cloud liquid water path （LWP） over ocean. The results show that the lowest frequency channels are the most appropriate for retrieving LWP when its values are large. Therefore, a modified LWP retrieval algorithm is developed for retrieving LWP of different magnitudes involving not only the high frequency channels but also the lowest frequency channels of FY-3 MWRI. The theoretical estimates of the LWP retrieval errors are between 0.11 and 0.06 mm for 10.65- and 18.7-GHz channels and between 0.02 and 0.04 mm for 36.5- and 89.0-GHz channels. It is also shown that the brightness temperature observations at 10.65 GHz can be utilized to better retrieve the LWP greater than 3 mm in the eyewall region of Super Typhoon Neoguri （2014）. The spiral structure of clouds within and around Typhoon Neoguri can be well captured by combining the LWP retrievals from different frequency channels.展开更多
Quantitative estimates of liquid water path （LWP） in clouds using satellite measurements are critical to understanding of cloud properties and the assessment of global climate change. In this paper, the relationship...Quantitative estimates of liquid water path （LWP） in clouds using satellite measurements are critical to understanding of cloud properties and the assessment of global climate change. In this paper, the relationship between microwave brightness temperature （TB） and LWP in the nonprecipitating clouds is studied by using satellite microwave measurements from the TRMM Microwave Imager （TMI） onboard the Tropical Rainfall Measuring Mission （TRMM）, together with a radiative transfer model for microwave radiance calculations. Radiative transfer modeling shows that the sensitivity is higher at both 37.0- and 85.5-GHz horizontal polarization channels for the LWP retrievals. Also, the differences between the retrieved values responding to TBs of various channels and the theoretical values are displayed by the model. Based upon above simulations, with taking into account the factor of resolution and retrieval bias for a single,channel, a nonprecipitating cloud LWP in the summer subtropical marine environment retrieval algorithm is formulated by the combination of the two TMI horizontal polarization channels, 37.0 and 85.5 GHz. Moreover,by using TMI measurements （1Bll）, this algorithm is applied to retrieving respectively LWPs for clear sky, nonprecipitating clouds, and typhoon precipitating clouds. In the clear sky case, the LWP cl^anges from -1 to 1 g m-2, and its mean value is about 10^-5 g m^-2. It indicates that, using this combination retrieval algorithm, there are no obvious systemic deviations when the LWP is low enough. The LWP values varying from 0 to 1000 g m^-2 in nonprecipitating clouds are reasonable, and its distribution pattern is very similar to the detected results in the visible channel of Visible and Infrared Scanner （VIRS） on the TRMM. In typhoon precipitating clouds, there is much more proportion of high LWP in the mature phase than the early stage. When surface rainfall rate is lower than 5 mm h^-1, the LWP increases with increasing rainfall rate.展开更多
In the application of the physical iterative method to retrieve millimeter-wave radar liquid water content(LWC)and liquid water path(LWP),particle parameter scheme is the main factor affecting retrieval performance.In...In the application of the physical iterative method to retrieve millimeter-wave radar liquid water content(LWC)and liquid water path(LWP),particle parameter scheme is the main factor affecting retrieval performance.In this paper,synchronous measurements of an airborne millimeter-wave radar and a hot-wire probe in stratus cloud are used to compare the LWC retrievals of the oceanic and continental particle parameter scheme with diameter less than 50μm and the particle parameter scheme with diameter less than 500μm and 1500μm(scheme 1,scheme 2,scheme 3,and scheme4,respectively).The results show that the particle parameter scheme needs to be selected according to the reflectivity factor when using the physical iterative method to retrieve the LWC and LWP.When the reflectivity factor is less than-30 d BZ,the retrieval error of scheme 1 is the minimum.When the reflectivity factor is greater than-30 d BZ,the retrieval error of scheme 4 is the minimum.Based on the reflectance factor value,the LWP retrievals of scheme 4 are closer to the measurements,the average relative bias is 5.2%,and the minimum relative bias is 4.4%.Compared with other schemes,scheme 4 seems to be more useful for the LWC and LWP retrieval of stratus cloud in China.展开更多
液态云水路径(liquid water path,LWP)和可降水量(precipitable water vapor,PWV)是描述天气和气候的两个重要物理量。目前,针对液态云水路径和可降水量的直接观测较少,特别是在我国干旱半干旱黄土高原地区,至今没有获得系统的观测值。...液态云水路径(liquid water path,LWP)和可降水量(precipitable water vapor,PWV)是描述天气和气候的两个重要物理量。目前,针对液态云水路径和可降水量的直接观测较少,特别是在我国干旱半干旱黄土高原地区,至今没有获得系统的观测值。本文利用兰州大学半干旱气候与环境监测站(SACOL)近两年的微波辐射仪观测资料,分析了黄土高原半干旱区液态云水路径和可降水量的变化特征。首先引入Liljegren et al.(2001)的反演方法并加以改进,计算得到适合黄土高原地区的反演参数,利用改进后的反演方法计算近两年的液态云水路径和可降水量。分析结果显示,与TP/WVP-3000型12通道微波辐射计的直接输出结果相比,本文反演结果与实际情况更加吻合。在SACOL代表的黄土高原地区,95%的云水路径值都在150g/m2以下,95%的可降水量值都在3cm以下。由于SACOL的降水受亚洲季风的影响,液态云水路径日均值冬季最小,秋季最大,其日变化规律显示半干旱区液态云水路径大体上呈双峰分布,峰值主要出现在日出和日落时分。卫星反演资料的年变化趋势与地基反演结果比较吻合。因此,运用卫星反演的液态云水路径来分析我国西北地区的空中云水资源是一种比较可信的手段。展开更多
采用NASA地球观测系统（EOS）“云与地球辐射能量系统（CERES）”2002年7月至2004年6月CERES SSF Aqua MODIS Edition 1B云资料，对天山山区和塔克拉玛干沙漠云水资源进行了研究。得到的结果不仅包括云量、云液态水柱含量，还包括云滴...采用NASA地球观测系统（EOS）“云与地球辐射能量系统（CERES）”2002年7月至2004年6月CERES SSF Aqua MODIS Edition 1B云资料，对天山山区和塔克拉玛干沙漠云水资源进行了研究。得到的结果不仅包括云量、云液态水柱含量，还包括云滴尺度，为无人区的人工增水作业和天气气候研究提供了基础数据。与以往的卫星观测云气候全球数据集相比，该资料具有更高的空间分辨率，且其观测仪器和云反演方法得到了进一步改善，因此其结果较以往更可信。研究结果表明，两地区云参量年变化规律不尽相同，在数值上有很大差别。除了动力条件和气候背景以外，这可能与沙尘气溶胶可以影响云的物理特性和生命期有关。由年变化来看，天山山区的月平均总云量为47％～72％，而塔克拉玛干沙漠为12％～50％；天山山区低云的月平均液态水柱含量为56．6～96．0g／cm^2，高云为30．5—59．8g／cm^2。而塔克拉玛干沙漠低云的月平均液态水柱含量为19．4～43．9g／cm^2，高云为9．3～59．0g／cm^2；天山山区的月平均云滴半径低云为12．6～16．0μm，高云为8．6-14．8μm。而塔克拉玛干沙漠地区低云云滴半径8．8～11．3μm，高云为6．1—11．1μm。展开更多
基于德国RPG公司研制的14通道地基微波辐射计(RPG-HATRPO-G3)反演的2014年10月至2015年9月济南地区的水汽和液态水产品,分析了济南地区水汽和云液态水不同季节的月变化、日变化特征及其在强对流天气与小雨天气中的变化趋势。结果表明:2...基于德国RPG公司研制的14通道地基微波辐射计(RPG-HATRPO-G3)反演的2014年10月至2015年9月济南地区的水汽和液态水产品,分析了济南地区水汽和云液态水不同季节的月变化、日变化特征及其在强对流天气与小雨天气中的变化趋势。结果表明:2014年10月至2015年9月济南地区柱大气积分水汽量(Integrated Water Vapour,IWV)具有明显的月变化特征,其变化趋势与多年(1981—2010年)月平均降水量相关性较好,IWV夏季最高、冬季最低,四季IWV均具有弱的日变化特征,四季IWV标准偏差按照夏季、秋季、春季、冬季的顺序递减。对于济南地区春季、夏季、秋季3个季节有云无雨和降水前后液态水路径(Liquid Water Path,LWP)的数据,春季LWP可用数据量最少,夏季LWP可用数据量最多;月LWP在0—200 g·m^(-2)范围内的数据占总数据的比例最多,LWP数值越大,其所占比例越小。月LWP大于1000 g·m^(-2)数据的比例随着夏季的临近和降水量的逐渐增加也呈增加的趋势。IWV和LWP在强对流过程发生前均明显增长,数值大于1000 g·m^(-2)的LWP数据比例为53.41%;而小雨天气发生前IWV呈波动上升的趋势,LWP仅在临近降水时才明显增大,LWP数值主要分布在0—200 g·m^(-2)之间,占总数据的比例为86.56%。展开更多
选取热带测雨卫星(Tropical Rainfall Measuring Mission,TRMM)微波成像仪(TRMM Microwave Imager,TMI)液态水路径(liquid water path,LWP)轨道像元数据为研究对象,探讨了将瞬时探测以及逐月的像元数据进行格点化(0.1°、0.25°...选取热带测雨卫星(Tropical Rainfall Measuring Mission,TRMM)微波成像仪(TRMM Microwave Imager,TMI)液态水路径(liquid water path,LWP)轨道像元数据为研究对象,探讨了将瞬时探测以及逐月的像元数据进行格点化(0.1°、0.25°、0.5°、1.0°和2.5°五种格点分辨率)时,格点数据的失真情况。对TMI瞬时探测的个例分析结果表明,细分辨率(0.1°、0.25°和0.5°)格点能保留原始像元数据的细节;而随着网格变粗,细节受到较大的平滑。因此对于中尺度到天气尺度的天气系统分析而言,将卫星轨道数据处理到网格尺度不大于0.5°的格点更合适。对逐月LWP像元资料格点化处理的分析表明,细分辨率格点能保留LWP空间分布细节,尽管5种分辨率下LWP的概率密度分布(probability density function,PDF)均相近。因此,对月尺度及以上的气候分析研究而言,格点尺度大小对卫星像元数据格点化的影响不显著。最后利用本实验室计算的TMI/LWP格点数据与欧洲中期数值预报中心再分析资料(European Centre for Medium-range Weather Forecasts Interim reanalysis,ERA-Interim)和NCEP再分析资料(NCEP Climate Forecast System Reanalysis,NCEP CFSR)进行了对比,发现两种再分析资料都高估了LWP;TMI/LWP格点数据与两种再分析资料LWP的多年变化趋势大致相同。展开更多
基金This work was jointly supported by the 973 Project(Grant No.2005CB321703)the National Natural Science Foundation of China(Grant No.40221503)the Chinese Academy of Sciences International Partnership Creative Group entitled"The Climate System Model Development and Application Studies".
文摘This paper documents a study to examine the sensitivity to cloud droplet effective radius and liquid water path and the alleviation the energy imbalance at the top of the atmosphere and at the surface in the latest version of the Grid-point Atmospheric Model of the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics （LASG）, Institute of Atmospheric Physics （IAP） （GAMIL1.1.0）. Considerable negative biases in all flux components, and thus an energy imbalance, are found in GAMIL1.1.0. In order to alleviate the energy imbalance, two modifications, namely an increase in cloud droplet effective radius and a decrease in cloud liquid water path, have been made to the cloud properties used in GAMIL. With the increased cloud droplet effective radius, the single scattering albedo of clouds is reduced, and thus the reflection of solar radiation into space by clouds is reduced and the net solar radiation flux at the top of the atmosphere is increased. With the reduced cloud optical depth, the net surface shortwave radiation flux is increased, causing a net warming over the land surface. This results in an increase in both sensible and latent heat fluxes over the land regions, which is largely balanced by the increased terrestrial radiation fluxes. Consequently, the energy balance at the top of atmosphere and at the surface is achieved with energy flux components consistent with available satellite observations.
基金ASCOS was made possible by grants from DAMOCLES and the Knut and Alice Wallenberg Foundation,and was organized by the Swedish Polar Research Secretariat
文摘Arctic clouds strongly influence the regional radiation balance, temperature, melting of sea ice, and freezing of sea water. Despite their importance, there is a lack of systematic and reliabie observations of Arctic clouds. The CloudSat satellite launched in 2006 with a 94GHz Cloud Profiling Radar （CPR） may contribute to close this gap. Here we compare one of the key parameters, the cloud liquid water path （LWP） retrieved from CloudSat observations and from microwave radiometer （MWR） data taken during the ASCOS （Arctic Summer Cloud Ocean Study） cruise of the research vessel Oden from August to September 2008. Over the 45 days of the ASCOS cruise, collocations closer than 3 h and 100 km were found in only 9 d, and collocations closer than 1 h and 30 km in only 2 d. The poor correlations in the scatter plots of the two LWP retrievals can be explained by the patchiness of the cloud cover in these two days （August 5th and September 7th）, as confirmed by coincident MODIS （Moderate-resolution Imaging Spectroradiome- ter） images. The averages of Oden-observed LWP values are systematically higher （40-70 g m-2） than the corresponding CloudSat observations （0-50 g m2）. These are cases of generally low LWP with presumably small droplets, and may be explained by the little sensitivity of the CPR to small droplets or by the surface clutter.
基金Supported by the National Natural Science Foundation of China(91337218 and 41475103)China Meteorological Administration Special Public Welfare Research Fund(GYHY201406008)
文摘The Microwave Radiation Imager （MWRI） on board Chinese Fengyun-3 （FY-3） satellites provides measurements at 10.65, 18.7, 23.8, 36.5, and 89.0 GHz with both horizontal and vertical polarization channels. Brightness temperature measurements of those channels with their central frequencies higher than 19 GHz from satellite-based microwave imager radiometers had traditionally been used to retrieve cloud liquid water path （LWP） over ocean. The results show that the lowest frequency channels are the most appropriate for retrieving LWP when its values are large. Therefore, a modified LWP retrieval algorithm is developed for retrieving LWP of different magnitudes involving not only the high frequency channels but also the lowest frequency channels of FY-3 MWRI. The theoretical estimates of the LWP retrieval errors are between 0.11 and 0.06 mm for 10.65- and 18.7-GHz channels and between 0.02 and 0.04 mm for 36.5- and 89.0-GHz channels. It is also shown that the brightness temperature observations at 10.65 GHz can be utilized to better retrieve the LWP greater than 3 mm in the eyewall region of Super Typhoon Neoguri （2014）. The spiral structure of clouds within and around Typhoon Neoguri can be well captured by combining the LWP retrievals from different frequency channels.
基金the NSFC under Grant Nos.40730950,40675027,and 40605010the Cooperate Project of LAPC,CAS(LAPCKF-2006-19),and AXA/EORC
文摘Quantitative estimates of liquid water path （LWP） in clouds using satellite measurements are critical to understanding of cloud properties and the assessment of global climate change. In this paper, the relationship between microwave brightness temperature （TB） and LWP in the nonprecipitating clouds is studied by using satellite microwave measurements from the TRMM Microwave Imager （TMI） onboard the Tropical Rainfall Measuring Mission （TRMM）, together with a radiative transfer model for microwave radiance calculations. Radiative transfer modeling shows that the sensitivity is higher at both 37.0- and 85.5-GHz horizontal polarization channels for the LWP retrievals. Also, the differences between the retrieved values responding to TBs of various channels and the theoretical values are displayed by the model. Based upon above simulations, with taking into account the factor of resolution and retrieval bias for a single,channel, a nonprecipitating cloud LWP in the summer subtropical marine environment retrieval algorithm is formulated by the combination of the two TMI horizontal polarization channels, 37.0 and 85.5 GHz. Moreover,by using TMI measurements （1Bll）, this algorithm is applied to retrieving respectively LWPs for clear sky, nonprecipitating clouds, and typhoon precipitating clouds. In the clear sky case, the LWP cl^anges from -1 to 1 g m-2, and its mean value is about 10^-5 g m^-2. It indicates that, using this combination retrieval algorithm, there are no obvious systemic deviations when the LWP is low enough. The LWP values varying from 0 to 1000 g m^-2 in nonprecipitating clouds are reasonable, and its distribution pattern is very similar to the detected results in the visible channel of Visible and Infrared Scanner （VIRS） on the TRMM. In typhoon precipitating clouds, there is much more proportion of high LWP in the mature phase than the early stage. When surface rainfall rate is lower than 5 mm h^-1, the LWP increases with increasing rainfall rate.
基金National Natural Science Foundation of China(41575031,41175089)China Postdoctoral Science Foundation(2015M580124)Key Laboratory of Geo-Information Engineering(S18701)
文摘In the application of the physical iterative method to retrieve millimeter-wave radar liquid water content(LWC)and liquid water path(LWP),particle parameter scheme is the main factor affecting retrieval performance.In this paper,synchronous measurements of an airborne millimeter-wave radar and a hot-wire probe in stratus cloud are used to compare the LWC retrievals of the oceanic and continental particle parameter scheme with diameter less than 50μm and the particle parameter scheme with diameter less than 500μm and 1500μm(scheme 1,scheme 2,scheme 3,and scheme4,respectively).The results show that the particle parameter scheme needs to be selected according to the reflectivity factor when using the physical iterative method to retrieve the LWC and LWP.When the reflectivity factor is less than-30 d BZ,the retrieval error of scheme 1 is the minimum.When the reflectivity factor is greater than-30 d BZ,the retrieval error of scheme 4 is the minimum.Based on the reflectance factor value,the LWP retrievals of scheme 4 are closer to the measurements,the average relative bias is 5.2%,and the minimum relative bias is 4.4%.Compared with other schemes,scheme 4 seems to be more useful for the LWC and LWP retrieval of stratus cloud in China.
文摘液态云水路径(liquid water path,LWP)和可降水量(precipitable water vapor,PWV)是描述天气和气候的两个重要物理量。目前,针对液态云水路径和可降水量的直接观测较少,特别是在我国干旱半干旱黄土高原地区,至今没有获得系统的观测值。本文利用兰州大学半干旱气候与环境监测站(SACOL)近两年的微波辐射仪观测资料,分析了黄土高原半干旱区液态云水路径和可降水量的变化特征。首先引入Liljegren et al.(2001)的反演方法并加以改进,计算得到适合黄土高原地区的反演参数,利用改进后的反演方法计算近两年的液态云水路径和可降水量。分析结果显示,与TP/WVP-3000型12通道微波辐射计的直接输出结果相比,本文反演结果与实际情况更加吻合。在SACOL代表的黄土高原地区,95%的云水路径值都在150g/m2以下,95%的可降水量值都在3cm以下。由于SACOL的降水受亚洲季风的影响,液态云水路径日均值冬季最小,秋季最大,其日变化规律显示半干旱区液态云水路径大体上呈双峰分布,峰值主要出现在日出和日落时分。卫星反演资料的年变化趋势与地基反演结果比较吻合。因此,运用卫星反演的液态云水路径来分析我国西北地区的空中云水资源是一种比较可信的手段。
文摘采用NASA地球观测系统（EOS）“云与地球辐射能量系统（CERES）”2002年7月至2004年6月CERES SSF Aqua MODIS Edition 1B云资料，对天山山区和塔克拉玛干沙漠云水资源进行了研究。得到的结果不仅包括云量、云液态水柱含量，还包括云滴尺度，为无人区的人工增水作业和天气气候研究提供了基础数据。与以往的卫星观测云气候全球数据集相比，该资料具有更高的空间分辨率，且其观测仪器和云反演方法得到了进一步改善，因此其结果较以往更可信。研究结果表明，两地区云参量年变化规律不尽相同，在数值上有很大差别。除了动力条件和气候背景以外，这可能与沙尘气溶胶可以影响云的物理特性和生命期有关。由年变化来看，天山山区的月平均总云量为47％～72％，而塔克拉玛干沙漠为12％～50％；天山山区低云的月平均液态水柱含量为56．6～96．0g／cm^2，高云为30．5—59．8g／cm^2。而塔克拉玛干沙漠低云的月平均液态水柱含量为19．4～43．9g／cm^2，高云为9．3～59．0g／cm^2；天山山区的月平均云滴半径低云为12．6～16．0μm，高云为8．6-14．8μm。而塔克拉玛干沙漠地区低云云滴半径8．8～11．3μm，高云为6．1—11．1μm。
文摘基于德国RPG公司研制的14通道地基微波辐射计(RPG-HATRPO-G3)反演的2014年10月至2015年9月济南地区的水汽和液态水产品,分析了济南地区水汽和云液态水不同季节的月变化、日变化特征及其在强对流天气与小雨天气中的变化趋势。结果表明:2014年10月至2015年9月济南地区柱大气积分水汽量(Integrated Water Vapour,IWV)具有明显的月变化特征,其变化趋势与多年(1981—2010年)月平均降水量相关性较好,IWV夏季最高、冬季最低,四季IWV均具有弱的日变化特征,四季IWV标准偏差按照夏季、秋季、春季、冬季的顺序递减。对于济南地区春季、夏季、秋季3个季节有云无雨和降水前后液态水路径(Liquid Water Path,LWP)的数据,春季LWP可用数据量最少,夏季LWP可用数据量最多;月LWP在0—200 g·m^(-2)范围内的数据占总数据的比例最多,LWP数值越大,其所占比例越小。月LWP大于1000 g·m^(-2)数据的比例随着夏季的临近和降水量的逐渐增加也呈增加的趋势。IWV和LWP在强对流过程发生前均明显增长,数值大于1000 g·m^(-2)的LWP数据比例为53.41%;而小雨天气发生前IWV呈波动上升的趋势,LWP仅在临近降水时才明显增大,LWP数值主要分布在0—200 g·m^(-2)之间,占总数据的比例为86.56%。
文摘选取热带测雨卫星(Tropical Rainfall Measuring Mission,TRMM)微波成像仪(TRMM Microwave Imager,TMI)液态水路径(liquid water path,LWP)轨道像元数据为研究对象,探讨了将瞬时探测以及逐月的像元数据进行格点化(0.1°、0.25°、0.5°、1.0°和2.5°五种格点分辨率)时,格点数据的失真情况。对TMI瞬时探测的个例分析结果表明,细分辨率(0.1°、0.25°和0.5°)格点能保留原始像元数据的细节;而随着网格变粗,细节受到较大的平滑。因此对于中尺度到天气尺度的天气系统分析而言,将卫星轨道数据处理到网格尺度不大于0.5°的格点更合适。对逐月LWP像元资料格点化处理的分析表明,细分辨率格点能保留LWP空间分布细节,尽管5种分辨率下LWP的概率密度分布(probability density function,PDF)均相近。因此,对月尺度及以上的气候分析研究而言,格点尺度大小对卫星像元数据格点化的影响不显著。最后利用本实验室计算的TMI/LWP格点数据与欧洲中期数值预报中心再分析资料(European Centre for Medium-range Weather Forecasts Interim reanalysis,ERA-Interim)和NCEP再分析资料(NCEP Climate Forecast System Reanalysis,NCEP CFSR)进行了对比,发现两种再分析资料都高估了LWP;TMI/LWP格点数据与两种再分析资料LWP的多年变化趋势大致相同。
