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- Author or Editor: Guosheng Liu x
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Abstract
As satellite high-frequency passive microwave data have recently become available, there is an increasing demand for an accurate and computationally efficient method to calculate the single scattering properties of nonspherical ice particles, so that it may be used in radiative transfer models for physical retrievals of ice water path and snowfall rate. In this study, two such approximations are presented for calculating the single scattering properties of three types of large ice particles: bullet rosettes, sector snowflakes, and dendrite snowflakes, for the frequency range of 85 to 220 GHz, based on results of discrete-dipole approximation (DDA) modeling. By analyzing the DDA modeling results, it is noted that, for nonspherical ice particles, the scattering and absorption cross sections and the asymmetry parameter have a magnitude between those of the two imaginary equal-mass spheres. One is a solid sphere, and the other is an ice–air mixed soft sphere whose diameter equals the particle's maximum dimension. Therefore, the first approximation involves substituting the single scattering properties of a nonspherical ice particle with those of an equal-mass sphere, which can be calculated by Lorenz–Mie theory, with an effective dielectric constant derived by mixing ice and air using the Maxwell–Garnett formula. The diameter of such an equal-mass sphere D is bigger than the diameter of the solid sphere D 0, but smaller than the particle's maximum dimension D max. Defining a softness parameter SP = (D − D 0)/(D max − D 0), it is found that the best-fit equal-mass sphere has an SP value of 0.2 ∼ 0.5 for calculating the volume scattering coefficient, depending on frequency and particle shape. At 150 GHz, the best-fit softness parameter is found to be ∼1/3 when averaging over all particle shapes. For calculating the asymmetry parameter, the DDA model results show that the best-fit softness parameter is close to 0 (i.e., the same as the solid sphere) for frequencies higher than 150 GHz, while it is about 0.3 for 85.5 GHz. The second approximation presented is a polynomial fit to the scattering and absorption cross sections and the asymmetry parameter using the particle size parameter as an independent variable. For the scattering cross section, three fitting curves are derived for, respectively, rosettes, sector snowflakes, and dendrite snowflakes. For the absorption cross section, a single curve is used to fit all particle shapes. For the asymmetry parameter, two curves are derived, one for rosettes and one for snowflakes. The best-fit softness parameter for three particular frequencies (85.5, 150, and 220 GHz) and for three particle shapes in the first approximation, as well as the coefficients of the polynomial fit in the second approximation, are presented. After implementing these approximations in a radiative transfer model, radiative transfer simulations are carried out for a snowfall and an ice cloud case. The simulated brightness temperatures based on the two approximations agree with each other within 3 K, but are significantly different from those based on the solid- and the soft-sphere approximations.
Abstract
As satellite high-frequency passive microwave data have recently become available, there is an increasing demand for an accurate and computationally efficient method to calculate the single scattering properties of nonspherical ice particles, so that it may be used in radiative transfer models for physical retrievals of ice water path and snowfall rate. In this study, two such approximations are presented for calculating the single scattering properties of three types of large ice particles: bullet rosettes, sector snowflakes, and dendrite snowflakes, for the frequency range of 85 to 220 GHz, based on results of discrete-dipole approximation (DDA) modeling. By analyzing the DDA modeling results, it is noted that, for nonspherical ice particles, the scattering and absorption cross sections and the asymmetry parameter have a magnitude between those of the two imaginary equal-mass spheres. One is a solid sphere, and the other is an ice–air mixed soft sphere whose diameter equals the particle's maximum dimension. Therefore, the first approximation involves substituting the single scattering properties of a nonspherical ice particle with those of an equal-mass sphere, which can be calculated by Lorenz–Mie theory, with an effective dielectric constant derived by mixing ice and air using the Maxwell–Garnett formula. The diameter of such an equal-mass sphere D is bigger than the diameter of the solid sphere D 0, but smaller than the particle's maximum dimension D max. Defining a softness parameter SP = (D − D 0)/(D max − D 0), it is found that the best-fit equal-mass sphere has an SP value of 0.2 ∼ 0.5 for calculating the volume scattering coefficient, depending on frequency and particle shape. At 150 GHz, the best-fit softness parameter is found to be ∼1/3 when averaging over all particle shapes. For calculating the asymmetry parameter, the DDA model results show that the best-fit softness parameter is close to 0 (i.e., the same as the solid sphere) for frequencies higher than 150 GHz, while it is about 0.3 for 85.5 GHz. The second approximation presented is a polynomial fit to the scattering and absorption cross sections and the asymmetry parameter using the particle size parameter as an independent variable. For the scattering cross section, three fitting curves are derived for, respectively, rosettes, sector snowflakes, and dendrite snowflakes. For the absorption cross section, a single curve is used to fit all particle shapes. For the asymmetry parameter, two curves are derived, one for rosettes and one for snowflakes. The best-fit softness parameter for three particular frequencies (85.5, 150, and 220 GHz) and for three particle shapes in the first approximation, as well as the coefficients of the polynomial fit in the second approximation, are presented. After implementing these approximations in a radiative transfer model, radiative transfer simulations are carried out for a snowfall and an ice cloud case. The simulated brightness temperatures based on the two approximations agree with each other within 3 K, but are significantly different from those based on the solid- and the soft-sphere approximations.
As satellite observations at high microwave frequencies have recently become available, there is an increasing demand for methods that accurately evaluate the single-scattering properties of nonspherical ice particles at these frequencies. Algorithm developers can use the single-scattering datasets in the retrievals of cloud ice water content and snowfall rate. However, the methods that correctly handle the scattering of complex nonspherical particles are computationally inefficient and impractical for physical retrieval algorithms, in which scattering needs to be evaluated many times for particles with various sizes and shapes. As a remedy, during the past several years we have computed the scattering properties—scattering and absorption cross sections, phase functions, asymmetric parameters, and backscattering cross sections —using an accurate discrete dipole approximation method and arranged the results into an easy-to-access database. The database contains the scattering properties at frequencies from 15 to 340 GHz, with temperatures from 0° to −40°C, of particle sizes (maximum dimension) from 50 to 12,500 μm, and for 11 particle shapes. The database along with an easy-to-use reading program is now made available to interested investigators. This article explains how this database is derived and how it can be used.
As satellite observations at high microwave frequencies have recently become available, there is an increasing demand for methods that accurately evaluate the single-scattering properties of nonspherical ice particles at these frequencies. Algorithm developers can use the single-scattering datasets in the retrievals of cloud ice water content and snowfall rate. However, the methods that correctly handle the scattering of complex nonspherical particles are computationally inefficient and impractical for physical retrieval algorithms, in which scattering needs to be evaluated many times for particles with various sizes and shapes. As a remedy, during the past several years we have computed the scattering properties—scattering and absorption cross sections, phase functions, asymmetric parameters, and backscattering cross sections —using an accurate discrete dipole approximation method and arranged the results into an easy-to-access database. The database contains the scattering properties at frequencies from 15 to 340 GHz, with temperatures from 0° to −40°C, of particle sizes (maximum dimension) from 50 to 12,500 μm, and for 11 particle shapes. The database along with an easy-to-use reading program is now made available to interested investigators. This article explains how this database is derived and how it can be used.
Abstract
The relative change in cloud droplet number concentration with respect to the relative change in aerosol number concentration, α, is an indicator of the strength of the aerosol indirect effect and is commonly used in models to parameterize this effect. Based on Twomey’s analytical expression, the values of α derived from measurements of an individual cloud (i.e., αT ) can be as large as 0.60–0.90. In contrast, the values of α derived from direct measurements of polluted and clean clouds (i.e., α Δ) typically range from 0.25 to 0.85, corresponding to a weaker but more uncertain cooling effect. Clearly, reconciling α Δ with αT is necessary to properly calculate the indirect aerosol forcing. In this study, the terms that are involved in determining αT and α Δ are first analytically examined. Then, by analyzing satellite data over subtropical oceans, the satellite-observed α Δ can be successfully related to Twomey’s analytical solution. It is found that except for the dust-influenced region of the northeastern Atlantic Ocean, injecting continental aerosols into a marine background may significantly reduce the average aerosols’ ability to act as cloud condensation nuclei. Taking this competing effect into account may reduce the cooling effect proposed by Twomey from 0.76 to 0.28. It is also found that the variability of the adiabaticity (i.e., the cloud dilution state with respect to adiabatic cloud) among different clouds accounts for ∼50% uncertainty in α Δ. Based on these results, the authors explain the claimed discrepancies in the first aerosol indirect effect (AIE) from different methods and on different scales and present an improved parameterization of the first AIE that can be used in global climate models.
Abstract
The relative change in cloud droplet number concentration with respect to the relative change in aerosol number concentration, α, is an indicator of the strength of the aerosol indirect effect and is commonly used in models to parameterize this effect. Based on Twomey’s analytical expression, the values of α derived from measurements of an individual cloud (i.e., αT ) can be as large as 0.60–0.90. In contrast, the values of α derived from direct measurements of polluted and clean clouds (i.e., α Δ) typically range from 0.25 to 0.85, corresponding to a weaker but more uncertain cooling effect. Clearly, reconciling α Δ with αT is necessary to properly calculate the indirect aerosol forcing. In this study, the terms that are involved in determining αT and α Δ are first analytically examined. Then, by analyzing satellite data over subtropical oceans, the satellite-observed α Δ can be successfully related to Twomey’s analytical solution. It is found that except for the dust-influenced region of the northeastern Atlantic Ocean, injecting continental aerosols into a marine background may significantly reduce the average aerosols’ ability to act as cloud condensation nuclei. Taking this competing effect into account may reduce the cooling effect proposed by Twomey from 0.76 to 0.28. It is also found that the variability of the adiabaticity (i.e., the cloud dilution state with respect to adiabatic cloud) among different clouds accounts for ∼50% uncertainty in α Δ. Based on these results, the authors explain the claimed discrepancies in the first aerosol indirect effect (AIE) from different methods and on different scales and present an improved parameterization of the first AIE that can be used in global climate models.
Abstract
The characteristics of ice clouds with a wide range of optical depths are studied based on satellite retrievals and radiative transfer modeling. Results show that the global-mean ice cloud optical depth, ice water path, and effective radius are approximately 2, 109 g m−2, and 48 
Abstract
The characteristics of ice clouds with a wide range of optical depths are studied based on satellite retrievals and radiative transfer modeling. Results show that the global-mean ice cloud optical depth, ice water path, and effective radius are approximately 2, 109 g m−2, and 48
Abstract
Whether precipitation falls in the form of rain or snow is of great importance to glacier accumulation and ablation. Assessments of phase-aware precipitation have been lacking over the vast area of the Tibetan Plateau (TP) due to the scarcity of surface measurements and the low quality of satellite estimates in this region. In this study, we attempt a satellite radar-based method for this precipitation partition, in which the CloudSat radar is used for snowfall while the Global Precipitation Measurement Mission radar is used for rainfall estimation. Assuming that 11-yr snowfall and 5-yr rainfall estimates represent the mean states of precipitation at each phase, the phase partition characteristics, including its annual mean, spatial pattern, seasonal dependence, and variation with elevations, are then discussed. Averaged over the highland area (over 1 km above mean sea level) in TP, the annual total precipitation is estimated to be around 400 mm, of which about 40% falls as snow. The snowfall mass fraction is about 45% in the northern and 30% in the southern part of TP, and about 80% in the cold and 30% in the warm half of the year. Surface elevation is found to be a high-impact factor on total precipitation and its phase partition, generally with total precipitation decreasing but snowfall fraction increasing with the increase of elevation. While there are some shortcomings, the current approach in combining snowfall and rainfall estimates from two satellite radars presents a useful pathway to assessing phase-aware precipitation over the TP region.
Abstract
Whether precipitation falls in the form of rain or snow is of great importance to glacier accumulation and ablation. Assessments of phase-aware precipitation have been lacking over the vast area of the Tibetan Plateau (TP) due to the scarcity of surface measurements and the low quality of satellite estimates in this region. In this study, we attempt a satellite radar-based method for this precipitation partition, in which the CloudSat radar is used for snowfall while the Global Precipitation Measurement Mission radar is used for rainfall estimation. Assuming that 11-yr snowfall and 5-yr rainfall estimates represent the mean states of precipitation at each phase, the phase partition characteristics, including its annual mean, spatial pattern, seasonal dependence, and variation with elevations, are then discussed. Averaged over the highland area (over 1 km above mean sea level) in TP, the annual total precipitation is estimated to be around 400 mm, of which about 40% falls as snow. The snowfall mass fraction is about 45% in the northern and 30% in the southern part of TP, and about 80% in the cold and 30% in the warm half of the year. Surface elevation is found to be a high-impact factor on total precipitation and its phase partition, generally with total precipitation decreasing but snowfall fraction increasing with the increase of elevation. While there are some shortcomings, the current approach in combining snowfall and rainfall estimates from two satellite radars presents a useful pathway to assessing phase-aware precipitation over the TP region.
Abstract
Rain-type statistics derived from Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) standard product show that some 70% of raining pixels in the central Tibetan Plateau summer are stratiform—a clear contradiction to the common knowledge that rain events during summer in this region are mostly convective, as a result of the strong atmospheric convective instability resulting from surface heating. In examining the vertical distribution of the stratiform rain-rate profiles, it is suspected that the TRMM PR algorithm misidentifies weak convective rain events as stratiform rain events. The possible cause for this misidentification is believed to be that the freezing level is close to the surface over the plateau, so that the ground echo may be mistakenly identified as the melting level in the PR rain classification algorithm.
Abstract
Rain-type statistics derived from Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) standard product show that some 70% of raining pixels in the central Tibetan Plateau summer are stratiform—a clear contradiction to the common knowledge that rain events during summer in this region are mostly convective, as a result of the strong atmospheric convective instability resulting from surface heating. In examining the vertical distribution of the stratiform rain-rate profiles, it is suspected that the TRMM PR algorithm misidentifies weak convective rain events as stratiform rain events. The possible cause for this misidentification is believed to be that the freezing level is close to the surface over the plateau, so that the ground echo may be mistakenly identified as the melting level in the PR rain classification algorithm.
Abstract
The Baiu front is a subtropical convergence zone that is formed over east Asia in early summer (hereinafter referred to as the Baiu period). In this study, an overocean precipitation retrieval algorithm is developed to retrieve precipitation for the Baiu period from brightness temperatures (TBs) supplied by the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). The basic idea of the algorithm is to find the optimal precipitation that gives radiative transfer model (RTM)-calculated, field-of-view–averaged TBs that fit best with the TMI TBs at 10.7, 19.7, and 85.5 GHz with vertical polarization. For the RTM calculation, spatial precipitation inhomogeneity and freezing-level height are estimated from TMI TBs. The optimal precipitation with 10-km resolution is obtained by solving the gradient equation of a cost function that is a weighted sum of squares of TB differences between the TMI observation and the RTM calculation. Precipitation retrieved by this algorithm was validated using TRMM precipitation radar (PR) data from the western part of Japan during June–July of 1998. The results indicate the following.
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Mesoscale (∼100 km) structures of precipitation disturbances were retrieved successfully with the algorithm. However, there were discrepancies in position and strength of individual rain cells between the precipitation retrievals and PR data.
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Precipitation retrieved by the algorithm agreed well with PR data within the precipitation range of 1–25 mm h−1, irrespective of precipitation type.
Abstract
The Baiu front is a subtropical convergence zone that is formed over east Asia in early summer (hereinafter referred to as the Baiu period). In this study, an overocean precipitation retrieval algorithm is developed to retrieve precipitation for the Baiu period from brightness temperatures (TBs) supplied by the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). The basic idea of the algorithm is to find the optimal precipitation that gives radiative transfer model (RTM)-calculated, field-of-view–averaged TBs that fit best with the TMI TBs at 10.7, 19.7, and 85.5 GHz with vertical polarization. For the RTM calculation, spatial precipitation inhomogeneity and freezing-level height are estimated from TMI TBs. The optimal precipitation with 10-km resolution is obtained by solving the gradient equation of a cost function that is a weighted sum of squares of TB differences between the TMI observation and the RTM calculation. Precipitation retrieved by this algorithm was validated using TRMM precipitation radar (PR) data from the western part of Japan during June–July of 1998. The results indicate the following.
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Mesoscale (∼100 km) structures of precipitation disturbances were retrieved successfully with the algorithm. However, there were discrepancies in position and strength of individual rain cells between the precipitation retrievals and PR data.
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Precipitation retrieved by the algorithm agreed well with PR data within the precipitation range of 1–25 mm h−1, irrespective of precipitation type.
Abstract
Precipitation radar and microwave radiometer data collected by the Tropical Rainfall Measuring Mission (TRMM) satellite are used to study the variability of precipitation profiles and the relationship between precipitation profile and microwave brightness temperature. The variability has been examined using empirical orthogonal function (EOF) analysis and microwave emission and scattering signatures. Precipitation profiles are divided into three groups according to emission signatures at 19.4 GHz and three groups according to scattering signatures at 85.5 GHz. For stratiform rain, the differences of vertical precipitation profiles among these groups are small and are mainly seen in the slope of profiles below the freezing level. However, clear differences in vertical precipitation profiles can be found among the deep-convective rain groups. The maximum rainfall rate occurs at a considerably lower altitude when low liquid-emission or low ice-scattering signatures are observed. When emission or scattering signatures are high, precipitation profiles peak near the freezing level, a feature that is similar to the one in stratiform precipitation profiles. The three patterns of the vertical profiles derived from microwave signatures are very similar to the three patterns derived by EOF analysis. This similarity suggests that the three patterns derived by microwave signatures represent the most significant variability in vertical precipitation profiles. Results also show that, for the same near-surface rainfall rate, the pixel group with anomalously high microwave emission also shows anomalously high microwave scattering, and vice versa, suggesting that the liquid and ice water amounts in tropical rains are correlated over scales the size of a satellite pixel. It is also found that, for a given surface rainfall rate, the brightness-temperature differences among the pixel groups are large, highlighting the importance of vertical precipitation profile in determining upwelling microwave radiation and, therefore, the need to incorporate realistic precipitation profile information in rain retrieval algorithms.
Abstract
Precipitation radar and microwave radiometer data collected by the Tropical Rainfall Measuring Mission (TRMM) satellite are used to study the variability of precipitation profiles and the relationship between precipitation profile and microwave brightness temperature. The variability has been examined using empirical orthogonal function (EOF) analysis and microwave emission and scattering signatures. Precipitation profiles are divided into three groups according to emission signatures at 19.4 GHz and three groups according to scattering signatures at 85.5 GHz. For stratiform rain, the differences of vertical precipitation profiles among these groups are small and are mainly seen in the slope of profiles below the freezing level. However, clear differences in vertical precipitation profiles can be found among the deep-convective rain groups. The maximum rainfall rate occurs at a considerably lower altitude when low liquid-emission or low ice-scattering signatures are observed. When emission or scattering signatures are high, precipitation profiles peak near the freezing level, a feature that is similar to the one in stratiform precipitation profiles. The three patterns of the vertical profiles derived from microwave signatures are very similar to the three patterns derived by EOF analysis. This similarity suggests that the three patterns derived by microwave signatures represent the most significant variability in vertical precipitation profiles. Results also show that, for the same near-surface rainfall rate, the pixel group with anomalously high microwave emission also shows anomalously high microwave scattering, and vice versa, suggesting that the liquid and ice water amounts in tropical rains are correlated over scales the size of a satellite pixel. It is also found that, for a given surface rainfall rate, the brightness-temperature differences among the pixel groups are large, highlighting the importance of vertical precipitation profile in determining upwelling microwave radiation and, therefore, the need to incorporate realistic precipitation profile information in rain retrieval algorithms.
Abstract
An ice water path retrieval algorithm, using airborne Millimeter-Wave Imaging Radiometer brightness temperatures at 89, 150, and 220 GHz, is developed for tropical clouds. This algorithm is based on the results of radiative transfer model simulations, using in situ ice particle properties measured from aircraft as model inputs. The scattering signatures at the 150- and 220-GHz channels are the primary inputs into the algorithm, while 89-GHz data are used for determining the nonice background radiation. The ice water path is first calculated from each of the 150- and 220-GHz scattering signatures, and then a combination of the two channels is used for the final retrieval, based on the consideration of the different channel sensitivities to the magnitude of the ice water path. The algorithm is evaluated by comparing the retrieved with in situ measured ice water paths for seven cases observed during the Tropical Oceans Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). Theoretical analysis shows that the uncertainty due to particle size could be the largest error in the retrievals and this error could be as large as plus or minus 50%. As an application of this algorithm, the ice water path characteristics during TOGA COARE are studied, including assessment of the mean of ice water path, its frequency distribution, and its relationships with cloud-top temperature and liquid water amount. Although tropical clouds are the target of this study, this algorithm could be modified and extended to other climatological regions.
Abstract
An ice water path retrieval algorithm, using airborne Millimeter-Wave Imaging Radiometer brightness temperatures at 89, 150, and 220 GHz, is developed for tropical clouds. This algorithm is based on the results of radiative transfer model simulations, using in situ ice particle properties measured from aircraft as model inputs. The scattering signatures at the 150- and 220-GHz channels are the primary inputs into the algorithm, while 89-GHz data are used for determining the nonice background radiation. The ice water path is first calculated from each of the 150- and 220-GHz scattering signatures, and then a combination of the two channels is used for the final retrieval, based on the consideration of the different channel sensitivities to the magnitude of the ice water path. The algorithm is evaluated by comparing the retrieved with in situ measured ice water paths for seven cases observed during the Tropical Oceans Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). Theoretical analysis shows that the uncertainty due to particle size could be the largest error in the retrievals and this error could be as large as plus or minus 50%. As an application of this algorithm, the ice water path characteristics during TOGA COARE are studied, including assessment of the mean of ice water path, its frequency distribution, and its relationships with cloud-top temperature and liquid water amount. Although tropical clouds are the target of this study, this algorithm could be modified and extended to other climatological regions.
Abstract
An over-ocean ice water path (IWP) algorithm, using satellite Special Sensor Microwave Water Vapor Sounder (SSM/T-2) data, is presented for clouds during the Tropical Oceans Global Atmosphere Coupled Ocean–Atmosphere Response Experiment. In developing the retrieval algorithm, clouds are first divided into 10 classes based on their top temperatures and microwave radiative properties. Radiative transfer model simulations are then performed for the different classes to establish a relation between IWP and the depression of 150-GHz brightness temperature. Correction to the effect of supercooled liquid water is done by incorporating data of liquid water path (LWP) retrievals from Special Sensor Microwave/Imager (SSM/I) and relative humidity profiles from the European Centre for Medium-Range Weather Forecasts analyses. The algorithm retrievals are compared with the analyses in the International Satellite Cloud Climatology Project (ISCCP) dataset. By using collocated SSM/T-2, SSM/I, and ISCCP data, the relations among IWP and other atmospheric hydrological properties including cloud-top temperature, LWP, rainfall rate, and precipitable water are investigated. The results indicate that IWP tends to increase with the decrease of cloud-top temperature and this correlation is particularly evident for precipitating clouds. LWP retrieved for nonprecipitating clouds has a similar tendency but only for those with top temperatures warmer than 0°C. There is no clear relation between IWP and LWP. The ratio of IWP to total condensed water (IWP + LWP) for nonprecipitating clouds seems to be negatively correlated with cloud-top temperature on an average of a large data volume, but this relationship differs substantially among individual cases. Rainfall rate has a strong correlation with IWP. High values of IWP and LWP are always associated with high precipitable water although high precipitable water does not automatically correspond to high IWP or high LWP.
Abstract
An over-ocean ice water path (IWP) algorithm, using satellite Special Sensor Microwave Water Vapor Sounder (SSM/T-2) data, is presented for clouds during the Tropical Oceans Global Atmosphere Coupled Ocean–Atmosphere Response Experiment. In developing the retrieval algorithm, clouds are first divided into 10 classes based on their top temperatures and microwave radiative properties. Radiative transfer model simulations are then performed for the different classes to establish a relation between IWP and the depression of 150-GHz brightness temperature. Correction to the effect of supercooled liquid water is done by incorporating data of liquid water path (LWP) retrievals from Special Sensor Microwave/Imager (SSM/I) and relative humidity profiles from the European Centre for Medium-Range Weather Forecasts analyses. The algorithm retrievals are compared with the analyses in the International Satellite Cloud Climatology Project (ISCCP) dataset. By using collocated SSM/T-2, SSM/I, and ISCCP data, the relations among IWP and other atmospheric hydrological properties including cloud-top temperature, LWP, rainfall rate, and precipitable water are investigated. The results indicate that IWP tends to increase with the decrease of cloud-top temperature and this correlation is particularly evident for precipitating clouds. LWP retrieved for nonprecipitating clouds has a similar tendency but only for those with top temperatures warmer than 0°C. There is no clear relation between IWP and LWP. The ratio of IWP to total condensed water (IWP + LWP) for nonprecipitating clouds seems to be negatively correlated with cloud-top temperature on an average of a large data volume, but this relationship differs substantially among individual cases. Rainfall rate has a strong correlation with IWP. High values of IWP and LWP are always associated with high precipitable water although high precipitable water does not automatically correspond to high IWP or high LWP.
