Journal of Geophysical Research: Atmospheres, 2013
Cumulus congestus clouds have long been identified as an important part of the spectrum of convec... more Cumulus congestus clouds have long been identified as an important part of the spectrum of convective clouds in the tropics. These clouds-which range in size from growing cumulus to slightly smaller than a cumulonimbus-make important contributions to precipitation and latent heat fluxes in the tropics. Past studies have used numerical simulations and satellite observations to examine these clouds globally, although definitions of congestus vary between studies. In this study, congestus in the tropics are identified using contiguous cloud area with cloud tops between 5 and 8 km from 5 years of CloudSat reflectivity data. Alternatively, congestus clouds are defined by contiguous cloud areas with infrared brightness temperature ranging from 273 to 260 K and radar-detected surface rainfall from 14 years of Tropical Rainfall Measuring Mission (TRMM) data. Due to the resolution of CloudSat, the congestus identified using this method represent groups of congestus clouds rather than individual turrets. The regional, seasonal variations of the population of congestus are presented globally. Congestus clouds are found most frequently over the Amazon. There is a strong diurnal variation of congestus clouds over land with a peak in the early afternoon shown by TRMM. General differences are found between the properties of congestus over land and those over ocean, especially the shapes of groups of congestus over land and ocean. Ocean congestus clusters are more bell shaped, while land congestus clusters tend to have flatter sides and larger area above the freezing level. These differences have important implications in the proper representation of congestus in numerical models.
Journal of Applied Meteorology and Climatology, 2008
An event-based method of analyzing the measurements from multiple satellite sensors is presented ... more An event-based method of analyzing the measurements from multiple satellite sensors is presented by using observations of the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR), Microwave Imager (TMI), Visible and Infrared Scanner (VIRS), and Lightning Imaging System (LIS). First, the observations from PR, VIRS, TMI, and LIS are temporally and spatially collocated. Then the cloud and precipitation features are defined by grouping contiguous pixels using various criteria, including surface rain, cold infrared, or microwave brightness temperature. The characteristics of measurements from different sensors inside these features are summarized. Then, climatological descriptions of many properties of the identified features are generated. This analysis method condenses the original information of pixellevel measurements into the properties of events, which can greatly increase the efficiency of searching and sorting the observed historical events. Using the TRMM cloud and precipitation feature database, the regional variations of rainfall contribution by features with different size, intensity, and PR reflectivity vertical structure are shown. Above the freezing level, land storms tend to have larger 20-dBZ area and reach higher altitude than is the case for oceanic storms, especially those land storms over central Africa. Horizontal size and the maximum reflectivity of oceanic storms decrease with altitude. For land storms, these intensity measures increase with altitude between 2 km and the freezing level and decrease more slowly with altitude above the freezing level than for ocean storms.
18 19 Using one year of CloudSat level 2B Cloud Geometrical Profile product, the vertical 20 stru... more 18 19 Using one year of CloudSat level 2B Cloud Geometrical Profile product, the vertical 20 structures, geographical distributions and seasonal variations of cloud occurrence at the 21 day time (1330 LT) and the night time (0130 LT) overpasses and their differences over 22
Tropical deep convection with overshooting tops is identified by defining five different referenc... more Tropical deep convection with overshooting tops is identified by defining five different reference heights using a 5-year TRMM database. The common properties of these extreme convective systems are examined from a global perspective. It is found that 1.3% of tropical convection systems reach 14 km and 0.1% of them may even penetrate the 380 K potential temperature level. Overshooting convection is more frequent over land than over water, especially over central Africa, Indonesia and South America. The seasonal, diurnal and geodistribution patterns of overshooting deep convection show very little sensitivity to the definition of the reference level. The global distribution of overshooting area, volume and precipitating ice mass shows that central Africa makes a disproportionately large contribution to overshooting convection. A semiannual cycle of total overshooting area, volume and precipitating ice mass is found.
Cold cloud features (CCFs) are defined by grouping six full years of Tropical Rainfall Measuring ... more Cold cloud features (CCFs) are defined by grouping six full years of Tropical Rainfall Measuring Mission (TRMM) infrared pixels with brightness temperature at 10.8-m wavelength (T B11 ) less than or equal to 210 and 235 K. Then the precipitation radar (PR)-observed precipitation area and reflectivity profiles inside CCFs are summarized and compared with the area and minimum temperature of the CCFs. Comparing the radar with the infrared data, significant regional differences are found, quantified, and used to describe regional differences in selected properties of deep convective systems in the Tropics. Inside 4 million CCFs, 35% (57%) of cold cloud area with T B11 Յ 235 K (210 K) have rain detected by the PR near the surface. Only ϳ1% of the area of T B11 Յ 210 K have 20 dBZ reaching 14 km. CCFs colder than 210 K occur most frequently over the west Pacific Ocean, but 20-dBZ echoes extending above 10 km in this region are disproportionately rare by comparison to many continental regions. Ratios of PR-detected raining area to area of T B11 Յ 235 K are higher over central Africa, Argentina, and India than over tropical oceans. After applying these ratios to the climatological Global Precipitation Index (GPI) tropical rainfall estimates, the regional distribution is more consistent with the rainfall retrieval from the PR. This suggests that the discrepancy between GPI-and PR-retrieved rainfall can be partly explained with the nonraining anvil. Categorization of CCFs based on the minimum T B11 , size of CCFs, and 20-dBZ heights demonstrates that 20-dBZ echoes above 17 km occur most frequently over land, while the coldest clouds occur most frequently over the west Pacific. The vertical distances between the cloud-top heights determined from T B11 and PR 20-dBZ echo-top heights are smaller over land than over ocean and may be considered as another proxy for convective intensity.
Rainfall characteristics and mesoscale properties of precipitation systems in mei-yu seasons over... more Rainfall characteristics and mesoscale properties of precipitation systems in mei-yu seasons over South China, Taiwan, and the South China Sea (SCS) during 1998-2007 are investigated in this study. Mei-yu rainbands are defined using the Tropical Rainfall Measuring Mission 3B42 rainfall product and then applied to divide the mei-yu season into the mei-yu and break periods. In the 10-yr ''climatology,'' on average, the mei-yu rainbands have a lifetime of 4-5 days and most frequently occur near the South China coast. During the mei-yu periods, rainfall maxima are found over the Pearl River Delta, the foothills of the Yun-Gui Plateau, and Wuyi Mountain, with the first two maxima corresponding to especially heavy rainfall. Intraseasonal variations on the convective structures, especially over land, are distinct among the mei-yu, break, pre-mei-yu, and post-mei-yu, based on analysis of convection intensity proxies and vertical radar reflectivity profiles of precipitation features. Lightning flash rates are consistent with the convective structure. The most frequent lightning over South China and Taiwan is in the pre-mei-yu and the least is during the mei-yu, which suggests different microphysical structures. Therefore, the discrimination of intraseasonal transitions on convective vertical structures may have important implications to the problems of cumulus parameterization, model validation, rainfall estimation, and latent heat retrievals. Intraseasonal variations of convective structures over the SCS are less evident than those over land. Storms over the SCS during the mei-yu are slightly convectively stronger than those in the break. Oceanic features with strong ice scattering have much lower lightning flash rates than their counterparts over land.
1] There are some interesting day versus night differences in the water vapor and carbon monoxide... more 1] There are some interesting day versus night differences in the water vapor and carbon monoxide concentrations near the tropopause over tropical land and ocean from 4 years of EOS Microwave Limb Sounder (MLS) observations. To interpret these differences, the diurnal cycle of deep convection reaching near tropical tropopause summarized from a decade of tropical rainfall measuring mission (TRMM) observations. We also present the diurnal cycle of the cold point tropopause temperature and height derived from 2 years of constellation observing system for meteorology ionosphere and climate (COSMIC) GPS temperature profiles, the day versus night differences of occurrence of thin clouds from 2 years of cloud-aerosol lidar and infrared pathfinder satellite observations (CALIPSO) and 16 years of stratospheric aerosol and gaseous experiment (SAGE) II. In the tropical upper troposphere, day versus night differences of water vapor and carbon monoxide are consistent with the diurnal cycle of the vertical transport of water vapor and carbon monoxide-rich air from the surface by deep convection. However, in the tropical tropopause layer (TTL) over land, day versus night differences of water vapor concentration are more consistent with the diurnal variations of temperature in a saturated TTL, which is related to the diurnal cycle of cooling in the TTL induced by deep convection. The day versus night differences of occurrences of thin clouds in the TTL are also consistent with the freeze drying, controlled by the diurnal cycles of temperature in the TTL.
Bulletin of The American Meteorological Society, 2006
A satellite mission aimed at rainfall measurements has also provided unparalleled information on ... more A satellite mission aimed at rainfall measurements has also provided unparalleled information on the global distribution of intense convective storms.
The long-standing mainstay of support for C. T. R. Wilson's global circuit hypothesis is the simi... more The long-standing mainstay of support for C. T. R. Wilson's global circuit hypothesis is the similarity between the diurnal variation of thunderstorm days in universal time and the Carnegie curve of electrical potential gradient. This rough agreement has sustained the widespread view that thunderstorms are the ''batteries'' for the global electrical circuit. This study utilizes 10 years of Tropical Rainfall Measuring Mission (TRMM) observations to quantify the global occurrence of thunderstorms with much better accuracy and to validate the comparison by F. J. W. Whipple 80 years ago. The results support Wilson's original ideas that both thunderstorms and electrified shower clouds contribute to the DC global circuit by virtue of negative charge carried downward by precipitation. First, the precipitation features (PFs) are defined by grouping the pixels with rain using 10 years of TRMM observations. Thunderstorms are identified from these PFs with lightning flashes observed by the Lightning Imaging Sensor. PFs without lightning flashes but with a 30-dBZ radar echotop temperature lower than 2108C over land and 2178C over ocean are selected as possibly electrified shower clouds. The universal diurnal variation of rainfall, the raining area from the thunderstorms, and possibly electrified shower clouds in different seasons are derived and compared with the diurnal variations of the electric field observed at Vostok, Antarctica. The result shows a substantially better match from the updated diurnal variations of the thunderstorm area to the Carnegie curve than Whipple showed. However, to fully understand and quantify the amount of negative charge carried downward by precipitation in electrified storms, more observations of precipitation current in different types of electrified shower clouds are required.
Tropical deep convection with overshooting tops is identified by defining five different referenc... more Tropical deep convection with overshooting tops is identified by defining five different reference heights using a 5-year TRMM database. The common properties of these extreme convective systems are examined from a global perspective. It is found that 1.3% of tropical convection systems reach 14 km and 0.1% of them may even penetrate the 380K potential temperature level. Overshooting convection is more frequent over land than over water, especially over central Africa, Indonesia, and South America. The seasonal, diurnal and geo-distribution patterns of overshooting deep convection show very little sensitivity to the definition of the reference level. The global distribution of overshooting area, volume and precipitating ice mass shows that central Africa makes a disproportionately large contribution to overshooting convection. A semi annual cycle of total overshooting area, volume and precipitating ice mass is found.
1] The diurnal cycles of surface rainfall, population of precipitation systems, deep intense conv... more 1] The diurnal cycles of surface rainfall, population of precipitation systems, deep intense convection reaching near the tropopause, lightning flash counts, cold clouds, and vertical structure of precipitation are analyzed over the tropics, using 9 years of TRMM Precipitation Radar, Visible and Infrared Scanner, and Lightning Imaging Sensor measurements. The diurnal cycles over land include a late afternoon maximum of precipitation systems, with phase differences among cloud, precipitation, flash counts, and radar echo at different altitudes. Over ocean, the diurnal cycles are interpreted as having contributions from nocturnal precipitation systems and early afternoon showers. There are double peaks of radar reflectivity above 12 km near 0230 and 0530 local time over oceans. The oceanic clouds with infrared brightness temperature < 235 K have two peaks, one during the night and the other in early afternoon.
Warm Rain'' in the Tropics: Seasonal and Regional Distributions Based on 9 yr of TRMM Data
Journal of Climate, 2009
ABSTRACT How much precipitation is contributed by warm rain systems over the tropics? What is the... more ABSTRACT How much precipitation is contributed by warm rain systems over the tropics? What is the typical size, intensity, and echo top of warm rain events observed by the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar over different regions of the tropics? What proportion of warm raining areas is actually attached to the edges of cold systems? Are there mesoscale warm raining systems, and if so, where and when do they occur? To answer these questions, a 9-yr TRMM precipitation feature database is used in this study. First, warm rain features in 20°S-20°N are selected by specifying precipitation features 1) with minimum infrared brightness temperature &gt; 0°C, 2) with TRMM Precipitation Radar (PR) echo top below freezing level, or 3) without any ice scattering signature in the microwave observations, respectively. Then, the geographical, seasonal and diurnal variations of the rain volume inside warm rain features defined in these three ways are presented. The characteristics of warm rain features are summarized. Raining pixels with cloud-top temperature above 0*C contribute 20% of the rainfall over tropical oceans and 7.5% over tropical land. However, about half of the warm pixels over oceans and two-thirds of the warm pixels over land are attached to cold precipitation systems. A large amount of warm rainfall occurs over oceans near windward coasts during winter. Most of the warm rain systems have small size &lt; 100 km2 and weak radar echo with a modal maximum near-surface reflectivity around 23 dBZ. However, mesoscale warm rain systems with strong radar echoes do occur in large regions of the tropical oceans, more during the nighttime thair during daytime. Though the mean height of the warm precipitation features over oceans is lower than that over land, there is no significant regional differencein its size and intensity.
Bulletin of The American Meteorological Society, 2006
A satellite mission aimed at rainfall measurements has also provided unparalleled information on ... more A satellite mission aimed at rainfall measurements has also provided unparalleled information on the global distribution of intense convective storms.
Uploads
Papers by Chuntao Liu