scholarly journals Revised identification of tropical oceanic cumulus congestus as viewed by CloudSat

2011 ◽  
Vol 11 (5) ◽  
pp. 14883-14902 ◽  
Author(s):  
S. P. F. Casey ◽  
E. J. Fetzer ◽  
B. H. Kahn
Keyword(s):  
Radar Reflectivity ◽  
Convective Clouds ◽  
Cumulus Congestus ◽  
One Year

Abstract. Congestus cloud convective features are examined in one year of tropical oceanic cloud observations from the CloudSat/CALIPSO instruments. Two types of convective clouds (cumulus and deep convective, based on classification profiles from radar), and associated differences in radar reflectivity and radar/lidar cloud-top height are considered. Congestus convective features are defined as contiguous convective clouds with heights between 3 and 9 km. A majority of congestus convective features satisfy one of three criteria used in previous studies: (1) CloudSat and CALIPSO cloud-top heights less than 1 km apart; (2) CloudSat 0 dBZ echo-top height less than 1 km from CloudSat cloud-top height, and (3) CloudSat 10 dBZ echo-top height less than 2 km from CloudSat cloud-top height. However, less than half of congestus convective features satisfy all three of these requirements. This implies that previous methods used to identify congestus clouds may be biased towards more vigorous convection, missing more than half of observed congestus and significantly misrepresenting the deduced relationship between congestus clouds and their surroundings.

scholarly journals Revised identification of tropical oceanic cumulus congestus as viewed by CloudSat

2012 ◽  
Vol 12 (3) ◽  
pp. 1587-1595 ◽  
Author(s):  
S. P. F. Casey ◽  
E. J. Fetzer ◽  
B. H. Kahn
Keyword(s):  
Convective Cloud ◽  
Radar Reflectivity ◽  
Convective Clouds ◽  
Surrounding Environment ◽  
Cumulus Congestus ◽  
One Year

Abstract. Congestus cloud convective features are examined in one year of tropical oceanic cloud observations from the CloudSat/CALIPSO instruments. Two types of convective clouds (cumulus and deep convective, based on classification profiles from radar), and associated differences in radar reflectivity and radar/lidar cloud-top height are considered. Congestus convective features are defined as contiguous convective clouds with heights between 3 and 9 km. Three criteria were used in previous studies to identify congestus: (1) CloudSat and CALIPSO cloud-top heights less than 1 km apart; (2) CloudSat 0 dBZ echo-top height less than 1 km from CloudSat cloud-top height, and (3) CloudSat 10 dBZ echo-top height less than 2 km from CloudSat cloud-top height. A majority of congestus convective features satisfy the second and third requirements. However, over 40% of convective features identified had no associated CALIPSO cloud-top height, predominantly due to the extinguishment of the lidar beam above the CloudSat-reported convective cloud. For the remaining cells, approximately 56% of these satisfy all three requirements; when considering the lidar beam-extinction issue, only 31% of congestus convective features are identified using these criteria. This implies that while previous methods used to identify congestus clouds may be accurate in finding vigorous convection (such as transient congestus rising toward the tropopause), these criteria may miss almost 70% of the total observed congestus convective features, suggesting a more general approach should be used to describe congestus and its surrounding environment.

Lightning Frequency and Microphysical Properties of Precipitating Clouds over the Western North Pacific during Winter as Derived from TRMM Multisensor Observations

2007 ◽  
Vol 135 (6) ◽  
pp. 2226-2241 ◽  
Author(s):  
Yasu-Masa Kodama ◽  
Haruna Okabe ◽  
Yukie Tomisaka ◽  
Katsuya Kotono ◽  
Yoshimi Kondo ◽  
...  
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Tropical Rainfall Measuring Mission ◽  
Radar Reflectivity ◽  
Phase Layer ◽  
Convective Clouds ◽  
Microphysical Properties ◽  
The Tropics ◽  
Precipitating Clouds

Abstract Tropical Rainfall Measuring Mission observations from multiple sensors including precipitation radar, microwave and infrared radiometers, and a lightning sensor were used to describe precipitation, lightning frequency, and microphysical properties of precipitating clouds over the midlatitude ocean. Precipitation over midlatitude oceans was intense during winter and was often accompanied by frequent lightning. Case studies over the western North Pacific from January and February 2000 showed that some lightning occurred in deep precipitating clouds that developed around cyclones and their attendant fronts. Lightning also occurred in convective clouds that developed in regions of large-scale subsidence behind extratropical cyclones where cold polar air masses were strongly heated and moistened from below by the ocean. The relationships between lightning frequency and the minimum polarization corrected temperature (PCT) at 37 and 85 GHz and the profile of the maximum radar reflectivity resembled relationships derived previously for cases in the Tropics. Smaller lapse rates in the maximum radar reflectivity above the melting level indicate vigorous convection that, although shallow and relatively rare, was as strong as convection over tropical oceans. Lightning was most frequent in systems for which the minimum PCT at 37 GHz was less than 260 K. Lightning and PCT at 85 GHz were not as well correlated as lightning and PCT at 37 GHz. Thus, lightning was frequent in convective clouds that contained many large hydrometeors in the mixed-phase layer, because PCT is more sensitive to large hydrometeors at 37 than at 85 GHz. The relationship between lightning occurrence and cloud-top heights derived from infrared observations was not straightforward. Microphysical conditions that support lightning over the midlatitude ocean in winter were similar to conditions in the Tropics and are consistent with Takahashi’s theory of riming electrification.

scholarly journals Lagrangian Investigation of the Precipitation Efficiency of Convective Clouds

2015 ◽  
Vol 72 (3) ◽  
pp. 1045-1062 ◽  
Author(s):  
Wolfgang Langhans ◽  
Kyongmin Yeo ◽  
David M. Romps
Keyword(s):  
Large Eddy Simulations ◽  
Cloud Base ◽  
Water Molecules ◽  
Lagrangian Particle ◽  
Surface Precipitation ◽  
Convective Clouds ◽  
Precipitation Efficiency ◽  
Surface Rainfall ◽  
Large Eddy ◽  
Cumulus Congestus

Abstract The precipitation efficiency of cumulus congestus clouds is investigated with a new Lagrangian particle framework for large-eddy simulations. The framework is designed to track particles representative of individual water molecules. A Monte Carlo approach facilitates the transition of particles between the different water classes (e.g., vapor, rain, or graupel). With this framework, it is possible to reconstruct the pathways of water as it moves from vapor at a particular altitude to rain at the surface. By tracking water molecules through both physical and microphysical space, the precipitation efficiency can be studied in detail as a function of height. Large-eddy simulations of individual cumulus congestus clouds show that the clouds convert entrained vapor to surface precipitation with an efficiency of around 10%. About two-thirds of all vapor that enters the cloud does so by entrainment in the free troposphere, but free-tropospheric vapor accounts for only one-third to one-half of the surface rainfall, with the remaining surface rainfall originating as vapor entrained through the cloud base. The smaller efficiency with which that laterally entrained water is converted into surface precipitation results from the smaller efficiencies with which it condenses, forms precipitating hydrometeors, and reaches the surface.

Should Interpolation of Radar Reflectivity be Performed in Z or dBZ?

2019 ◽  
Vol 36 (6) ◽  
pp. 1143-1156 ◽  
Author(s):  
Robert A. Warren ◽  
Alain Protat
Keyword(s):  
Cartesian Grid ◽  
Radar Reflectivity ◽  
Spherical Coordinates ◽  
Mapping Data ◽  
High Reflectivity ◽  
Valid Data ◽  
Radar Measurements ◽  
One Year

AbstractInterpolation of ground-based radar measurements is required when mapping data from their native spherical coordinates to a Cartesian grid. For reflectivity the question arises as to whether this processing should be performed in units of Z (mm6 m−3) or dBZ. This study addresses this question using one year of data from three radars, operating in diverse climates across Australia. For each radar, a subset of 800 volume scans is processed to identify “triads”—groups of three consecutive gates with valid data—in each of the three coordinate directions: range, azimuth, and elevation. For every triad, the reflectivity at the central gate is estimated by linearly interpolating between the outer two gates in both Z and dBZ. The resulting values are then compared with the true reflectivity at the central gate to quantify the interpolation errors. For all three sites and in all three coordinate directions, we find that interpolation in Z is more accurate on average, especially in regions of high reflectivity and strong reflectivity gradient (i.e., convective cores). However, interpolation in dBZ is better in regions of low and monotonically increasing/decreasing reflectivity. It is therefore recommended that reflectivities be converted from dBZ to Z prior to interpolation except when identifying echo-top height or other low-reflectivity boundaries.

scholarly journals A CloudSat Perspective on the Cloud Climatology and Its Association with Aerosol Perturbations in the Vertical over Eastern China

2016 ◽  
Vol 73 (9) ◽  
pp. 3599-3616 ◽  
Author(s):  
Tianmeng Chen ◽  
Jianping Guo ◽  
Zhanqing Li ◽  
Chuanfeng Zhao ◽  
Huan Liu ◽  
...  
Keyword(s):  
Cloud Condensation Nuclei ◽  
Eastern China ◽  
Three Dimensional ◽  
Warm Season ◽  
Radar Reflectivity ◽  
Cumulus Clouds ◽  
Convective Clouds ◽  
Aerosol Effect ◽  
Aerosol Cloud Interactions ◽  
Level 2

Abstract Many efforts have been taken to investigate aerosol–cloud interactions from space, but only a few studies have examined the response of vertical cloud structure to aerosol perturbations. Three-dimensional cloud climatologies of eight different cloud types identified from the CloudSat level-2 cloud product during the warm season (May–September) in 2008–10 over eastern China were first generated and analyzed. Using visibility as a proxy for cloud condensation nuclei, in combination with satellite-observed radar reflectivity, normalized contoured frequency by altitude diagrams of the differences in cloud radar reflectivity Z profiles under polluted and clean conditions were constructed. For shallow cumulus clouds (shallow Cu) Z tends to be inhibited, and it is enhanced in the upper layers for deep cumulus (deep Cu), nimbostratus (Ns), and deep convective clouds (DCC) under polluted conditions. Overall, analyses of the modified center of gravity (MCOG) and cloud-top height (CTH) also point to a similar aerosol effect, except for the nonsignificant changes in MCOGs and CTHs in deep Cu. The impacts of environmental factors such as lower-tropospheric stability and vertical velocity are also discussed for these types of clouds. Although consistent aerosol-induced elevations in MCOGs and CTHs for Ns and DCC clouds are observed, the effect of meteorology cannot be completely ruled out, which merits further analysis.

scholarly journals Correlations of Multispectral Infrared Indicators and Applications in the Analysis of Developing Convective Clouds

2016 ◽  
Vol 55 (4) ◽  
pp. 945-960 ◽  
Author(s):  
Qiong Wu ◽  
Hong-Qing Wang ◽  
Yi-Zhou Zhuang ◽  
Yin-Jing Lin ◽  
Yan Zhang ◽  
...  
Keyword(s):  
Life Cycle ◽  
Water Vapor ◽  
Conceptual Model ◽  
Time Trend ◽  
Preliminary Test ◽  
Two Dimensional ◽  
Test Results ◽  
Frequency Distributions ◽  
Convective Clouds ◽  
Cumulus Congestus

AbstractThree infrared (IR) indicators were included in this study: the 10.8-μm brightness temperature (BT10.8), the BT difference between 12.0 and 10.8 μm (BTD12.0–10.8), and the BT difference between 6.7 and 10.8 μm (BTD6.7–10.8). Correlations among these IR indicators were investigated using MTSAT-1R images for summer 2007 over East Asia. Temporal, spatial, and numerical frequency distributions were used to represent the correlations. The results showed that large BTD12.0–10.8 values can be observed in the growth of cumulus congestus and associated with the boundary of different terrain where convection was more likely to generate and develop. The results also showed that numerical correlation between any two IR indicators could be expressed by two-dimensional histograms (HT2D). Because of differences in the tropopause heights and in the temperature and water vapor fields, the shapes of the HT2Ds varied with latitude and the type of underlying surface. After carefully analyzing the correlations among the IR indicators, a conceptual model of the convection life cycle was constructed according to these HT2Ds. A new cloud convection index (CCI) was defined with the combination of BTD12.0–10.8 and BTD6.7–10.8 on the basis of the conceptual model. The preliminary test results demonstrated that CCI could effectively identify convective clouds. CCI value and its time trend could reflect the growth or decline of convective clouds.

scholarly journals Static Mode Seeding of Summer Cumuli—A Review

1986 ◽  
Vol 43 ◽  
pp. 7-24 ◽  
Author(s):  
Bernard A. Silverman
Keyword(s):  
Field Studies ◽  
Static Mode ◽  
Convective Clouds ◽  
Cumulus Congestus ◽  
Past Experimental Work ◽  
Static Seeding ◽  
Glaciogenic Seeding ◽  
Physical Reasons ◽  
Future Work ◽  
Precipitation Enhancement

Abstract A review of the state of knowledge of the physics of the static mode seeding hypothesis for convective clouds is presented. The central thesis of the review is that the results of past experimental work are diverse but valid and that credibility of the science depends on understanding the physical reasons for the diverse results. Areas of uncertainty and conflicts in evidence associated with the statement of physical hypothesis, the concept of seedability, the seeding operation, and the chain of physical events following seeding are highlighted to identify what issues need to be resolved to further progress in precipitation enhancement research and application. It is concluded that the only aspect of static seeding that meets scientific standards of cause-and-effect relationships and repeatability is that glaciogenic seeding agents can produce distinct “seeding signatures” in clouds. However, the reviewer argues that a body of inferential physical evidence has been amassed that provides a better understanding of which clouds are seedable (susceptible to precipitation enhancement by artificial seeding) and which are not, even though the tools for recognizing and properly treating them are imperfect. In particular, the inferred evidence appears to support the claims of physical plausibility for the positive statistical results of the Israeli experiments. It is suggested that future work continue to be designed for physical understanding and evaluation through comprehensive field studies and numerical modeling. Duplicating the Israeli experiments in another location should receive high priority but, in general, future experiments should move upscale from cumulus congestus to convective complexes. In doing so, a new, more complex physical hypothesis that accounts for cloud–environment and microphysical–dynamical interactions and their response to seeding will have to be developed.

Utilizing Spaceborne Radars to Retrieve Dry Snowfall

2009 ◽  
Vol 48 (12) ◽  
pp. 2564-2580 ◽  
Author(s):  
Mark S. Kulie ◽  
Ralf Bennartz
Keyword(s):  
Cross Sections ◽  
Dominant Mode ◽  
Radar Reflectivity ◽  
Particle Model ◽  
Dual Frequency ◽  
Active Sensors ◽  
Near Surface ◽  
Ground Clutter ◽  
One Year ◽  
Global Precipitation

Abstract A dataset consisting of one year of CloudSat Cloud Profiling Radar (CPR) near-surface radar reflectivity Z associated with dry snowfall is examined in this study. The CPR observations are converted to snowfall rates S using derived Ze–S relationships, which were created from backscatter cross sections of various nonspherical and spherical ice particle models. The CPR reflectivity histograms show that the dominant mode of global near-surface dry snowfall has extremely light reflectivity values (∼3–4 dBZe), and an estimated 94% of all CPR dry snowfall observations are less than 10 dBZe. The average conditional global snowfall rate is calculated to be about 0.28 mm h−1, but is regionally highly variable as well as strongly sensitive to the ice particle model chosen. Further, ground clutter contamination is found in regions of complex terrain even when a vertical reflectivity continuity threshold is utilized. The potential of future multifrequency spaceborne radars is evaluated using proxy 35–13.6-GHz reflectivities and sensor specifications of the proposed Global Precipitation Measurement dual-frequency precipitation radar (DPR). It is estimated that because of its higher detectability threshold, only about 7%–1% of the near-surface radar reflectivity values and about 17%–4% of the total accumulation associated with global dry snowfall would be detected by a DPR-like instrument, but these results are very sensitive to the chosen ice particle model. These potential detection shortcomings can be partially mitigated by using snowfall-rate distributions derived by the CPR or other similar high-frequency active sensors.

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