Structure Of Convective Clouds Research Articles

Combining CloudSat/CALIPSO and MODIS measurements to reconstruct tropical convective cloud structure

Tropical convective clouds are a crucial component of the Earth's weather and climate system. However, there are still large uncertainties in model simulations of tropical convective clouds and precipitation. In this study, CloudSat/CALIPSO and MODIS measurements are combined to provide vertical convective cloud structures under horizontal storm context and structures of convective cores. Convective cells are identified with MODIS brightness temperature at 11 μm (BT11) and convective centers are determined for each cell by finding the minimum BT11 (BT11min). The difference between BT11 and BT11min is calculated to provide the distance to the convective center as in brightness temperature. Therefore, detailed convective cloud structures from centers to the stratiform regions could be shown as in the contoured frequency by temperature diagram (CFTD) of radar reflectivity factor (Ze). A group of strongly attenuated Ze profiles is identified near the convective center in Africa during daytime, and the occurrence of this group of profiles is much smaller in the west Pacific during daytime. The out-of-phase day/night variations of convective system structures over ocean and over land are also analyzed. It is shown that over ocean regions, rather than land regions, nighttime convective clouds have larger Ze than daytime ones between 210 K to 260 K, but they have smaller Ze at temperatures colder than 210 K near the cloud top. The convective cores are analyzed by separating and classifying those strongly attenuated Ze profiles as group one convective cores representing the developing stage, and the rest regular profiles as group two convective cores representing the later stage. As BT11min decreases for group one, the cores grow stronger with the maximum Ze shifts into lower temperature; and as BT11min decreases for group two, the CFTD for the cores gradually shifts to larger Ze for temperatures colder than 273.15 K and smaller Ze for temperatures warmer than 273.15 K. These observed composite structures of convective clouds and land/ocean and day/night variations provide crucial information for model evaluations.

Aircraft observation of fast initiation of mixed phase precipitation in convective cloud over the Tibetan Plateau

The Tibetan Plateau is known as the water tower of Southeast Asia, and precipitation processes on the Tibetan Plateau is complex, especially in convective cloud precipitation. Many remote sensing and ground observations have been analyzed, but the in-situ measurements of cloud microphysical characteristics are rare. Here we present aircraft observations of the microphysics of convective clouds over the Qinghai Tibet Plateau in China. These results show the microphysical structure of convective clouds and the triggering characteristics of precipitation in summer in Tibet. The vertical profile of July 9th was selected for a detailed analysis of microphysical characteristics. Mixed phase precipitation was initiated above the 7000 m above sea level over the TP, which is only about 500 m above cloud base height. Riming was the dominant precipitation forming process over the TP, leading to graupel formation, which was the primary form of precipitation of the convective clouds. Although the dust was a large fraction of the overall aerosols over the TP during the flights, it was not likely a major contribution to the early ice formation because of the temperature limit of the Ice Nuclei (IN) parameterization. The secondary ice process (SIP) appears to be the main source of ice crystals.

Determining Spatial Scales of Soil Moisture—Cloud Coupling Pathways Using Semi‐Idealized Simulations

AbstractThe spatial scales of land‐atmosphere interactions over heterogeneous, realistic soil moisture patterns are critical to improve our understanding of land‐atmosphere interactions. However, these scales are poorly quantified. We use high‐resolution numerical experiments to quantify the spatial scales for a selected day during the Holistic Interactions of Shallow Clouds, Aerosols, and Land‐Ecosystems (HI‐SCALE) campaign in Oklahoma. A semi‐idealized approach (removing background winds and surface topography while retaining the real‐world data for other boundary conditions) enables examination of the local influence from the surface. Simulations that apply uniform surface, variable land cover with uniform soil moisture, and variable land cover with variable soil moisture are then compared. Land cover variations, especially water and urban surfaces, create two variance peaks in the surface sensible heat flux in the scales >10 km (meso‐β) and <6 km (meso‐γ). Both peaks are enhanced by the observation‐based soil moisture distribution that has most of its variance in the meso‐β scale. Atmospheric response in the meso‐β scale is hydrostatic with weak vertical motion. The land cover variations induce secondary circulations in the scales of 2.5–6 km. The additional soil moisture variability intensifies extreme circulations over dry soil patches and sharp sensible heat flux gradients, slightly extending the characteristic scales to 2.5–9 km. While their areal coverage is small, soil moisture variations on such “hotspots” lead to substantially larger convective cloud structure and domain‐mean rainfall, calling for a consideration of their non‐linear effect in large‐scale models.

Interpretation of the Precipitation Structure Contained in Polarimetric Radio Occultation Profiles Using Passive Microwave Satellite Observations

AbstractObservationally, a major source of uncertainty in evaluation of climate models arises from the difficulty in obtaining globally distributed, fine scale profiles of temperature, pressure and water vapor, that probe through convective precipitating clouds, from the boundary layer to the upper levels of the free troposphere. In this manuscript, a two-year analysis of data from the Radio Occultations through Heavy Precipitation (ROHP) polarimetric RO demonstration mission onboard the Spanish PAZ spacecraft is presented. ROHP measures the difference in the differential propagation phase delay (Δ𝜙) between two orthogonal polarization receive states that is induced from the presence of non-spherically shaped hydrometeors along the Global Navigation Satellite System (GNSS) propagation path, complementing the standard RO thermodynamic profile. Since Δφ is a net path-accumulated depolarization and does not resolve the precipitation structure along the propagation path, orbital coincidences between ROHP and the Global Precipitation Measurement (GPM) constellation passive MW radiometers are identified to provides three-dimensional precipitation context to the RO thermodynamic profile. Passive MW-derived precipitation profiles are used to simulate the Δφalong the ROHP propagation paths. Comparison between the simulated and observed Δφare indicative of the ability of ROHP to detect threshold levels of ray path-averaged condensed water content, as well as to suggest possible inferences on the average ice phase hydrometeor non-sphericity. The use of the polarimetric RO vertical structure is demonstrated as a means to condition the lower tropospheric humidity by the top-most height of the associated convective cloud structure.

GPM‐DPR Observations on TGFs Producing Storms

AbstractUnique spaceborne measurements of the three‐dimensional structure of convective clouds producing terrestrial gamma ray flashes (TGFs) were performed using both active and passive microwave sensors on board the Global Precipitation Measurement (GPM)‐Core Observatory satellite, finding coherent features for nine TGF‐producing storms. The delineation of cloud structure using the radar reflectivity factor shows convective cells with significant vertical development and thick layers with high ice content. Compared to other cumulonimbus clouds in the tropics, the TGFs counterparts have higher reflectivity values above 3 and 8 km altitude showing in all cases a cumulonimbus tower and the TGFs locations are very close, or coincident, to these high Z columns, where reflectivity exceeds 50 dBz. Using the GPM Microwave Imager radiometer, most thunderstorms show a very strong depression of polarization corrected temperature (PCT) at channel 89 GHz, indicating a strong scattering signal by ice in the upper cloud layers. At channel 166 GHZ, the difference between vertical and horizontal brightness temperature signal always returns positive values, from 0.2 up to 13.7 K indicating a complex structure with randomly/vertically oriented ice particles. The PCT was used to characterize the analyzed storms in terms of hydrometeor types, confirming in 7/9 cases a high likelihood of hail/graupel presence. To perform analysis on the TGFs parent flashes, radio atmospherics data from the Earth Networks Total Lightning Network lightning network were used. Waveform data indicate that all cases are intra‐cloud events and TGFs typically take place during the peak of flash rate production. Finally, the analysis of the most intense event is shown.

Relationships between the Structure of Convective Clouds and Lightning Frequency Derived from Radiophysical Measurements

The results of simultaneous radar, radiometric, and lightning location measurements are analyzed to reveal interrelations between the characteristics of electric discharges and the parameters of a cumulonimbus cloud developing near Saint Petersburg. The dependences of the cloud electric activity on the radar characteristics as well as on the parameters derived from the Meteosat SEVIRI radiometer measurements are considered. It is found that lightning frequency highly correlates with the volume of supercooled cloud regions with high values of reflectivity. An increase in the lightning frequency occurs about 20 minutes after the moment when supercooled cloud volumes with reflectivity above 35–55 dBZ reach the maximum values. The maximum precipitation flux precedes the maximum lightning frequency.

3D modelling strategy for weather radar data analysis

Weather radar data, which have obvious spatial characteristics, represent an important and essential data source for weather identification and prediction, and the multi-dimensional visualization and analysis of such data in a three-dimensional (3D) environment are important strategies for meteorological assessments of potentially disastrous weather. The previous studies have generally used regular 3D raster grids as a basic structure to represent radar data and reconstruct convective clouds. However, conducting weather radar data analyses based on regular 3D raster grids is time-consuming and inefficient, because such analyses involve considerable amounts of tedious data interpolation, and they cannot be used to address real-time situations or provide rapid-response solutions. Therefore, a new 3D modelling strategy that can be used to efficiently represent and analyse radar data is proposed in this article. According to the mode by which the radar data are obtained, the proposed 3D modelling strategy organizes the radar data using logical objects entitled radar-point, radar-line, radar-sector, and radar-cluster objects. In these logical objects, the radar point is the basic object that carries the real radar data unit detected from the radar scan, and the radar-line, radar-sector, and radar-cluster objects organize the radar-point collection in different spatial levels that are consistent with the intrinsic spatial structure of the radar scan. Radar points can be regarded as spatial points, and their spatial structure can support logical objects; thus, the radar points can be flexibly connected to construct continuous surface data with quads and volume data with hexahedron cells without additional tedious data interpolation. This model can be used to conduct corresponding operations, such as extracting an isosurface with the marching cube method and a radar profile with a designed sectioning algorithm to represent the outer and inner structure of a convective cloud. Finally, a case study is provided to verify that the proposed 3D modelling strategy has a better performance in radar data analysis and can intuitively and effectively represent the 3D structure of convective clouds.

The Unexpected Rapid Intensification of Tropical Cyclones in Moderate Vertical Wind Shear. Part I: Overview and Observations

AbstractA satellite-based investigation is performed of a class of tropical cyclones (TCs) that unexpectedly undergo rapid intensification (RI) in moderate vertical wind shear between 5 and 10 m s−1 calculated as 200–850-hPa shear. This study makes use of both infrared (IR; 11 μm) and water vapor (WV; 6.5 μm) geostationary satellite data, the Statistical Hurricane Prediction Intensity System (SHIPS), and model reanalyses to highlight commonalities of the six TCs. The commonalities serve as predictive guides for forecasters and common features that can be used to constrain and verify idealized modeling studies. Each of the TCs exhibits a convective cloud structure that is identified as a tilt-modulated convective asymmetry (TCA). These TCAs share similar shapes, upshear-relative positions, and IR cloud-top temperatures (below −70°C). They pulse over the core of the TC with a periodicity of between 4 and 8 h. Using WV satellite imagery, two additional features identified are asymmetric warming/drying upshear of the TC relative to downshear, as well as radially thin arc-shaped clouds on the upshear side. The WV brightness temperatures of these arcs are between −40° and −60°C. All of the TCs are sheared by upper-level anticyclones, which limits the strongest environmental winds to near the tropopause.

Vertical Characteristics of Reflectivity in Intense Convective Clouds using TRMM PR Data

Tropical Rainfall Measuring Mission Precipitation Radar (TRMM-PR) based vertical structure in intense convective precipitation is presented here for Indian and Austral summer monsoon seasons. TRMM 2A23 data is used to identify the convective echoes in PR data. Two types of cloud cells are constructed here, namely intense convective cloud (ICC) and most intense convective cloud (MICC). ICC consists of PR radar beams having Ze>=40 dBZ above 1.5 km in convective precipitation area, whereas MICC, consists of maximum reflectivity at each altitude in convective precipitation area, with at least one radar pixel must be higher than 40 dBZ or more above 1.5 km within the selected areas. We have selected 20 locations across the tropics to see the regional differences in the vertical structure of convective clouds. One of the important findings of the present study is identical behavior in the average vertical profiles in intense convective precipitation in lower troposphere across the different areas. MICCs show the higher regional differences compared to ICCs between 5-12 km altitude. Land dominated areas show higher regional differences and Southeast south America (SESA) has the strongest vertical profile (higher Ze at higher altitude) followed by Indo-Gangetic plain (IGP), Africa, north Latin America whereas weakest vertical profile occurs over Australia. Overall SESA (41%) and IGP (36%) consist higher fraction of deep convective clouds (>10 km), whereas, among the tropical oceanic areas, Western (Eastern) equatorial Indian ocean consists higher fraction of low (high) level of convective clouds. Nearly identical average vertical profiles over the tropical oceanic areas, indicate the similarity in the development of intense convective clouds and useful while considering them in model studies.

A-Train-Based Case Study of Stratiform–Convective Transition within a Warm Conveyor Belt

Abstract Clouds are both produced by and interact with the mesoscale and synoptic-scale structure of extratropical cyclones (ETCs) in ways that are still not well understood. Cloud-scale radiative and latent heating modifies the thermal environment, leading to a response in the dynamics that can in turn feed back on cloud distribution and microphysical properties. Key to the structure of ETCs is the warm conveyor belt (WCB); the poleward-ascending airstream that produces the bulk of the clouds and precipitation. This paper examines a long-lived WCB that persisted over the western North Atlantic Ocean in nearly the same location for several days. During this time, the storm was sampled multiple times by NASA’s A-Train satellite constellation, and a clear transition from stratiform to convective clouds was observed. Examination of coincident temperature and water vapor data reveals destabilization of the thermodynamic profile after the cyclone reached maturity. CloudSat radar reflectivity from two sequential overpasses of the warm front depicts a change from stratiform to convective cloud structure, and high-frequency microwave data reveal an increase in the amount of ice hydrometeors. The presence of convection may serve to strengthen the warm frontal trough while slowing the movement of the primary low pressure center. The stratiform–convective transition cannot be detected from passive measurements of cloud-top pressure. The results demonstrate the effectiveness of multivariate satellite observations for examining the outcome of dynamic processes in ETCs, and highlight the need for more rapid temporal profiling in future remote sensing observing systems.

A 10-year climatology of vertical properties of most active convective clouds over the Indian regions using TRMM PR

Vertical distribution of hydrometeors in the most intense convective clouds over the Indian region during the summer monsoon season (JJAS) is described for ten climatologically important areas. Tropical Rainfall Measuring Mission Precipitation Radar (TRMM PR) 3D radar reflectivity data is used in the present study for 10 years (2001-2010). The study constructs a convective cloud cell based on reflectivity thresholds, known as most intense convective cloud. The cloud cells are formed by taking the maximum reflectivity (Ze) at each altitude in the convective area with at least one radar pixel containing reflectivity of 40 dBZ or more. TRMM 2A23 data was used to eliminate the stratiform clouds from our analyses. The Vertical structure of convective clouds were studied over the east and west coast of India, and observation shows that the east coast consists of a higher frequency of convective clouds with high reflectivity values in average vertical profiles. It is observed that over the northeastern parts of the Indian subcontinent, similar to 30 % of convective cells extend beyond 15-km height whereas it is only similar to 4 % over the central Bay of Bengal. Over the Western Ghats, similar to 13 % of the cells have their tops below the freezing level, i.e. warm clouds do give heavy rain here. The regional differences in the vertical profile are high between the 5- and 12-km altitude. Most intense convective cells (MICCs) with a cloud top height more than 10 and 15 km show different characteristics, and the Western Ghats shows the most intense average vertical profile. Above 12 km, the western coast shows increased reflectivity value. Convective intensity is higher over the land-dominated areas for the cloud cells and decreases when we restrict the cloud cells to a certain altitude.

Comparison of CloudSat and TRMM radar reflectivities

Comparison of reflectivity data of radars onboard CloudSat and TRMM is performed using coincident overpasses. The contoured frequency by altitude diagrams (CFADs) are constructed for two cases: (a) only include collocated vertical profiles that are most likely to be raining and (b) include all collocated profiles along with cloudy pixels falling within a distance of about 50 km from the centre point of coincidence. Our analysis shows that for both cases, CloudSat underestimates the radar reflectivity by about 10 dBZ compared to that of TRMM radar below 15 km altitude. The difference is well outside the uncertainty value of ~2 dBZ of each radar. Further, CloudSat reflectivity shows a decreasing trend while that of TRMM radar an increasing trend below 4 km height. Basically W-band radar that CloudSat flies suffers strong attenuation in precipitating clouds and its reflectivity value rarely exceeds 20 dBZ though its technical specification indicates the upper measurement limit to be 40 dBZ. TRMM radar, on the other hand, cannot measure values below 17 dBZ. In fact combining data from these two radars seems to give a better overall spatial structure of convective clouds.

Behavior and Structure of Convective Clouds Developing around a Mountainous Area Observed by Stereo Photogrammetry and Ka-Band and X-Band Radars: Case Study of Northern Kanto, Japan

Behavior and Structure of Convective Clouds Developing around a Mountainous Area Observed by Stereo Photogrammetry and Ka-Band and X-Band Radars: Case Study of Northern Kanto, Japan

An EOF‐based comparison and evaluation of simulated passive microwave signatures to observations over tropical oceans

Bayesian algorithms are a common method of retrieving cloud properties from a set of observed passive microwave brightness temperature (TB) measurements. In practice, such methods often use predefined databases from cloud‐resolving models to perform the retrieval. Successful performance in these types of Bayesian retrievals is greatly affected by the similarity of TBs between observed and predefined databases. Here empirical orthogonal function (EOF) analysis methods were used to illustrate the importance of predefined simulation databases on the ability to retrieve known regional variability in cloud structures across different parts of the tropical oceans and to provide insight on the relative impact of environmental conditions to limitations in cloud model microphysical parameterizations in retrieving different types of cloud structures. The spatial distributions of EOF coefficients in EOF space showed that there were both underrepresentation and overrepresentation between manifolds of the predefined and observed databases. Moreover, there was poor alignment in the frequency distribution between observed and simulated clouds structures. Additionally, the ability to retrieve known regional variability in convective cloud structure was dependent on the environmental conditions used to generate the simulated data set more so than limitations in the model microphysical parameterizations. The opposite was true for stratiform rain, as the dominant EOF patterns of the radiation indices for the predefined databases exhibit overproduction of large‐sized high‐density ice‐phase hydrometeors for a given rain content in comparison to the observations. Improvements to microphysical parameterization schemes appear to be necessary to produce radiance index vectors that are consistent with observations.

Observations of tropical cyclone structure from WindSat

Passive microwave (PMW) radiometric observations of clouds from multichannel imaging sensors onboard low Earth-orbiting environmental satellites are now a vital operational dataset. The first operational passive microwave sensor was the Special Sensor Microwave/Imager onboard the Defense Meteorological Satellite Program satellites, which has been gathering hydrological data records since 1987, and continued with the Tropical Rainfall Measuring Mission (TRMM) and the Advanced Microwave Scanning Radiometer onboard Aqua. These sensors view the underlying scene with an Earth incidence angle near 53/spl deg/ and with a variable azimuthal angle, depending upon the orbit direction and scan position. The WindSat sensor onboard the Coriolis satellite, launched in January 2003, is a five-channel polarimetric PMW radiometer designed to optimize ocean surface wind vector retrievals. While it does not have 85-GHz channels, an added feature is its unique fore-aft viewing capability across a portion of its fore scan swath. This provides a view of the underlying scene from two separate azimuthal directions, which provides added information on the three-dimensional (3-D) structure of clouds and their evolution. In this paper, we compare WindSat and TRMM Precipiation Radar observations of tropical cyclones (TCs) with Monte Carlo radiative transfer simulations performed on idealized 3-D convective cloud structures. The TC 3-D structure and possible tilt in the convective cloud structure are inferred from the difference between the 37-GHz equivalent blackbody brightness temperatures (T/sub B/) from the corresponding fore and aft view observations. The information gained from this analysis is important since asymmetries in the cloud vertical and horizontal structure may be an indication of upper level wind shear, which plays a major role in influencing changes of the TC intensity.

On the fine structure of thunderstorms leading to the generation of sprites and elves: Fractal analysis

The fine structure of convective clouds leading to the generation of sprites and elves has been studied using radar images. Sprites and elves were observed on two days, 19 December 1998 and 27 January 1999, in lightning during winter thunderstorms on the Sea of Japan. Fractal analyses of the radar images (as an ensemble and as separate clusters) for those two days have been performed with respect to the occurrence of sprites and elves. We have found that a sprite and/or an elve is triggered when and just after the image cluster maximum size increases to a certain value (∼150 km) and the ensemble fractal dimension approaches a threshold (i.e., percolation threshold).

The Motion of Uneven Structure of Convective Clouds

Abstract An observational study on the motion of the uneven structure on the surface of convective clouds is carried out using a lime-lapse video recorder. The development of the uneven structure shows that the mixing near the cloud-environmental interface occurs through outward motion of the projected part (turret) and inward motion of the depressed part, which are quite different from the winding billowlike motion. The theory presented here predicts the growth direction of the turret in its growing stage. Namely, two angles, one between a vertical line and the growing direction of the turret (=α) and the other between the normal to the mean cloud surface at the place of the turret and the growing direction of the turret (=β), are equal (α = β). Nine turrets are selected from three cumuli to compare the observation with the prediction, and a reasonable result was obtained. Average values of 2α/(α + β) and 2β/(α + β) over the nine samples are 1.11 and 0.89, respectively, with the standard deviation 0.26.

The estimation of heavy rainfall using INSAT-IB Satellite data

A scheme for the estimation of heavy convective rainfall over India during the monsoon season using 3-hourly INSAT-1B satellite data has been presented in this paper. The scheme uses 'life history' approach, taking into account the convective cloud structure, cloud growth in space & time and the prevailing environmental conditions. The role of mesoscale convective complex, overshooting tops and cloud mergers in producing heavy rains is discussed. The scheme is applied to two very heavy rainfall events of August 1986 and August 1987 and some important aspects of the rainfall estimation have been discussed. For an independent data set, the percentage deviations of the rainfall estimates from actual lie between + 111% and -43 %, and 85% of the estimates lie within an error of +-5%. The scheme provides rainfall estimates on a near real-time basis and its accuracy is expected to Improve with the experience gamed In future.

A study of mesoscale convective bands behind cold fronts. Part I: Mesoscale organization

AbstractThis paper reports observations made over the North Atlantic of a system of convective cloud bands found within the cold air behind an occluded front. The observations were made from an instrumented aircraft which additionally released a pattern of dropsondes, measuring temperature, relative humidity and wind, as functions of pressure. These data are analysed to establish some of the mesoscale, cloud‐scale and microphysical properties of the system.Here, in part I, the mesoscale structure is described and compared with the predictions of various theoretical models. The convective cloud structure emerges as a consequence of the mesoscale organization but appears to play only a minor role in its creation and maintenance. One of the theoretical models considered, conditional symmetric instability, provides a piausible explanation of the mesoscale observations.

A Satellite Study of Cloud Clusters over the Tropical North Atlantic Ocean

Signal enhancement is advanced as a method for isolating selected features of ATS images. The discussion covers enhancement theory, limitations, and one important application, the isolation of deep convection within tropical cloud clusters. Comparisons of brightness contoured ATS images with radar images from BOMEX test the validity of associating deep convection with very bright clouds. The enhancement technique is then applied in a census of Atlantic cloud clusters, and in case studies of individual clusters. It is shown that in spite of difficulties involving control of the ATS signal, enhancement is an effective, precise tool for isolating selected features of ATS images. Comparisons of ATS and radar images establish a high correlation of bright areas on ATS with large radar echoes; therefore, enhanced ATS pictures emphasizing the upper levels of the brightness range effectively isolate deep convection. The brightness structure of convective clouds is such that they can be studied over a three-to four-hour period around local noon on pictures uncorrected for changes of incident and reflected radiation. A simple cosine law correction for incident radiation can appreciably extend this period. The census and case studies show that the eastern Atlantic was at least as convectively active as the western Atlantic during June and July, 1969, and had a significantly greater total area of cloud clusters in 1969 and 1970. Convective cores have a great range of size, spacing, and lifetime: nevertheless, an ordering invariably can be perceived. This most often is in the form of lines or bands; waves, spirals, or solitary cores are also observed. Lifetimes are a few minutes to several hours or more; large cores last longer. Displacement of cloud clusters is accomplished by a complex combination of band and cell movement and propagation. Structure, as evidenced by core behavior, is varied and complex.