On the Atmospheric Regulation of the Growth of Moderate to Deep Cumulonimbus in a Tropical Environment

2014 ◽  
Vol 71 (3) ◽  
pp. 1105-1120 ◽  
Author(s):  
Vickal V. Kumar ◽  
Alain Protat ◽  
Christian Jakob ◽  
Peter T. May
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Atmospheric Conditions ◽  
Wet Season ◽  
Cumulus Clouds ◽  
Significant Difference ◽  
The Hours ◽  
Using Data ◽  
Cumulus Congestus ◽  
Rain Rates

Abstract Some cumulus clouds with tops between 3 and 7 km (Cu3km–7km) remain in this height region throughout their lifetime (congestus) while others develop into deeper clouds (cumulonimbus). This study describes two techniques to identify the congestus and cumulonimbus cloud types using data from scanning weather radar and identifies the atmospheric conditions that regulate these two modes. A two-wet-season cumulus cloud database of the Darwin C-band polarimetric radar is analyzed and the two modes are identified by examining the 0-dBZ cloud-top height (CTH) of the Cu3km–7km cells over a sequence of radar scans. It is found that ~26% of the classified Cu3km–7km population grow into cumulonimbus clouds. The cumulonimbus cells exhibit reflectivities, rain rates, and drop sizes larger than the congestus cells. The occurrence frequency of cumulonimbus cells peak in the afternoon at ~1500 local time—a few hours after the peak in congestus cells. The analysis of Darwin International Airport radiosonde profiles associated with the two types of cells shows no noticeable difference in the thermal stability rates, but a significant difference in midtropospheric (5–10 km) relative humidity. Moister conditions are found in the hours preceding the cumulonimbus cells when compared with the congestus cells. Using a moisture budget dataset derived for the Darwin region, it is shown that the existence of cumulonimbus cells, and hence deep convection, is mainly determined by the presence of the midtroposphere large-scale upward motion and not merely by the presence of congestus clouds prior to deep convection. This contradicts the thermodynamic viewpoint that the midtroposphere moistening prior to deep convection is solely due to the preceding cumulus congestus cells.

scholarly journals Sensitivity of Rain-Rate Estimates Related to Convective Organization: Observations from the Kwajalein, RMI, Radar

2017 ◽  
Vol 56 (4) ◽  
pp. 1099-1119 ◽  
Author(s):  
David S. Henderson ◽  
Christian D. Kummerow ◽  
David A. Marks
Keyword(s):  
Large Scale ◽  
Rain Rate ◽  
Deep Convection ◽  
Marshall Islands ◽  
Shallow Convection ◽  
Wet Season ◽  
Precipitation Regime ◽  
Radar Rainfall ◽  
Precipitation Regimes ◽  
Rain Rates

AbstractGround radar rainfall, necessary for satellite rainfall product (e.g., TRMM and GPM) ground validation (GV) studies, is often retrieved using annual or climatological convective/stratiform Z–R relationships. Using the Kwajalein, Republic of the Marshall Islands (RMI), polarimetric S-band weather radar (KPOL) and gauge network during the 2009 and 2011 wet seasons, the robustness of such rain-rate relationships is assessed through comparisons with rainfall retrieved using relationships that vary as a function of precipitation regime, defined as shallow convection, isolated deep convection, and deep organized convection. It is found that the TRMM-GV 2A53 rainfall product underestimated rain gauges by −8.3% in 2009 and −13.1% in 2011, where biases are attributed to rainfall in organized precipitation regimes. To further examine these biases, 2A53 GV rain rates are compared with polarimetrically tuned rain rates, in which GV biases are found to be minimized when rain relationships are developed for each precipitation regime, where, for example, during the 2009 wet-season biases in isolated deep precipitation regimes were reduced from −16.3% to −4.7%. The regime-based improvements also exist when specific convective and stratiform Z–R relationships are developed as a function of precipitation regime, where negative biases in organized convective events (−8.7%) are reduced to −1.6% when a regime-based Z–R is implemented. Negative GV biases during the wet seasons lead to an underestimation in accumulated rainfall when compared with ground gauges, suggesting that satellite-related bias estimates could be underestimated more than originally described. Such results encourage the use of the large-scale precipitation regime along with their respective locally characterized convective or stratiform classes in precipitation validation endeavors and in development of Z–R rainfall relationships.

scholarly journals Atmospheric Conditions Associated with Labrador Sea Deep Convection: New Insights from a Case Study of the 2006/07 and 2007/08 Winters

2016 ◽  
Vol 29 (14) ◽  
pp. 5281-5297 ◽  
Author(s):  
Who M. Kim ◽  
Stephen Yeager ◽  
Ping Chang ◽  
Gokhan Danabasoglu
Keyword(s):  
North America ◽  
North Atlantic ◽  
Large Scale ◽  
Initial Conditions ◽  
Deep Convection ◽  
La Niña ◽  
Labrador Sea ◽  
Atmospheric Conditions ◽  
Circulation Anomaly ◽  
La Nina

Abstract Deep convection in the Labrador Sea (LS) resumed in the winter of 2007/08 under a moderately positive North Atlantic Oscillation (NAO) state. This is in sharp contrast with the previous winter with weak convection, despite a similar positive NAO state. This disparity is explored here by analyzing reanalysis data and forced-ocean simulations. It is found that the difference in deep convection is primarily due to differences in large-scale atmospheric conditions that are not accounted for by the conventional NAO definition. Specifically, the 2007/08 winter was characterized by an atmospheric circulation anomaly centered in the western North Atlantic, rather than the eastern North Atlantic that the conventional NAO emphasizes. This anomalous circulation was also accompanied by anomalously cold conditions over northern North America. The controlling influence of these atmospheric conditions on LS deep convection in the 2008 winter is confirmed by sensitivity experiments where surface forcing and/or initial conditions are modified. An extended analysis for the 1949–2009 period shows that about half of the winters with strong heat losses in the LS are associated with such a west-centered circulation anomaly and cold conditions over northern North America. These are found to be accompanied by La Niña–like conditions in the tropical Pacific, suggesting that the atmospheric response to La Niña may have a strong influence on LS deep convection.

scholarly journals Cloud-to-ground lightning in Portugal: patterns and dynamical forcing

2012 ◽  
Vol 12 (3) ◽  
pp. 639-649 ◽  
Author(s):  
J. A. Santos ◽  
M. A. Reis ◽  
J. Sousa ◽  
S. M. Leite ◽  
S. Correia ◽  
...  
Keyword(s):  
Large Scale ◽  
Bimodal Distribution ◽  
Lightning Activity ◽  
Atmospheric Conditions ◽  
Remote Forcing ◽  
Cloud To Ground Lightning ◽  
Using Data ◽  
Number Of Discharges ◽  
Low Pressures ◽  
Large Scale Atmospheric Circulation

Abstract. An analysis of the cloud-to-ground discharges (CGD) over Portugal is carried out using data collected by a network of sensors maintained by the Portuguese Meteorological Institute for 2003–2009 (7 yr). Only cloud-to-ground flashes are considered and negative polarity CGD are largely dominant. The total number of discharges reveals a considerable interannual variability and a large irregularity in their distribution throughout the year. However, it is shown that a large number of discharges occur in the May–September period (71%), with a bimodal distribution that peaks in May and September, with most of the lightning activity recorded in the afternoon (from 16:00 to 18:00 UTC). In spring and autumn the lightning activity tends to be scattered throughout the country, whereas in summer it tends to be more concentrated over northeastern Portugal. Winter generally presents low lightning activity. Furthermore, two significant couplings between the monthly number of days with discharges and the large-scale atmospheric circulation are isolated: a regional forcing, predominantly in summer, and a remote forcing. In fact, the identification of daily lightning regimes revealed three important atmospheric conditions for triggering lightning activity: regional cut-off lows, cold troughs induced by remote low pressure systems and summertime regional low pressures at low-tropospheric levels combined with a mid-tropospheric cold trough.

Diurnal Cycle of Shallow and Deep Convection for a Tropical Land and an Ocean Environment and Its Relationship to Synoptic Wind Regimes

2006 ◽  
Vol 134 (10) ◽  
pp. 2688-2701 ◽  
Author(s):  
L. Gustavo Pereira ◽  
Steven A. Rutledge
Keyword(s):  
Diurnal Cycle ◽  
Large Scale ◽  
Field Experiments ◽  
Deep Convection ◽  
Shallow Convection ◽  
Wind Regime ◽  
Diurnal Variability ◽  
Synoptic Wind ◽  
Wind Regimes ◽  
Rain Rates

Abstract The characteristics of shallow and deep convection during the Tropical Rainfall Measuring Mission/Large-Scale Biosphere–Atmosphere Experiment in Amazonia (TRMM/LBA) and the Eastern Pacific Investigation of Climate Processes in the Coupled Ocean–Atmosphere System (EPIC) are evaluated in this study. Using high-quality radar data collected during these two tropical field experiments, the reflectivity profiles, rain rates, fraction of convective area, and fraction of rainfall volume in each region are examined. This study focuses on the diurnal cycle of shallow and deep convection for the identified wind regimes in both regions. The easterly phase in TRMM/LBA and the northerly wind regime in EPIC were associated with the strongest convection, indicated by larger rain rates, higher reflectivities, and deeper convective cores compared to the westerly phase in TRMM/LBA and the southerly regime in EPIC. The diurnal cycle results indicated that convection initiates in the morning and peaks in the afternoon during TRMM/LBA, whereas in the east Pacific the diurnal cycle of convection is very dependent on the wind regime. Deep convection in the northerly regime peaks around midnight, nearly 6 h before its southerly regime counterpart. Moreover, the northerly regime of EPIC was dominated by convective rainfall, whereas the southerly regime was dominated by stratiform rainfall. The diurnal variability was more pronounced during TRMM/LBA than in EPIC. Shallow convection was associated with 10% and 3% of precipitation during TRMM/LBA and EPIC, respectively.

scholarly journals Statistics of Drop Size Distribution Parameters and Rain Rates for Stratiform and Convective Precipitation during the North Australian Wet Season

2013 ◽  
Vol 141 (9) ◽  
pp. 3222-3237 ◽  
Author(s):  
Guillaume Penide ◽  
Vickal V. Kumar ◽  
Alain Protat ◽  
Peter T. May
Keyword(s):  
Size Distribution ◽  
Large Scale ◽  
Drop Size ◽  
Drop Size Distribution ◽  
The Other ◽  
Convective Precipitation ◽  
Trade Wind ◽  
High Concentration ◽  
Wet Season ◽  
Rain Rates

Abstract C-band polarimetric radar measurements spanning two wet seasons are used to study the effects of the large-scale environment on the statistical properties of stratiform and convective rainfall around Darwin, Australia. The rainfall physical properties presented herein are the reflectivity fields, daily rainfall accumulations and raining area, rain rates, and drop size distribution (DSD) parameters (median volume diameter and “normalized” intercept parameter). Each of these properties is then analyzed according to five different atmospheric regimes and further separated into stratiform or convective rain categories following a DSD-based approach. The regimes, objectively identified by radiosonde thermodynamic and wind measurements, represent typical wet-season atmospheric conditions: the active monsoon regime, the “break” periods, the “buildup” regime, the trade wind regime, and a mixture of inactive/break periods. The large-scale context is found to strongly modulate rainfall and cloud microphysical properties. For example, during the active monsoon regime, the daily rain accumulation is higher than in the other regimes, while this regime is associated with the lowest rain rates. Precipitation in this active monsoon regime is found to be widespread and mainly composed of small particles in high concentration compared to the other regimes. Vertical profiles of reflectivity and DSD parameters suggest that warm rain processes are dominant during this regime. In contrast, rainfall properties in the drier regimes (trade wind/buildup regimes) are mostly of continental origin, with rain rates higher than in the moister regimes. In these drier regimes, precipitation is mainly formed of large raindrops in relatively low concentration due to a larger contribution of the ice microphysical processes on the rainfall formation.

scholarly journals Shallow and Deep Latent Heating Modes over Tropical Oceans Observed with TRMM PR Spectral Latent Heating Data

2010 ◽  
Vol 23 (8) ◽  
pp. 2030-2046 ◽  
Author(s):  
Yukari N. Takayabu ◽  
Shoichi Shige ◽  
Wei-Kuo Tao ◽  
Nagio Hirota
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Three Dimensional ◽  
Tropical Rainfall Measuring Mission ◽  
Radiative Heating ◽  
Latent Heating ◽  
Tropical Oceans ◽  
Trmm Precipitation ◽  
Subtropical Oceans ◽  
Cumulus Congestus

Abstract Three-dimensional distributions of the apparent heat source (Q1) − radiative heating (QR) estimated from Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) utilizing the spectral latent heating (SLH) algorithm are analyzed. Mass-weighted and vertically integrated Q1 − QR averaged over the tropical oceans is estimated as ∼72.6 J s−1 (∼2.51 mm day−1) and that over tropical land is ∼73.7 J s−1 (∼2.55 mm day−1) for 30°N–30°S. It is shown that nondrizzle precipitation over tropical and subtropical oceans consists of two dominant modes of rainfall systems: deep systems and congestus. A rough estimate of the shallow-heating contribution against the total heating is about 46.7% for the average tropical oceans, which is substantially larger than the 23.7% over tropical land. Although cumulus congestus heating linearly correlates with SST, deep-mode heating is dynamically bounded by large-scale subsidence. It is notable that a substantial amount of rain, as large as 2.38 mm day−1 on average, is brought from congestus clouds under the large-scale subsiding circulation. It is also notable that, even in the region with SSTs warmer than 28°C, large-scale subsidence effectively suppresses the deep convection, with the remaining heating by congestus clouds. The results support that the entrainment of mid–lower-tropospheric dry air, which accompanies the large-scale subsidence, is the major factor suppressing the deep convection. Therefore, a representation of the realistic entrainment is very important for proper reproduction of precipitation distribution and the resultant large-scale circulation.

scholarly journals Meteorological context of the onset and end of the rainy season in Central Amazonia during the 2014–15 Go-Amazon Experiment

2017 ◽  
Author(s):  
Jose A. Marengo ◽  
Gilberto F. Fisch ◽  
Lincoln M. Alves ◽  
Natanael V. Sousa ◽  
Rong Fu ◽  
...  
Keyword(s):  
Rainy Season ◽  
Large Scale ◽  
Meteorological Data ◽  
Austral Summer ◽  
Thermodynamic Characteristics ◽  
Weather Conditions ◽  
Wet Season ◽  
Significant Difference ◽  
Central Amazonia ◽  
Consecutive Dry Days

Abstract. The onset and demise of the rainy season in Amazonia are assessed in this study using meteorological data from the Go Amazon experiment, with focus is on the 2014–15 rainy season. In addition, global reanalyses are also used to identify changes in circulation leading to the establishment of the rainy season in the region. Our results show that the onset occurred in January 2015, 2–3 pentads later than normal, and the rainy season during austral summer of 2015 exhibited several periods with consecutive dry days in both Manacapuru and Manaus, which are not common for the wet season, and thus determining below normal precipitation. The onset of the rainy season has been strongly associated with changes in large-scale weather conditions in the region due to the effect of the MJO. Regional thermodynamic indices (CAPE, CIN) and the height of the PBL did not present a significant difference between the onset and demise of wet season 2015. This suggests that local changes such the regional thermodynamic characteristics may have not influenced the onset of the rainy season. Variability of the large-scale circulation was responsible for regional convection and rainfall changes in Amazonia during the austral summer of 2014–15.

scholarly journals A data-driven multi-cloud model for stochastic parametrization of deep convection

2013 ◽  
Vol 371 (1991) ◽  
pp. 20120374 ◽  
Author(s):  
J. Dorrestijn ◽  
D. T. Crommelin ◽  
J. A. Biello ◽  
S. J. Böing
Keyword(s):  
Markov Chains ◽  
General Circulation ◽  
Large Scale ◽  
Cloud Model ◽  
Deep Convection ◽  
General Circulation Models ◽  
Data Driven ◽  
Persistent Problem ◽  
Spatial Coupling ◽  
Using Data

Stochastic subgrid models have been proposed to capture the missing variability and correct systematic medium-term errors in general circulation models. In particular, the poor representation of subgrid-scale deep convection is a persistent problem that stochastic parametrizations are attempting to correct. In this paper, we construct such a subgrid model using data derived from large-eddy simulations (LESs) of deep convection. We use a data-driven stochastic parametrization methodology to construct a stochastic model describing a finite number of cloud states. Our model emulates, in a computationally inexpensive manner, the deep convection-resolving LES. Transitions between the cloud states are modelled with Markov chains. By conditioning the Markov chains on large-scale variables, we obtain a conditional Markov chain, which reproduces the time evolution of the cloud fractions. Furthermore, we show that the variability and spatial distribution of cloud types produced by the Markov chains become more faithful to the LES data when local spatial coupling is introduced in the subgrid Markov chains. Such spatially coupled Markov chains are equivalent to stochastic cellular automata.

scholarly journals Preconditioning Deep Convection with Cumulus Congestus

2013 ◽  
Vol 70 (2) ◽  
pp. 448-464 ◽  
Author(s):  
Cathy Hohenegger ◽  
Bjorn Stevens
Keyword(s):  
Time Scale ◽  
Large Scale ◽  
Deep Convection ◽  
Surface Fluxes ◽  
Scale Analysis ◽  
Convective Initiation ◽  
Clear Sky ◽  
Probability Of Transition ◽  
Cumulus Congestus ◽  
Sky Conditions

Abstract Recent studies have pushed forward the idea that congestus clouds, through their moistening of the atmosphere, could promote deep convection. On the other hand, older studies have tended to relate convective initiation to the large-scale forcing. These two views are here contrasted by performing a time-scale analysis. The analysis combines ship observations, large-eddy simulations, and 1 month of brightness temperature measurements with a focus on the tropical Atlantic and adjacent land areas. The time-scale analysis suggests that previous work may have overstated the importance of congestus moistening in the preconditioning of deep convection. It is found that cumuli congestus transition very rapidly to deep convection, in 2 h over land and 4 h over ocean. This is much faster than the time needed (10 h and longer) by congestus clouds to sufficiently moisten the atmosphere. Moreover, the majority of congestus clouds seem unable to grow into cumulonimbus and the probability of transition does not increase with increasing congestus lifetime (i.e., more moistening). Finally, the presence of cumuli congestus over a given region generally does not enhance the likelihood for deep convection development, either with respect to other regions or to clear-sky conditions. Hence, the results do not support the view of an atmosphere slowly deepening by local moistening, but rather, they may be interpreted as reminiscent of an atmosphere marked by violent and sudden outbursts of convection forced by dynamical effects. This also implies that moisture convergence is more important than local surface fluxes to trigger deep convection over a certain region.

scholarly journals Diurnal cycle of precipitation and near-surface atmospheric conditions over the maritime continent: land–sea contrast and impacts of ambient winds in cloud-permitting simulations

2021 ◽  
Author(s):  
Yuntao Wei ◽  
Zhaoxia Pu
Keyword(s):  
Diurnal Cycle ◽  
Large Scale ◽  
Deep Convection ◽  
Vertical Motion ◽  
Sea Breeze ◽  
Return Flow ◽  
Atmospheric Conditions ◽  
Maritime Continent ◽  
Regional Variability ◽  
Near Surface

AbstractA set of cloud-permitting-scale numerical simulations during January–February 2018 is used to examine the diurnal cycle (DC) of precipitation and near-surface variables (e.g., 2 m temperature, 10 m wind and convergence) over the Indo-Pacific Maritime Continent under the impacts of shore-orthogonal ambient winds (SOAWs). It is found that the DC of these variables and their variabilities of daily maxima, minima, and diurnal amplitudes vary over land, sea, and coastal regions. Among all variables, the DC of precipitation has the highest linear correlation with near-surface convergence (near-surface temperature) over coastal (noncoastal) regions. The correlations among the DCs of precipitation, wind, and heating are greater over the ocean than over land. Sine curves can model accurately the DCs of most variables over the ocean, but not over land. SOAWs act to influence the DC mainly by affecting the diurnal amplitude of the considered variables, with DC being stronger under more strengthened offshore SOAWs, though variable dependence and regional variability exist. Composite analysis over Sumatra reveals that under weak SOAWs, shallow clouds are dominant and cause a pre-moistening effect, supporting shallow-to-deep convection transition. A sea breeze circulation (SBC) with return flow aloft can develop rapidly. Cold pools are better able to trigger new updrafts and contribute to the upscale growth and inland migration of deep convection. In addition, warm gravity waves can propagate upward throughout the troposphere, thereby supporting a strong DC. In contrast, under strong SOAWs, both shallow and middle-high clouds prevail and persist throughout the day. The evolution of moistening and SBC is reduced, leading to weak variation in vertical motion and rainwater confined to the boundary layer. Large-scale winds, moisture, and convection are discussed to interpret how strong SOAWs affect the DC of Sumatra.

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