scholarly journals On the Controls of Daytime Precipitation in the Amazonian Dry Season

2016 ◽  
Vol 17 (12) ◽  
pp. 3079-3097 ◽  
Author(s):  
Virendra P. Ghate ◽  
Pavlos Kollias
Keyword(s):  
Large Scale ◽  
Amazon Basin ◽  
Deep Convection ◽  
Critical Role ◽  
Dry Season ◽  
Diurnal Cycles ◽  
Squall Lines ◽  
Dry Seasons ◽  
Rain Events ◽  
Precipitation Events

Abstract The Amazon plays an important role in the global energy and hydrological budgets. The precipitation during the dry season (June–September) plays a critical role in maintaining the extent of the rain forest. The deployment of the first Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF-1) in the context of the Green Ocean Amazon (GOAmazon) field campaign at Manacapuru, Brazil, provided comprehensive measurements of surface, cloud, precipitation, radiation, and thermodynamic properties for two complete dry seasons (2014 and 2015). The precipitation events occurring during the nighttime were associated with propagating storm systems (nonlocal effects), while the daytime precipitation events were primarily a result of local land–atmosphere interactions. During the two dry seasons, precipitation was recorded at the surface on 106 days (43%) from 158 rain events with 82 daytime precipitation events occurring on 64 days (60.37%). Detailed comparisons between the diurnal cycles of surface and profile properties between days with and without daytime precipitation suggested the increased moisture at low and midlevels to be responsible for lowering the lifting condensation level, reducing convective inhibition and entrainment, and thus triggering the transition from shallow to deep convection. Although the monthly accumulated rainfall decreased during the progression of the dry season, the contribution of daytime precipitation to it increased, suggesting the decrease to be mainly due to reduction in propagating squall lines. The control of daytime precipitation during the dry season on large-scale moisture advection above the boundary layer and the total rainfall on propagating squall lines suggests that coarse-resolution models should be able to accurately simulate the dry season precipitation over the Amazon basin.

Cloud macrophysical properties from airborne observations during EUREC4A

2020 ◽  
Author(s):  
Heike Konow ◽  
Marcus Klingebiel ◽  
Felix Ament
Keyword(s):  
Deep Convection ◽  
Dry Season ◽  
Trade Wind ◽  
Special Focus ◽  
Wet Season ◽  
Diurnal Cycles ◽  
Cloud Radar ◽  
Wide Range ◽  
Macrophysical Properties ◽  
Different Response

<p><span>Trade wind cumulus clouds are the predominant cloud type over the tropical Atlantic east of the island of Barbados. Parameters describing their macroscopic shape can help characterizing and comparing general features of clouds. This characterizing will indirectly help to constrain estimates of climate sensitivity, because models with different structures of trade wind cumuli feature different response to increased CO2 contents.</span></p><p><span>Two aircraft campaigns with the HALO (High Altitude LOng range) aircraft took place in the recent past in this region: NARVAL-South (Next-generation Aircraft Remote-Sensing for VALidation studies) in December 2013, during the dry season, and NARVAL2 in August 2016, during the wet season. During these two campaigns, a wide range of cloud regimes from shallow to deep convection were sampled. This past observations are now extended with observations from this year’s measurement campaign EUREC<sup>4</sup>A, again during the dry season. EUREC<sup>4</sup>A is endorsed as WCRP capstone experiment and the synergy of four research aircraft, four research vessels and numerous additional observations will provide comprehensive characterizations of trade wind clouds and their environment.</span></p><p><span>Part of the NARVAL payload on HALO is a 35 GHz cloud radar, which has been deployed on HALO on several missions since 2013. These cloud radar measurements are used to segment individual clouds entities by applying connected component analysis to the radar cloud mask. From these segmented individual clouds, macrophysical parameters are derived to characterize each individual cloud. </span></p><p><span>This presentation will give an overview of the cloud macrophysics observed from HALO during EUREC<sup>4</sup>A. Typical macrophysical parameters, i.e. cloud depth, cloud length, cloud fraction, are analyzed. We will relate these to observations from past campaigns and assess the representativeness of EUREC<sup>4</sup>A. As special focus of the EUREC<sup>4</sup>A campaign, measurements will be performed during different times of the day to detect diurnal cycles. Macrophysical parameters can be used to characterize changes over the day and cloud scenes of similar clouds types can be identified.</span></p>

Response of Humidity and Clouds to Tropical Deep Convection

2009 ◽  
Vol 22 (9) ◽  
pp. 2389-2404 ◽  
Author(s):  
Mark D. Zelinka ◽  
Dennis L. Hartmann
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Lower Troposphere ◽  
Upward Motion ◽  
Temporal Separation ◽  
Convective Event ◽  
Clear Sky ◽  
Intense Precipitation ◽  
Upper Level ◽  
Precipitation Events

Abstract Currently available satellite data can be used to track the response of clouds and humidity to intense precipitation events. A compositing technique centered in space and time on locations experiencing high rain rates is used to detail the characteristic evolution of several quantities measured from a suite of satellite instruments. Intense precipitation events in the convective tropics are preceded by an increase in low-level humidity. Optically thick cold clouds accompany the precipitation burst, which is followed by the development of spreading upper-level anvil clouds and an increase in upper-tropospheric humidity over a broader region than that occupied by the precipitation anomalies. The temporal separation between the convective event and the development of anvil clouds is about 3 h. The humidity increase at upper levels and the associated decrease in clear-sky longwave emission persist for many hours after the convective event. Large-scale vertical motions from reanalysis show a coherent evolution associated with precipitation events identified in an independent dataset: precipitation events begin with stronger upward motion anomalies in the lower troposphere, which then evolve toward stronger upward motion anomalies in the upper troposphere, in conjunction with the development of anvil clouds. Greater upper-tropospheric moistening and cloudiness are associated with larger-scale and better-organized convective systems, but even weaker, more isolated systems produce sustained upper-level humidity and clear-sky outgoing longwave radiation anomalies.

scholarly journals Intense Rainfall Events Affecting the La Plata Basin

2006 ◽  
Vol 7 (4) ◽  
pp. 769-787 ◽  
Author(s):  
Viviane B. S. Silva ◽  
Ernesto H. Berbery
Keyword(s):  
Large Scale ◽  
Amazon Basin ◽  
Level Structure ◽  
Intense Rainfall ◽  
Rainfall Events ◽  
La Plata ◽  
La Plata Basin ◽  
Intense Precipitation ◽  
Eta Model ◽  
Precipitation Events

Abstract The circulation features associated with intense precipitation events over the La Plata Basin (LPB) during the austral summers of 2001/02 and 2002/03 are investigated using the Eta Model runs generated at the University of Maryland. Based on the main mode of variability over LPB, two regions were selected: (i) the region of Brazil that is at the core of the South American summer monsoon system (SAMS) and (ii) the central region of LPB in southeastern South America (SESA). First, a comparison between the 24-h total precipitation in the Eta Model and the 24-h observed precipitation was made. Results show that the Eta Model captures well the temporal variability of precipitation events in both regions, although a positive bias is noticed over SAMS. Likewise, the model reproduces the distribution of precipitation rate over SESA, but not over SAMS. Nevertheless, the distribution of the moisture flux convergence intensity, which represents the dynamical forcing, is closer in shape to the observed precipitation distribution, suggesting that the model can be a useful tool in identifying the forcing for heavy precipitation events over both regions. Composites of atmospheric and surface variables were constructed for intense precipitation events during austral summer over both regions. Intense rainfall over the central La Plata Basin (SESA) is linked to an amplified upper-tropospheric midlatitude wave pattern in which rainfall occurs just east of an enhanced cyclonic circulation. Accompanying this circulation pattern, an enhanced low-level jet (LLJ) transports warm, moist air from the Amazon toward the region, contributing to an increase in the thermal contrast over SESA. The combined patterns of thermal and dynamical variables suggest that large-scale systems, like frontal systems, are important in producing intense rainfall events. The SAMS region events have a similar upper-level structure as in SESA, but they are longer lived. In this case, the moisture fluxes are determined by an eastward shift of the LLJ, but also directly from the Amazon Basin to the north. As expected, precipitation events produce large increases of simulated runoff. The largest impact is on the SESA region, affecting the streamflow of the Paraná, Paraguay, and Uruguay, the three main rivers of the LPB.

scholarly journals Wet Days in the Dry Quarter of the Alcântara Launch Center Region: Observational Features

2019 ◽  
Author(s):  
Paulo César Silva da Costa ◽  
Marcos Daisuke Oyama ◽  
Rosa de Fátima Cruz Marques
Keyword(s):  
Large Scale ◽  
Daily Precipitation ◽  
Weather Forecasting ◽  
Deep Convection ◽  
Longwave Radiation ◽  
Heavy Precipitation ◽  
Large Area ◽  
Launch Site ◽  
Precipitation Total ◽  
Precipitation Events

Precipitation events are infrequent in the dry quarter (SON) of the Alcântara Launch Center (Centro de Lançamento de Alcântara, CLA), the main launch site of the Brazilian Space Program. However, their occurrence could be a risk for activities during launch missions. In this work, the observational features of wet days (daily precipitation total ≥ 1 mm/day) in the dry quarter of the CLA region were studied. Daily precipitation totals over the course of 37 years (1979-2016, except 2006), outgoing longwave radiation (OLR) data and ERA-Interim reanalysis data were used. On average, in the dry quarter, there were 9 wet days, which accumulated 32 mm. The number and quarterly precipitation total of wet days showed pronounced interannual variability. This variability was negatively and significantly correlated with the interhemispheric sea surface temperature anomalies gradient in the Atlantic Ocean and the wind speed at 925 hPa over the CLA region. Based on a theoretical distribution (log-normal), the probability of occurrence of heavy precipitation days (daily total ≥ 10 mm/day) was only 0.5%. For days with heavy precipitation and deep convection (OLR ≤ 230 W·m-2), over a large area along the northeastern coast of South America including the CLA region, negative OLR differences (from the mean) and the strengthening of favorable conditions for deep convection were found. The large-scale organization of the convective activity and atmospheric features for higher precipitation events obtained in this work could be helpful for nowcasting and short-range weather forecasting during launch missions at the CLA.

scholarly journals Cloud characteristics, thermodynamic controls and radiative impacts during the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) experiment

2017 ◽  
Vol 17 (23) ◽  
pp. 14519-14541 ◽  
Author(s):  
Scott E. Giangrande ◽  
Zhe Feng ◽  
Michael P. Jensen ◽  
Jennifer M. Comstock ◽  
Karen L. Johnson ◽  
...  
Keyword(s):  
Large Scale ◽  
Amazon Basin ◽  
Department Of Energy ◽  
Cloud Characteristics ◽  
Radiative Impacts ◽  
Atmospheric Radiation Measurement ◽  
Dry Seasons ◽  
Basin Region ◽  
Cloud Regimes ◽  
Wet And Dry Seasons

Abstract. Routine cloud, precipitation and thermodynamic observations collected by the Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) and Aerial Facility (AAF) during the 2-year US Department of Energy (DOE) ARM Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) campaign are summarized. These observations quantify the diurnal to large-scale thermodynamic regime controls on the clouds and precipitation over the undersampled, climatically important Amazon basin region. The extended ground deployment of cloud-profiling instrumentation enabled a unique look at multiple cloud regimes at high temporal and vertical resolution. This longer-term ground deployment, coupled with two short-term aircraft intensive observing periods, allowed new opportunities to better characterize cloud and thermodynamic observational constraints as well as cloud radiative impacts for modeling efforts within typical Amazon wet and dry seasons.

scholarly journals What Controls Evapotranspiration in the Amazon Basin?

2007 ◽  
Vol 8 (3) ◽  
pp. 380-395 ◽  
Author(s):  
Natalia Hasler ◽  
Roni Avissar
Keyword(s):  
Water Stress ◽  
Large Scale ◽  
Amazon Basin ◽  
Climate Models ◽  
Global Climate ◽  
Regional Climate ◽  
Dry Season ◽  
Global Climate Models ◽  
Net Radiation ◽  
Wet Season

Abstract Global climate models (GCMs) and regional climate models (RCMs) generally show a decrease in the dry season evapotranspiration (ET) rate over the entire Amazon basin. Based on anecdotal observations, it has been suggested that they probably overestimate tropical rain forest water stress. In this study, eddy covariance flux measurements from eight different towers of the Large-Scale Biosphere–Atmosphere Experiment in Amazonia (LBA) were used to provide a first look at the spatial variability and temporal cycle of ET throughout the basin. Results show strong seasonality in ET for stations near the equator (2°–3°S), with ET increasing during the dry season (June–September) and decreasing during the wet season (December–March), both correlated (0.75 to 0.94) and in phase with the net radiation annual cycle. In stations located farther south (9°–11°S) no clear seasonality could be identified in either net radiation or ET. For these more southerly stations, net radiation and ET are still correlated (0.76–0.92) in the wet season, but correlations decrease in the dry season (0–0.71), which is likely associated with water stress. For both pasture sites, located in southern Amazonia, ET decreases during the second half of the dry season, indicating progressively increased water stress. GCMs and RCMs indeed tend to overestimate dry season water stress in the Amazon basin and, therefore, should be revised to better simulate this region, which has a key role in the global hydrometeorology.

scholarly journals Prediction and Diagnosis of Tropical Cyclone Formation in an NWP System. Part I: The Critical Role of Vortex Enhancement in Deep Convection

2006 ◽  
Vol 63 (12) ◽  
pp. 3077-3090 ◽  
Author(s):  
K. J. Tory ◽  
M. T. Montgomery ◽  
N. E. Davidson
Keyword(s):  
Tropical Cyclone ◽  
Large Scale ◽  
Deep Convection ◽  
Weather Prediction ◽  
Critical Role ◽  
Research Programme ◽  
Limited Area ◽  
Tropical Ocean ◽  
Enhancement Mechanism ◽  
Toga Coare

This is the first of a three-part investigation into tropical cyclone (TC) genesis in the Australian Bureau of Meteorology’s Tropical Cyclone Limited Area Prediction System (TC-LAPS), an operational numerical weather prediction (NWP) forecast model. The primary TC-LAPS vortex enhancement mechanism is presented in Part I, the entire genesis process is illustrated in Part II using a single TC-LAPS simulation, and in Part III a number of simulations are presented exploring the sensitivity and variability of genesis forecasts in TC-LAPS. The primary vortex enhancement mechanism in TC-LAPS is found to be convergence/stretching and vertical advection of absolute vorticity in deep intense updrafts, which result in deep vortex cores of 60–100 km in diameter (the minimum resolvable scale is limited by the 0.15° horizontal grid spacing). On the basis of the results presented, it is hypothesized that updrafts of this scale adequately represent mean vertical motions in real TC genesis convective regions, and perhaps that explicitly resolving the individual convective processes may not be necessary for qualitative TC genesis forecasts. Although observations of sufficient spatial and temporal resolution do not currently exist to support or refute this proposition, relatively large-scale (30 km and greater), lower- to midlevel tropospheric convergent regions have been observed in tropical oceanic environments during the Global Atmospheric Research Programme (GARP) Atlantic Tropical Experiment (GATE), the Equatorial Mesoscale Experiment (EMEX), and the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE), and regions of extreme convection of the order of 50 km are often (remotely) observed in TC genesis environments. These vortex cores are fundamental for genesis in TC-LAPS. They interact to form larger cores, and provide net heating that drives the system-scale secondary circulation, which enhances vorticity on the system scale akin to the classical Eliassen problem of a balanced vortex driven by heat sources. These secondary vortex enhancement mechanisms are documented in Part II. In some recent TC genesis theories featured in the literature, vortex enhancement in deep convective regions of mesoscale convective systems (MCSs) has largely been ignored. Instead, they focus on the stratiform regions. While it is recognized that vortex enhancement through midlevel convergence into the stratiform precipitation deck can greatly enhance midtropospheric cyclonic vorticity, it is suggested here that this mechanism only increases the potential for genesis, whereas vortex enhancement through low- to midlevel convergence into deep convective regions is necessary for genesis.

scholarly journals Cloud Characteristics, Thermodynamic Controls and Radiative Impacts During the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) Experiment

2017 ◽  
Author(s):  
Scott E. Giangrande ◽  
Zhe Feng ◽  
Michael P. Jensen ◽  
Jennifer Comstock ◽  
Karen L. Johnson ◽  
...  
Keyword(s):  
Large Scale ◽  
Amazon Basin ◽  
Short Term ◽  
Cloud Characteristics ◽  
Cloud Regime ◽  
Radiative Impacts ◽  
Dry Seasons ◽  
Thermodynamic Regime ◽  
Basin Region ◽  
Wet And Dry Seasons

Abstract. Routine cloud, precipitation and thermodynamic observations collected by the ARM Mobile Facility (AMF) and Aerial Facility (AAF) during the two-year DOE ARM Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) campaign are summarized. These observations quantify the diurnal to large-scale thermodynamic regime controls on the clouds and precipitation over the undersampled, climatically important, Amazon basin region. The extended ground deployment of cloud-profiling instrumentation enabled a unique look at multiple cloud regime controls at high temporal and vertical resolution. This longer-term ground deployment coupled with two short-term aircraft intensive observing periods allowed new opportunities to better characterize cloud and thermodynamic observational constraints as well as cloud radiative impacts for modeling efforts within typical Amazon ‘wet’ and ‘dry’ seasons.

scholarly journals Diurnal variations of southerly monsoon surge and their impacts on East Asian summer rainfall

2021 ◽  
pp. 1-49
Author(s):  
Biqi Liu ◽  
Guixing Chen ◽  
Wenxin Zeng ◽  
Lanqiang Bai ◽  
Huiling Qin
Keyword(s):  
Water Vapor ◽  
East Asia ◽  
Large Scale ◽  
Western Pacific Subtropical High ◽  
Summer Rainfall ◽  
Diurnal Variations ◽  
Water Vapor Transport ◽  
Diurnal Cycles ◽  
The North ◽  
Rain Events

AbstractMonsoon southerlies can be particularly active for days and produce substantial rainfall over East Asia. These multiday episodes of southerly monsoon surge may exhibit distinct diurnal variations due to regional forcings under given large-scale conditions. This study categorizes the southerly surges into two types with different wind diurnal variations to clarify their influence on rainfall over East Asia. In the summer of 1998–2019, there are 63 episodes of southerly surge with large wind diurnal cycles and 55 episodes with small diurnal cycles. The first type of southerly surges usually occurs with anomalous low-level warming over southeastern China related to the westward extension of the western Pacific subtropical high. The second type of southerly surges instead occurs with anomalous cooling due to the deepened midlatitude trough. They thus represent the different mechanisms downscaling from large-scale conditions to regional diurnal forcings. After the onset of the first type, the intensified monsoon southerlies at night lead to the northward displacement of large-scale ascent and northward water vapor transport with warm moist energy. The monsoon rainband tends to move to the north of 35°N with a robust response in precipitation systems, especially in the meso-α-scale rain events from midnight to morning. As a comparison, the rainband stays at 30°–35°N after the onset of the second type when the strengthened large-scale ascent and water vapor convergence are located relatively south. These differences between the two types of southerly monsoon surges highlight that the multiday large-scale conditions interact with sub-daily regional forcings and greatly regulate the detailed evolution of summer rainband over East Asia.

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