Environmental Characteristics of Convective Systems during TRMM-LBA

Halverson, Jeffrey B.; Rickenbach, Thomas M.; Roy, Biswadev; Pierce, Harold F.; Williams, Earle

doi:10.1175/1520-0493(2002)130<1493:ecocsd>2.0.co;2

Cited by 65 publications

(87 citation statements)

References 19 publications

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“…The lack of early-morning convection may also reflect the over-prediction of PBL stratocumulus simulated by the model at night above cold ground. Halverson et al (2002) reported that low-and mid-level humidity show substantial variation between the different wind regimes. This finding is important in terms of the formation of stratiform rain, cloud cover, and thermal instability during the regimes.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…In both wind regimes, maximum precipitation occurs during the early afternoon, although the peak on EWR days is slightly later than that on WWR days. Halverson et al (2002) used radar and local sounding-network data at the Abracos site to study the thermodynamics and kinematics of air mass properties during the two wind regimes. They found that on EWR days, rainfall is higher and convective precipitation makes a greater contribution to the daily total.…”

Section: Introductionmentioning

confidence: 99%

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Submonthly Variability in the South American Monsoon System

Mechoso

2007

Journal of the Meteorological Society of Japan

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In this study, we examine the South American Monsoon System (SAMS) variability with an emphasis on three-day periods or longer during which time the low-level wind in central Amazonia is consistently from the west or the east (westerly and easterly wind regimes, WWRs and EWRs, respectively). We use observational and Reanalysis datasets for the southern summer, as in previous studies on SAMS variability. Our research methodology involves the addition of model data that consists of the Coordinated Enhanced Observing Period (CEOP) Model Output Location Time Series (MOLTS) at locations in the SAMS region, and ensemble atmospheric general circulation model (AGCM) simulations of the southern summer season.For both wind regimes, the observed and simulated composites of anomalous precipitation over South America show a dipole pattern with poles in northwestern and central-southeastern Brazil. During WWRs (EWRs), precipitation anomalies at the central-southeastern pole are positive (negative), indicating a stronger (weaker) SACZ. In addition, during WWRs the upper-level monsoon high is stronger and the subtropical jet in the South American sector is stronger and closer to the equator.We also examine the diurnal cycle of rainfall from three CEOP MOLTS for Rondonia and Brasilia, which are situated at different poles of the rainfall anomalies dipole. The diurnal cycle in precipitation during both wind regimes shows an early-afternoon maximum at the selected locations. At Rondonia (Brasilia), there is a second early-morning (nocturnal) maximum on EWR (WWR) days. The diurnal mean precipitation in the regime that shows this maximum value, which is primarily due to enhanced cumulus convection, is higher than that in the other regime. In the simulation, WWRs and EWRs occur with approximately equal frequency. There is also a dipole pattern in anomalous precipitation during the days of each regime, although the poles are displaced relative to the observations. The simulated diurnal cycles of rainfall for the different wind regimes are nearly identical. Possible explanations for these AGCM difficulties are briefly discussed.Lag composites of geopotential height anomalies at 700 mb prior to the establishment of the wind regimes in Amazonia show the development of structures in the South Pacific that resemble the principal modes of variability in that region. This indicates the existence of links between the wind regimes and the modes of intraseasonal variability over South America. It is proposed that the wind regimes are associated with low-frequency variability in the extratropical circulation.

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Section: Summary and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Submonthly Variability in the South American Monsoon System

Mechoso

2007

Journal of the Meteorological Society of Japan

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“…Variability in microphysical structure is commonly observed as a function of meteorological forcing. For example, in the Amazon basin easterly low-level winds typically result in convection that is more continental in character, whereas westerly flow results in a more maritime structure Halverson et al 2002;Petersen et al 2002;Rickenbach et al 2002;Silva Dias et al 2002). Another example is in northern Australia, with ''monsoon'' versus ''break'' convection taking on characteristics of the maritime versus continental archetypes, respectively Williams et al 1992;Randell et al 1994;May and Ballinger 2007;May et al 2008).…”

Section: Introduction a Backgroundmentioning

confidence: 99%

Polarimetric Radar Observations of Convection in Northwestern Mexico during the North American Monsoon Experiment

Lang

Rutledge

Cifelli

2010

Journal of Hydrometeorology

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The spatial and temporal variability of convection during the North American Monsoon Experiment (NAME) was examined via analysis of three-dimensional polarimetric radar data. Terrain bands were defined as the Gulf of California (over water) and elevations of 0-500 m above mean sea level (MSL; coastal plain), 500-1500 m MSL, and .1500 m MSL. Convective rainfall over the Gulf typically featured the smallest values of median volume diameter (D 0 ) regardless of rain rate. Gulf convection also contained reduced precipitationsized ice water mass but proportionally more liquid water mass compared to convection over land. These maritime characteristics were magnified during disturbed meteorological regimes, which typically featured increased precipitation over the Gulf and adjacent coastal plain. Overall, the results suggest increased reliance on warm-rain collision and coalescence at the expense of ice-based precipitation growth processes for convective rainfall over the Gulf, relative to the land. Over land D 0 , ice, and liquid water mass all increased with decreasing terrain elevation, suggesting intensification of convection as it moved off the Sierra Madre Occidental. The results are consistent with the hypothesis that both warm-rain and ice-based rainfall processes play important roles in precipitation formation over land. Coastal-plain convection underwent microphysical modifications during disturbed meteorological regimes that were similar to Gulf convection, but the changes were less dramatic. High-terrain convection experienced little microphysical variability regardless of meteorological regime.

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“…In the ER, convection typically occurs in high convective available potential energy (CAPE) and vertical shear environments and is more vertically developed and electrified compared to the WR (Cifelli et al 2002;Halverson et al 2002;Petersen et al 2002).…”

Section: Introductionmentioning

confidence: 99%

An Ensemble Study of Wet Season Convection in Southwest Amazonia: Kinematics and Implications for Diabatic Heating

et al. 2004

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Dual-Doppler radar data from the Tropical Rainfall Measuring Mission Large Scale Biosphere–Atmosphere Experiment in Amazonia (TRMM-LBA) field campaign are used to determine characteristic kinematic and reflectivity vertical structures associated with precipitation features observed during the wet season in the southwest region of Amazonia. Case studies of precipitating systems during TRMM-LBA as well as overarching satellite studies have shown large differences in convective intensity associated with changes that develop in low-level easterly flow [east regime (ER)] and westerly flow [west regime (WR)]. This study attempts to examine the vertical kinematic and heating structure of convection across the spectrum of precipitation features that occurred in each regime. Results show that convection in the ER is characterized by more intense updrafts and larger radar reflectivities above the melting level, in agreement with results from lightning detection networks. These regime differences are consistent with contrasts in composite thermal buoyancy between the regimes: above the boundary layer, the environment in the ER is characterized by a greater virtual temperature excess for near-surface rising parcels. Both regimes showed a peak in intensity during the late afternoon hours, as evidenced by radar reflectivity and kinematic characteristics, consistent with previous studies of rainfall and lightning in the Rondônia (TRMM-LBA) region. After sunset, however, convective intensity in the WR decreases much more abruptly compared to the ER. In the stratiform–weak convective region, the ER showed both reflectivity and kinematic characteristics of classic stratiform structure after sunset through the early morning hours, consistent with the life cycle of mesoscale conjective systems (MCSs). Apparent heating (Q1) profiles were constructed for each regime assuming the vertical advection of dry static energy was the dominant forcing term. The resulting profiles show a peak centered near 8 km in the convective regions of both regimes, although the ER has a broader maximum compared to the WR. The breadth of the ER diabatic heating peak is consistent with the more dominant role of ice processes in ER convection.

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Environmental Characteristics of Convective Systems during TRMM-LBA

Cited by 65 publications

References 19 publications

Submonthly Variability in the South American Monsoon System

Submonthly Variability in the South American Monsoon System

Polarimetric Radar Observations of Convection in Northwestern Mexico during the North American Monsoon Experiment

An Ensemble Study of Wet Season Convection in Southwest Amazonia: Kinematics and Implications for Diabatic Heating

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