scholarly journals Baroclinicity Influences on Storm Divergence and Stratiform Rain: Subtropical Upper-Level Disturbances

2009 ◽  
Vol 137 (4) ◽  
pp. 1338-1357 ◽  
Author(s):  
Larry J. Hopper ◽  
Courtney Schumacher
Keyword(s):  
Diabatic Heating ◽  
Doppler Radar ◽  
Mesoscale Model ◽  
Deep Convection ◽  
Separation Algorithm ◽  
Rain Area ◽  
Stratiform Rain ◽  
Wide Range ◽  
Upper Level ◽  
The Tropics

Abstract Divergence structures associated with the spectrum of precipitating systems in the subtropics and midlatitudes are not well documented. A mesoscale model is used to quantify the relative importance different baroclinic environments have on divergence profiles for storms primarily caused by upper-level disturbances in southeastern Texas, a subtropical region. The divergence profiles simulated for a subset of the modeled storms are consistent with those calculated from an S-band Doppler radar. Realistic convective and stratiform divergence signals are also generated when applying a two-dimensional convective–stratiform separation algorithm to reflectivities derived from the mesoscale model, although the model appears to underestimate stratiform rain area. Divergence profiles from the modeled precipitating systems vary in magnitude and structure across the wide range of baroclinicities common in southeastern Texas. Barotropic storms more characteristic of the tropics generate the most elevated divergence (and thus diabatic heating) structures with the largest magnitudes. In addition, stratiform rain regions in barotropic storms contain thicker, more elevated midlevel convergence signatures than more baroclinic storms. As the degree of baroclinicity increases, stratiform area fractions generally increase while the levels of nondivergence (LNDs) decrease. However, some weakly baroclinic storms contain stratiform area fractions and/or divergence profiles with magnitudes and LNDs that are similar to barotropic storms, despite having lower tropopause heights and less deep convection. Additional convection forms after the passage of barotropic and weakly baroclinic storms that contain elevated divergence signatures, circumstantially suggesting that heating at upper levels may cause diabatic feedbacks that help to drive regions of persistent convection in the subtropics.

Assessing the Applicability of the Tropical Convective–Stratiform Paradigm in the Extratropics Using Radar Divergence Profiles

2014 ◽  
Vol 27 (17) ◽  
pp. 6673-6686 ◽  
Author(s):  
Cameron R. Homeyer ◽  
Courtney Schumacher ◽  
Larry J. Hopper
Keyword(s):  
Large Scale ◽  
Diabatic Heating ◽  
Horizontal Wind ◽  
Stratiform Rain ◽  
Vertical Divergence ◽  
Upper Level ◽  
The Tropics ◽  
The Impact ◽  
Level Disturbance

Abstract Long-term radar observations from a subtropical location in southeastern Texas are used to examine the impact of storm systems with tropical or extratropical characteristics on the large-scale circulation. Climatological vertical profiles of the horizontal wind divergence are analyzed for four distinct storm classifications: cold frontal (CF), warm frontal (WF), deep convective upper-level disturbance (DC-ULD), and nondeep convective upper-level disturbances (NC-ULD). DC-ULD systems are characterized by weakly baroclinic or equivalent barotropic environments that are more tropical in nature, while the remaining classifications are representative of common midlatitude systems with varying degrees of baroclinicity. DC-ULD systems are shown to have the highest levels of nondivergence (LND) and implied diabatic heating maxima near 6 km, whereas the remaining baroclinic storm classifications have LND altitudes that are about 0.5–1 km lower. Analyses of climatological mean divergence profiles are also separated by rain regions that are primarily convective, stratiform, or indeterminate. Convective–stratiform separations reveal similar divergence characteristics to those observed in the tropics in previous studies, with higher altitudes of implied heating in stratiform rain regions, suggesting that the convective–stratiform paradigm outlined in previous studies is applicable in the midlatitudes. Divergence profiles that cannot be classified as primarily convective or stratiform are typically characterized by large regions of stratiform rain with areas of embedded convection of shallow to moderate extent (i.e., echo tops <10 km). These indeterminate profiles illustrate that, despite not being very deep and accounting for a relatively small fraction of a given storm system, convection dominates the vertical divergence profile and implied heating in these cases.

scholarly journals Airborne Doppler Radar and Sounding Analysis of an Oceanic Cold Front

2008 ◽  
Vol 136 (4) ◽  
pp. 1475-1491 ◽  
Author(s):  
Roger M. Wakimoto ◽  
Hanne V. Murphey
Keyword(s):  
Diabatic Heating ◽  
Doppler Radar ◽  
Frontal Zone ◽  
Cold Front ◽  
Deep Convection ◽  
Dominant Term ◽  
Low Level ◽  
Frontal Zones ◽  
Low Level Jet ◽  
Upper Level

Abstract An analysis of a cold front over the eastern Atlantic Ocean based on airborne Doppler wind syntheses and dropsonde data is presented. The focus and unique aspect of this study is a segment of the front that was near the center of the cyclone. The dual-Doppler wind synthesis of the frontal zone combined with an average dropsonde spacing of ∼30 km covers a total distance of >450 km in the cross-frontal direction. The finescale resolution and areal coverage of the dataset are believed to be unprecedented. The cold front was characterized by a distinct wind shift and a strong horizontal temperature gradient. The latter was most intense aloft and not at the surface, in contrast to the classical paradigm of surface cold fronts. The shear of the alongfront component of the wind was relatively uniform as a function of height within the frontal zone. This observation is contrary to studies suggesting that frontal zones decrease in intensity above the surface. The surface convergence within the frontal zone was weak. This may have been related to the closeness of the analysis region to the surface low pressure. The prefrontal low-level jet and the upper-level polar jet were both shown to be supergeostrophic based on the analysis of the geopotential height field. It is believed that a major contributing factor to the former was the isallobaric wind from the large pressure tendencies associated with the moving cyclone. A dry pocket accompanied by descending air was noted out ahead of the low-level jet. This pocket produced a region of potential instability that could have supported deep convection, although none was observed on this day. The vertical structure of the front revealed couplets of potential vorticity that appeared to be the result of diabatic heat sources from condensation. The diabatic effect in the frontogenesis equation was the dominant term, exceeding the combined effects of the confluence and tilting terms. As a result, an alternating pattern of frontogenesis–frontolysis developed along the flanks of the maxima of diabatic heating. This study highlights the importance of taking diabatic heating into account even in the absence of deep convection.

scholarly journals Modeled and Observed Variations in Storm Divergence and Stratiform Rain Production in Southeastern Texas

2012 ◽  
Vol 69 (4) ◽  
pp. 1159-1181 ◽  
Author(s):  
Larry J. Hopper ◽  
Courtney Schumacher
Keyword(s):  
Doppler Radar ◽  
Mesoscale Model ◽  
Warm Season ◽  
Rain Area ◽  
Stratiform Rain ◽  
Ensemble Mean ◽  
Mesoscale Convective ◽  
Single Moment ◽  
Double Moment ◽  
Mesoscale Convective Vortex

Abstract Storm divergence profiles observed by an S-band Doppler radar are compared to ensemble simulations of 10 disparate precipitating systems occurring in warm-season, weakly baroclinic, and strongly baroclinic environments in southeastern Texas. Eight triply nested mesoscale model simulations are conducted for each case using single- and double-moment microphysics with four convective treatments (i.e., two convective parameterizations and explicit versus parameterized convection at 9 km). Observed and simulated radar reflectivities are objectively separated into convective, stratiform, and nonprecipitating anvil columns and comparisons are made between ensemble mean echo coverages and levels of nondivergence (LNDs). In both the model and observations, storms occurring in less baroclinic environments have more convective rain area, less stratiform rain area, and more elevated divergence profiles. The model ensemble and observations agree best for well-organized leading-line trailing-stratiform systems. Excessive convective area fractions are simulated for several less-organized cases, especially those whose ensemble mean LNDs are about 1–2 km more elevated than observed. Simulations parameterizing convection on the intermediate grid produced less-elevated divergence profiles with smaller magnitudes compared to their explicit counterparts. In one warm-season case, utilizing double-moment microphysics when parameterizing convection on both outer grids generated lower LNDs associated with variations in convective intensity and depth, detraining less ice to anvil and stratiform regions at midlevels relative to its single-moment counterpart. Similarly, mesoscale convective vortex simulations employing an ensemble-based versus a single-closure convective parameterization on both outer grids produced the least-elevated heating structures (closer to observed), resulting in the weakest midlevel vortices.

scholarly journals Land–atmosphere interactions in the tropics

2019 ◽  
Author(s):  
Pierre Gentine ◽  
Adam Massmann ◽  
Benjamin R. Lintner ◽  
Sayed Hamed Alemohammad ◽  
Rong Fu ◽  
...  
Keyword(s):  
Land Surface ◽  
Deep Convection ◽  
Lower Troposphere ◽  
Surface Fluxes ◽  
Surface Radiation ◽  
Spatial And Temporal Scales ◽  
Wide Range ◽  
Shallow Clouds ◽  
The Tropics ◽  
The Impact

Abstract. The continental tropics play a leading role in the terrestrial water and carbon cycles. Land–atmosphere interactions are integral in the regulation of surface energy, water and carbon fluxes across multiple spatial and temporal scales over tropical continents. We review here some of the important characteristics of tropical continental climates and how land–atmosphere interactions regulate them. Along with a wide range of climates, the tropics manifest a diverse array of land–atmosphere interactions. Broadly speaking, in tropical rainforests, light and energy are typically more limiting than precipitation and water supply for photosynthesis and evapotranspiration; whereas in savanna and semi-arid regions water is the critical regulator of surface fluxes and land–atmosphere interactions. We discuss the impact of the land surface, how it affects shallow clouds and how these clouds can feedback to the surface by modulating surface radiation. Some results from recent research suggest that shallow clouds may be especially critical to land–atmosphere interactions as these regulate the energy budget and moisture transport to the lower troposphere, which in turn affects deep convection. On the other hand, the impact of land surface conditions on deep convection appear to occur over larger, non-local, scales and might be critically affected by transitional regions between the climatologically dry and wet tropics.

scholarly journals A statistical analysis of the influence of deep convection on water vapor variability in the tropical upper troposphere

2009 ◽  
Vol 9 (15) ◽  
pp. 5847-5864 ◽  
Author(s):  
J. S. Wright ◽  
R. Fu ◽  
A. J. Heymsfield
Keyword(s):  
Water Vapor ◽  
Deep Convection ◽  
Tropical Rainfall Measuring Mission ◽  
Upper Troposphere ◽  
Ambient Relative Humidity ◽  
Wide Range ◽  
Ice Water Content ◽  
The Tropics ◽  
Ice Water ◽  
Tropical Upper Troposphere

Abstract. The factors that control the influence of deep convective detrainment on water vapor in the tropical upper troposphere are examined using observations from multiple satellites in conjunction with a trajectory model. Deep convection is confirmed to act primarily as a moisture source to the upper troposphere, modulated by the ambient relative humidity (RH). Convective detrainment provides strong moistening at low RH and offsets drying due to subsidence across a wide range of RH. Strong day-to-day moistening and drying takes place most frequently in relatively dry transition zones, where between 0.01% and 0.1% of Tropical Rainfall Measuring Mission Precipitation Radar observations indicate active convection. Many of these strong moistening events in the tropics can be directly attributed to detrainment from recent tropical convection, while others in the subtropics appear to be related to stratosphere-troposphere exchange. The temporal and spatial limits of the convective source are estimated to be about 36–48 h and 600–1500 km, respectively, consistent with the lifetimes of detrainment cirrus clouds. Larger amounts of detrained ice are associated with enhanced upper tropospheric moistening in both absolute and relative terms. In particular, an increase in ice water content of approximately 400% corresponds to a 10–90% increase in the likelihood of moistening and a 30–50% increase in the magnitude of moistening.

scholarly journals The Role of Observed Environmental Conditions and Precipitation Evolution in the Rapid Intensification of Hurricane Earl (2010)

2015 ◽  
Vol 143 (6) ◽  
pp. 2207-2223 ◽  
Author(s):  
Gabriel Susca-Lopata ◽  
Jonathan Zawislak ◽  
Edward J. Zipser ◽  
Robert F. Rogers
Keyword(s):  
Structural Changes ◽  
Doppler Radar ◽  
Deep Convection ◽  
Vertical Wind Shear ◽  
Radar Data ◽  
Rapid Intensification ◽  
Low Level ◽  
Upper Level ◽  
Wind Retrievals

Abstract An investigation into the possible causes of the rapid intensification (RI) of Hurricane Earl (2010) is carried out using a combination of global analyses, aircraft Doppler radar data, and observations from passive microwave satellites and a long-range lightning network. Results point to an important series of events leading to, and just after, the onset of RI, all of which occur despite moderate (7–12 m s−1) vertical wind shear present. Beginning with an initially vertically misaligned vortex, observations indicate that asymmetric deep convection, initially left of shear but not distinctly up- or downshear, rotates into more decisively upshear regions. Following this convective rotation, the vortex becomes aligned and precipitation symmetry increases. The potential contributions to intensification from each of these structural changes are discussed. The radial distribution of intense convection relative to the radius of maximum wind (RMW; determined from Doppler wind retrievals) is estimated from microwave and lightning data. Results indicate that intense convection is preferentially located within the upper-level (8 km) RMW during RI, lending further support to the notion that intense convection within the RMW promotes tropical cyclone intensification. The distribution relative to the low-level RMW is more ambiguous, with intense convection preferentially located just outside of the low-level RMW at times when the upper-level RMW is much greater than the low-level RMW.

scholarly journals Thick Anvils as Viewed by the TRMM Precipitation Radar

2011 ◽  
Vol 24 (6) ◽  
pp. 1718-1735 ◽  
Author(s):  
Wei Li ◽  
Courtney Schumacher
Keyword(s):  
Southern Oscillation ◽  
Deep Convection ◽  
Tropical Rainfall Measuring Mission ◽  
Precipitation Radar ◽  
Central Pacific ◽  
Rain Area ◽  
Areal Coverage ◽  
Trmm Precipitation ◽  
Upper Level ◽  
Highly Correlated

Abstract This study investigates anvils from thick, nonprecipitating clouds associated with deep convection as observed in the tropics by the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) during the 10-yr period, 1998–2007. Anvils observable by the PR occur, on average, 5 out of every 100 days within grid boxes with 2.5° resolution and with a conditional areal coverage of 1.5%. Unconditional areal coverage is only a few tenths of a percent. Anvils also had an average 17-dBZ echo top of ∼8.5 km and an average thickness of ∼2.7 km. Anvils were usually higher and thicker over land compared to ocean, and occurred most frequently over Africa, the Maritime Continent, and Panama. Anvil properties were intimately tied to the properties of the parent convection. In particular, anvil area and echo-top heights were highly correlated to convective rain area. The next best predictor for anvil areal coverage and echo tops was convective echo tops, while convective reflectivities had the weakest correlation. Strong upper-level wind shear also may be associated with anvil occurrence over land, especially when convection regularly attains echo-top heights greater than 7 km. Some tropical land regions, especially those affected by monsoon circulations, experience significant seasonal variability in anvil properties—strong interannual anvil variability occurs over the central Pacific because of the El Niño–Southern Oscillation. Compared to the CloudSat Cloud Profiling Radar, the TRMM PR underestimates anvil-top height by an average of ∼5 km and underestimates their horizontal extent by an average factor of 4.

scholarly journals Factors Affecting the Evolution of Hurricane Erin (2001) and the Distributions of Hydrometeors: Role of Microphysical Processes

2006 ◽  
Vol 63 (1) ◽  
pp. 127-150 ◽  
Author(s):  
Greg M. McFarquhar ◽  
Henian Zhang ◽  
Gerald Heymsfield ◽  
Jeffrey B. Halverson ◽  
Robbie Hood ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Doppler Radar ◽  
Mesoscale Model ◽  
Potential Temperature ◽  
Vertical Motion ◽  
Rain Area ◽  
Microphysics Scheme ◽  
Factors Affecting ◽  
Mixing Ratios ◽  
Microphysical Processes

Abstract Fine-resolution simulations of Hurricane Erin are conducted using the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) to investigate roles of thermodynamic, boundary layer, and microphysical processes on Erin’s structure and evolution. Choice of boundary layer scheme has the biggest impact on simulations, with the minimum surface pressure (Pmin) averaged over the last 18 h (when Erin is relatively mature) varying by over 20 hPa. Over the same period, coefficients used to describe graupel fall speeds (Vg) affect Pmin by up to 7 hPa, almost equivalent to the maximum 9-hPa difference between microphysical parameterization schemes; faster Vg and schemes with more hydrometeor categories generally give lower Pmin. Compared to radar reflectivity factor (Z) observed by the NOAA P-3 lower fuselage radar and the NASA ER-2 Doppler radar (EDOP) in Erin, all simulations overpredict the normalized frequency of occurrence of Z larger than 40 dBZ and underpredict that between 20 and 40 dBZ near the surface; simulations overpredict Z larger than 25 to 30 dBZ and underpredict that between 15 and 25 or 30 dBZ near the melting layer, the upper limit depending on altitude. Brightness temperatures (Tb) computed from modeled fields at 37.1- and 85.5-GHz channels that respond to scattering by graupel-size ice show enhanced scattering, mainly due to graupel, compared to observations. Simulated graupel mixing ratios are about 10 times larger than values observed in other hurricanes. For the control run at 6.5 km averaged over the last 18 simulated hours, Doppler velocities computed from modeled fields (Vdop) greater than 5 m s−1 make up 12% of Erin’s simulated area for the base simulation but less than 2% of the observed area. In the eyewall, 5% of model updrafts above 9 km are stronger than 10 m s−1, whereas statistics from other hurricanes show that 5% of updrafts are stronger than only 5 m s−1. Variations in distributions of Z, vertical motion, and graupel mixing ratios between schemes are not sufficient to explain systematic offsets between observations and models. A new iterative condensation scheme, used with the Reisner mixed-phase microphysics scheme, limits unphysical increases of equivalent potential temperature associated with many condensation schemes and reduces the frequency of Z larger than 50 dBZ, but has minimal effect on Z below 50 dBZ, which represent 95% of the modeled hurricane rain area. However, the new scheme changes the Erin simulations in that 95% of the updrafts are weaker than 5 m s−1 and Pmin is up to 12 hPa higher over the last 18 simulated hours.

scholarly journals Land–atmosphere interactions in the tropics – a review

2019 ◽  
Vol 23 (10) ◽  
pp. 4171-4197 ◽  
Author(s):  
Pierre Gentine ◽  
Adam Massmann ◽  
Benjamin R. Lintner ◽  
Sayed Hamed Alemohammad ◽  
Rong Fu ◽  
...  
Keyword(s):  
Land Surface ◽  
Deep Convection ◽  
Feedback Mechanism ◽  
Surface Fluxes ◽  
Surface Radiation ◽  
Spatial And Temporal Scales ◽  
Leading Role ◽  
Wide Range ◽  
The Tropics ◽  
The Impact

Abstract. The continental tropics play a leading role in the terrestrial energy, water, and carbon cycles. Land–atmosphere interactions are integral in the regulation of these fluxes across multiple spatial and temporal scales over tropical continents. We review here some of the important characteristics of tropical continental climates and how land–atmosphere interactions regulate them. Along with a wide range of climates, the tropics manifest a diverse array of land–atmosphere interactions. Broadly speaking, in tropical rainforest climates, light and energy are typically more limiting than precipitation and water supply for photosynthesis and evapotranspiration (ET), whereas in savanna and semi-arid climates, water is the critical regulator of surface fluxes and land–atmosphere interactions. We discuss the impact of the land surface, how it affects shallow and deep clouds, and how these clouds in turn can feed back to the surface by modulating surface radiation and precipitation. Some results from recent research suggest that shallow clouds may be especially critical to land–atmosphere interactions. On the other hand, the impact of land-surface conditions on deep convection appears to occur over larger, nonlocal scales and may be a more relevant land–atmosphere feedback mechanism in transitional dry-to-wet regions and climate regimes.

scholarly journals Drop-Size Distribution Variations Associated with Different Storm Types in Southeast Texas

Atmosphere ◽  
2019 ◽  
Vol 11 (1) ◽  
pp. 8 ◽  
Author(s):  
Larry J. Hopper ◽  
Courtney Schumacher ◽  
Karen Humes ◽  
Aaron Funk
Keyword(s):  
Tropical Cyclones ◽  
Drop Size ◽  
Deep Convection ◽  
Stratiform Rain ◽  
Cold Fronts ◽  
Southeast Texas ◽  
Dynamic Forcing ◽  
Upper Level ◽  
Rain Events ◽  
Rainfall Estimates

Drop-size distributions (DSDs) provide important microphysical information about rainfall and are used in rainfall estimates from radar. This study utilizes a four-year DSD dataset of 163 rain events obtained using a Joss–Waldvogel impact disdrometer located in southeast Texas. A seasonal comparison of the DSD data shows that small (~1 mm diameter) drops occur more frequently in winter and fall, whereas summer and spring months see an increase in the relative frequency of medium and large (~>2 mm diameter) drops, with notable interannual variability in all seasons. Each rain event is classified by dynamic forcing and radar precipitation structure to more directly link environmental and storm organization properties to storm microphysics. Cold fronts and upper-level disturbances account for 80% of the rain events, whereas warm fronts, weakly forced situations, and tropical cyclones comprise the other 20%. Warm frontal storms and upper-level disturbances have smaller drops compared to the climatological DSD for southeast Texas, whereas the more dynamically vigorous cold fronts and weakly forced environments have larger drops. Tropical cyclones generally produce smaller drops than the climatology, but their DSD anomalies are sensitive to what part of the storm is sampled. Regardless of dynamic forcing, storms with precipitation structures that are mostly deep convective or stratiform rain formed from deep convection have larger drops, whereas stratiform rain formed from non-deep convection has smaller drops. Reflectivity-rain rate (Z-R) relationships that account for dynamic forcing and precipitation structures improve rainfall estimates compared to climatological Z-R relationships despite a wide spread in Z-R relationships by storm.

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