scholarly journals Climatology of Warm Rain and Associated Latent Heating Derived from TRMM PR Observations

2009 ◽  
Vol 22 (18) ◽  
pp. 4908-4929 ◽  
Author(s):  
Yasu-Masa Kodama ◽  
Masaki Katsumata ◽  
Shuichi Mori ◽  
Sinsuke Satoh ◽  
Yuki Hirose ◽  
...  
Keyword(s):  
Lower Latitude ◽  
Convergence Zone ◽  
Small Contribution ◽  
Latent Heating ◽  
The South ◽  
Low Level ◽  
Warm Rain ◽  
Convergence Zones ◽  
Subtropical Oceans ◽  
The Tropics

Abstract The large-scale distribution of precipitation and latent heating (LH) profiles in the tropics, subtropics, and part of the midlatitudes was studied using a 9-yr dataset derived from Tropical Rainfall Measuring Mission precipitation radar observations, with emphasis on the contribution of warm rain. The distribution of warm rain showed features unique from those of rain in other categories and those of outgoing longwave radiation. Warm rain was weak over land but widely distributed over oceans, especially along the intertropical convergence zone (ITCZ) and the western part of the subtropical oceans. The observed amount of warm rain depended on the rainfall intensity rather than on the frequency of warm rain events. The amount of warm rain over ocean was positively correlated with sea surface temperature (SST); this dependency was found in the tropics, subtropics, and part of the midlatitudes, whereas dependency of SST on total rain was confined to the tropics. Both total rain and warm rain were concentrated in the ITCZ, which elongated along the local SST maximum. Small amounts of warm rain were found along subtropical convergence zones (the baiu frontal zone and subtropical portions of the South Pacific convergence zone and the South Atlantic convergence zone) with ample total rainfall. However, larger amounts of warm rain were observed at the lower-latitude sides of these zones in the upstream portions of low-level moisture flow toward the zones. Warm rain may cultivate the subtropical convergence zones by deepening the moist boundary layer and increasing moisture flux toward the zones. The statistical relationship between warm rain and low-level cloudiness showed that the warm rain amount was large when low-level cloudiness was 20%–30% and small when low-level cloudiness was greater than 40%. This indicates that intense warm rain is provided by convective clouds, not by stratiform clouds, in conditions of substantial cloudiness. Despite the small contribution to total rain, warm rain maintained positive LH values over most of the tropical and subtropical oceans. The LH by warm rain masked low-level cooling observed in stratiform rain and maintained positive LH in the lower atmosphere below the melting layer. Because warm rain was confined to oceans, a strong LH contrast was maintained along the coast; this contrast reached values of 1–2 K day−1 in certain places and may affect local and monsoonal circulation across continental coasts.

scholarly journals On the Likelihood of Tropical–Extratropical Cloud Bands in the South Indian Convergence Zone during ENSO Events

2018 ◽  
Vol 31 (7) ◽  
pp. 2797-2817 ◽  
Author(s):  
Neil C. G. Hart ◽  
Richard Washington ◽  
Chris J. C. Reason
Keyword(s):  
Southern Africa ◽  
Convective Instability ◽  
Convergence Zone ◽  
The South ◽  
Band Frequency ◽  
Cloud Band ◽  
Enso Events ◽  
South Indian ◽  
Convergence Zones ◽  
Mean State

The Southern Hemisphere subtropical convergence zones are important regions of rainfall in the subtropics. The south Indian Ocean convergence zone (SICZ) has the strongest seasonality and exhibits substantial interannual variability in strength and position during austral summer. On synoptic time scales, the SICZ is a preferred region for the formation of tropical–extratropical (TE) cloud bands with local maxima over the southern African mainland and Madagascar. This study investigates how the seasonality in satellite-observed cloud band frequency emerges from the interplay between the asynchronous seasonal cycles in convective instability and upper-level flow, as represented by reanalysis data. These atmospheric mean states are diagnosed with a gross convective instability metric and a method to distinguish between subtropical and eddy-driven jet axes. Month-by-month analysis of these diagnostics elucidates how mean-state perturbations during ENSO events modify cloud band likelihood. Typically, 150%–200% more cloud bands develop during La Niña seasons supported by 5°–10° latitudinal separation between the local subtropical and eddy-driven jets and higher values of convective instability, especially in semiarid parts of mainland southern Africa. During El Niño events, fewer cloud bands develop over southern Africa in a more convectively stable environment without a distinct subtropical jet. However, east of Madagascar cloud bands are 150% more likely. Plausible teleconnection pathways based on these ENSO-related perturbations are discussed. The paper concludes with a conceptual framing of the seasonal cycle in the mean-state pertinent to TE cloud band likelihood.

How volcanism impact on the variability of the South American Monsoon System and the associated Atlantic Subtropical Cell

2020 ◽  
Author(s):  
Laura Sobral Verona ◽  
Ilana Wainer ◽  
Myriam Khodri
Keyword(s):  
Atlantic Ocean ◽  
Ocean Circulation ◽  
Global Climate ◽  
Volcanic Eruptions ◽  
The South ◽  
Climatic Feature ◽  
Monsoon System ◽  
Convergence Zones ◽  
The Tropics ◽  
Subtropical Cell

<p>Large volcanic eruptions can affect the global climate through changes in atmospheric and ocean circulation. Understanding the influence of volcanic eruptions on the hydroclimate over monsoon regions is of great scientific and social importance. The South America Monsoon System (SAMS) is the most important climatic feature of the continent. Both the Intertropical and the South Atlantic wind convergence zones (ITCZ and SACZ, respectively) are fundamental components of the SAMS. They show variations on a broad range of scales, dependent on complex multi-system interactions with the adjacent Atlantic Ocean and teleconnections. Also driven by the winds, the Atlantic Subtropical Cell (STC) is the link between the subduction zone in the subtropical gyre with the tropics. Hence, the STC influence equatorial sea surface temperature variability on interannual to decadal scales in the tropical Atlantic Ocean. In order to improve our understanding of the responses of the ocean-atmosphere system to the volcanic forcing, we aim to identify the dominant mechanisms of seasonal-to-interdecadal variability of the SAMS and the Atlantic STC after large Pinatubo-like (1991) and Tambora-like (1815) eruptions relying on the VolMIP model intercomparison project experiments.</p>

scholarly journals Atmospheric convergence zones stemming from large-scale mixing

2021 ◽  
Vol 2 (2) ◽  
pp. 475-488
Author(s):  
Gabriel M. P. Perez ◽  
Pier Luigi Vidale ◽  
Nicholas P. Klingaman ◽  
Thomas C. M. Martin
Keyword(s):  
South America ◽  
Large Scale ◽  
Hydrological Cycle ◽  
Moisture Flux ◽  
South Atlantic Convergence Zone ◽  
South Atlantic ◽  
Convergence Zone ◽  
The South ◽  
Atmospheric Flow ◽  
Convergence Zones

Abstract. Organised cloud bands are important features of tropical and subtropical rainfall. These structures are often regarded as convergence zones, alluding to an association with coherent atmospheric flow. However, the flow kinematics is not usually taken into account in classification methods for this type of event, as large-scale lines are rarely evident in instantaneous diagnostics such as Eulerian convergence. Instead, existing convergence zone definitions rely on heuristic rules of shape, duration and size of cloudiness fields. Here we investigate the role of large-scale turbulence in shaping atmospheric moisture in South America. We employ the finite-time Lyapunov exponent (FTLE), a metric of deformation among neighbouring trajectories, to define convergence zones as attracting Lagrangian coherent structures (LCSs). Attracting LCSs frequent tropical and subtropical South America, with climatologies consistent with the South Atlantic Convergence Zone (SACZ), the South American Low-Level Jet (SALLJ) and the Intertropical Convergence Zone (ITCZ). In regions under the direct influence of the ITCZ and the SACZ, rainfall is significantly positively correlated with large-scale mixing measured by the FTLE. Attracting LCSs in south and southeast Brazil are associated with significant positive rainfall and moisture flux anomalies. Geopotential height composites suggest that the occurrence of attracting LCSs in these regions is related with teleconnection mechanisms such as the Pacific–South Atlantic. We believe that this kinematical approach can be used as an alternative to region-specific convergence zone classification algorithms; it may help advance the understanding of underlying mechanisms of tropical and subtropical rain bands and their role in the hydrological cycle.

scholarly journals Atmospheric convergence zones stemming from large-scale mixing

2020 ◽  
Author(s):  
Gabriel M. P. Perez ◽  
Pier Luigi Vidale ◽  
Nicholas P. Klingaman ◽  
Thomas C. M. Martin
Keyword(s):  
South America ◽  
Large Scale ◽  
Hydrological Cycle ◽  
Moisture Flux ◽  
South Atlantic Convergence Zone ◽  
South Atlantic ◽  
Convergence Zone ◽  
The South ◽  
Atmospheric Flow ◽  
Convergence Zones

Abstract. Organised cloud bands are important features of tropical and subtropical rainfall. These structures are often regarded as convergence zones, alluding to an association with coherent atmospheric flow. However, the flow kinematics is not usually taken into account in classification methods for this type of event, as large-scale lines are rarely evident in instantaneous diagnostics such as Eulerian convergence. Instead, existing convergence zone definitions rely on heuristic rules of shape, duration and size of cloudiness fields. Here we investigate the role of large-scale turbulence in shaping atmospheric moisture in South America. We employ the Finite-Time Lyapunov Exponent (FTLE), a metric of deformation among neighboring trajectories, to define convergence zones as attracting Lagrangian Coherent Structures (LCSs). Attracting LCSs frequent tropical and subtropical South America, with climatologies consistent with the South Atlantic Convergence Zone (SACZ), the South American Low-level Jet (SALLJ) and the Intertropical Convergence Zone (ITCZ). In regions under the direct influence of the ITCZ and the SACZ, rainfall is significantly positively correlated with large-scale mixing measured by the FTLE. Attracting LCSs in South and Southeast Brazil are associated with significant positive rainfall and moisture flux anomalies. Geopotential height composites suggest that the occurrence of attracting LCSs in these regions is related with teleconnection mechanisms such as the Pacific-South Atlantic. We believe that this kinematical approach can be used as an alternative to region-specific convergence zone classification algorithms; it may help advance the understanding of underlying mechanisms of tropical and subtropical rain bands and their role in the hydrological cycle.

Nocturnal Low-Level Jet in a Mountain Basin Complex. Part I: Evolution and Effects on Local Flows

2004 ◽  
Vol 43 (10) ◽  
pp. 1348-1365 ◽  
Author(s):  
Robert M. Banta ◽  
Lisa S. Darby ◽  
Jerome D. Fast ◽  
James O. Pinto ◽  
C. David Whiteman ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Salt Lake ◽  
Great Salt Lake ◽  
Vertical Motion ◽  
Cold Pool ◽  
Lake Basin ◽  
The South ◽  
Low Level ◽  
Low Level Jet ◽  
Convergence Zones

Abstract A Doppler lidar deployed to the center of the Great Salt Lake (GSL) basin during the Vertical Transport and Mixing (VTMX) field campaign in October 2000 found a diurnal cycle of the along-basin winds with northerly up-basin flow during the day and a southerly down-basin low-level jet at night. The emphasis of VTMX was on stable atmospheric processes in the cold-air pool that formed in the basin at night. During the night the jet was fully formed as it entered the GSL basin from the south. Thus, it was a feature of the complex string of basins draining toward the Great Salt Lake, which included at least the Utah Lake basin to the south. The timing of the evening reversal to down-basin flow was sensitive to the larger-scale north–south pressure gradient imposed on the basin complex. On nights when the pressure gradient was not too strong, local drainage flow (slope flows and canyon outflow) was well developed along the Wasatch Range to the east and coexisted with the basin jet. The coexistence of these two types of flow generated localized regions of convergence and divergence, in which regions of vertical motion and transport were focused. Mesoscale numerical simulations captured these features and indicated that updrafts on the order of 5 cm s−1 could persist in these localized convergence zones, contributing to vertical displacement of air masses within the basin cold pool.

scholarly journals Circulation, Moisture, and Precipitation Relationships along the South Pacific Convergence Zone in Reanalyses and CMIP5 Models

2013 ◽  
Vol 26 (24) ◽  
pp. 10174-10192 ◽  
Author(s):  
Matthew J. Niznik ◽  
Benjamin R. Lintner
Keyword(s):  
Storm Track ◽  
South Pacific ◽  
South Pacific Convergence Zone ◽  
Specific Humidity ◽  
Cmip5 Models ◽  
Convergence Zone ◽  
Synoptic Scale ◽  
The South ◽  
Theoretical Understanding ◽  
Low Level

Abstract One theorized control on the position of the South Pacific convergence zone (SPCZ) is the amount of low-level inflow from the relatively dry southeastern Pacific basin. Building on an analysis of observed SPCZ region synoptic-scale variability by Lintner and Neelin, composite analysis is performed here on two reanalysis products as well as output from 17 models in phase 5 of the Coupled Model Intercomparison Project (CMIP5). Using low-level zonal wind as a compositing index, it is shown that the CMIP5 ensemble mean, as well as many of the individual models, captures patterns of wind, specific humidity, and precipitation anomalies resembling those obtained for reanalysis fields between weak- and strong-inflow phases. Lead–lag analysis of both the reanalyses and models is used to develop a conceptual model for the formation of each composite phase. This analysis indicates that an equatorward-displaced Southern Hemisphere storm track and an eastward-displaced equatorial eastern Pacific westerly (wind) duct are features of the weak-inflow phase although, as indicated by additional composite analyses based on these features, each appears to account weakly for the details of the low-level inflow composite anomalies. Despite the presence of well-known biases in the CMIP5 simulations of the SPCZ region climate, the models appear to have some fidelity in simulating synoptic-scale relationships between low-level winds, moisture, and precipitation, consistent with observations and simple theoretical understanding of interactions of dry air inflow with deep convection.

6. Weather in the tropics

2017 ◽  
Author(s):  
Storm Dunlop
Keyword(s):  
Winter Season ◽  
Walker Circulation ◽  
Intertropical Convergence Zone ◽  
South Pacific Convergence Zone ◽  
Convergence Zone ◽  
Trade Winds ◽  
Northern Summer ◽  
The Indian Ocean ◽  
Convergence Zones ◽  
The Tropics

‘Weather in the tropics’ considers the weather systems between the two subtropical anticyclones, lying at approximately latitudes 30 °N and S. The trade winds consist of air that flows out of the subtropical anticyclones towards the equatorial trough. They are strongest in the winter season, tending to weaken during the summer. The northern and southern hemisphere trade winds converge at the Intertropical Convergence Zone, whose position is variable. The South Pacific Convergence Zone is closely associated with the changes involved in the Walker Circulation and El Niño events. The convergence zones over the Indian Ocean show major changes in location during the northern summer, and these are related to seasonal monsoons.

scholarly journals Tropical Cyclone Formations in the South China Sea Associated with the Mei-Yu Front

2006 ◽  
Vol 134 (10) ◽  
pp. 2670-2687 ◽  
Author(s):  
Cheng-Shang Lee ◽  
Yung-Lan Lin ◽  
Kevin K. W. Cheung
Keyword(s):  
Tropical Cyclone ◽  
South China Sea ◽  
South China ◽  
The South China Sea ◽  
Lower Latitude ◽  
The South ◽  
Low Level ◽  
China Sea ◽  
Tropical Depression ◽  
Stationary Front

Abstract This study examines the 119 tropical cyclone (TC) formations in the South China Sea (SCS) during 1972–2002, and in particular the 20 in May and June. Eleven of these storms are associated with the weak baroclinic environment of a mei-yu front, while the remaining nine are nonfrontal. Seven of the 11 initial disturbances originated over land and have a highly similar evolution. Comparison of the frontal and nonfrontal formation shows that a nonfrontal formation usually occurs at a lower latitude, is more barotropic, develops faster, and possibly intensifies into a stronger TC. Six nonformation cases in the SCS are also identified that have similar low-level disturbances near the western end of a mei-yu front but did not develop further. In the nonformation cases, both the northeasterlies north of the front and the monsoonal southwesterlies are intermittent and weaker in magnitude so that the vorticity in the northern SCS does not spin up to tropical depression intensity. Because of the influence of a strong subtropical high, convection is suppressed in the SCS. The nonformation cases also have an average of 2–3 m s−1 larger vertical wind shear than the formation cases. A conceptual model is proposed for the typical frontal-type TC formations in the SCS that consists of three essential steps. First, an incipient low-level disturbance that originates over land moves eastward along the stationary mei-yu front. Second, the low-level circulation center with a relative vorticity maximum moves to the open ocean with the stationary front. Last, with strengthened northeasterlies, cyclonic shear vorticity continues to increase in the SCS, and after detaching from the stationary front, the system becomes a tropical depression.

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