Multiscale Aspects of the Storm Producing the June 2013 Flooding in Uttarakhand, India

2017 ◽  
Vol 145 (11) ◽  
pp. 4447-4466 ◽  
Author(s):  
R. A. Houze ◽  
L. A. McMurdie ◽  
K. L. Rasmussen ◽  
A. Kumar ◽  
M. M. Chaplin
Keyword(s):  
Water Vapor ◽  
Rocky Mountains ◽  
Deep Convection ◽  
Himalayan Region ◽  
The South ◽  
Low Level ◽  
Convective Event ◽  
Upper Level

Conditions producing disastrous flooding in Uttarakhand, India, in June 2013 differed from conditions that produced other notorious floods in the Himalayan region in recent years. During the week preceding the Uttarakhand flood, deep convection moistened the mountainsides, making them vulnerable to flooding. However, the precipitation producing the flood was not associated with a deep convective event. Rather, an eastward-propagating upper-level trough in the westerlies extended abnormally far southward, with the jet reaching the Himalayas. The south end of the trough merged with a monsoon low moving westward across India. The merged system produced persistent moist low-level flow oriented normal to the Himalayas that advected large amounts of water vapor into the Uttarakhand region. The flow was moist neutral when it passed over the Himalayan barrier, and orographic lifting produced heavy continuous rain over the region for 2–3 days. The precipitation was largely stratiform in nature although embedded convection of moderate depth occurred along the foothills, where some mild instability was being released. The Uttarakhand flood had characteristics in common with major 2013 floods in the Rocky Mountains in Colorado and Alberta, Canada.

scholarly journals The South Carolina Flood of October 2015: Moisture Transport Analysis and the Role of Hurricane Joaquin

2017 ◽  
Vol 18 (11) ◽  
pp. 2973-2990 ◽  
Author(s):  
Christopher G. Marciano ◽  
Gary M. Lackmann
Keyword(s):  
South Carolina ◽  
Water Vapor ◽  
Moisture Transport ◽  
Heavy Precipitation ◽  
Water Vapor Content ◽  
Precipitation Event ◽  
The South ◽  
Flooding Event ◽  
Additional Water ◽  
Upper Level

Abstract Record-setting rainfall occurred over the state of South Carolina in early October 2015, with maximum accumulations exceeding 500 mm. During the heavy rainfall, Hurricane Joaquin was located offshore to the southeast of the flooding event. Prior research, storm summaries, satellite imagery, and media accounts suggest that Joaquin played a major role in the flooding, mostly through the provision of additional water vapor. Here, numerical simulations are utilized to elucidate Joaquin’s role in the flooding and to diagnose moisture transport mechanisms. The South Carolina precipitation event and the track of Hurricane Joaquin are reasonably represented by two control simulations, a 36-km simulation without nesting and another with 12- and 4-km nests added; the latter improves upon a negative intensity bias for Joaquin. A band of intense moisture transport into the flooding region is associated with a narrow, diabatically produced cyclonic lower-tropospheric potential vorticity (PV) maximum. Simulations in which Joaquin is removed exhibit a similar moisture transport mechanism and also produce a band of heavy precipitation, though the axis of heaviest precipitation shifts northward into North Carolina, and there is a modest reduction (~7%) in area-averaged rainfall. Removing Joaquin produces negligible changes in regional total water vapor content but diminished upper-tropospheric diabatic outflow. The diminished outflow allows greater eastward progression of an upper-level trough, consistent with the northward precipitation shift and with weaker forcing for ascent. Changes in the upper jet associated with Joaquin appear to exert a greater influence on the flooding event than Joaquin’s contribution to water vapor content.

scholarly journals Numerical simulation of a winter hailstorm event over Delhi, India on 17 January 2013

2014 ◽  
Vol 2 (9) ◽  
pp. 6033-6067
Author(s):  
A. Chevuturi ◽  
A. P. Dimri ◽  
U. B. Gunturu
Keyword(s):  
Numerical Simulation ◽  
Deep Convection ◽  
Baroclinic Instability ◽  
Wrf Model ◽  
Cloud Formation ◽  
New Delhi ◽  
National Capital Region ◽  
Microphysics Scheme ◽  
Low Level ◽  
Upper Level

Abstract. This study analyzes the cause of rare occurrence of winter hailstorm over New Delhi/NCR (National Capital Region), India. The absence of increased surface temperature or low level of moisture incursion during winter cannot generate the deep convection required for sustaining a hailstorm. Consequently, NCR shows very few cases of hailstorms in the months of December-January-February, making the winter hail formation a question of interest. For this study, recent winter hailstorm event on 17 January 2013 (16:00–18:00 UTC) occurring over NCR is investigated. The storm is simulated using Weather Research and Forecasting (WRF) model with Goddard Cumulus Ensemble (GCE) microphysics scheme with two different options, hail or graupel. The aim of the study is to understand and describe the cause of hailstorm event during over NCR with comparative analysis of the two options of GCE microphysics. On evaluating the model simulations, it is observed that hail option shows similar precipitation intensity with TRMM observation than the graupel option and is able to simulate hail precipitation. Using the model simulated output with hail option; detailed investigation on understanding the dynamics of hailstorm is performed. The analysis based on numerical simulation suggests that the deep instability in the atmospheric column led to the formation of hailstones as the cloud formation reached upto the glaciated zone promoting ice nucleation. In winters, such instability conditions rarely form due to low level available potential energy and moisture incursion along with upper level baroclinic instability due to the presence of WD. Such rare positioning is found to be lowering the tropopause with increased temperature gradient, leading to winter hailstorm formation.

Driving mechanisms of South Atlantic storm track changes in an extreme climate scenario according to HadGEM2-ES and WRF downscaling

2021 ◽  
Author(s):  
Carolina Gramcianinov ◽  
Ricardo de Camargo ◽  
Pedro Silva Dias
Keyword(s):  
Storm Track ◽  
Static Stability ◽  
South Atlantic ◽  
Brazilian Coast ◽  
The South ◽  
La Plata ◽  
Low Level ◽  
Upper Level ◽  
Upper Level Jet ◽  
Projected Changes

<p>This work aims to assess the future projected changes in the cyclones originated in the South Atlantic, focusing on their genesis and intensifying mechanisms. The TRACK program was used to identify and track cyclones based on the relative vorticity from winds at 850 hPa. Spatial distribution maps of the atmospheric environment at the time of genesis were built using information sampled from individual features, e.g., mean upper-level jet speed, low-level moisture transport. First, we evaluated the HadGEM2-ES ability to reproduce the main characteristics of the South Atlantic cyclones and access their future projected changes using the RCP8.5 scenario. Then, we performed a dynamical downscaling using the WRF model to improve the resolution of the climate model in the historical (ExpHad-HIST) and RCP8.5 (ExpHad-RCP85) scenarios. Our results showed that HadGEM2-ES were able to reproduce the South Atlantic storm track pattern and its four main cyclogenesis regions: (1) Southern Brazilian coast (SE-BR, 30ºS); (2) Northern Argentina, Uruguay, and Southern Brazil (LA PLATA, 35ºS); (3) central coast of Argentina (ARG, 40ºS-55º) and; (4) Southeastern South Atlantic (SE-SAO, 55ºS and 10ºW). However, HadGEM-ES presented less intense cyclones and a negative density bias on the subtropical storm track, as a consequence of an underestimated genesis in the LA PLATA and SE-BR regions. The ExpHad-HIST provided a better representation of these two genesis regions, where the effects of an improved orography, mesoscale processes and strong and more organized low-level jet seem to reduce the static stability and support cyclone development. HadGEM2-ES RCP8.5 future projection showed a decrease of 10% in the number of cyclones over South Atlantic and a poleward shift of the main storm track, linked to the larger reduction of systems in mid than high latitudes. This increase in the cyclone activity at 30ºS led to the high track density in the South Atlantic subtropical storm track, both in the summer and winter. The ExpHad-RCP85 also showed a poleward shift of the main storm track, but mainly in the summer. The reduction and southward displacement of the cyclone occurrences can be addressed to the increase in the static stability at mid-latitudes. However, the increase in the moisture content at low levels seems to balance the effect of the static stability as long as there is an increase in the genesis in the equatorward genesis regions. In fact, the ExpHad-RCP85 simulated growth in the genesis in the northern edge of SE-BR (20ºS, 50ºW) and ARG (45ºS) regions, in the summer, and the LA PLATA region in the winter - being the last change also observed in HadGEM2-ES RCP8.5. The large increase in the low-level moisture and a strengthening of the equatorward flank of the upper-level jet could justify more genesis at these locations, competing with the increase in static stability. Moreover, the large content of low-level moisture available in the future simulation may also be connected to the observed intensification of the cyclones over the Uruguayan and Brazilian coast.</p>

scholarly journals The MJO Transition from Shallow to Deep Convection in CloudSat/CALIPSO Data and GISS GCM Simulations

2012 ◽  
Vol 25 (11) ◽  
pp. 3755-3770 ◽  
Author(s):  
Anthony D. Del Genio ◽  
Yonghua Chen ◽  
Daehyun Kim ◽  
Mao-Sung Yao
Keyword(s):  
Water Vapor ◽  
General Circulation ◽  
Deep Convection ◽  
General Circulation Models ◽  
Lapse Rate ◽  
Shallow Convection ◽  
Large Variability ◽  
Earth Observing System ◽  
Upper Level ◽  
Goddard Institute

The relationship between convective penetration depth and tropospheric humidity is central to recent theories of the Madden–Julian oscillation (MJO). It has been suggested that general circulation models (GCMs) poorly simulate the MJO because they fail to gradually moisten the troposphere by shallow convection and simulate a slow transition to deep convection. CloudSat and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) data are analyzed to document the variability of convection depth and its relation to water vapor during the MJO transition from shallow to deep convection and to constrain GCM cumulus parameterizations. Composites of cloud occurrence for 10 MJO events show the following anticipated MJO cloud structure: shallow and congestus clouds in advance of the peak, deep clouds near the peak, and upper-level anvils after the peak. Cirrus clouds are also frequent in advance of the peak. The Advanced Microwave Scanning Radiometer for Earth Observing System (EOS) (AMSR-E) column water vapor (CWV) increases by ~5 mm during the shallow–deep transition phase, consistent with the idea of moisture preconditioning. Echo-top height of clouds rooted in the boundary layer increases sharply with CWV, with large variability in depth when CWV is between ~46 and 68 mm. International Satellite Cloud Climatology Project cloud classifications reproduce these climatological relationships but correctly identify congestus-dominated scenes only about half the time. A version of the Goddard Institute for Space Studies Model E2 (GISS-E2) GCM with strengthened entrainment and rain evaporation that produces MJO-like variability also reproduces the shallow–deep convection transition, including the large variability of cloud-top height at intermediate CWV values. The variability is due to small grid-scale relative humidity and lapse rate anomalies for similar values of CWV.

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 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 Invigoration and Capping of a Convective Rainband ahead of a Potential Vorticity Anomaly

2017 ◽  
Vol 145 (6) ◽  
pp. 2093-2117 ◽  
Author(s):  
Geraint Vaughan ◽  
Bogdan Antonescu ◽  
David M. Schultz ◽  
Christopher Dearden
Keyword(s):  
Potential Vorticity ◽  
Dominant Role ◽  
Deep Convection ◽  
Convective Available Potential Energy ◽  
Static Stability ◽  
Causal Link ◽  
Minor Role ◽  
Low Level ◽  
Upper Level ◽  
A Minor

Abstract Deep convection frequently occurs on the eastern side of upper-level troughs, or potential vorticity (PV) anomalies. This is consistent with uplift ahead of a cyclonic PV anomaly, and consequent reduction in static stability and increase of convective available potential energy (CAPE). Nevertheless, the causal link between upper-level PV and deep convection has not been proven, and given that lift, moisture, and instability must all be present for deep convection to occur it is not clear that upper-level forcing is sufficient. In this paper a convective rainband that intensified ahead of a cyclonic PV anomaly in an environment with little CAPE (~10 J kg−1) is examined to determine the factors responsible for its intensification. The key feature was a low-level convergence line, arising from the remnants of an occluded front embedded in the low-level cyclonic flow. The rainband’s intensity and morphology was influenced by the remnants of a tropopause fold that capped convection at midlevels in the southern part of the band, and by a reduction in upper-level static stability in the northern part of the band that allowed the convection to reach the tropopause. Ascent ahead of the trough appears to have played only a minor role in conditioning the atmosphere to convection: in most cases the ascending airstream had previously descended in the flow west of the trough axis. Thus, simple “PV thinking” is not capable of describing the development of the rainband, and it is concluded that preexisting low-level wind and humidity features played the dominant role.

scholarly journals Genesis of Hurricane Julia (2010) within an African Easterly Wave: Low-Level Vortices and Upper-Level Warming

2013 ◽  
Vol 70 (12) ◽  
pp. 3799-3817 ◽  
Author(s):  
Stefan F. Cecelski ◽  
Da-Lin Zhang
Keyword(s):  
Model Simulation ◽  
Deep Convection ◽  
Mesoscale Convective System ◽  
Tropical Cyclogenesis ◽  
Convective System ◽  
Easterly Waves ◽  
Low Level ◽  
Mesoscale Convective ◽  
Upper Level ◽  
Scale Surface

Abstract While a robust theoretical framework for tropical cyclogenesis (TCG) within African easterly waves (AEWs) has recently been developed, little work explores the development of low-level meso-β-scale vortices (LLVs) and a meso-α-scale surface low in relation to deep convection and upper-tropospheric warming. In this study, the development of an LLV into Hurricane Julia (2010) is shown through a high-resolution model simulation with the finest grid size of 1 km. The results presented expand upon the connections between LLVs and the AEW presented in previous studies while demonstrating the importance of upper-tropospheric warming for TCG. It is found that the significant intensification phase of Hurricane Julia is triggered by the pronounced upper-tropospheric warming associated with organized deep convection. The warming is able to intensify and expand during TCG owing to formation of a storm-scale outflow beyond the Rossby radius of deformation. Results confirm previous ideas by demonstrating that the intersection of the AEW's trough axis and critical latitude is a preferred location for TCG, while supplementing such work by illustrating the importance of upper-tropospheric warming and meso-α-scale surface pressure falls during TCG. It is shown that the meso-β-scale surface low enhances boundary layer convergence and aids in the bottom-up vorticity development of the meso-β-scale LLV. The upper-level warming is attributed to heating within convective bursts at earlier TCG stages while compensating subsidence warming becomes more prevalent once a mesoscale convective system develops.

scholarly journals A Cloud-Resolving Simulation Study on the Merging Processes and Effects of Topography and Environmental Winds

2012 ◽  
Vol 69 (4) ◽  
pp. 1232-1249 ◽  
Author(s):  
Danhong Fu ◽  
Xueliang Guo
Keyword(s):  
Water Vapor ◽  
Pressure Gradient ◽  
Large Scale ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Low Level ◽  
Level Pressure ◽  
Merging Process ◽  
Upper Level ◽  
Water Vapor Convergence

Abstract The cloud-resolving fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) was used to study the cloud interactions and merging processes in the real case that generated a mesoscale convective system (MCS) on 23 August 2001 in the Beijing region. The merging processes can be grouped into three classes for the studied case: isolated nonprecipitating and precipitating cell merging, cloud cluster merging, and echo core or updraft core merging within cloud systems. The mechanisms responsible for the multiscale merging processes were investigated. The merging process between nonprecipitating cells and precipitating cells and that between clusters is initiated by forming an upper-level cloud bridge between two adjacent clouds due to upper-level radial outflows in one vigorous cloud. The cloud bridge is further enhanced by a favorable middle- and upper-level pressure gradient force directed from one cloud to its adjacent cloud by accelerating cloud particles being horizontally transported from the cloud to its adjacent cloud and induce the redistribution of condensational heating, which destabilizes the air at and below the cloud bridge and forms a favorable low-level pressure structure for low-level water vapor convergence and merging process. The merging of echo cores within the mesoscale cloud happens because of the interactions between low-level cold outflows associated with the downdrafts formed by these cores. Further sensitivity studies on the effects of topography and large-scale environmental winds suggest that the favorable pressure gradient force from one cloud to its adjacent cloud and stronger low-level water vapor convergence produced by the topographic lifting of large-scale low-level airflow determine further cloud merging processes over the mountain region.

scholarly journals Mesoscale Aspects of the Rapid Intensification of a Tornadic Convective Line across Central Florida: 22–23 February 1998

2007 ◽  
Vol 22 (2) ◽  
pp. 223-243 ◽  
Author(s):  
Alicia C. Wasula ◽  
Lance F. Bosart ◽  
Russell Schneider ◽  
Steven J. Weiss ◽  
Robert H. Johns ◽  
...  
Keyword(s):  
Rapid Development ◽  
Vertical Wind Shear ◽  
Surface Flow ◽  
The South ◽  
Southeast United States ◽  
Central Florida ◽  
Low Level ◽  
Surface Front ◽  
Upper Level ◽  
The Relationship

Abstract The 22–23 February 1998 central Florida tornado outbreak was one of the deadliest and costliest in Florida’s history; a number of long-track tornadoes moved across the Florida peninsula after 0000 UTC 23 February 1998. In the 12–24 h prior to 0000 UTC 23 February, a vigorous upper-level synoptic system was tracking across the southeast United States, and a north–south-oriented convective band located ahead of the cold front was moving eastward across the Gulf of Mexico. Strong vertical wind shear was present in the lowest 1 km, due to a ∼25 m s−1 low-level jet at 925 hPa and south-southeasterly surface flow over the Florida peninsula. Further, CAPE values across the central Florida peninsula exceeded 2500 J kg−1. Upon making landfall on the Florida peninsula, the convective band rapidly intensified and developed into a line of tornadic supercells. This paper examines the relationship between a diabatically induced front across the central Florida peninsula and the rapid development of tornadic supercells in the convective band after 0000 UTC 23 February. Results suggest that persistent strong frontogenesis helped to maintain the front and enhanced ascent in the warm, moist unstable air to the south of the east–west-oriented front on the Florida peninsula, thus allowing the updrafts to rapidly intensify as they made landfall. Further, surface observations from three key locations along the surface front suggest that a mesolow moved eastward along the front just prior to the time when supercells developed. It is hypothesized that the eastward-moving mesolow may have caused the winds in the warm air to the south of the surface front to back to southeasterly and create a favorable low-level wind profile in which supercells could rapidly develop.

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