Multiscale Convective Wave Disturbances in the Tropics: Insights from a Two-Dimensional Cloud-Resolving Model

2008 ◽  
Vol 65 (1) ◽  
pp. 140-155 ◽  
Author(s):  
Stefan N. Tulich ◽  
Brian E. Mapes
Keyword(s):  
Cloud Model ◽  
Wave Packets ◽  
Deep Convection ◽  
Critical Role ◽  
Convective Cloud ◽  
Two Dimensional ◽  
Shallow Convection ◽  
Low Level ◽  
Wave Disturbances ◽  
Mesoscale Convective

Abstract Multiscale convective wave disturbances with structures broadly resembling observed tropical waves are found to emerge spontaneously in a nonrotating, two-dimensional cloud model forced by uniform cooling. To articulate the dynamics of these waves, model outputs are objectively analyzed in a discrete truncated space consisting of three cloud types (shallow convective, deep convective, and stratiform) and three dynamical vertical wavelength bands. Model experiments confirm that diabatic processes in deep convective and stratiform regions are essential to the formation of multiscale convective wave patterns. Specifically, upper-level heating (together with low-level cooling) serves to preferentially excite discrete horizontally propagating wave packets with roughly a full-wavelength structure in troposphere and “dry” phase speeds cn in the range 16–18 m s−1. These wave packets enhance the triggering of new deep convective cloud systems, via low-level destabilization. The new convection in turn causes additional heating over cooling, through delayed development of high-based deep convective cells with persistent stratiform anvils. This delayed forcing leads to an intensification and then widening of the low-level cold phases of wave packets as they move through convecting regions. Additional widening occurs when slower-moving (∼8 m s−1) “gust front” wave packets excited by cooling just above the boundary layer trigger additional deep convection in the vicinity of earlier convection. Shallow convection, meanwhile, provides positive forcing that reduces convective wave speeds and destroys relatively small-amplitude-sized waves. Experiments with prescribed modal wind damping establish the critical role of short vertical wavelengths in setting the equivalent depth of the waves. However, damping of deep vertical wavelengths prevents the clustering of mesoscale convective wave disturbances into larger-scale envelopes, so these circulations are important as well.

scholarly journals Mesoscale Convection and Bimodal Cyclogenesis over the Bay of Bengal

2015 ◽  
Vol 143 (9) ◽  
pp. 3495-3517 ◽  
Author(s):  
Nasreen Akter
Keyword(s):  
Bay Of Bengal ◽  
Deep Convection ◽  
Leading Edge ◽  
Vertical Shear ◽  
Squall Line ◽  
Convergence Zone ◽  
Low Level ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Long Time

Abstract Mesoscale convective systems (MCSs) are an essential component of cyclogenesis, and their structure and characteristics determine the intensity and severity of associated cyclones. Case studies were performed by simulating tropical cyclones that formed during the pre- and postmonsoon periods in 2007 and 2010 over the Bay of Bengal (BoB). The pre- (post) monsoon environment was characterized by the coupling of northwesterly (southwesterly) wind to the early advance southwesterly (northeasterly) monsoonal wind in the BoB. The surges of low-level warm southwesterlies with clockwise-rotating vertical shear in the premonsoon period and moderately cool northeasterlies with anticlockwise-rotating vertical shear in the postmonsoon period transported moisture and triggered MCSs within preexisting disturbances near the monsoon trough over the BoB. Mature MCSs associated with bimodal cyclone formations were quasi linear, and they featured leading-edge deep convection and a trailing stratiform precipitation region, which was very narrow in the postmonsoon cases. In the premonsoon cases, the MCSs became severe bow echoes when intense and moist southwesterlies were imposed along the dryline convergence zone in the northern and northwestern BoB. However, the development formed a nonsevere and nonorganized linear system when the convergence zone was farther south of the dryline. In the postmonsoon cases, cyclogenesis was favored by squall-line MCSs with a north–south orientation over the BoB. All convective systems moved quickly, persisted for a long time, and contained suitable environments for developing low-level cyclonic mesovortices at their leading edges, which played an additional role in forming mesoscale convective vortices during cyclogenesis in the BoB.

scholarly journals Characteristics of Vertical Velocity Cores in Different Convective Systems Observed over Gadanki, India

2009 ◽  
Vol 137 (3) ◽  
pp. 954-975 ◽  
Author(s):  
K. N. Uma ◽  
T. Narayana Rao
Keyword(s):  
Deep Convection ◽  
Horizontal Wind ◽  
Air Velocity ◽  
Low Level ◽  
Convective Systems ◽  
Vertical Extent ◽  
Mesoscale Convective ◽  
Data Points ◽  
Radar Measurements ◽  
High Level

Abstract The Indian mesosphere–stratosphere–troposphere (MST) radar measurements during the passage of 60 convective systems are used to study the vertical air velocity (w) characteristics of tropical convection. The up- and downdraft cores and various stages/types of convection (shallow, deep, and decaying) are discerned from radar time–intensity maps of w. The characteristics of cores (speed, size, orientation, vertical extent, gravity wave activity, etc.) at different stages of convection are discussed with the help of three case studies. The cores stratified based on the type of convection are mostly erect in nature in all types of convective systems, except for deep updraft cores. A considerable percentage (35%) of deep updraft cores show inclined structure with elevation angles as low as 0°–20°. The variation of the horizontal wind field with height and the internal dynamics of mesoscale convective systems (MCSs) are thought to be responsible for this geometry. Further, the vertical extent of draft cores is limited in all types of convection, except for deep updraft cores. About 77% of deep updraft cores have a vertical extent greater than 10 km and ∼23% of these cores reach an altitude of 16 km. The size (overpass time) of the core shows an increasing trend with altitude up to 10–12 km and then decreases. Among different types of convection, the size of core is larger for deep updraft cores and smaller for shallow updraft cores. The variation of w distribution with height is different for different convection categories. The mode (and also the mean) of the distribution shows low-level descent (below 3 km) and mid–high-level ascent in shallow and deep convection categories, while nearly uniform distribution is seen in decaying convection. Strong updrafts are seen in deep convective systems in the upper troposphere (of the order of 15–20 m s−1), followed by shallow and decaying systems, while downdrafts are generally weaker in all types of convection. The variability (within the cores and also with altitude) and the number of data points are larger in updraft cores than in downdraft cores corresponding to shallow and deep convection. Contrasting the composite w profile at Gadanki with those obtained elsewhere revealed interesting features: the absence of subsidence at higher levels, the presence of low-level subsidence, a single ascent peak in the middle troposphere, etc. Further, the magnitude of composite w derived from wind profiler measurements is larger than that obtained with other techniques.

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 Utilizing a Storm-Generating Hotspot to Study Convective Cloud Transitions: The CACTI Experiment

2021 ◽  
pp. 1-67
Author(s):  
Adam C. Varble ◽  
Stephen W. Nesbitt ◽  
Paola Salio ◽  
Joseph C. Hardin ◽  
Nitin Bharadwaj ◽  
...  
Keyword(s):  
Deep Convection ◽  
Convective Cloud ◽  
Life Cycles ◽  
Field Campaign ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Atmospheric Radiation Measurement ◽  
Cumulus Congestus ◽  
Orographic Cloud ◽  
Convection Initiation

AbstractThe Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign was designed to improve understanding of orographic cloud life cycles in relation to surrounding atmospheric thermodynamic, flow, and aerosol conditions. The deployment to the Sierras de Córdoba range in north-central Argentina was chosen because of very frequent cumulus congestus, deep convection initiation, and mesoscale convective organization uniquely observable from a fixed site. The C-band Scanning Atmospheric Radiation Measurement (ARM) Precipitation Radar was deployed for the first time with over 50 ARM Mobile Facility atmospheric state, surface, aerosol, radiation, cloud, and precipitation instruments between October 2018 and April 2019. An intensive observing period (IOP) coincident with the RELAMPAGO field campaign was held between 1 November and 15 December during which 22 flights were performed by the ARM Gulfstream-1 aircraft.A multitude of atmospheric processes and cloud conditions were observed over the 7-month campaign, including: numerous orographic cumulus and stratocumulus events; new particle formation and growth producing high aerosol concentrations; drizzle formation in fog and shallow liquid clouds; very low aerosol conditions following wet deposition in heavy rainfall; initiation of ice in congestus clouds across a range of temperatures; extreme deep convection reaching 21-km altitudes; and organization of intense, hail-containing supercells and mesoscale convective systems. These comprehensive datasets include many of the first ever collected in this region and provide new opportunities to study orographic cloud evolution and interactions with meteorological conditions, aerosols, surface conditions, and radiation in mountainous terrain.

Characteristics of an African Easterly Wave Observed during NAMMA

2010 ◽  
Vol 67 (1) ◽  
pp. 3-25 ◽  
Author(s):  
Robert Cifelli ◽  
Timothy Lang ◽  
Steven A. Rutledge ◽  
Nick Guy ◽  
Edward J. Zipser ◽  
...  
Keyword(s):  
West Africa ◽  
Deep Convection ◽  
Extended Period ◽  
Appreciable Change ◽  
Low Level ◽  
Convective Systems ◽  
African Easterly Wave ◽  
Wave Trough ◽  
Easterly Wave ◽  
Mesoscale Convective

Abstract The evolution of an African easterly wave is described using ground-based radar and ancillary datasets from three locations in West Africa: Niamey, Niger (continental), Dakar, Senegal (coastal), and Praia, Republic of Cape Verde (oceanic). The data were collected during the combined African Monsoon Multidisciplinary Analyses (AMMA) and NASA AMMA (NAMMA) campaigns in August–September 2006. Two precipitation events originated within the wave circulation and propagated with the wave across West Africa. Mesoscale convective systems (MCSs) associated with these events were identified at all three sites ahead of, within, and behind the 700-mb wave trough. An additional propagating event was indentified that originated east of the wave and moved through the wave circulation. The MCS activity associated with this event did not show any appreciable change resulting from its interaction with the wave. The MCS characteristics at each site were different, likely due to a combination of life cycle effects and changes in relative phasing between the propagating systems and the position of low-level convergence and thermodynamic instability associated with the wave. At the ocean and coastal sites, the most intense convection occurred ahead of the wave trough where both high CAPE and low-level convergence were concentrated. At the continental site, convection was relatively weak owing to the fact that the wave dynamics and thermodynamics were not in sync when the systems passed through Niamey. The only apparent effect of the wave on MCS activity at the continental site was to extend the period of precipitation activity during one of the events that passed through coincident with the 700-mb wave trough. Convective organization at the land sites was primarily in the form of squall lines and linear MCSs oriented perpendicular to the low-level shear. The organization at the oceanic site was more complicated, transitioning from linear MCSs to widespread stratiform cloud with embedded convection. The precipitation activity was also much longer lived at the oceanic site due to the wave becoming nearly stationary near the Cape Verdes, providing an environment supportive of deep convection for an extended period.

scholarly journals Numerical Simulation of Radial Cloud Bands within the Upper-Level Outflow of an Observed Mesoscale Convective System

2010 ◽  
Vol 67 (9) ◽  
pp. 2990-2999 ◽  
Author(s):  
S. B. Trier ◽  
R. D. Sharman ◽  
R. G. Fovell ◽  
R. G. Frehlich
Keyword(s):  
Deep Convection ◽  
Vertical Wind Shear ◽  
Mesoscale Convective System ◽  
Static Stability ◽  
Vertical Shear ◽  
Convective System ◽  
Shallow Convection ◽  
Band Formation ◽  
Mesoscale Convective ◽  
Radial Outflow

Abstract Turbulence affecting aircraft is frequently reported within bands of cirrus anvil cloud extending radially outward from upstream deep convection in mesoscale convective systems (MCSs). A high-resolution convection permitting model is used to simulate bands of this type observed on 17 June 2005. The timing, location, and orientation of these simulated bands are similar to those in satellite imagery for this case. The 10–20-km horizontal spacing between the bands is also similar to typical spacing found in a recent satellite-based climatology of MCS-induced radial outflow bands. The simulated bands result from shallow convection in the near-neutral to weakly unstable MCS outer anvil. The weak stratification of the anvil, the ratio of band horizontal wavelength to the depth of the near-neutral anvil layer (5:1 to 10:1), and band orientation approximately parallel to the vertical shear within the same layer are similar to corresponding aspects of horizontal convective rolls in the atmospheric boundary layer, which result from thermal instability. The vertical shear in the MCS outflow is important not only in influencing the orientation of the radial bands but also for its role, through differential temperature advection, in helping to thermodynamically destabilize the environment in which they originate. High-frequency gravity waves emanating from the parent deep convection are trapped in a layer of strong static stability and vertical wind shear beneath the near-neutral anvil and, consistent with satellite studies, are oriented approximately normal to the developing radial bands. The wave-generated vertical displacements near the anvil base may aid band formation in the layer above.

Evolution of the Vertical Thermodynamic Profile during the Transition from Shallow to Deep Convection during CuPIDO 2006*

2009 ◽  
Vol 137 (3) ◽  
pp. 937-953 ◽  
Author(s):  
Joseph A. Zehnder ◽  
Jiuxiang Hu ◽  
Anshuman Radzan
Keyword(s):  
Field Experiment ◽  
Gravity Waves ◽  
Deep Convection ◽  
Shallow Convection ◽  
Stable Layer ◽  
Dry Air ◽  
Low Level ◽  
Orographic Convection ◽  
Santa Catalina Mountains

Abstract The evolution of the vertical thermodynamic profile associated with two cases of deep orographic convection were studied with data from an instrumented aircraft, mobile surface based radiosondes, and stereo photogrammetric analyses. The data were collected during a field experiment [i.e., the Cumulus Photogrammetric, In Situ, and Doppler Observations (CuPIDO) experiment in 2006] performed over the Santa Catalina Mountains in southern Arizona. In both cases the vertical thermodynamic profile was modified in a way that supported subsequent deep convection. In one case, a midtropospheric stable layer was eroded through low-level warming and cooling at the cloud-top level that was likely due to an adiabatic adjustment of the profile through the action of gravity waves. In the second case, dry air aloft was moistened through the action of the shallow convection thus preventing the erosion of the convective turrets through entrainment of dry air. These cases illustrate mechanisms for convective conditioning of the atmosphere that may organize deep convection in general.

Use of the GOES-R Split-Window Difference to Diagnose Deepening Low-Level Water Vapor

2014 ◽  
Vol 53 (8) ◽  
pp. 2005-2016 ◽  
Author(s):  
Daniel T. Lindsey ◽  
Louie Grasso ◽  
John F. Dostalek ◽  
Jochen Kerkmann
Keyword(s):  
Water Vapor ◽  
Numerical Models ◽  
Critical Role ◽  
Warm Season ◽  
Convective Cloud ◽  
Cloud Formation ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Low Level ◽  
Free Environment

AbstractThe depth of boundary layer water vapor plays a critical role in convective cloud formation in the warm season, but numerical models often struggle with accurate predictions of above-surface moisture. Satellite retrievals of water vapor have been developed, but they are limited by the use of a model’s first guess, instrument spectral resolution, horizontal footprint size, and vertical resolution. In 2016, Geostationary Operational Environmental Satellite-R (GOES-R), the first in a series of new-generation geostationary satellites, will be launched. Its Advanced Baseline Imager will provide unprecedented spectral, spatial, and temporal resolution. Among the bands are two centered at 10.35 and 12.3 μm. The brightness temperature difference between these bands is referred to as the split-window difference, and has been shown to provide information about atmospheric column water vapor. In this paper, the split-window difference is reexamined from the perspective of GOES-R and radiative transfer model simulations are used to better understand the factors controlling its value. It is shown that the simple split-window difference can provide useful information for forecasters about deepening low-level water vapor in a cloud-free environment.

Convective Coupling in Tropical-Depression-Type Waves. Part II: Moisture and Moist Static Energy Budgets

2020 ◽  
Vol 77 (10) ◽  
pp. 3423-3440 ◽  
Author(s):  
Tao Feng ◽  
Jia-Yuh Yu ◽  
Xiu-Qun Yang ◽  
Ronghui Huang
Keyword(s):  
Deep Convection ◽  
Critical Role ◽  
Precipitation Rate ◽  
Moist Static Energy ◽  
Shallow Convection ◽  
Convective Rainfall ◽  
Horizontal Advection ◽  
Tropical Depression ◽  
Moisture Advection ◽  
Static Energy

AbstractThe companion of this paper, Part I, discovered the characteristics of the rainfall progression in tropical-depression (TD)-type waves over the western North Pacific. In Part II, the large-scale controls on the convective rainfall progression have been investigated using the ERA-Interim data and the TRMM 3B42 precipitation-rate data during June–October from 1998 to 2013 through budgets of moist static energy (MSE) and moisture. A buildup of column-integrated MSE occurs in advance of deep convection, and an export of MSE occurs following deep convection, which is consistent with the MSE recharge–discharge paradigm. The MSE recharge–discharge is controlled by horizontal processes, whereby horizontal moisture advection causes net MSE import prior to deep convection. Such moistening by horizontal advection creates a moist midtroposphere, which helps destabilize the atmospheric column, leading to the development of deep convective rainfall. Following the heaviest rainfall, negative horizontal moisture advection dries the troposphere, inhibiting convection. Such moistening and drying processes explain why deep convection can develop without preceding shallow convection. The advection of moisture anomalies by the mean horizontal flow controls the tropospheric moistening and drying processes. As the TD-type waves propagate northwestward in coincidence with the northwestward environmental flow, the moisture, or convective rainfall, is phase locked to the waves. The critical role of the MSE import by horizontal advection in modulating the rainfall progression is supported by the anomalous gross moist stability (AGMS), where the lowest AGMS corresponds to the quickest increase in the precipitation rate prior to the rainfall maximum.

scholarly journals Tropical Cyclone Mekkhala’s (2008) Formation over the South China Sea: Mesoscale, Synoptic-Scale, and Large-Scale Contributions

2015 ◽  
Vol 143 (1) ◽  
pp. 88-110 ◽  
Author(s):  
Myung-Sook Park ◽  
Hyeong-Seog Kim ◽  
Chang-Hoi Ho ◽  
Russell L. Elsberry ◽  
Myong-In Lee
Keyword(s):  
Tropical Cyclone ◽  
Large Scale ◽  
Wave Train ◽  
Critical Role ◽  
Intraseasonal Variability ◽  
The Philippines ◽  
Synoptic Scale ◽  
Low Level ◽  
Convective Systems ◽  
Mesoscale Convective

Abstract Tropical cyclone formation close to the coastline of the Asian continent presents a significant threat to heavily populated coastal countries. A case study of Tropical Storm Mekkhala (2008) that developed off the coast of Vietnam is presented using the high-resolution analyses of the European Centre for Medium-Range Weather Forecasts/Year of Tropical Convection and multiple satellite observations. The authors have analyzed contributions to the formation from large-scale intraseasonal variability, synoptic perturbations, and mesoscale convective systems (MCSs). Within a large-scale westerly wind burst (WWB) associated with the Madden–Julian oscillation (MJO), synoptic perturbations generated by two preceding tropical cyclones initiated the pre-Mekkhala low-level vortex over the Philippine Sea. Typhoon Hagupit produced a synoptic-scale wave train that contributed to the development of Jangmi, but likely suppressed the Mekkhala formation. The low-level vortex of the pre-Mekkhala disturbance was then initiated in a confluent zone between northeasterlies in advance of Typhoon Jangmi and the WWB. A key contribution to the development of Mekkhala was from diurnally varying MCSs that were invigorated in the WWB. The oceanic MCSs, which typically develop off the west coast of the Philippines in the morning and dissipate in the afternoon, were prolonged beyond the regular diurnal cycle. A combination with the MCSs developing downstream of the Philippines led to the critical structure change of the oceanic convective cluster, which implies the critical role of mesoscale processes. Therefore, the diurnally varying mesoscale convective processes over both the ocean and land are shown to have an essential role in the formation of Mekkhala in conjunction with large-scale MJO and the synoptic-scale TC influences.

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