Large-Scale Environmental Influences on Tropical Cyclone Formation Processes and Development Time

2020 ◽  
Vol 33 (22) ◽  
pp. 9763-9782
Author(s):  
Hsu-Feng Teng ◽  
James M. Done ◽  
Cheng-Shang Lee ◽  
Huang-Hsiung Hsu ◽  
Ying-Hwa Kuo
Keyword(s):  
Large Scale ◽  
Development Time ◽  
Analysis Method ◽  
Short Term ◽  
Convective Systems ◽  
Cloud Clusters ◽  
Mesoscale Convective ◽  
Environmental Transitions ◽  
Cluster Analysis Method ◽  
Low Levels

AbstractThe development of tropical cloud clusters (TCCs) to tropical cyclones (TCs) is the process of TC formation. This study identifies five main environmental transitions for the development of TCCs to TCs in the western North Pacific by using a cluster analysis method. Of these, three transitions indicate TCCs that develop in monsoon environments and two in easterly environments. Their numbers, distributions, and interannual variability differ. On average, the development time, defined as the period from the TCC forming to it developing into a TC, for TCCs that develop in easterly environments is shorter than that in monsoon environments. For the development of TCC to TC in easterly environments, TCCs have fewer embedded mesoscale convective systems (MCSs), which are located closer to the TCC center. Moreover, there is a stronger inward short-term (less than 10 days) angular momentum flux (AMF) at middle levels (800–500 hPa) before TCC formation. Conversely, in monsoon environments, TCCs have more MCSs, which are located farther from the TCC center. A stronger inward short-term AMF at low levels (1000–850 hPa) is observed before TCC formation and develops upward during the development of TCC to TC. The characteristics of MCS and AMF are significantly correlated with the development time of TCC to TC. In summary, large-scale easterly and monsoon environments cause TCCs to have different MCS and AMF characteristics, leading to higher efficiency for TCCs developing into TCs in easterly environments compared to monsoon environments.

Lake-effect rains over Lake Victoria and their association with Mesoscale Convective Systems

2021 ◽  
Author(s):  
Sharon E. Nicholson ◽  
Douglas Klotter ◽  
Adam T. Hartman
Keyword(s):  
Large Scale ◽  
Lake Victoria ◽  
Ground Truth ◽  
Mesoscale Convective Systems ◽  
Convective Systems ◽  
Lake Effect ◽  
Mesoscale Convective ◽  
Strong Convection ◽  
Short Rains ◽  
Lake Catchment

AbstractThis article examined rainfall enhancement over Lake Victoria. Estimates of over-lake rainfall were compared with rainfall in the surrounding lake catchment. Four satellite products were initially tested against estimates based on gauges or water balance models. These included TRMM 3B43, IMERG V06 Final Run (IMERG-F), CHIRPS2, and PERSIANN-CDR. There was agreement among the satellite products for catchment rainfall but a large disparity among them for over-lake rainfall. IMERG-F was clearly an outlier, exceeding the estimate from TRMM 3B43 by 36%. The overestimation by IMERG-F was likely related to passive microwave assessments of strong convection, such as prevails over Lake Victoria. Overall, TRMM 3B43 showed the best agreement with the "ground truth" and was used in further analyses. Over-lake rainfall was found to be enhanced compared to catchment rainfall in all months. During the March-to-May long rains the enhancement varied between 40% and 50%. During the October-to-December short rains the enhancement varied between 33% and 44%. Even during the two dry seasons the enhancement was at least 20% and over 50% in some months. While the magnitude of enhancement varied from month to month, the seasonal cycle was essentially the same for over-lake and catchment rainfall, suggesting that the dominant influence on over-lake rainfall is the large-scale environment. The association with Mesoscale Convective Systems (MCSs) was also evaluated. The similarity of the spatial patterns of rainfall and MCS count each month suggested that these produced a major share of rainfall over the lake. Similarity in interannual variability further supported this conclusion.

Deep Convective Systems Observed by A-Train in the Tropical Indo-Pacific Region Affected by the MJO

2013 ◽  
Vol 70 (2) ◽  
pp. 465-486 ◽  
Author(s):  
Jian Yuan ◽  
Robert A. Houze
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Active Phase ◽  
Maximum Height ◽  
Pacific Region ◽  
Convective Envelope ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Deep Convective Systems ◽  
Cloud Tops

Abstract In the Indo-Pacific region, mesoscale convective systems (MCSs) occur in a pattern consistent with the eastward propagation of the large-scale convective envelope of the Madden–Julian oscillation (MJO). MCSs are major contributors to the total precipitation. Over the open ocean they tend to be merged or connected systems, while over the Maritime Continent area they tend to be separated or discrete. Over all regions affected by the MJO, connected systems increase in frequency during the active phase of the MJO. Characteristics of each type of MCS (separated or connected) do not vary much over MJO-affected regions. However, separated and connected MCSs differ in structure from each other. Connected MCSs have a larger size and produce less but colder-topped anvil cloud. For both connected and separated MCSs, larger systems tend to have colder cloud tops and less warmer-topped anvil cloud. The maximum height of MCS precipitating cores varies only slightly, and the variation is related to sea surface temperature. Enhanced large-scale convection, greater frequency of occurrence of connected MCSs, and increased midtroposphere moisture coincide, regardless of the region, season, or large-scale conditions (such as the concurrent phase of the MJO), suggesting that the coexistence of these phenomena is likely the nature of deep convection in this region. The increase of midtroposphere moisture observed in all convective regimes during large-scale convectively active phases suggests that the source of midtroposphere moisture is not local or instantaneous and that the accumulation of midtroposphere moisture over MJO-affected regions needs to be better understood.

scholarly journals Lightning and precipitation produced by severe weather systems over Belém, Brazil

2014 ◽  
Vol 29 (spe) ◽  
pp. 41-59 ◽  
Author(s):  
Wanda Maria do Nascimento Ribeiro ◽  
José Ricardo Santos Souza ◽  
Márcio Nirlando Gomes Lopes ◽  
Renata Kelen Cardoso Câmara ◽  
Edson José Paulino Rocha ◽  
...  
Keyword(s):  
Large Scale ◽  
Electric Activity ◽  
Weather Conditions ◽  
Rain Gauge ◽  
Mesoscale Convective Systems ◽  
Major Influence ◽  
Rainfall Events ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Cg Lightning

CG Lightning flashes events monitored by a LDN of the Amazon Protection System, which included 12 LPATS IV VAISALA sensors distributed over eastern Amazonia, were analyzed during four severe rainstorm occurrences in Belem-PA-Brazil, in the 2006-2007 period. These selected case studies referred to rainfall events, which produced more than 25 mm/hour, or more than 40 mm/ 2 hours of precipitation rate totals, registered by a tipping bucket automatic high-resolution rain gauge, located at 1º 47' 53" S and 48º 30' 16" W. Centered at this location, a 30 ,10 and 5 km radius circles were drawn by means of a geographic information system, and the data from lightning occurrences within this larger area, were set apart for analysis. During these severe storms the CG lightning events, occurred almost randomly over the surrounding defined circle, previously covered by mesoscale convective systems, for all cases studied. This work also showed that the interaction between large-scale and mesoscale weather conditions have a major influence on the intensity of the storms studied cases. In addition to the enhancement of the lightning and precipitation rates, the electric activity within the larger circles can precede the rainfall at central point of the areas

The diurnal cycle can trigger convective self-aggregation 

2021 ◽  
Author(s):  
Gorm Gruner Jensen ◽  
Romain Fiévet ◽  
Jan O. Haerter
Keyword(s):  
Surface Temperature ◽  
Diurnal Cycle ◽  
Large Scale ◽  
Horizontal Resolution ◽  
Cold Pool ◽  
Atmospheric Sciences ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Spatio Temporal ◽  
Self Aggregation

<p>Convective self-aggregation (CSA) is an established modelling paradigm for large-scale thunderstorm clusters, as they form in mesoscale convective systems, the Madden-JulianOscillation or tropical cyclo-genesis [1]. The onset of CSA is characterized by the spontaneous formation of persistently dry patches with suppressed deep convective rainfall. Recently another type of spatio-temporal pattern formation was observed in simulations where the diurnal cycle was mimicked by a sinusoidally varying surface temperature [2]. This diurnal aggregation (DA) is characterized by clusters of intense rain that correlate negatively from one day to the next. </p><p>Here we demonstrate that the diurnal cycle can also act as a trigger of persistently dry patches resembling the early stages of CSA. When the surface temperature is held constant, CSA has been shown to occur within simulations of coarse horizontal model resolution, but not when the resolution was increased [3]. We show that, when a temporally periodic surface temperature forcing is imposed, persistently convection free patches occur even faster when the spatial resolution is increased. The failure to achieve CSA at high horizontal resolution has so far been attributed to the more pronounced cold pool effects at such resolution. In our simulations these cold pools in fact play a key role in promoting CSA. Our results have implications for the origin of persistent convective organization over continents and the sea — and point a path towards achieving such clustering under realistic conditions.</p><p><br>[1]  Christopher S Bretherton, Peter N Blossey, and Marat Khairoutdinov.  An energy-balance analysisof deep convective self-aggregation above uniform SST.Journal of the Atmospheric Sciences, 62(12):4273–4292, 2005.<br>[2]  J. O. Haerter, B. Meyer, and S. B. Nissen.  Diurnal self-aggregation.npj Climate and AtmosphericScience, 3:30, 2020.<br>[3]  Caroline  Muller  and  Sandrine  Bony.   What  favors  convective  aggregation  and  why?GeophysicalResearch Letters, 42(13):5626–5634, 2015.  doi:  https://doi.org/10.1002/2015GL064260.</p>

A Wave-Relative Framework Analysis of AEW–MCS Interactions Leading to Tropical Cyclogenesis

2020 ◽  
Vol 148 (11) ◽  
pp. 4657-4671
Author(s):  
Kelly M. Núñez Ocasio ◽  
Jenni L. Evans ◽  
George S. Young
Keyword(s):  
West Africa ◽  
Thermodynamic Characteristics ◽  
Convective Cloud ◽  
Type Systems ◽  
Squall Line ◽  
Tropical Cyclogenesis ◽  
Framework Analysis ◽  
Convective Systems ◽  
Cloud Clusters ◽  
Mesoscale Convective

AbstractAn African easterly wave (AEW) and associated mesoscale convective systems (MCSs) dataset has been created and used to evaluate the propagation of MCSs, AEWs, and, especially, the propagation of MCSs relative to the AEW with which they are associated (i.e., wave-relative framework). The thermodynamic characteristics of AEW–MCS systems are also analyzed. The analysis is done for both AEW–MCS systems that develop into tropical cyclones and those that do not to quantify significant differences. It is shown that developing AEWs over West Africa are associated with a larger number of convective cloud clusters (CCCs; squall-line-type systems) than nondeveloping AEWs. The MCSs of developing AEWs propagate at the same speed of the AEW trough in addition to being in phase with the trough, whereas convection associated with nondeveloping AEWs over West Africa moves faster than the trough and is positioned south of it. These differences become important for the intensification of the AEW vortex as this slower-moving convection (i.e., moving at the same speed of the AEW trough) spends more time supplying moisture and latent heat to the AEW vortex, supporting its further intensification. An analysis of the rainfall rate (MCS intensity), MCS area, and latent heating rate contribution reveals that there are statistically significant differences between developing AEWs and nondeveloping AEWs, especially over West Africa where the fraction of extremely large MCS areas associated with developing AEWs is larger than for nondeveloping AEWs.

The Atmospheric Controls of Extreme Convective Events over the Southern Arabian Peninsula during the Transition Seasons

2021 ◽  
Author(s):  
Narendra Reddy Nelli ◽  
Diana Francis ◽  
Ricardo Fonseca ◽  
Rachid Abida ◽  
Michael Weston ◽  
...  
Keyword(s):  
Large Scale ◽  
Arabian Peninsula ◽  
Arabian Gulf ◽  
Reanalysis Data ◽  
Convective Systems ◽  
Stratospheric Temperature ◽  
Moisture Advection ◽  
Mesoscale Convective ◽  
Upper Level ◽  
Warming World

<p>In this paper, the processes behind severe convective events over the Arabian Peninsula during spring and autumn seasons and their local-scale impacts are investigated using reanalysis data, satellite-derived and observational products. The focus on the transition seasons is justified as Mesoscale Convective Systems (MCSs) are more common at that time of the year, in particular in the months of March and April. The analysis of 48 events from 2000 to 2019 revealed that they are triggered by low-level wind convergence and moisture advection from the Arabian Sea, Arabian Gulf and/or Red Sea. An equatorward displacement and strengthening of the subtropical jet also precondition the environment, as does the presence of a mid-level trough. The latter is generally part of a large-scale pattern of anomalies that are equivalent barotropic in nature, and therefore likely a response to tropical or subtropical forcing. At more local-scales, a drying of the mid-troposphere between 850 and 250 hPa typically by 50%, a reduction of the upper-level winds by about 5 m s<sup>-1</sup>, and an increase in the upper-tropospheric and lower-stratospheric temperature on averaged by 2-3 K, are typically observed during a MCS event. Over the 20-year period, a statistically significant increase in the MCSs’ spatial extent, intensity and duration over the UAE and surrounding region has been found, suggesting that such extreme events may be even more impactful in a hypothetical warming world. The rainfall they generate, on the other hand, shows an increase that is not statistically significant.</p>

Soil Moisture Influence on the Incidence of Summer Mesoscale Convective Systems in the U.S. Great Plains

2021 ◽  
Author(s):  
Rachel Gaal ◽  
James L. Kinter
Keyword(s):  
Soil Moisture ◽  
Great Plains ◽  
Land Surface ◽  
Large Scale ◽  
Mesoscale Convective Systems ◽  
Antecedent Soil Moisture ◽  
Initiation Point ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
The U.S

AbstractMesoscale convective systems (MCS) are known to develop under ideal conditions of temperature and humidity profiles and large-scale dynamic forcing. Recent work, however, has shown that summer MCS events can occur under weak synoptic forcing or even unfavorable large-scale environments. When baroclinic forcing is weak, convection may be triggered by anomalous conditions at the land surface. This work evaluates land surface conditions for summer MCS events forming in the U.S. Great Plains using an MCS database covering the contiguous United States east of the Rocky Mountains, in boreal summers 2004-2016. After isolating MCS cases where synoptic-scale influences are not the main driver of development (i.e. only non-squall line storms), antecedent soil moisture conditions are evaluated over two domain sizes (1.25° and 5° squares) centered on the mean position of the storm initiation. A negative correlation between soil moisture and MCS initiation is identified for the smaller domain, indicating that MCS events tend to be initiated over patches of anomalously dry soils of ~100-km scale, but not significantly so. For the larger domain, soil moisture heterogeneity, with anomalously dry soils (anomalously wet soils) located northeast (southwest) of the initiation point, is associated with MCS initiation. This finding is similar to previous results in the Sahel and Europe that suggest that induced meso-β circulations from surface heterogeneity can drive convection initiation.

scholarly journals Structure and Motion of Severe-Wind-Producing Mesoscale Convective Systems and Derechos in Relation to the Mean Wind

2017 ◽  
Vol 32 (2) ◽  
pp. 423-439 ◽  
Author(s):  
Matthew A. Campbell ◽  
Ariel E. Cohen ◽  
Michael C. Coniglio ◽  
Andrew R. Dean ◽  
Stephen F. Corfidi ◽  
...  
Keyword(s):  
Large Scale ◽  
Mean Flow ◽  
Convective Systems ◽  
Structure And Motion ◽  
Mesoscale Convective ◽  
The Mean ◽  
Wind Events ◽  
Motion Characteristics ◽  
Definition Of ◽  
Convective Vortices

Abstract The goal of this study is to document differences in the convective structure and motion of long-track, severe-wind-producing MCSs from short-track severe-wind-producing MCSs in relation to the mean wind. An ancillary goal is to determine if these differences are large enough that some criterion for MCS motion relative to the mean wind could be used in future definitions of “derechos.” Results confirm past investigations that well-organized MCSs, including those that produce derechos, tend to move faster than the mean wind, exhibiting a significantly larger degree of propagation (component of MCS motion in addition to the component contributed by the mean flow). Furthermore, well-organized systems that produce shorter-track swaths of damaging winds likewise tend to move faster than the mean wind with a significant propagation component along the mean wind. Therefore, propagation in the direction of the mean wind is not necessarily a characteristic that can be used to distinguish derechos from nonderechos. However, there is some indication that long-track damaging wind events that occur without large-scale or persistent bow echoes and mesoscale convective vortices (MCVs) require a strong propagation component along the mean wind direction to become long lived. Overall, however, there does not appear to be enough separation in the motion characteristics among the MCS types to warrant the inclusion of a mean-wind criterion into the definition of a derecho at this time.

Organizational Modes of Mesoscale Convective Systems over Central East China

2013 ◽  
Vol 28 (5) ◽  
pp. 1081-1098 ◽  
Author(s):  
Linlin Zheng ◽  
Jianhua Sun ◽  
Xiaoling Zhang ◽  
Changhai Liu
Keyword(s):  
Severe Weather ◽  
Mesoscale Convective Systems ◽  
East China ◽  
Short Term ◽  
Low Level ◽  
Convective Systems ◽  
Intense Precipitation ◽  
Stratiform Precipitation ◽  
Mesoscale Convective ◽  
High Winds

Abstract Composite reflectivity Doppler radar data from June to September of 2007–2010 were used to classify mesoscale convective systems (MCSs) over central east China into seven morphologies. The morphologies included one nonlinear mode (NL) and six linear modes: convective lines with no stratiform precipitation (NS), trailing stratiform precipitation (TS), leading stratiform precipitation (LS), parallel stratiform precipitation (PS), bow echoes (BE), and embedded lines (EL). Nonlinear and linear systems composed 44.7% and 55.3% of total MCSs, respectively, but there was no primary linear mode. All MCS morphologies attained their peak occurrence in July, except BE systems, which peaked in June. On average, TS and PS modes had relatively longer lifespans than did other modes. Significant differences in MCS-produced severe weather existed between dry and moist environments. High winds and hail events were mainly observed in dry environments, and in contrast, short-term intense precipitation occurred more frequently in moist environments. BE systems generated the most severe weather on average, while most TS systems were attendant with short-term intense precipitation and high winds. EL and PS systems were most frequently associated with extreme short-time intense precipitation (≥50 mm h−1) as these systems preferentially developed in moist environments. BE systems generally occurred under strong low-level shear and intermediately moist conditions. LS systems were observed in weak low-level shear, whereas EL systems often developed in relatively stable conditions and weak low- to middle-level shear. The largest instability was present in the environment for NS systems. The environmental parameters for TS systems featured the largest differences between the dry and moist cases.

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