The role of mesoscale convective systems in the diurnal cycle of rainfall and its seasonality over sub-Saharan Northern Africa

2018 ◽  
Vol 52 (1-2) ◽  
pp. 729-745 ◽  
Author(s):  
Weiran Liu ◽  
Kerry H. Cook ◽  
Edward K. Vizy
Keyword(s):  
Diurnal Cycle ◽  
Northern Africa ◽  
Mesoscale Convective Systems ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Sub Saharan

scholarly journals Long-Lived Mesoscale Systems in a Low–Convective Inhibition Environment. Part I: Upshear Propagation

2015 ◽  
Vol 72 (11) ◽  
pp. 4297-4318 ◽  
Author(s):  
Todd P. Lane ◽  
Mitchell W. Moncrieff
Keyword(s):  
Standard Model ◽  
Gravity Waves ◽  
Propagation Speed ◽  
Mesoscale Convective Systems ◽  
Dynamical Models ◽  
Convective Systems ◽  
The Standard Model ◽  
Mesoscale Convective ◽  
Convective Inhibition

Abstract Dynamical models of organized mesoscale convective systems have identified the important features that help maintain their overarching structure and longevity. The standard model is the trailing stratiform archetype, featuring a front-to-rear ascending circulation, a mesoscale downdraft circulation, and a cold pool/density current that affects the propagation speed and the maintenance of the system. However, this model does not represent all types of mesoscale convective systems, especially in moist environments where the evaporation-driven cold pools are weak and the convective inhibition is small. Moreover, questions remain about the role of gravity waves in creating and maintaining organized systems and affecting their propagation speed. This study presents simulations and dynamical models of self-organizing convection in a moist, low–convective inhibition environment and examines the long-lived convective regimes that emerge spontaneously. This paper, which is Part I of this study, specifically examines the structure, kinematics, and maintenance of long-lived, upshear-propagating convective systems that differ in important respects from the standard model of long-lived convective systems. Linear theory demonstrates the role of ducted gravity waves in maintaining the long-lived, upshear-propagating systems. A steady nonlinear model approximates the dynamics of upshear-propagating density currents that are key to the maintenance of the mesoscale convective system.

On the diurnal cycle of rainfall and convection over Lake Victoria and its catchment. Part 1: Rainfall and Mesoscale Convective Systems

2021 ◽  
Author(s):  
Sharon E. Nicholson ◽  
Adam T. Hartman ◽  
Douglas A. Klotter
Keyword(s):  
Diurnal Cycle ◽  
Lake Victoria ◽  
Mesoscale Convective Systems ◽  
Convective Systems ◽  
Early Evening ◽  
Lake Effect ◽  
Mesoscale Convective ◽  
Dry Seasons

AbstractThis article examines the diurnal cycle of lake-effect rains over Lake Victoria and of rainfall in the surrounding catchment. The analysis focuses on four months, which represent the two wet seasons (April and November) and the two dry seasons (February and July). Lake-effect rains are strongest in April, weakest in July. In all cases there is a nocturnal rainfall maximum over the lake and a daytime maximum over the catchment, with the transition between rainfall over the lake and over the catchment occurring between 1200 and 1500 LST. During the night the surrounding catchment is mostly dry. Conversely, little to no rain falls over the lake during the afternoon and early evening. In most cases the maximum over the lake occurs at either 0600 or 0900 LST and the maximum over the catchment occurs around 1500 to 1800 LST. The diurnal cycle of Mesoscale Convective Systems (MCSs) parallels that of over-lake rainfall. MCS initiation generally begins over the catchment around 1500 LST and increases at 1800 LST. MCS initiation over the lake begins around 0300 LST and continues until 1200 LST. While some MCSs originate over the highlands to the east of the lake, most originate in situ over the lake. Maximum MCS activity over the lake occurs at 0600 LST and is associated with the systems that initiate in situ.

scholarly journals Precipitation and Mesoscale Convective Systems: Radiative Impact of Dust over Northern Africa

2018 ◽  
Vol 146 (9) ◽  
pp. 3011-3029 ◽  
Author(s):  
Irene Reinares Martínez ◽  
Jean-Pierre Chaboureau
Keyword(s):  
Convective Available Potential Energy ◽  
Dust Emission ◽  
Northern Africa ◽  
Mesoscale Convective Systems ◽  
Lower Atmosphere ◽  
Radiative Effect ◽  
Near Surface ◽  
Convective Systems ◽  
African Easterly Jet ◽  
Mesoscale Convective

Abstract The radiative effect of dust on precipitation and mesoscale convective systems (MCSs) is examined during a case of dust emission and transport from 9 to 14 June 2006 over northern Africa. The same method to identify and track different cloud types is applied to satellite observations and two convection-permitting simulations (with grid mesh of 2.5 km), with and without the radiative effect of dust, performed with the MesoNH model. The MCSs produce most of the observed total precipitation (66%), and the long-lived systems (lasting 6 h or more) are responsible for 55% of the total. Both simulations reproduce the observed distribution of precipitation between the cloud categories but differ due to the radiative effects of dust. The overall impacts of dust are a warming of the midtroposphere; a cooling of the near surface, primarily in the western parts of northern Africa; and a decrease in precipitation due to a too-low number of long-lived MCSs. The drop in their number is due to the stabilization of the lower atmosphere, which inhibits the triggering of convection. The long-lived MCSs are a little longer lived, faster, and more efficient in rainfall production when accounting for the dust–radiation interaction. This higher degree of organization is due to the larger convective available potential energy and an intensified African easterly jet. The latter is, in turn, a response to the variation in the meridional gradient of the temperature induced by the dust.

scholarly journals Mesoscale Convective Systems over Western Equatorial Africa and Their Relationship to Large-Scale Circulation

2009 ◽  
Vol 137 (4) ◽  
pp. 1272-1294 ◽  
Author(s):  
Brian Jackson ◽  
Sharon E. Nicholson ◽  
Douglas Klotter
Keyword(s):  
Diurnal Cycle ◽  
Rainy Season ◽  
Large Scale ◽  
Critical Role ◽  
Mesoscale Convective Systems ◽  
Convective Systems ◽  
Continental Scale ◽  
Equatorial Africa ◽  
Mesoscale Convective ◽  
The Right

Abstract This study examines mesoscale convective systems (MCSs) over western equatorial Africa using data from the Tropical Rainfall Measuring Mission (TRMM) satellite. This region experiences some of the world’s most intense thunderstorms and highest lightning frequency, but has low rainfall relative to other equatorial regions. The analyses of MCS activity include the frequency of occurrence, diurnal and annual cycles, and associated volumetric and convective rainfall. Also evaluated is the lightning activity associated with the MCSs. Emphasis is placed on the diurnal cycle and on the continental-scale motion fields in this region. The diurnal cycle shows a maximum in MCS count around 1500–1800 LT, a morning minimum, and substantial activity during the night; there is little seasonal variation in the diurnal cycle, suggesting stationary influences such as orography. Our analysis shows four maxima in MCS activity, three of which are related to local geography (two orographic and one over Lake Victoria). The fourth coincides with a midtropospheric convergence maximum in the right entrance quadrant of the African easterly jet of the Southern Hemisphere (AEJ-S). This maximum is substantially stronger in the September–November rainy season, when the jet is well developed, than in the March–May rainy season, when the jet is absent. Lightning frequency and flashes per MCS are also greatest during September–November; maxima occur in the right entrance quadrant of the AEJ-S. The lightning maximum is somewhat south of the MCS maximum and coincides with the low-lying areas of central Africa. Overall, the results of this study suggest that large-scale topography plays a critical role in the spatial and diurnal patterns of convection, lightning, and rainfall in this region. More speculative is the role of the AEJ-S, but this preliminary analysis suggests that it does play a role in the anomalous intensity of convection in western equatorial Africa.

scholarly journals On the role of ice‐nucleating aerosol in the formation of ice particles in tropical mesoscale convective systems

2017 ◽  
Vol 44 (3) ◽  
pp. 1574-1582 ◽  
Author(s):  
Luis A. Ladino ◽  
Alexei Korolev ◽  
Ivan Heckman ◽  
Mengistu Wolde ◽  
Ann M. Fridlind ◽  
...  
Keyword(s):  
Mesoscale Convective Systems ◽  
Convective Systems ◽  
Ice Particles ◽  
Mesoscale Convective
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