Differences in deep convective transport characteristics between quasi-isolated strong convection and mesoscale convective systems using seasonal WRF simulations

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.

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Convective and Slantwise Trajectory Ascent in Convection-Permitting Simulations of Midlatitude Cyclones

Monthly Weather Review ◽

10.1175/mwr-d-16-0112.1 ◽

2016 ◽

Vol 144 (10) ◽

pp. 3961-3976 ◽

Cited By ~ 10

Author(s):

Stephan Rasp ◽

Tobias Selz ◽

George C. Craig

Keyword(s):

Cold Front ◽

Conveyor Belt ◽

Mesoscale Convective Systems ◽

Convective Systems ◽

Mesoscale Convective ◽

Order Of Magnitude ◽

Unstable Layer ◽

Strong Convection ◽

The Mean ◽

Midlatitude Cyclones

Air parcel ascent in midlatitude cyclones driven by latent heat release has been investigated using convection-permitting simulations together with an online trajectory calculation scheme. Three cyclones were simulated to represent different ascent regimes: one continental summer case, which developed strong convection organized along a cold front; one marine winter case representing a slantwise ascending warm conveyor belt; and one autumn case, which contains both ascent types as well as mesoscale convective systems. Distributions of ascent times differ significantly in mean and shape between the convective summertime case and the synoptic wintertime case, with the mean ascent time being one order of magnitude larger for the latter. For the autumn case the distribution is a superposition of both ascent types, which could be separated spatially and temporally in the simulation. In the slowly ascending airstreams a significant portion of the parcels still experienced short phases of convective ascent. These are linked to line convection in the boundary layer for the wintertime case and an elevated conditionally unstable layer in the autumn case. Potential vorticity (PV) modification during ascent has also been investigated. Despite the different ascent characteristics it was found that net PV change between inflow and outflow levels is very close to zero in all cases. The spread of individual PV values, however, is increased after the ascent. This effect is more pronounced for convective trajectories.

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Comparison of lightning activity in the two most active areas of the Congo Basin

Natural Hazards and Earth System Science ◽

10.5194/nhess-18-479-2018 ◽

2018 ◽

Vol 18 (2) ◽

pp. 479-489

Author(s):

Jean K. Kigotsi ◽

Serge Soula ◽

Jean-François Georgis

Keyword(s):

Thunderstorm Activity ◽

Lightning Activity ◽

Congo Basin ◽

Mesoscale Convective Systems ◽

Flash Rate ◽

Convective Systems ◽

African Easterly Jet ◽

The World ◽

Mesoscale Convective ◽

Strong Convection

Abstract. A comparison of the lightning activity in the two most active areas (Area_max for the main maximum and Area_sec for the secondary maximum) of the Congo Basin is made with data obtained by the World Wide Lightning Location Network (WWLLN) during 2012 and 2013. Both areas of same size (5°  ×  5°) exhibit flash counts in a ratio of about 1.32 for both years and very different distributions of the flash rate density (FRD) with maximums in a ratio of 1.94 and 2.59 for 2012 and 2013, respectively. The FRD is much more widely distributed in Area_sec, which means the whole area contributes more or less equal to the lightning activity. The diurnal cycle is much more pronounced in Area_max than in Area_sec with a ratio between the maximum and the minimum of 15.4 and 4.7, respectively. However, the minimum and maximum of the hourly flash rates are observed roughly at the same time in both areas, between 07:00 and 09:00 UTC and between 16:00 and 17:00 UTC, respectively. In Area_sec the proportion of days with low lightning rate (0–1000 flashes per day) is much larger (∼  45 % in 2013) compared to Area_max (∼  23 % in 2013). In Area_max the proportion of days with moderate lightning rate (1001–6000 flashes per day) is larger (∼  68.5 % in 2013) compared to Area_sec (∼  46 % in 2013). The very intense convective events are slightly more numerous in Area_sec. In summary, the thunderstorm activity in Area_sec is more variable at different scales of time (annually and daily), in intensity and in location. Area_max combines two favourable effects for thunderstorm development, the convergence associated with the African easterly jet of the Southern Hemisphere (AEJ-S) and a geographic effect due to the orography and the presence of a lake. The location of the strong convection in Area_sec is modulated by the distance of westward propagation/regeneration of mesoscale convective systems (MCSs) in relation to the phase of Kelvin waves.

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WRF simulations of mesoscale convective systems at convection-allowing resolutions

10.31274/etd-180810-2826 ◽

2011 ◽

Author(s):

Jeffrey Dean Duda

Keyword(s):

Mesoscale Convective Systems ◽

Convective Systems ◽

Mesoscale Convective

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The role of the convective ?trigger function? in numerical forecasts of mesoscale convective systems

Meteorology and Atmospheric Physics ◽

10.1007/bf01025402 ◽

1992 ◽

Vol 49 (1-4) ◽

pp. 93-106 ◽

Cited By ~ 119

Author(s):

J. S. Kain ◽

J. M. Fritsch

Keyword(s):

Mesoscale Convective Systems ◽

Convective Systems ◽

Trigger Function ◽

Mesoscale Convective

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A five-year climatological lightning characteristics of linear mesoscale convective systems over North China

Atmospheric Research ◽

10.1016/j.atmosres.2021.105580 ◽

2021 ◽

Vol 256 ◽

pp. 105580

Author(s):

Dongxia Liu ◽

Mengyu Sun ◽

Debin Su ◽

Wenjing Xu ◽

Han Yu ◽

...

Keyword(s):

North China ◽

Mesoscale Convective Systems ◽

Convective Systems ◽

Mesoscale Convective

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An Observational Study of Mesoscale Convective Systems with Heavy Rainfall over the Korean Peninsula

Weather and Forecasting ◽

10.1175/waf912.1 ◽

2006 ◽

Vol 21 (2) ◽

pp. 125-148 ◽

Cited By ~ 33

Author(s):

Hyung Woo Kim ◽

Dong Kyou Lee

Keyword(s):

Observational Study ◽

Korean Peninsula ◽

Wind Shear ◽

Heavy Rainfall ◽

Vertical Wind Shear ◽

Vertical Wind ◽

Mesoscale Convective Systems ◽

Low Level ◽

Convective Systems ◽

Mesoscale Convective

Abstract A heavy rainfall event induced by mesoscale convective systems (MCSs) occurred over the middle Korean Peninsula from 25 to 27 July 1996. This heavy rainfall caused a large loss of life and property damage as a result of flash floods and landslides. An observational study was conducted using Weather Surveillance Radar-1988 Doppler (WSR-88D) data from 0930 UTC 26 July to 0303 UTC 27 July 1996. Dominant synoptic features in this case had many similarities to those in previous studies, such as the presence of a quasi-stationary frontal system, a weak upper-level trough, sufficient moisture transportation by a low-level jet from a tropical storm landfall, strong potential and convective instability, and strong vertical wind shear. The thermodynamic characteristics and wind shear presented favorable conditions for a heavy rainfall occurrence. The early convective cells in the MCSs initiated over the coastal area, facilitated by the mesoscale boundaries of the land–sea contrast, rain–no rain regions, saturated–unsaturated soils, and steep horizontal pressure and thermal gradients. Two MCSs passed through the heavy rainfall regions during the investigation period. The first MCS initiated at 1000 UTC 26 July and had the characteristics of a supercell storm with small amounts of precipitation, the appearance of a mesocyclone with tilting storm, a rear-inflow jet at the midlevel of the storm, and fast forward propagation. The second MCS initiated over the upstream area of the first MCS at 1800 UTC 26 July and had the characteristics of a multicell storm, such as a broken areal-type squall line, slow or quasi-stationary backward propagation, heavy rainfall in a concentrated area due to the merging of the convective storms, and a stagnated cluster system. These systems merged and stagnated because their movement was blocked by the Taebaek Mountain Range, and they continued to develop because of the vertical wind shear resulting from a low-level easterly inflow.

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