Tracking mesoscale convective systems in the Sahel: relation between cloud parameters and precipitation

Goyens, Clémence; Lauwaet, Dirk; Schröder, Marc; Demuzere, Matthias; Lipzig, Nicole Van

doi:10.1002/joc.2407

Cited by 46 publications

(50 citation statements)

References 33 publications

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“…MCS are identified assuming that strong convective activity is related to low brightness temperatures, using an algorithm developed by Schröder et al (2009) and applied over the Lake Chad region by Goyens et al (2011). A single system is defined as a contiguous area of pixels with a brightness temperature below 233 K exceeding 30 000 km 2 .…”

Section: Comparison With Observationsmentioning

confidence: 99%

The precipitation response to the desiccation of Lake Chad

Lauwaet

Lipzig

Weverberg

et al. 2011

Quart J Royal Meteoro Soc

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Located in the semi-arid African Sahel, Lake Chad has shrunk from a surface area of 25 000 km 2 in 1960 to about 1350 km 2 due to a series of droughts and anthropogenic influences. The disappearance of such a large open-water body can be expected to have a noticeable effect on the meteorology in the surroundings of the lake. The impact could extend even further to the west as westward propagating convective systems pass Lake Chad in the rainfall season. This study examines the sensitivity of the regional hydrology and convective processes to the desiccation of the lake using a regional atmospheric model. Three Lake Chad scenarios are applied reflecting the situation in 1960, the current situation and a potential future scenario in which the lake and the surrounding wetlands have disappeared. The model simulations span the months July-September in 2006, which includes the rainfall season in the Lake Chad area. Total precipitation amounts and the components of the hydrological cycle are found to be hardly affected by the existence of the lake. A filled Lake Chad does, however, increase the precipitation at the east side of the lake. The model results indicate that the boundary layer moisture and temperature are significantly altered downwind of the lake. By investigating a mesoscale convective system (MCS) case, this is found to affect the development and progress of the system. At first, the MCS is intensified by the more unstable boundary layer air but the persistence of the system is altered as the cold pool propagation becomes less effective. The proposed mechanism is able to explain the differences in the rainfall patterns nearby Lake Chad between the scenarios. This highlights the local sensitivity to the desiccation of Lake Chad whereas the large-scale atmospheric processes are not affected. Copyright

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Section: Comparison With Observationsmentioning

confidence: 99%

The precipitation response to the desiccation of Lake Chad

Lauwaet

Lipzig

Weverberg

et al. 2011

Quart J Royal Meteoro Soc

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“…Laurent et al [10] and Mathon et al [11] found that cloud life duration and propagation speed are positively related to the induced precipitation. Goyens et al [12] analyzed the relationship between five cloud parameters (the average propagation speed (Vav), the cloud area at maximum extent (Amax), the life duration (LD), the minimum in BT when averaged over the very cold convective core (BTmin), the time during which the system shows a very cold convective core (LDcc)) and three precipitation variables (3-hourly precipitation averaged over the 10 most rainy pixels (Pmax), averaged over entire cloud cover (Pav), summed over entire cloud cover (Ptot)) in the Sahel based on tracking mesoscale convective systems (MCSs). Vondou et al [13] investigated the lifecycles of cumulus clouds with cloud-resolving model simulations and found a considerable increase across the composite lifecycles.…”

Section: Introductionmentioning

confidence: 99%

Analysis and Application of the Relationship between Cumulonimbus (Cb) Cloud Features and Precipitation Based on FY-2C Image

Liu

et al. 2014

Atmosphere

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Although cumulonimbus (Cb) clouds are the main source of precipitation in south China, the relationship between Cb cloud characteristics and precipitation remains unclear. Accordingly, the primary objective of this study was to thoroughly analyze the relationship between Cb cloud features and precipitation both at the pixel and cloud patch scale, and then to apply it in precipitation estimation in the Huaihe River Basin using China's first operational geostationary meteorological satellite, FengYun-2C (FY-2C), and the hourly precipitation data of 286 gauges from 2007. First, 31 Cb parameters (14 parameters of three pixel features and 17 parameters of four cloud patch features) were extracted based on a Cb tracking method using an artificial neural network (ANN) cloud classification as a pre-processing procedure to identify homogeneous Cb patches. Then, the relationship between Cb cloud properties and precipitation was analyzed and applied in a look-up table algorithm to estimate precipitation. The results were as follows: (1) Precipitation increases first and then declines with increasing values for cold cloud and time evolution parameters, OPEN ACCESSAtmosphere 2014, 5 212 and heavy precipitation may occur not only near the convective center, but also on the front of the Cb clouds on the pixel scale. (2) As for the cloud patch scale, precipitation is typically associated with cold cloud and rough cloud surfaces, whereas the coldest and roughest cloud surfaces do not correspond to the strongest rain. Moreover, rainfall has no obvious relationship with the cloud motion features and varies significantly over different life stages. The involvement of mergers and splits of minor Cb patches is crucial for precipitation processes. (3) The correlation coefficients of the estimated rain rate and gauge rain can reach 0.62 in the cross-validation period and 0.51 in the testing period, which indicates the feasibility of the further application of the relationship in precipitation estimation.

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“…In contrast, the maximum is depicted in the noon over ocean. Our analysis suggests intense rains in continental regions in the afternoon, knowing the very tight correlation between HLC and precipitation [1,12,16,28,45]. Figures 8 and 9 show that diurnal phase displays a distinct local shifting within each region.…”

Section: Regional Distributionsmentioning

confidence: 61%

“…The analysis focused on these thresholds in view of a better modeling of events potentially dangerous for agriculture, health and flash floods. The threshold temperature 233 K has been widely used for identifying convection associated likely to precipitating systems [12,27,28]. The convection index used in this work is cloud fraction (CF), also known as the cloud frequency index.…”

Section: Determination Of the Convection Indexmentioning

confidence: 99%

Spatio-Temporal Variability of Western Central African Convection from Infrared Observations

Vondou

2012

Atmosphere

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The present study has used Meteosat infrared brightness temperature images to investigate the regional and interannual variability of Central African cloudiness. Spatial and temporal variability were investigated using half-hourly data from the Meteosat-7 during June-July-August (JJA) of 1998-2002. The full domain of study (1.5• E-17was divided into six regions and statistics in each region were derived. Analysis of the dependence of cloud fraction to the brightness temperature threshold is explored both over land and ocean. Three diurnal cycle regimes (continental, oceanic, and coastal) are depicted according to the amplitude and peak time. Over regions of relatively flat terrain, results indicate enhancement of deep convection in the afternoon followed by a gradual decrease in the night. The diurnal cycle of convection is characterised by afternoon and early evening (around 15:00-18:00 LST) maxima located mainly downwind of the major mountain chains, and a more rapid nighttime decay. In terms of the harmonic amplitude, the diurnal signal shows significant regional contrast with the strongest manifestation over the Adamaoua Plateau and the weakest near the South Cameroon Plateau. This remarkable spatial dependence is clear evidence of orographic and heterogeneous land-surface impacts on convective development. Oceanic region exhibits weak activity of convective cloudiness with a maximum at noon. It is suggested that daytime heating of the land surface and moist environment may play a role in determining the spatial distribution of cloud fraction. This study further demonstrates the importance of the Cameroon coastline concavity and coastal mountains in regulating regional frequencies of convection and their initialization. The strength of the diurnal cycle of convective activity depends on mountain height, mean flow, coastal geometry.

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Tracking mesoscale convective systems in the Sahel: relation between cloud parameters and precipitation

Cited by 46 publications

References 33 publications

The precipitation response to the desiccation of Lake Chad

The precipitation response to the desiccation of Lake Chad

Analysis and Application of the Relationship between Cumulonimbus (Cb) Cloud Features and Precipitation Based on FY-2C Image

Spatio-Temporal Variability of Western Central African Convection from Infrared Observations

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