Automatic Tracking and Characterization of African Convective Systems on Meteosat Pictures

Arnaud, Yves; Des̄bois, M.; Maizi, Joel

doi:10.1175/1520-0450(1992)031<0443:atacoa>2.0.co;2

Cited by 114 publications

(62 citation statements)

References 11 publications

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“…Duvel (1989) and Machado et al (1993) used 253 K as the threshold for clouds associated with deep convection. Arnaud et al (1992) used 233 K to identify convective clouds that are most likely to precipitate. Mathon et al (2002a) found that Sahelian organized systems identified by the 233 K threshold accounted for 90% of the seasonal rainfall observed by theÉtudes des Précipitations par Satellite (EPSAT)-Niger rain-gauge network over a nine-year period.…”

Section: Methodsmentioning

confidence: 99%

The propagation and diurnal cycles of deep convection in northern tropical Africa

Laing

Carbone

Levizzani

et al. 2008

Quart J Royal Meteoro Soc

148

132

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ABSTRACT:The propagation and diurnal cycle of organized convection in northern tropical Africa are examined using five years (1999)(2000)(2001)(2002)(2003) of digital infrared imagery for May-August. Reduced-dimension techniques are used to document the properties of cold clouds -proxies for deep convection and precipitation. Large-scale environments are diagnosed from global analyses.Organized convection in Africa consists of coherent sequences or episodes which span an average distance of about 1000 km and last about 25 h. A substantial fraction of events exhibits systematic propagation at regional to continental scales while undergoing decay and regeneration. Episodes with 36 h duration and 1472 km span recur at a one-per-day interval. Most episodes have phase speed of 10-20 m s −1 , which is faster than most African easterly waves. Convective episodes tend to initiate in the lee of high terrain, consistent with thermal forcing from elevated heat sources. Average diurnal frequency maxima result from the superposition of local diurnal maximum with the delayed-phase arrival of systems propagating from the east. Propagation occurs with moderate low-to mid-tropospheric shear, which varies with the African easterly jet migration and West African monsoon phases. Frequent deep convection occurs with local shear maxima near high terrain. For the peak monsoon period and for 10°W-10°E, where easterly waves and convective systems are frequent, 35% of cold cloud episodes occur east of the wave trough compared with about 24% to the west. Based on the coherent behaviour of organized, propagating convection, inferences may be made regarding the prediction of precipitation beyond one or two days.

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Section: Methodsmentioning

confidence: 99%

The propagation and diurnal cycles of deep convection in northern tropical Africa

Laing

Carbone

Levizzani

et al. 2008

Quart J Royal Meteoro Soc

148

132

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“…Here we investigate whether C1 SVC can be linked to convective systems, identified as cold areas in maps of brightness temperature (BT) indicative of optically thick high altitude clouds (Arnaud et al, 1992), against the warm background of surface emissions. In order to get global coverage, we used the MERG dataset from the Climate Prediction Center (Janowiak et al, 2001).…”

Section: Convective Activitymentioning

confidence: 99%

On the origin of subvisible cirrus clouds in the tropical upper troposphere

et al. 2012

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Abstract. Spaceborne lidar observations have recently revealed a previously undetected significant population of Subvisible Cirrus (SVC). We show them to be colder than −74 • , with an optical depth below 0.0015 on average. The formation and persistence over time of this new cloud population could be related to several atmospheric phenomena. In this paper, we investigate if these clouds follow the same formation mechanisms as the general tropical cirrus population (including convection and in-situ ice nucleation), or if specific nucleation sites and trace species play a role in their formation. The importance of three scenarios in the formation of the global SVC population is investigated through different approaches that include comparisons with data imaging from several spaceborne instruments and back-trajectories that document the history and behavior of air masses leading to the point in time and space where subvisible cirrus were detected. In order to simplify the study of their formation, we singled out SVC with coherent temperature histories (mean variance lower than 4 K) according to back-trajectories along 5, 10 or 15 days (respectively 58, 25 and 11 % of SVC). Our results suggest that external processes, including local increases in liquid and hygroscopic aerosol concentration (either through biomass burning or volcanic injection forming sulfate-based aerosols in the troposphere or the stratosphere) have very limited short-term or mid-term impact on the SVC population. On the other hand, we find that ∼ 20 % of air masses leading to SVC formation interacted with convective activity 5 days before they led to cloud formation and detection, a number that climbs to 60 % over 15 days. SVC formation appears especially linked to convection over Africa and Central America, more so during JJA than DJF. These results support the view that the SVC population observed by CALIOP is an extension of the general upper tropospheric ice clouds population with its extreme thinness as its only differentiating factor.

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“…The reason lies in that the determination of Cb cloud patches is a challenging issue in remote sensing sequences, for they are deformable in nature. In addition, it has been observed that Cb cloud patches commonly evolve through a sequence of pulse-like events and are subject to splits and mergers during their lifecycles, which may complicate the tracking of Cb clouds, because the identification criteria that distinguish individual Cb patches are difficult to determine [16][17][18].…”

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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Automatic Tracking and Characterization of African Convective Systems on Meteosat Pictures

Cited by 114 publications

References 11 publications

The propagation and diurnal cycles of deep convection in northern tropical Africa

The propagation and diurnal cycles of deep convection in northern tropical Africa

On the origin of subvisible cirrus clouds in the tropical upper troposphere

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

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