Intraseasonal Rainfall Variability over Madagascar

Macron, Clémence; Richard, Yves; Garot, Thomas; Bessafi, Miloud; Pohl, Benjamin; Ratiarison, Adolphe; Razafindrabe, Andrianaharimanana

doi:10.1175/mwr-d-15-0077.1

Cited by 26 publications

(39 citation statements)

References 25 publications

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“…A study by Macron et al () reported a general consistency between local‐scale rainfall variability in Madagascar and regional‐scale features of climate variability. On their part, Morel et al () analysed the capability of the Weather Research and Forecasting ( WRF) regional climate model in regionalizing rainfall variability at very high resolution (680 m) over Réunion Island for daily to seasonal scales and year‐to‐year differences for two contrasted summer seasons (from November to April): 2000–2001 (abnormally dry) and 2004–2005 (abnormally wet).…”

Section: Introductionmentioning

confidence: 89%

Spatio‐temporal variability of rainfall in a high tropical island: Patterns and large‐scale drivers in Réunion Island

Réchou¹,

Flores

Jumaux

et al. 2019

Quart J Royal Meteoro Soc

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Weather forecasting is challenging because of the complex interplay between local conditions and regional atmospheric forcings. In this article, we analyse the relationships between local daily rainfall and large‐scale synoptic patterns in the geographical context of Réunion Island, a high volcanic island in the southwestern Indian Ocean basin. Given the critical role of trade winds on weather conditions at island scale, we analyse those relationships across seasons defined with respect to yearly trade‐wind regimes. The analysis of the distribution of inversion events' elevation and frequency allows us to characterize the trade‐wind inversion layer (TWIL) and identify four seasons with homogeneous distributions. We characterize the spatio‐temporal variability of rainfall measured at island scale by a dense network of rain‐gauges over 37 years and relate it to large‐scale weather regimes identified using geopotential height meteorological data. After seasonal signal removal using Fourier transforms and dimension reduction via Principal Component Analysis, we perform Canonical Correlation Analysis to identify canonical variables relating rainfall and geopotential height patterns at the two different studied spatial scales. We then combine Ascending Hierarchical Classification and partitioning k‐means methods to identify homogeneous large‐scale synoptic conditions within each season. From this information, we build composite maps of geopotential height that characterize weather regimes and further analyse rainfall patterns at island scale in each regime. Elevation and orientation are used as descriptive variables at island scale as they strongly structure the patterns. Overall, four homogeneous seasons were identified based on trade‐wind regimes, within which six large‐scale weather regimes were identified for summer, the most variable season, and four for the others. Finally, rainfall patterns at island scale are described in relation to the highlighted synoptic regimes and local descriptive variables.

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Section: Introductionmentioning

confidence: 89%

Spatio‐temporal variability of rainfall in a high tropical island: Patterns and large‐scale drivers in Réunion Island

Réchou¹,

Flores

Jumaux

et al. 2019

Quart J Royal Meteoro Soc

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“…The location of the maximum of cloud occurrence (12°S–50°S; 45°E–50°E) north of Madagascar (Figures a and b) is consistent with the location of the most rainy region in summer found by Macron et al . (). Figure represents the 2007–2010 average monthly evolution of total rain occurrence (i.e.…”

Section: Seasonal Cloud Distribution Over the Southwest Indian Oceanmentioning

confidence: 99%

“…In Madagascar, the wet season lasts from November to April (Nassor and Jury, ). This deep convection in the northwest of Madagascar results from the convergence of northwesterly monsoon flow with easterly trade winds (Jury et al ., ; Nassor and Jury, ; Macron et al ., ). High occurrence of clouds northwest of Madagascar can also be associated with mesoscale convective systems of the ITCZ (Figure ).…”

Section: Seasonal Cloud Distribution Over the Southwest Indian Oceanmentioning

confidence: 99%

Spatial and seasonal variability of clouds over the southwest Indian Ocean based on the DARDAR mask product

Vérèmes

Listowski

Delanoë

et al. 2019

Quart J Royal Meteoro Soc

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We present a characterization of the variability of clouds over the southwest Indian Ocean between 2007 and 2010. Cloud occurrence is derived from the DARDAR (raDAR/liDAR) mask, a synergistic product based on Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) and CloudSat measurements. It provides a target classification for hydrometeors. We demonstrate that this product is suitable for studying the vertical, spatial and seasonal cloud distribution in the southwest Indian Ocean. The variability of cloud occurrence increases approaching the tropics: the average maximum amplitude of monthly occurrence is ∼7% between 30°S and 60°S and ∼14% between 10°S and 30°S. The 10–30°S latitudinal band exhibits the largest contrasts: summer (winter) total cloud occurrence is mainly driven by high‐ (low‐) level clouds. The vertical distribution of clouds differs on either side of 55°E and this is related to a land–ocean contrast and to large‐scale influence. In winter, east of 55°E, the maximum of cloud occurrence corresponds to warm and mixed‐phased precipitating clouds associated with the Mascarene High. In summer, west of 55°E, the vertical distribution of cloud occurrence is driven by deep convection associated with the InterTropical Convergence Zone and the Near Equatorial Trough. The vertical distribution of cloud occurrence shows an interannual variability that is related to El Niño events. The influence of other oscillation modes should be further investigated.

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“…The diurnal cycle and high-elevated topography (up to 1700 m) causes more rainfall interacting with these background winds over Madagascar. Macron et al (2016) showed a connection among Madagascar rainfall intra-seasonal variability, the Madden Julian Oscillation (MJO, e.g. Madden and Julian, 1971) and TTT in austral summer season.…”

Section: Introductionmentioning

confidence: 97%

“…Macron et al . () showed a connection among Madagascar rainfall intra‐seasonal variability, the Madden Julian Oscillation (MJO, e.g. Madden and Julian, ) and TTT in austral summer season.…”

Section: Introductionmentioning

confidence: 99%

Unique relationship between tropical rainfall and SST to the north of the Mozambique Channel in boreal winter

Koseki

Bhatt

2017

Intl Journal of Climatology

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In this study, we investigate a possible mechanism for the dichotomy in climatology of marine rainfall and sea surface temperature (SST) over a part of the Southwest Indian Ocean (SWIO) during boreal winter (January and February) with state‐of‐the‐art satellite and reanalysis data sets. Rainfall to the north of the Mozambique Channel, bounded 10°–5°S and 40°–50°E, is found to be quite feeble despite being in the warm SST regime of up to 29–29.5 °C. The rainfall intensity is rather found to be highly associated with the atmospheric surface divergence. The vigorous rainfall is associated with the more convergence over the Intertropical Convergence Zone (ITCZ), while the weak rainfall is linked with the divergence to the north of the Mozambique Channel. The surface divergent flow to the north of the Mozambique Channel is associated with a deep southward penetration of the northerly Indian Winter Monsoon (IWM). Corresponding to the surface divergent field, a relatively high sea level pressure (SLP) compared to the SLP in the ITCZ, weak subsidence, and low‐level stratiform clouds are formed to the north of the Mozambique Channel, despite the warm, tropical SST. These atmospheric conditions are most likely conductive to the inhibition of cumulus convection over the region and the unique relationship between rainfall and SST seems peculiar. Our analysis also shows that the rare occurrence of tropical cyclones over the area is attributed to a high‐pressure surge and the associated positive surface vorticity (anti‐cyclonic). This study suggests that the area to the north of the Mozambique Channel is dynamically interesting for climatological studies.

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Intraseasonal Rainfall Variability over Madagascar

Cited by 26 publications

References 25 publications

Spatio‐temporal variability of rainfall in a high tropical island: Patterns and large‐scale drivers in Réunion Island

Spatio‐temporal variability of rainfall in a high tropical island: Patterns and large‐scale drivers in Réunion Island

Spatial and seasonal variability of clouds over the southwest Indian Ocean based on the DARDAR mask product

Unique relationship between tropical rainfall and SST to the north of the Mozambique Channel in boreal winter

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