Please use this identifier to cite or link to this item: http://hdl.handle.net/10553/59378
Title: Cut-off low systems over Iraq: Contribution to annual precipitation and synoptic analysis of extreme events
Authors: Al-Nassar, Ali Raheem
Pelegri, Josep L.
Sangrá Inciarte, Pablo 
Alarcon, Marta
Jansa, Agusti
UNESCO Clasification: 250207 Climatología regional
Keywords: Climate
Variability
Moisture
Flow
Cut-off low, et al
Issue Date: 2019
Project: Flujos de Carbono en Un Sistema de Afloramiento Costero (Cabo Blanco, Nw de África); Modulación A Submesoscala de la Producción, Exportación y Consumo de Carbono 
Journal: International Journal of Climatology 
Abstract: We combine daily in situ precipitation data with meteorological reanalysis data in order to explore the contribution of cut-off low systems to the seasonal and inter-annual rainfall variations over Baghdad from 2005 to 2016. During these 12 years (average rainfall of 131 +/- 67 mm/year), 38 rainy cut-off lows brought 43% of the total precipitation, with extreme inter-annual variations. Indeed, precipitation associated with autumn cut-off lows was the principal factor that turned an arid into a wet year: during the three most arid years cut-off lows contributed about 25% of the average rainfall (10 out of 40 mm/year) while during the three wettest years they contributed near 67% (171 out of 254 mm/year). The extreme-rain cut-off low systems displayed analogous synoptic characteristics: upper-atmosphere divergence, upwards vertical motions in the middle atmosphere, and lower-atmosphere winds into central Iraq at times when the surface Red Sea and Persian Gulf waters were warmer than the surface air. During those days previous to an extreme event, the surface waters cooled substantially and the amount of precipitable water increased largely, suggesting high latent heat transfer. In order to characterize those conditions that favour rainfall, we focus on the November 18-20, 2013 cut-off low system, which led to the largest flooding and wettest year in Baghdad between 2005 and 2016. The distribution of properties in the middle (500 hPa) and upper (250 hPa) troposphere shows that the region was affected by intense horizontal divergence and upwards motions, coinciding with a surface low over the Arabian Peninsula that caused intense northwards winds over the Persian Gulf and brought substantial moisture to central Iraq. The analysis of several stability indexes indicates that convective instability played a secondary role during the episode.
URI: http://hdl.handle.net/10553/59378
ISSN: 0899-8418
DOI: 10.1002/joc.6247
Source: International Journal Of Climatology [ISSN 0899-8418], 1-19
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