Variability of the subtropical highs, African easterly jet and easterly wave intensities over North Africa and Arabian Peninsula in late summer

Spinks, James; Lin, Yuh-Lang

doi:10.1002/joc.4226

Cited by 13 publications

(5 citation statements)

References 22 publications

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“…Mera et al (2014) also found the levels of the atmosphere from which the air origi nated as the seasons progressed. Using the ECMWF global dataset at 600 hPa, Spinks and Lin (2015) Fig. 1.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Low-Level Atmospheric Moisture Transport Associated with the West African Monsoon

2015

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The major objective of this study is to re-evaluate the ocean-land transport of moisture for rainfall in West Africa using 1979-2008 NCEP-NCAR reanalysis data. The vertically integrated atmospheric water vapor flux for the surface-850 hPa is calculated to account for total low-level moisture flux contribution to rainfall over West Africa. Analysis of mean monthly total vapor fluxes shows a progressive penetration of the flux into West Africa from the south and west. During spring (April-June), the northward flux forms a "moisture river" transporting moisture current into the Gulf of Guinea coast. In the peak monsoon season (JulySeptember), the southerly transport weakens, but westerly transport is enhanced and extends to 20°N owing to the strengthening West African jet off the west coast. Mean seasonal values of total water vapor flux components across boundaries indicate that the zonal component is the largest contributor to mean moisture transport into the Sahel, while the meridional transport contributes the most over the Guinea coast. For the wet years of the Sahel rainy season (July-September), active anomalies are displaced farther north compared to the long-term average. This includes the latitude of the intertropical front (ITF), the extent of moisture flux, and the zone of strong moisture flux convergence, with an enhanced westerly flow. For the dry Sahel years, the opposite patterns are observed. Statistically significant positive correlations between the zonal moisture fluxes and Sudan-Sahel rainfall totals are most pronounced when the zonal fluxes lead by 1-4 pentads. However, although weak, they still are statistically significant at lags 3 and 4 for meridional moisture fluxes.

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Section: Introductionmentioning

confidence: 99%

Analysis of Low-Level Atmospheric Moisture Transport Associated with the West African Monsoon

2015

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“…These results are in line with more complex models and with observational evidence (e.g. Thorncroft and Blackburn, ; Lavaysse et al , ; ; Spinks and Lin, ; Spinks et al , ). Hence this simple model is a powerful tool for investigating the behaviour of the North African winds under different climatological conditions.…”

Section: Discussionmentioning

confidence: 99%

“…Since recent studies have shown a non‐negligible contribution by the Arabian heat low to the AEJ (Spinks and Lin, ; Spinks et al , ), and that the development of the SHL is concomitant with the development of the WAM and with the Saharan dust emission peak (Engelstaedter et al , ), the influence of these contributors to the African winds is also analyzed.…”

Section: Introductionmentioning

confidence: 99%

Simple solutions for the summer shallow atmospheric circulation over North Africa

Dalu¹,

Gaetani

Lavaysse

et al. 2018

Quart J Royal Meteoro Soc

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The spring‐to‐summer shallow atmospheric circulation over North Africa is driven by two desert heat lows (DHLs), one over the Sahara (SHL) and one over Arabia (AHL), with cyclones embedded in the convective layer, capped by mid‐tropospheric anticyclones. The aim of this work is to produce a minimal theoretical framework for these dynamical features in terms of Kelvin, mixed and planetary mode solutions to a two‐layer Matsuno–Gill model with a lower Rayleigh frictional layer dynamically coupled to an almost frictionless upper layer. Results show that a DHL drives a Walker‐like cell with rising air over the low and subsiding air to its west, with the lower‐level cyclone to the east of the mid‐tropospheric anticyclone, the latter being bounded to the southwest by an unstable easterly jet. These features, related to frictional differences between the two layers, are enhanced by ambient easterly winds. In spring, the stronger SHL drives a cell with rising air over West Africa and subsiding air over the Atlantic. The weaker AHL drives a cell with rising air over Arabia and subsiding air over East Africa. In summer, the stronger AHL drives a cell with rising air over Arabia and subsiding air over Libya, and the weaker SHL drives a cell with rising air over West Sahara and subsiding air over the Atlantic. The concurrent contributions of easterly winds, monsoonal low‐level convergence, and seasonal airborne dust warming strengthen the SHL, making its winds stronger than those of the AHL. In addition, a third‐order expansion of the Coriolis parameter strengthens the zonal winds and weakens the meridional winds. These contributors strengthen anticyclones over the eastern Mediterranean and to the west of Gibraltar. The ability of the model to represent the main features of the North African atmospheric circulations suggests a potential for better understanding of climate dynamics in connected regions (Mediterranean, Tropical Atlantic).

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“…Many authors have used different methodologies, mostly based on Eulerian analysis, to identify the sources of moisture over West Africa. Most of these studies investigated the sources of water vapour fluxes into West Africa using different sets of data 4 , 21 – 24 . The Eulerian approaches are used to estimate the ratio of advected to recycled moisture and to calculate moisture transport from predetermined source regions, although they are unable to identify the moisture source regions directly.…”

Section: Introductionmentioning

confidence: 99%

Transport pathways across the West African Monsoon as revealed by Lagrangian Coherent Structures

Niang

Mancho

García-Garrido

et al. 2020

Sci Rep

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The West African Monsoon (WAM) system is the main source of rainfall in the agriculturally based region of the Sahel. Understanding transport across the WAM is of crucial importance due to the strong impact of humidity and dust pathways on local cloud formation. However, the description of this transport is challenging due to its 3D complex nature. Lagrangian Coherent Structures (LCS) simplify transport description across the WAM by providing a geometrical partition of the troposphere into domains. Air parcels within each domain have similar dynamical characteristics. LCS make it possible to achieve an integrated vision of transport pathways across this system. Using this approach we unveil new connections in the WAM system. In particular, we identify transport pathways between the Tropical Easterly Jet (TEJ) and the African Easterly Jet (AEJ). Furthermore, the clockwise circulation associated with the divergent upper part of the Sahara heat low is clearly delimitated. Additionally, we show the presence of mixing regions in the AEJ and the lower part of the TEJ that are linked to pathways to sources of dust and humidity.

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Variability of the subtropical highs, African easterly jet and easterly wave intensities over North Africa and Arabian Peninsula in late summer

Cited by 13 publications

References 22 publications

Analysis of Low-Level Atmospheric Moisture Transport Associated with the West African Monsoon

Analysis of Low-Level Atmospheric Moisture Transport Associated with the West African Monsoon

Simple solutions for the summer shallow atmospheric circulation over North Africa

Transport pathways across the West African Monsoon as revealed by Lagrangian Coherent Structures

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