Development and application of a mesoscale climate model for the tropics: Influence of sea surface temperature anomalies on the West African monsoon

2002 ◽  
Vol 107 (D3) ◽  
Author(s):  
Edward K. Vizy
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Climate Model ◽  
West African Monsoon ◽  
West African ◽  
Sea Surface ◽  
The West ◽  
African Monsoon ◽  
Sea Surface Temperature Anomalies ◽  
The Tropics

Reduced eastern tropical Atlantic sea surface temperature variability at the end of the Green Sahara

2021 ◽  
Author(s):  
Gerald Rustic ◽  
Francesco SR Pausata ◽  
Peter DeMenocal
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
West African Monsoon ◽  
Walker Circulation ◽  
West African ◽  
Temperature Variability ◽  
Sea Surface ◽  
Tropical Atlantic ◽  
The West ◽  
Monsoon System

<p>Mid-Holocene proxy evidence records profound climatic changes, including alteration of the West African Monsoon system and the end of the ‘Green Sahara’ period. Model simulations have related changes in the West African Monsoon system, which controls present-day seasonal hydroclimate over much of the African continent north of the equator, to alterations of the tropical Walker circulation. Here we investigate the change in tropical sea surface temperature variability in the eastern tropical Atlantic, where ocean-atmosphere coupling is robust. Through analysis of the distribution of oxygen isotopes from the tests of individual specimens of the surface-dwelling foraminifer <em>Globigerinoides ruber</em>, we find that SST variability is significantly decreased at the end of the Green Sahara period ~3.5-5kya. During the period of reduced variability we also observe changes in the background state of the tropical Atlantic as characterized by the east-west SST gradient, linking variability to background conditions. We compare our record to co-eval records of tropical Pacific variability that describe changes to the El Niño Southern Oscillation, as well as to records of hydroclimate change in Southeast Asia, and find similarities in these records, suggesting a common origin of these climate signals. Taken together, this evidence points toward an alteration of the tropical Walker circulation which may, in part, be related to changes in vegetation and dust loading occurring during the drying of the Sahara at mid-Holocene.</p>

Leading Tropical Modes Associated with Interannual and Multidecadal Fluctuations in North Atlantic Hurricane Activity

2006 ◽  
Vol 19 (4) ◽  
pp. 590-612 ◽  
Author(s):  
Gerald D. Bell ◽  
Muthuvel Chelliah
Keyword(s):  
West African Monsoon ◽  
West African ◽  
Sea Surface ◽  
Sea Surface Temperatures ◽  
African Monsoon ◽  
Atlantic Hurricane ◽  
Enso Teleconnections ◽  
Surface Temperatures ◽  
Hurricane Activity ◽  
The Tropics

Abstract Interannual and multidecadal extremes in Atlantic hurricane activity are shown to result from a coherent and interrelated set of atmospheric and oceanic conditions associated with three leading modes of climate variability in the Tropics. All three modes are related to fluctuations in tropical convection, with two representing the leading multidecadal modes of convective rainfall variability, and one representing the leading interannual mode (ENSO). The tropical multidecadal modes are shown to link known fluctuations in Atlantic hurricane activity, West African monsoon rainfall, and Atlantic sea surface temperatures, to the Tropics-wide climate variability. These modes also capture an east–west seesaw in anomalous convection between the West African monsoon region and the Amazon basin, which helps to account for the interhemispheric symmetry of the 200-hPa streamfunction anomalies across the Atlantic Ocean and Africa, the 200-hPa divergent wind anomalies, and both the structure and spatial scale of the low-level tropical wind anomalies, associated with multidecadal extremes in Atlantic hurricane activity. While there are many similarities between the 1950–69 and 1995–2004 periods of above-normal Atlantic hurricane activity, important differences in the tropical climate are also identified, which indicates that the above-normal activity since 1995 does not reflect an exact return to conditions seen during the 1950s–60s. In particular, the period 1950–69 shows a strong link to the leading tropical multidecadal mode (TMM), whereas the 1995–2002 period is associated with a sharp increase in amplitude of the second leading tropical multidecadal mode (TMM2). These differences include a very strong West African monsoon circulation and near-average sea surface temperatures across the central tropical Atlantic during 1950–69, compared with a modestly enhanced West African monsoon and exceptionally warm Atlantic sea surface temperatures during 1995–2004. It is shown that the ENSO teleconnections and impacts on Atlantic hurricane activity can be substantially masked or accentuated by the leading multidecadal modes. This leads to the important result that these modes provide a substantially more complete view of the climate control over Atlantic hurricane activity during individual seasons than is afforded by ENSO alone. This result applies to understanding differences in the “apparent” ENSO teleconnections not only between the above- and below-normal hurricane decades, but also between the two sets of above-normal hurricane decades.

scholarly journals Dynamics of the West African Monsoon Jump

2007 ◽  
Vol 20 (21) ◽  
pp. 5264-5284 ◽  
Author(s):  
Samson M. Hagos ◽  
Kerry H. Cook
Keyword(s):  
Climate Model ◽  
Regional Climate ◽  
West African Monsoon ◽  
Lower Troposphere ◽  
West African ◽  
Moisture Convergence ◽  
The West ◽  
African Monsoon ◽  
Sahel Region ◽  
Continental Interior

Abstract The observed abrupt latitudinal shift of maximum precipitation from the Guinean coast into the Sahel region in June, known as the West African monsoon jump, is studied using a regional climate model. Moisture, momentum, and energy budget analyses are used to better understand the physical processes that lead to the jump. Because of the distribution of albedo and surface moisture, a sensible heating maximum is in place over the Sahel region throughout the spring. In early May, this sensible heating drives a shallow meridional circulation and moisture convergence at the latitude of the sensible heating maximum, and this moisture is transported upward into the lower free troposphere where it diverges. During the second half of May, the supply of moisture from the boundary layer exceeds the divergence, resulting in a net supply of moisture and condensational heating into the lower troposphere. The resulting pressure gradient introduces an inertial instability, which abruptly shifts the midtropospheric meridional wind convergence maximum from the coast into the continental interior at the end of May. This in turn introduces a net total moisture convergence, net upward moisture flux and condensation in the upper troposphere, and an enhancement of precipitation in the continental interior through June. Because of the shift of the meridional convergence into the continent, condensation and precipitation along the coast gradually decline. The West African monsoon jump is an example of multiscale interaction in the climate system, in which an intraseasonal-scale event is triggered by the smooth seasonal evolution of SSTs and the solar forcing in the presence of land–sea contrast.

scholarly journals Feedback of observed interannual vegetation change: a regional climate model analysis for the West African monsoon

2016 ◽  
Vol 48 (9-10) ◽  
pp. 2837-2858 ◽  
Author(s):  
Cornelia Klein ◽  
Jan Bliefernicht ◽  
Dominikus Heinzeller ◽  
Ursula Gessner ◽  
Igor Klein ◽  
...  
Keyword(s):  
Regional Climate Model ◽  
Vegetation Change ◽  
Climate Model ◽  
Regional Climate ◽  
West African Monsoon ◽  
Model Analysis ◽  
West African ◽  
The West ◽  
African Monsoon

scholarly journals Improving the Simulation of the West African Monsoon Using the MIT Regional Climate Model

2014 ◽  
Vol 27 (6) ◽  
pp. 2209-2229 ◽  
Author(s):  
Eun-Soon Im ◽  
Rebecca L. Gianotti ◽  
Elfatih A. B. Eltahir
Keyword(s):  
Regional Climate Model ◽  
Land Surface ◽  
Climate Model ◽  
Regional Climate ◽  
West African Monsoon ◽  
Convective Cloud ◽  
West African ◽  
The West ◽  
African Monsoon ◽  
Convection Schemes

Abstract This paper presents an evaluation of the performance of the Massachusetts Institute of Technology (MIT) regional climate model (MRCM) in simulating the West African monsoon. The MRCM is built on the Regional Climate Model, version 3 (RegCM3), but with several improvements, including coupling of Integrated Biosphere Simulator (IBIS) land surface scheme, a new surface albedo assignment method, new convective cloud and convective rainfall autoconversion schemes, and a modified scheme for simulating boundary layer height and boundary layer clouds. To investigate the impact of these more physically realistic representations when incorporated into MRCM, a series of experiments were carried out implementing two land surface schemes [IBIS with a new albedo assignment, and the Biosphere–Atmosphere Transfer Scheme (BATS)] and two convection schemes (Grell with the Fritsch–Chappell closure, and Emanuel in both the default form and modified with the new convective cloud cover and a rainfall autoconversion scheme). The analysis primarily focuses on comparing the rainfall characteristics, surface energy balance, and large-scale circulations against various observations. This work documents significant sensitivity in simulation of the West African monsoon to the choices of the land surface and convection schemes. Despite several deficiencies, the simulation with the combination of IBIS and the modified Emanuel scheme with the new convective cloud cover and a rainfall autoconversion scheme shows the best performance with respect to the spatial distribution of rainfall and the dynamics of the monsoon. The coupling of IBIS leads to representations of the surface energy balance and partitioning that show better agreement with observations compared to BATS. The IBIS simulations also reasonably reproduce the dynamical structures of the West African monsoon circulation.

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