Observation of the marine atmospheric boundary layer in the Gulf of Guinea during the 2006 boreal spring

Abstract

In situ, satellite and model analyses data in April-July 2006 are used to investigate the links between sea surface temperature (SST) and the marine atmospheric boundary layer (MABL) in the Gulf of Guinea. The study region between 10• W and 6• E is divided into three areas with different characteristics: the North Area (4.5• N to 1 • N) with the wettest atmosphere and the warmest SST, the Upwelling Area (1 • N to 4 • S) with the strongest SST decrease, and the South Area (4 • S to 8 • S) with a drier atmosphere and a more slowly decreasing SST than in the Upwelling Area. The key zone of the air-sea interactions in this region seems to be the SST front between North and Upwelling Areas. On the one hand, the study of the MABL on either side of the front shows a well-mixed layer between the surface and about 500 m high, sensitive to surface variations, which gets shallower (deeper) when the SST decreases (increases). The MABL height (about 1500 m) follows the same variations but is not exactly collocated with the SST variations. On the other hand, the observation of the MABL across the SST front shows a strengthening of southeasterlies in the South Area coinciding with a strong SST decrease in the Upwelling Area. In the latter, the wind weakens above the colder SST. Besides, in the North Area, the wind strengthens above the warmer SST. However, the wind acceleration spans from the equator to 2 • N in April and as far as 4 • N in June. A convergence zone is observed in the vicinity of 2 • N in April, suggesting a convection activity there, favoured by the SST front.

Air–sea interaction in the Gulf of Guinea at intraseasonal time‐scales: wind bursts and coastal precipitation in boreal spring

“…In parallel, a cross-equatorial pressure gradient develops and also contributes to the surface wind strengthening between the Equator and the Guinean coast. This confirms that the wind surface strengthening results from the air-sea interaction trough the equatorial SST front, as suggested in Leduc-Leballeur et al (2011) for the 2006 season. This mechanism transports moisture in the Gulf of Guinea toward the coast, which increases the coastal convection and favours a deep circulation between the ocean and the coast: the coastal precipitation is thus intensified during one or two days.…”

“…In turn, this cold SST anomaly slows down the overlying wind within a few days. This feedback is found again and detailed for April to July 2006 in Leduc-Leballeur et al (2011). Moreover, the latter note that an acceleration of southeasterlies over the EEA is associated with a local acceleration of southerlies just north of the Equator, through the SST front located around 1…”

“…Moreover, some hints were shown in Leduc-Leballeur et al (2011) that an equatorial SST cooling could influence deep atmospheric convection in the north of the Gulf of Guinea. It is thus of particular interest to investigate the fluctuations of the Guinean coastal rainfall induced by an acceleration of surface oceanic southerlies in the vertical atmospheric circulation.…”

“…As Leduc-Leballeur et al (2011) only investigated the year 2006, an extension over the whole 2000-2009 decade motivates a new study.…”

Temporal Variation and Vertical Structure of the Marine Atmospheric Mixed Layer over the East China Sea from Mie-Scattering Lidar Data

“…The structure of the marine atmospheric mixed layer (MAML) over the East China Sea is an important factor in chemical transport models used to predict the behavior of pollutants in East Asia. Leduc-Leballeur et al (2011) used radiosonde data to show that the height of the MAML in the Gulf of Guinea increases with increasing sea surface temperature (SST ). Sempreviva et al (2010) used radiosonde and ceilometer data acquired over the Mediterranean to show that the vertical structure of the MAML is dependent on synoptic conditions, such as advection by different air masses.…”