The Barrier Layer of the Atlantic warm pool: Formation mechanism and influence on the mean climate

Abstract

A B S T R A C T Many coupled general circulation models (CGCMs) tend to overestimate the salinity in the Atlantic warm pool or the Northwestern Tropical Atlantic (NWTA) and underestimate the surface salinity in the subtropical salinity maxima region. Most of these models also suffer from a sea-surface temperature (SST) bias in the NWTA region, leading to suggestions that the upper ocean salinity stratification may need to be improved in order to improve the barrier layer (BL) simulations and thus the SST through BL-SST-intertropical convergence zone feedbacks. In the present study, we use a CGCM to perform a set of idealised numerical experiments to test and understand the sensitivity of the BL and consequently SST in the NWTA region to freshwater flux and hence the upper ocean salinity stratification. We find that the BL of the NWTA is sensitive to upper ocean salinity changes in the Amazon river discharge region and the subtropical salinity maxima region. The BL phenomenon is further manifested by the formation of winter temperature inversions in our model simulations, the maximum magnitude of inversions being about 0.2 8C. The atmospheric response causes a statistically significant reduction of mean precipitation and SST in the equatorial Atlantic region and helps improve the respective biases by 10Á15%. In the region of improved BL simulation, the SST change is positive and in the right direction of bias correction, albeit weak.

Drastic thickening of the barrier layer off the western coast of Sumatra due to the Madden-Julian oscillation passage during the Pre-Years of the Maritime Continent campaign

“…The temperature at approximately 10 m depth was continuously higher than 29.5°C after 1 December and reached up to 30°C, resulting in a surface temperature The IL was drastically deepened just after the MJO arrived on 13 December, and the temperature inversion in the BL (Balaguru et al 2012;Cronin and McPhaden 2002;Mignot et al 2012;Thadathil et al 2002;Vinayachandran et al 2002;Vissa et al 2013b) is significant during the MJO passage. Meanwhile, the contour of the 29°C contour, which is indicative of the top of the thermocline, was continuously sinking throughout the observation period.…”

Seasonal Cycle of the Mixed Layer Heat Budget in the Northeastern Tropical Atlantic Ocean

“…The region with the thickest mixed layer between 208 and 258N also experiences a thick barrier layer (.30 m), consistent with Tanguy et al (2010). The barrier layer is maintained by the combination of northward advection of low-salinity water from the ITCZ and the subduction and southward movement of subtropical salinity-maximum water from the subtropical North Atlantic (e.g., Balaguru et al 2012;Mignot et al 2012). There is a thinner barrier layer in the southern NETA region (,20 m) that is most likely maintained by strong precipitation associated with the ITCZ.…”

Do the Amazon and Orinoco freshwater plumes really matter for hurricane‐induced ocean surface cooling?

“…This is in agreement with earlier modeling results by Masson and Delecluse [], Balaguru et al . [], White and Toumi [], Newinger and Toumi [], who found no significant SST change in response to the presence or absence of large tropical rivers such as the Amazon, Orinoco or Congo rivers. The impact of the barrier layer and haline stratification on the SST could be damped by the fact that we use an ocean model forced through bulk formulae [ Large and Yeager , ], but the weak differences of the net air‐sea fluxes in the plume region (weaker than 5 W m −2 out of the coastal region) suggest that this potential effect is weak.…”