Stratification and Double-Diffusive Convection in the Bab-el-Mandeb Strait during Winter Monsoon

Investigation of stratification in marine environments is always considered by researchers. In this study double-diffusive convection and stratification in the Bab el Mandeb strait is investigated by analyzing of field data. Measurement of seawater temperature and salinity from ARGO project (2009 to2014) and also R-V Knorr (2001) cruise with the daily average of seawater temperature and salinity at different levels of HYCOM+NCODA (2001 to 2014) are used in this research. For a better understanding of the physical condition of the study area, seawater temperature, salinity, density, buoyancy frequency, density ratio and Turner angle changes versus depth are plotted and analyzed. The results illustrated that the depth of mixed layer is almost 100 meters during the winter monsoon and there is a stable stratified structure at this time of the year. Due to a thermohaline intrusion from the Red Sea, a temperature inversion is occurred, while below 150 meters the upper and lower boundary diffusive convection and a salt fingering established, respectively. In the northern part of the strait, the temperature inversion occurs below the depth of 200 meters. The double-diffusive convection is moderately weak in the northern part whereas, in the western part of the strait, it is mostly diffusive convection. Around 62.4% of the Bab el Mandeb strait exhibited favorable conditions for double diffusion processes during the winter monsoon; among that, ~4% was associated to salt fingering and ~96% to diffusive convection. Considering the fact that these conditions have been observed in different years, stable stratification and double-diffusive convection can be considered as a characteristic for the Bab el Mandeb strait during the winter monsoon.