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A Southern Ocean Pilot cruise covering the latitudes from 10°N to 56°S in the open Indian Ocean was car-
ried out during January–February 2004. Surface and upper air data collected during this cruise are re-
ported here. It is shown that the broad features of the atmosphere, in particular that of temperature, follow
the tropical and mid-latitude weather expected during January–February in this region. However, the atmo-
spheric boundary-layer shows large variations, both in its height and structure between tropics and high
latitudes. Strong influence of the surface heat flux on boundary layer structure is clearly seen. Humidity
field reveals several local maxima and minima, suggesting a laminated atmosphere with air from different
sources moving almost unmixed in adjacent layers.