ALBERT

Description: The Azores Current originating as a branch of the Gulf Stream is a highly dynamic system in the subtropical North Atlantic. The associated front forms the northeastern boundary of the North Atlantic Subtropical Gyre. In this study we analyzed 42 years of assimilated modeled temperature fields to localize the position of the Azores Front at 22°W and observed a fast north- and southward propagation between 30°N and 37°N on monthly to decadal time scales. The North Atlantic Oscillation with correlated changes of the wind direction was identified as one driving mechanism. As the front is acting as a guide for Rossby waves, the signal of the front’s propagation is transferred to the western Atlantic and, among other atmospheric forcing mechanisms, induces a shifting of the Northern Wall of the Gulf Stream with one year delay. Shallower mixed layer depths in the northern frontal region of the Azores Current caused by the rise of the isotherms lead to nutrient supply and primary production different from those found in the southern frontal region of the current system. A high interannual variability is manifested in deep ocean particle flux, derived from a sediment trap in 2000 m water depth at the mooring site KIEL276 (33°N, 22°W) from 1993 to 2008, which is directly related to the phytoplankton bloom in the euphotic zone. This variability is explained by the propagation of the front and strong variations in the catchment areas of the sediment trap due to the associated eddy activity in the frontal region.

Description: Drop size spectra were measured by using an optical disdrometer of type ODM 470 at 2 different locations. They were subdivided in four data sets: measurements over land, in 3 coastal areas, over semi-enclosed seas, and over the open sea. Based on 1 minute 4 measurement intervals no differences were found in drop size spectra between continental and 5 maritime areas. An exponential model with a rain rate depending interception number and 6 pre-factor in the exponent fits well the spectra, maximum drop sizes depend strongly on 7 estimated rain rates. In contrast to other investigations there are no significant differences 8 between spectra of convective and stratiform rain based on 1 minute measurement intervals. 9 However, spectra integrated over 10 minutes show the expected differences.