4-dimensional Variational Assimilation of Ground-based Microwave Observations during a Winter Fog Event

1. Introduction To measure the vertical profiles of temperature and water vapor that are essential for modeling atmospheric processes, radiosondes are traditionally the privileged way to obtain upper-air information. Radiosondes, however, present certain limitations. It typically takes 40 minutes for a radiosonde to ascend through the troposphere and about 2 hours to ascend to full height. Cost and other practical considerations further limit the temporal sampling interval (i.e. launch frequency) to one or two a day. As a result, radiosonde networks, which are already very coarse in spatial distribution, are inadequate to temporally and spatially resolve mesoscale features.