Atmospheric Lee waves over the Eastern Mediterranean Basin as seen by the AIRWAVE Total Column Water Vapor and the WRF model

Downstream atmospheric gravity waves (denoted as Lee waves) are generated by orographic effects on stratied airflow in the lower troposphere. We observed, over water and in clear sky conditions, such phenomena using the Advanced Infra-Red WAter Vapour Estimator (AIRWAVE) Total Column of Water Vapour (TCWV) dataset, which contains about 20-year day-night products, obtained from the measurements of the Along Track Scanning Radiometer (ATSR) instrument series. The good accuracy of such data along with the high native 1 km spatial resolution grid allows the investigation of small scale structures such as Lee waves. We focused our analysis in the Mediterranean region, the largest semi-enclosed basin on the Earth. The peculiarities of this area, which is characterized by complex orography and coastlines, lead indeed to possible development of these structures both over land and over sea. We developed an automatic tool for a quick detection of areas having high Lee waves probability, exploiting the TCWV standard deviation in spatial regions of 0.15 x 0.15 deg2 (about 17 x 17 km2). Through this analysis, within the years, several occurrences of structures connected with Lee waves have been observed. The waves are exclusively detected in spring, fall and summer seasons, with TCWV values usually falling in the range from 15 to 35 kg/m2. Here we show some cases over the Central Mediterranean basin (Italy) and over the Eastern Mediterranean basin (Greece, Turkye, Cypro). One particular case is investigated more in detail: on the 2 August 2002 the Aegean sea region was sounded by both ATSR-2 and AATSR instruments that were simultaneously flying. The AIRWAVE TCWV fields derived from the two sensors have been compared with the vertically integrated water vapour simulated with the Weather Research and Forecasting (WRF) model for the same time, supporting our findings. The wave parameters are described through the use of the \Morlet" Continuous Wavelet Transformation (CWT).