A new approach to sensitivity climatologies: the DTS-MEDEX-2009 campaign

Adaptive observation is an approach to improving the quality of numerical weather forecasts through the optimization of observing networks. It is sometimes referred to as Data Targeting (DT). This approach has been applied to high impact weather during specific field campaigns in the past decade. Adaptive observations may involve various types of observations, including either specific research observing platforms or routine observing platforms employed in an adaptive way. The North-Atlantic TReC 2003 and the EURORISK-PREVIEW 2008 exercises focused on the North-Atlantic and Western Europe areas using mainly routine observing systems. These campaigns also included Mediterranean cases. <br><br> The most recent campaign, DTS-MEDEX-2009, is the first campaign in which the DT method has been used to address exclusively Mediterranean high impact weather events. In this campaign, which is an important stage in the MEDEX development, only operational radiosonde stations and commercial aircraft data (AMDAR) have provided additional observations. Although specific diagnostic studies are needed to assess the impact of the extra-observations on forecast skill and demonstrate the effectiveness of DTS-MEDEX-2009, some preliminary findings can be deduced from a survey of this targeting exercise. <br><br> After a description of the data targeting system and some illustrations of particular cases, this paper attempts some comparisons of additional observation needs (through effectively deployed radio-soundings) with sensitivity climatologies in the Mediterranean. The first step towards a sensitivity climatology for Mediterranean cases of high impact weather is indirectly given by the frequency of extra-soundings launched from the network of radiosonde stations involved in the DTS-MEDEX-2009 campaign

Meteorological and Internal Wave Forcing of Seiches along the Sri Lanka Coast

Regularly observed seiches from tide gauge records around the Sri Lanka coast have been analysed to determine the forcing mechanisms. The seiche periods range from a few tens of minutes to 2 hr. Fortnightly and seasonal variations of seiche amplitudes are clearly visible on the east coast. These seiche amplitudes are particularly large approximately 6-8 days after spring tides, with maximum seiche amplitudes observed during March-April and October-November, suggesting that the seiche variation could be related to stratification and internal wave activity. There is no visible fortnightly and seasonal variation of seiche amplitudes in west coast records. Instead, they show a daily pattern with relatively larger seiches around 10:00 hrs local time, suggesting that the seiches on the west coast could result from diurnal atmospheric forcing. Barotropic and 2-layer models have been developed to investigate the influence of atmospheric forcing and internal wave activity on the seiches. A barotropic model applied to the west coast shows that the daily seiche amplitude variation could be simulated with cyclic diurnal meteorological forcing. Two-layer model runs for Trincomalee Bay and the adjacent east coast shelf suggest that seiche amplitudes are proportional to vertical stratification and mixed layer depths. Therefore, the observed seiches there could be excited by internal waves which originate as far away as the Andaman Sea during spring tides and have a travel time of 6-8 days to the Sri Lankan east coast. However, further studies, including direct measurements of internal wave activity within the region are required to confirm this hypothesis