Marine Atmospheric Boundary Layer Height Estimations during the LASIE Experiment

The evolution of the height, H, of the Atmospheric Boundary Layer (ABL) over land and over the sea is caused by different mechanisms. Over land, the daily solar radiation cycle leads to a well recognized picture of the daily evolution of the vertical structure of the ABL (Stull 1988). Over the ocean, due to the high thermal capacity of the water body, the surface fluxes and the evolution of the Marine ABL (MABL) depend on several factors: mainly the geographic location (open ocean, coastal waters, enclosed seas) and the synoptic conditions. During the last decade, the depth of the ABL has been progressively recognized as playing a key role in the surface layer turbulence structure, and the interplay of processes at different spatial and temporal scales (Sempreviva and Gryning, 2000; Gryning et al. 2007; Smedman et al., 2007; Katul et al., 2008). Furthermore, the key physical problems, fundamental for the improvement of the high-resolution prediction systems, are associated with the atmospheric and oceanic boundary layers, and at the present stage of environmental prediction science and technology, it is possible to start developing efficient and accurate high-resolution coupled coastal prediction systems. In the marine environment, complete datasets describing the surface layer and the vertical structure of the Marine Atmospheric Boundary Layer (MABL), through its entire depth, are less frequent than over land, due to the high cost of measuring campaigns. The LASIE experiment (Sempreviva et al 2010) is a multi-institutional intensive field campaign carried out in the Ligurian Sea from 14th June 2007 to 5th July 2007. The main scientific goal of the campaign is to contribute to the development and evaluation of parameterizations of the atmospheric and oceanic boundary layers and their interactions. During the field experiment, a detailed characterization of the mean and turbulent structure of the atmospheric and the oceanic boundary layers were carried out using ship-based meteorological and oceanographic observations and taking advantage of two meteo-oceanographic buoys. Furthermore, two radiosonde systems Vaisala DigiCORA Sounding System MW21, and a ceilometers Vaisala CL31 were monitoring the vertical structure of the MABL. In this contribution, we present the evolution of the height of the MABL derived applying different methods to radiosonde vertical profiles and to the ceilometer backscatter signal (Emeis et al . Furthermore, we compared the experimental estimates against values derived from two mesoscale models i.e. MM5 and WRF. The comparison of the evolution of the height of the MABL from all methods shows a satisfying agreement though the WRF model appears to overestimate the H values. The comparison between experimental values shows good agreement leading the author to believe in an increasing use of optical systems such as LIDARS to retrieve the mixing height. Emeis, S., Schäfer K., and Münkel C.: Surface-based remote sensing of the mixing-layer height – a review. Meteorologische Zeitschrift, Vol. 17, No. 5, 621-630 (October 2008) Gryning S.-E., Batchvarova E., Brümmer, B., Jørgensen, HE., Larsen SE., 2007: On the extension of the wind profile over homogeneous terrain beyond the surface boundary layer. Boundary-Layer Meteor. 124 , 251-268 Katul, G.G., Sempreviva, A.M. and Cava, D.: The Temperature–Humidity Covariance in the Marine Surface Layer: A One-dimensional Analytical Model Boundary-Layer Meteorology, Volume 126, Number 2 / February, 2008. Sempreviva, Anna Maria ; Schiano, M.E. ; Pensieri, S. ; Semedo, Alvaro ; Tome, R. ; Bozzano, R. ; Borghini, M. ; Grasso, F. ; Sørensen, L.L. ; Teixeira, J. ; Transerici, C.: Observed development of the vertical structure of the marine boundary layer during the LASIE experiment in the Ligurian Sea. Annales Geophysicae, vol: 28, issue: 1, pages: 17-25, 2010. Sempreviva, A.M. and Gryning, S.-E.: Mixing height over water and its role on the correlation between temperature and humidity fluctuations in the unstable surface layer. Boundary-Layer Meteorol 97:273-291, 2000. Smedman, A.-S., Hogstrom, U., Hunt, J.C.R. and Salee, E.: Heat/mass transfer in the slightly unstable atmospheric surface layer. Quarterly Journal of the Royal Meteorological Society 133, 37-51, 2007. Stull, R.: An Introduction to Boundary Layer Meteorology, Kluwer Academic Press, Dordredht, 666 pp., 1988.