INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 20: 1791–1808 (2000) SEA BREEZES AND COASTAL JETS IN SOUTHEASTERN SPAIN CHRISTOPH KOTTMEIER*, PABLO PALACIO-SESE, NORBERT KALTHOFF, ULRICH CORSMEIER and FRANZ FIEDLER Uniersita ¨t /Forschungszentrum Karlsruhe, Institut fu ¨r Meteorologie and Klimaforschung, Kaiserstraße 12, D-76128 Karlsruhe, Germany Receied 1 September 1999 Reised 14 April 2000 Accepted 18 April 2000 ABSTRACT Sea breezes and low-level jet (LLJ) streams are studied in the region between the Eastern Castilla-La Mancha and the Mediterranean coast of southeastern Spain. The simplified concept of two-dimensional terrain and meteorological conditions explains the spatially and diurnally varying wind system consistently. The changes, as a function of time, height and distance to the coast, of temperature, pressure and wind as well as of certain observed phenomena, such as LLJs and strongly baroclinic zones, result from the response of the mesoscale flow to differential heating. Wind changes are generally found to be consistent with mesoscale changes in geostrophic winds as estimated from station pressure measurements. The LLJs mark the penetration depth of the sea breeze during daytime, where a baroclinic zone develops at the transition between continental air masses and marine air masses, typically at a distance of 150 km from the coast. The analysis is based on aerological data and ground-based measurements from the European Field Experiment in a Desertification Threatened Area (EFEDA) experiments in 1991 and 1994 as well as on 3-hourly data from three synoptic stations of the Spanish meteorological network for April – October in 1991 and 1994. After corrections were made for instrument errors and atmospheric tides, diurnal pressure variations document vertically integrated mass fluxes perpendicular to the coast. Amplitudes of diurnal pressure and temperature changes scatter significantly and are largest in midsummer. They are weakly correlated and pressure amplitudes remain large in spring and autumn when diurnal temperature changes are reduced. With about 6 h delay to the regular development of onshore winds at the coast during daytime, pronounced wind peaks are observed over the eastern plateau at Albacete and Barrax in the late afternoon. Case studies show that they are accompanied by development of baroclinically driven LLJs, whereas winds at Tomelloso, 220-km inland, show less pronounced diurnal changes and are beyond the normal penetration distance of sea breezes. Copyright © 2000 Royal Meteorological Society. KEY WORDS: boundary layer height; convective boundary layer; desertification; low-level jet; sea breeze; Spain 1. INTRODUCTION Land and sea breeze effects can be defined as periodic changes of wind and temperature on a coast with a period of  d 24 h, caused by different energy balances of the solid earth and sea surfaces. Differential heating causes the air above a landmass to become warmer than the air above the sea during the daytime on sunny days. The expansion of warm air over land causes the surfaces of constant pressure to be lifted aloft, thus creating a pressure gradient perpendicular to the coast at the upper levels. The imbalance of forces causes upper-level flow towards the sea, which is responsible for the decrease of pressure on the surface over land. The resultant pressure gradient force near the surface is directed from the sea to the land, initiating the sea breeze from sea to land at low levels. Due to the Coriolis force, this initial direct circulation is bound to adjust to the geostrophic flow or, at levels with significant effects of surface friction, to the geotriptic flow. The relevant time scale for this process is  f =2/f, the period of inertial oscillations. Undamped or damped inertial oscillations may occur in flows where the velocity is not in a steady equilibrium with the forces. Adjustment towards a new equilibrium may also generate gravity inertia waves propagating in both directions perpendicular to the coast (Holton, 1992; van Delden, 1993). * Correspondence to: Universita ¨t/Forschungszentrum Karlsruhe, Institut fu ¨ r Meteorologie and Klimaforschung, Kaiserstraße 12, D-76128 Karlsruhe, Germany. Copyright © 2000 Royal Meteorological Society