Abstract. We describe the application of a nowcast/forecast system for three-dimensional currents, temperature, and salinity to the Red Sea. The modeling system is constructed around a high-resolution (6 x 7 km) primitive-equation numerical circulation model with complete thermodynamics and an imbedded turbulence closure submodel. It is coupled to near-real-time databases containing meteorological forecasts and remotely sensed and in situ temperature and salinity data. The temperature and salinity data are ingested into the model daily using a nudged objective analysis technique. Because the Red Sea is a relatively narrow basin bounded by typically high and complex orography, a single-layer atmospheric boundary layer submodel has been used to increase the effective resolution of the original 40-km resolution meteorological fields by taking into account orographic steering of the low-level winds. In order to validate the modeling system, two very complete hydrographic surveys of the Red Sea were undertaken, and their results are described. Both the surveys and the modeling system nowcasts demonstrate that the circulation pattern of the Red Sea is variable and often composed of a series of eddies or subgyres, mainly anticyclones. Immediately before one survey, the winds tended to be along axis, while just before the second, they tended to be cross axis. The Red Sea circulation was much more eddy-like when the winds were cross-axis. By forcing the modeling system with and without orographically steered winds we were able to establish that the complex eddy structure is a response to a wind field which can be highly structured and vorticity rich because of interaction with the high and variable adjacent orography. When the winds are more along axis, there is less interaction with the adjacent orography, and consequently, there are fewer eddies in the Red Sea.

Abstract. We describe here a nowcast/forecast system for the entire Mediterranean Sea, designed for real-time forecasts and closely resembling operational numerical weather prediction systems. The core of the system is a high-resolution (10 km) three-dimensional primitive equation-based, sigma-coordinate numerical circulation model, assimilating remotely sensed multi-channel sea surface temperature and in situ expendable bathythermograph/conductivity-temperature-depth observational data, using an optimal-interpolational scheme. We present results for 1993 and 1994 from this data-assimilation model, focusing principally on the mesoscale features prevalent in the western and eastern Mediterranean Sea. We show that the model exhibits considerable skill in simulating both the permanent and transient mesoscale features in the Mediterranean. In particular, hitherto less well-known and less well-studied circulation features in the Adriatic and Aegean Seas are carefully examined and presented. Particular care is given to discussing the circulation in the entire Mediterranean, with particular attention to flows through various straits and their variability.

Two extensive airborne expendable bathythermograph (AXBT) surveys of the eastern Mediterranean were conducted during December 1991 and July 1992 from a Naval Oceanographic Office RP‐3 aircraft. Larger areas were sampled over shorter periods of time than is possible with conventional surveys carried out by ships. The circulation of the eastern Mediterranean consists of a collection of subgyres and fronts which show surprising seasonal and interannual variability. These surveys help to describe further this variability which is only partially understood. In particular, the surveys provide additional evidence that a relatively strong anticyclone located adjacent to the southeast corner of Crete during the late summer and through fall is a consequence of strong north winds from the Aegean, the Etesians, being blocked by Crete. Also notable in both surveys was the absence of “a” strong Mersa‐Matruh gyre, an anticyclone or anticyclonic subgyre off the Egyptian coast generally considered to be permanent. In contrast to published earlier observations, the Mersa Matruh gyre system was more a collection of weaker anticyclones rather than a single, sometimes double centered, strong feature. In both surveys we saw a string of anticyclones off the African coast between about 24° and 32°E. In general, these eddies did not exhibit a significant surface thermal structure, but were most evident in the 200 m to 300 m‐depth depictions. It may be that the formation of a strong southeast Crete anticyclone inhibits the formation of a large, relatively strong Mersa‐Matruh subgyre by interacting with the mid‐Mediterranean jet. If so, then both the southeast Crete anticyclone and the Mersa‐Matruh anticyclone could both be recurrent but tend to occur at different times.

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