This note focuses on thermodynamic changes caused by Eastern Mediterranean (EM) subsidence anomalies. Subsidence anomalies are shown to modulate EM-wide stability with respect to moist ascent. Additionally, convective available potential energy (CAPE) generation rates, as well as mean CAPE, change coherently during extreme EM rainfall anomalies. It is suggested that the resulting modulation of convective rain generation is the process directly responsible for the observed rainfall anomalies.

This paper presents a simple theory for the association between observed eastern Mediterranean (EM) rainfall anomalies and North Atlantic (NA) climate variability. Large-scale NA atmospheric mass rearrangements, pri- marily a modulation of the Icelandic low and the subtropical high pressure systems, tend to extend beyond the NA. A particularly strong such teleconnection exists between the northern NA and southern Europe and the Mediterranean Basin. Pressure anomalies over Greenland-Iceland are thus associated with reversed-polarity anomalies centered over the northern Adriatic, affecting the entire Mediterranean Basin; elevated Greenland pressure is accompanied by an anomalous cyclone over the Mediterranean, and a Mediterranean high pressure system is present when pressure over Greenland is reduced. In the EM, these anomalies result in anomalous southerlies during Greenland highs, and northerlies during Greenland lows. Eastern Mediterranean southerlies warm the EM, while northerlies cool locally. Because heat advection by horizontal and vertical motions dominate the EM thermodynamic equation (or, put differently, because thickness advection dominates the omega equation), cooling by northerly winds results in enhanced subsidence. Conversely, warming by anomalous EM southerlies produces enhanced ascent. These vertical motion anomalies modify the stability of the mean column, resulting in the observed EM rainfall anomalies.

A dynamically motivated statistical forecasting scheme for eastern Mediterranean winter rainfall is presented. 
The scheme is based on North Atlantic sea level pressure precursors. The resulting forecasts are robust and 
statistically significant at ;13 months lead time, and improve at ;7 months lead. It is suggested that these 
forecasts form a foundation for an operational early-warning system for eastern Mediterranean droughts.

A time series of oxygen isotope (d18O) measurements of a coral from the northern Red Sea (RS) is presented and used as a direct proxy for water surface density rs . With a relatively constant subsurface density, the generated surface density time series closely tracks water mass formation variability. Two positive and two negative high-amplitude rs anomalies are studied, and associated atmospheric and oceanic data are analyzed to understand large-scale ocean-atmosphere processes. The dominant process is lower-tropospheric subsidence. It dries the boundary layer (BL), increases surface evaporation and rs , and ultimately drives water mass formation. The main cause of the subsidence is a temperature increase along the principal axis of the RS from the eastern Mediterranean to the convergence zone (CZ, 188-228N). The increase entails isentropes sloping down to the southeast, crossing pressure surfaces due to their tilt. With nearly adiabatic flow along the principal axis, air parcels move roughly along the sloped isentropes toward ever increasing pressure; that is, they subside. The subsidence supplies the northern RS BL with upstream air from higher altitudes (where humidity is low), thus drying the BL. The resultant high evaporation north of ;258N (with low evaporation minus precipitation south of ;228N) depresses sea levels in the northern RS, and thus drives the RS thermohaline circulation and controls water mass formation. Excluded from the presented picture, but probably very important, is mixing with the hot, dry air of the surrounding deserts.

As the record of past climate becomes clearer, the existence of regimes has emerged as a primary characteristic of the climate system. Present climate is now known to represent one regime among others including glacial climates such as characterized recent intervals of the Pleistocene and the much warmer equable climates of the Eocene and Cretaceous. An important test of climate theory is the ability to explain the record of climate change in terms of atmosphere-ocean dynamics, and the response of the dynamics to internal and external changes.

The hypothesis is advanced that variation in the strength and extent of the symmetric circulation is an important mechanism meditating climate change. Using a simplified model we explore dynamical variables that influence the symmetric circulation and the physical processes that may have been modified these dynamical variables to maintain the warm equable climates.