The Balearic rissaga: from pioneering research to present-day knowledge

The pioneering work done in late 1970s and early 1980s on research into rissaga events or meteotsunamis in the Balearic Islands is briefly reviewed in this paper and contrasted with the present state of the art on the phenomenon. The early research phase used existing observational evidence to construct a doctrine for the initial comprehension and forecasting of the phenomenon. By the beginning of the 1980s, it had already been established that the rissaga is a marine response to quick atmospheric pressure oscillations in resonance conditions, initially attributed exclusively to internal atmospheric gravity waves and later to convective pressure jumps too. Forty years later, new observational methods have provided a much richer database, with theoretical research and the use of forecasts using numerical models underpinning a much more solid perspective. With regard to predictability, quick atmospheric pressure oscillations were associated with a three-layer atmospheric vertical structure from the beginning: a thermodynamically neutral lower layer of Mediterranean air, a thermal inversion layer (Saharan air lying above and Mediterranean air below) and a deep upper layer with conditional instability in at least some strata. This structure is compatible with a high-level trough or cut-off low over the Iberian Peninsula; strong south-westerly flow over the Western Mediterranean area; jet stream speed being reached at the highest tropospheric levels, and forced Saharan air advection at the low/medium levels. A weak low-pressure area is usually present at low levels in the Mediterranean. The identification of the meteorological framework favourable to a rissaga event soon led to a probabilistic and purely meteorological forecasting method for the rissaga phenomenon. This method is still used today, albeit in combination with objective methods, some of which are based on the use of coupled atmospheric and oceanic forecasting models.