Gravitiy Wave Forcing: Mountain Waves (Mc Wave)

The Scandinavian mountain ridge is a unique laboratory for studying gravity waves triggered by "deflection" of prevailing winds coming from the North Sea. The extensive ground based instrumentation co-located with the Scandinavian rocket ranges makes this region ideal for studying gravity waves at high latitudes.Two sequences of sounding rockets with two large instrumented payloads each are envisaged to study atmospheric fine structure in situ and combine these results with ground based data on radar reflectivity and aerosol distribution. One sequence will take place in Winter from Esrange, Sweden, when westerlies prevail, the other in Summer with emphasis on the Norwegian range Andoya, when other mechanisms are expected to be active. Both sequences will have hourly background measurements of the development of neutral densities up to the mesopause by balloons and meteorological rockets in the 12 hours between the flights of the instrumented payloads of each of the two sequences.

The energy contained in the upper atmosphere is not only a function of the solar flux absorbed by the particular region, but also of the energy of upward propagating waves which may deposit their energy by wave breaking. In summer such conditions are mainly caused by wind shears. The relevant rocket salvoes, launched from the Norwegian rocket range Andøya in 2002, revealed pronounced regions of turbulence near 85 km associated with large charged aerosols. The aerosols are believed to be ice particles formed around smoke or volcanic nuclei in the presence of the extremely low Arctic summer temperatures of the mesopause. The layer was also detected by radars, both by the one adjacent to the rocket range, but also by EISCAT 100 km away in Tromsø. The associated electron density "bite-outs" (= pronounced minima) were for the first time not only detected by the rocket-borne probes, but notable also by the Austrian radio wave propagation experiment which is inherently unambiguous in its absolute values. In winter gravity waves are generally expected to be triggered by mountains deflecting winds near the ground. The Scandinavia mountain range represents such an obstacle for the prevailing winds from the North Sea. The rocket salvoes dedicated to the study of the ensuing upward propagating waves were launched from Esrange, Sweden, i.e. downwind from the anticipated source of the gravity waves. In early January 2003 a stratospheric warming developed which inhibits upward propagation of gravity waves; some of the campaign aims therefore had to be modified since the duration of these strat-warms can not be predicted and could well have lasted beyond the period available for this campaign. The first salvo therefore showed gravity wave perturbations up to only 65 km and a smoothly varying electron density profile; in the second flight gravity waves were observed to much greater heights and apparently were the cause of the significantly larger turbulent energy around 85 km as derived from a variety of temperature measurements. The high quality of the ionospheric rocket measurements allows for the first time to calibrate both the IRIS imaging riometer located in northern Finland and the incoherent scatter radar EISCAT near Tromsø.