Computer Science – Sound
Scientific paper
Aug 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001esasp.471..171l&link_type=abstract
In: 15th ESA Symposium on European Rocket and Balloon Programmes and Related Research, 28 - 31 May 2001, Biarritz, France. Ed.:
Computer Science
Sound
Summer Mesosphere, Polar Mesosphere, Summer Echoes
Scientific paper
In the last ten years a total of 8 in situ measurements of neutral number densities were performed in the polar summer mesosphere during nearly co-located observations of very strong radar echoes called "polar mesosphere summer echoes" (PMSE). The in situ density measurements were used to derive turbulent parameters, such as the turbulent energy dissipation rate ɛ. From the same instrument high resolution temperature profiles in the altitude range of approximately 110 to 70 km are derived. There is no apparent correlation between PMSE and neutral air turbulence, however, occasionally both PMSE and turbulence coincide. The temperature gradient within the PMSE layer shows no tendency for an adiabatic lapse rate, which indicates that persistent turbulent mixing cannot have taken place. We note that PMSE was present for typically more than one hour before the sounding rocket was launched, thus long enough to affect the thermal structure if PMSE were related to turbulence. The fact that the thermal structure is not affected leads us to the conclusion that the occasional coincidence of PMSE and turbulene deduced from in situ measurements is accidental. This also implies that the main mechanism creating PMSE remains unidentified. We performed a detailed analysis of the high resolution temperature measurements in the vicinity of PMSE. In the PMSE layer the temperatures are generally small enough for water ice particles to exist, i.e., the degree of saturation of water vapor over ice is significantly larger than unity (we assume a water vapor mixing ratio of 4 ppmv constant with altitude). It is interesting to note that in most of the flights the PMSE layer covers less than half of the altitude range where ice particles can exist. This stresses the importance of other physical mechanisms required to create PMSE except the presence of water ice particles.
Hoffmann Peter
Lübken Franz-Josef
Rapp Markus
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