We report a surprising absence of PMSE (Polar Mesospheric Summer Echoes) in VHF radar observations of the southern summer high‐latitude mesosphere. Our observations cover about twenty days during January‐February, 1993, from King George Island, Antarctica.
We report VHF radar observations of the southern high‐latitude mesopause region using wind profilers that were installed recently on King George Island, Antarctica, and Ushuaia, Argentina. Briefly, our observations, which were made during January and February 1993, show almost no evidence of so‐called polar mesosphere summer echoes, or PMSE. Since these echoes are a predominant feature of the northern high‐latitude mesosphere in summer, their absence in the southern hemisphere is both surprising and intriguing. In this paper we present evidence demonstrating the virtual absence of the echoes and demonstrate that our systems were capable of detecting them had they been present. We also outline some of the consequences of this intriguing result, which are supported by observed hemispheric differences in polar mesospheric clouds, mesospheric temperatures, upper atmospheric gravity wave activity, and mean circulation patterns.
The stability of a DC power distribution system is a key design aspect. The presence of constant-power load induces negative impedance instabilities which should be considered during system design. In this paper the problem of DC power system stability is addressed and two solutions are proposed and compared. The former exploits the insertion of a suitably sized capacitor in parallel to the constant-power converter, while the latter makes use of a storage system controlled through a PI regulator. Simulation results are reported to verify the analysis
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