Temperatures and horizontal winds in the Antarctic summer mesosphere

Abstract

A series of 26 meteorological rockets (“falling spheres,” FS) were launched in January and February 1998 from the Antarctic research station Rothera (68°S, 68°W). These flights gave densities and temperatures below ∼93 km and horizontal winds below ∼75 km, respectively. The lowest altitude is approximately 35 km. The instrumental technique is identical to the one applied in similar studies in the Northern Hemisphere (NH). In this paper, we summarize the experimental results and compare them with climatologies in the NH summer and with empirical models. We concentrate on the mesosphere. In January, temperatures in the upper mesosphere are very low (<135 K) and are very similar to the NH. In February, temperatures increase substantially, certainly more than in the corresponding time period in the NH. The zonal winds show a similar behavior: SH/NH values are very similar in January/July but differ in February/August. This indicates that (at least in 1998) the seasonal transition from summer to winter occurs earlier in the SH compared to the NH. Mass densities are generally similar in both hemispheres. The difference is less than 2–6% and shows a seasonal variation similar to temperatures and zonal winds. Our experimental results at Rothera differ significantly from empirical reference atmospheres such as the COSPAR International Reference Atmosphere (CIRA). For example, in the upper mesosphere our mass densities are up to 35–40% smaller compared to CIRA. Such differences can be important, for example, when modeling the sedimentation of ice particles leading to noctilucent clouds (NLC) and polar mesosphere summer echoes (PMSE). Furthermore, zonal winds in the mesosphere in January/July in the SH/NH are very similar in our measurements but different in CIRA. Recent lidar and radar measurements of NLC at Rothera and PMSE at Davis (68.6°S), respectively, show very similar mean altitudes compared to the NH supporting the similarity of the thermal structures in both hemispheres in January/July.