Jonathan Holt

Long-term temperature trends in the ionosphere above Millstone Hill

[1]xa0Increasing concentrations of greenhouse gases are expected on theoretical grounds to lead to a cooling of the upper atmosphere. Due to the close thermal coupling of the neutral and ionized components of the upper atmosphere the effects of this cooling are also expected to be seen in the ionospheric ion temperature. Long-term satellite observations of neutral density show a trend consistent with the expected cooling. Temperature data from the Millstone Hill incoherent scatter radar (46.2°N, 288.5°E) from 1978 to 2007 have been analyzed to provide a direct estimate of the temperature trend above the radar. The long-term trend in the directly measured ion temperature Ti at 375 km is found to be −4.7 K/year with a 95% confidence interval of −3.6 to −5.8 K. The estimated trend in the neutral temperature Tn is −5.0 K/year. These are significantly larger than predicted by theory.

Westward plasma drift in the midlatitude ionospheric F region in the midnight-dawn sector

In this paper we report the observations of a sharp ionospheric plasma velocity reversal boundary at subauroral latitudes during magnetic storms in the midnight-dawn sector. The zonal plasma drift was eastward poleward of the velocity boundary and became westward equatorward of the boundary. The latitudinal extent of the westward drifts was ∼20°. A local maximum of the drift occurred only 2°–5° below the boundary; the magnitude of the maximum velocity was 200–400 m s−1 between 2100 and 0300 local time (LT) and as high as 780 m s−1 near midnight. The large westward plasma drift immediately equatorward of the velocity boundary first occurred at 2100 LT and continuously extended across midnight to the dawn sector. The location of the maximum velocity coincided with the minimum density within the midlatitude ionospheric trough. The latitude of the velocity boundary decreased from geographic latitude ∼53° to ∼43° (corresponding to geomagnetic latitude ∼65° to ∼55°) between 2100 and 0800 LT. We propose that the large westward drift at subauroral latitudes is driven by the polarization jet electric fields in the ring current and that the lower-latitude westward drift with moderate magnitude is caused by the disturbance wind dynamo.

Two-Dimensional Mapping of Dayside Convection

Millstone Hill radar azimuth scans have been used to map the large-scale features of the ionospheric convection pattern in the vicinity of the cusp and cleft. Each scan covers 5 hours of MLT and 20° of invariant latitude, Λ, with 30 minute temporal resolution Individual “snapshots” of the convection pattern for disturbed conditions on 31 January 1982 span the entire region of convection convergence near noon and compare favorably with average model representations of the dayside region. The characteristic features of ion and electron precipitation observed during satellite overflights of the radar field of view are used to identify the cusp and cleft and to relate the location of these magnetospheric features to the pattern of ionospheric convection electric field. Cusp precipitation is seen at 70°Λ and 09 MLT at the sunward/anti-sunward convection reversal immediately after a sudden turning of interplanetary magnetic field (IMF) By from -5 nT to +5 nT while IMF Bz was-10 nT.