Thermospheric temperatures above Poker Flat, Alaska, during the stratospheric warming event of January and February 2009

Abstract

We report observations of neutral and ion temperatures at approximately 240 km altitude above Poker Flat, Alaska, taken during the stratospheric warming event of January and February 2009. Neutral temperatures were recorded by a single‐etalon Fabry‐Perot spectrometer observing the nighttime airglow and aurora at 630 nm wavelength, whereas ion temperatures were obtained with the Poker Flat Incoherent Scatter Radar, mostly during daylight. Neutral and ion temperatures generally tracked each other closely; both data sets exhibited a similar overall seasonal trend during January to April 2009 and even showed similar short‐term day‐to‐day fluctuations. Further, the daily fluctuations correlated highly with geomagnetic activity. Both the short‐term temperature fluctuations and their overall seasonal trend matched expectations based on the MSIS model evaluated for this period at hourly intervals. A cooling response was seen in neutral temperature over a 2–3 week period during the main phase of the stratospheric warming. The magnitude of this cooling was around 50 K relative to the seasonal trend. A corresponding signature was also discernible in the ion temperatures, although it was less prominent than the neutral response. This was largely because the cooling was masked by ion temperature perturbations driven by magnetic activity. The strength of the response in ion temperature was observed to depend on the local time of the observations, which is consistent with results presented previously.