Temperature trends at 90 km over Svalbard, Norway (78°N 16°E), seen in one decade of meteor radar observations

Abstract

Temperatures at 90 km altitude above Svalbard (78°N, 16°E) have been determined using a meteor wind radar and subsequently calibrated by satellite measurements for the period autumn 2001 to present. The dependence of the temperatures on solar driving has been investigated using the Ottawa 10.7 cm flux as a proxy. Removing the response of the temperatures to the seasonal and solar cycle variations yields a residual time series which exhibits the negative trend of −4 ± 2 K decade⁻¹. We indicate that, given the month‐to‐month variability and memory in the time series, for a 90% confidence in this trend, we require only 55 months of data – considerably less than the amount available. Cooling of the middle atmosphere, which would be strongly supported by these results, would result in contraction and subsequent lowering of pressure surfaces; we explain that including a negative trend in the pressure model used to obtain temperatures from meteor train echo fading times would also merely serve to augment the observed 90 km cooling.