Solar cycle signature and secular long‐term trend in OH airglow temperature observations at South Pole, Antarctica

Abstract

We have examined Michelson Interferometer OH airglow temperature data to investigate solar cycle and long‐term variations of mesospheric temperatures at South Pole Station (SPS), Antarctica (90°S). The data set used here is continuous (24 hours a day) and taken during 1994–2004 austral winters. We have used a Multiple Linear Regression (MLR) technique to elucidate solar cycle and the trend term in the MI temperature time series data. The 11‐year time series of OH rotational temperature shows a strong correlation with F10.7 radio flux (R = 0.60). The amplitude of solar cycle response seen in the mesopause temperature records at South Pole is about 0.04 ± 0.01 K/sfu (Solar Flux Units), however, the trend term is statistically insignificant and is about 0.1 ± 0.2 K/year. Superposed epoch studies have been carried out in order to determine climatological variations in OH temperatures above South Pole derived from 11 years of austral winter observations. The mean amplitude of this variation is about 12.6 K and its maximum occurs near 30 May which is in agreement with the Fabry‐Perot Spectrometer (FPS) observations of OH temperatures at SPS (Hernandez, 2003). However, whereas Hernandez (2003) reported 35 K cooling in 2002, MI OH temperatures at SPS do not show any significant deviation from previous years.

Correlations of mesospheric variability and their relation to the large-scale circulation during polar winter

“…The possible correlation of high-latitude OH temperatures with the solar flux is open to question as studies of OH temperatures at mid-to-high latitudes by Bittner et al (2002) found no such correlation, and an analysis by Sigernes et al (2003) of 20 years of data acquired at Svalbard, 781N also found no solar influence. However, in the Antarctic, Azeem et al (2007) did find a strong correlation of OH rotational temperatures with the solar flux. It will be of great interest to extend this apparent correlation in relation to the solar flux.…”

Long‐term trends and the effect of solar cycle variations on mesospheric winter temperatures over Longyearbyen, Svalbard (78°N)

“…Correlation between SSN and the OH* residuals may be biased by that even though the number of sunspots may be zero for many days in a row, the OH* temperatures still vary. The correlations are overall lower than correlations achieved for some other high‐latitude sites [ Azeem et al ., ; French and Klekociuk , ]. The correlation increases slightly when excluding SSW months, except for SSN.…”

Daytime upper mesospheric energetics over a tropical station, Trivandrum (8.5°N, 77°E): An investigation using the multiwavelength dayglow photometry

“…The solar heating is dominated by the absorption of solar UV radiation by O 2 and O 3 [Mlynczak and Solomon, 1993]. Many studies in the past attempted to find out the contribution of solar heating on the mesopause temperatures Azeem et al, 2007]. These studies reported a strong linear relation between the mesopause temperature and the F10.7 cm radio flux using the nighttime hydroxyl measurements Azeem et al, 2007].…”

“…Many studies in the past attempted to find out the contribution of solar heating on the mesopause temperatures Azeem et al, 2007]. These studies reported a strong linear relation between the mesopause temperature and the F10.7 cm radio flux using the nighttime hydroxyl measurements Azeem et al, 2007]. In addition to the solar heating, a significant part of the mesospheric energetics is contributed by the exothermic reactions involving odd-oxygen and odd-hydrogen species, including quenching of excited photolysis products [Mlynczak and Solomon, 1993], by radiative cooling associated with infrared emission of CO 2 at 15 mm [Andrews et al, 1987;Rodgers et al, 1992].…”