Response of OH airglow temperatures to neutral air dynamics at 78°N, 16°E during the anomalous 2003–2004 winter

Abstract

[1] Hydroxyl (OH) brightness temperatures from the mesopause region derived from temperature profiles from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) satellite are compared with OH(6-2) rotational temperatures measured by spectrometer from Longyearbyen, Norway (78°N, 16°E), during the winter [2003][2004]. The two series correspond well, although the satellite measurements are higher by an average of 5.6 K ± 4.4 K. Reasons for this apparent bias are discussed. The two series give a near-continuous temperature record from this winter, making it possible to study the response of the temperatures to neutral air dynamics observed from meteor radar measurements of meridional and zonal wind. Vertical profiles of 1.6 mm OH volume emission rates from SABER reveal that the unusually high temperatures observed during January and February 2004 (240-250 K) correspond to a very low and bright OH layer. Significant linear correlations are found between meridional wind, OH temperature, and peak altitude. These data support the theory that the high temperatures result from an anomalously strong upper stratospheric vortex that confined air to the polar regions, coupled with meridional transport, which led to a strong downwelling of atomic oxygen-rich air, thereby lowering the altitude of the OH layer. The SABER data reveal that the re-formation of the OH layer at approximately 78 km altitude accounted for an increase in temperature of approximately 15 K, while the remaining temperature increase (20-35 K) is attributed to adiabatic heating and chemical heating from the exothermic reactions involved in producing the vibrationally excited OH.

Optimizing hydroxyl airglow retrievals from long-slit astronomical spectroscopic observations

“…This is consistent with previous observations using ground-based spectrometers or interferometers (e.g. Innis et al, 2001;Oberheide et al, 2006;French and Mulligan, 2010;Dyrland et al, 2010). However, it must be pointed out that the NOTCam measurements cover a very short time span and may be affected by gravity-wave perturbations of the climatological temperature gradient of the atmosphere represented by NRLMSISE.…”

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

“…The low altitudes were attributed to downwelling due to the strengthening of the polar vortex after an SSW in January–February 2004 [ Dyrland et al ., ]. A temperature increase of the order of 15 K was attributed to the lowering of the layer, so the altitude is definitely a key factor in determining the OH* temperature [ Dyrland et al ., ]. Similarly, low OH* peak altitudes were observed after the SSW in 2006 [ Winick et al ., 2009].…”

On the dependence of the OH<sup>*</sup> Meinel emission altitude on vibrational level: SCIAMACHY observations and model simulations

“…If simultaneous observations of the vertical volume emission rate profile of the OH band analyzed are not available, the interpretation of the temperature retrievals may be difficult. An extreme example is the dramatic decrease of the OH emission layer altitude down to about 78 km observed in early 2004 at high northern latitudes, leading to an apparent temperature increase of about 15 K (Dyrland et al, 2010). Long-term, solar cycle and seasonal variations in OH emission altitude can also lead to apparent variations in ground-based OH temperature measurements, and may interfere with the determination of the actual long-term, solar cycle and seasonal variations of upper mesospheric temperatures.…”