The airglow layer emission altitude cannot be determined unambiguously from temperature comparison with lidars

Abstract

I investigate the nightly mean emission height and width of the OH * (3-1) layer by comparing nightly mean temperatures measured by the ground-based spectrometer GRIPS 9 and the Na lidar at ALOMAR. The data set contains 42 coincident measurements between November 2010 and February 2014, when GRIPS 9 was in operation at the ALO-MAR observatory (69.3 • N, 16.0 • E) in northern Norway. To closely resemble the mean temperature measured by GRIPS 9, I weight each nightly mean temperature profile measured by the lidar using Gaussian distributions with 40 different centre altitudes and 40 different full widths at half maximum. In principle, one can thus determine the altitude and width of an airglow layer by finding the minimum temperature difference between the two instruments. On most nights, several combinations of centre altitude and width yield a temperature difference of ±2 K. The generally assumed altitude of 87 km and width of 8 km is never an unambiguous, good solution for any of the measurements. Even for a fixed width of ∼8.4 km, one can sometimes find several centre altitudes that yield equally good temperature agreement. Weighted temperatures measured by lidar are not suitable to determine unambiguously the emission height and width of an airglow layer. However, when actual altitude and width data are lacking, a comparison with lidars can provide an estimate of how representative a measured rotational temperature is of an assumed altitude and width. I found the rotational temperature to represent the temperature at the commonly assumed altitude of 87.4 km and width of 8.4 km to within ±16 K, on average. This is not a measurement uncertainty.

Rotational temperatures retrival from the Arecibo Observatory Ebert-Fastie spectrometer and their inter-comparison with Lidar and SABER measurements

“…Even though such mean temporal trends may not exactly replicate the actual magnitude of these parameters on some occasions, it is the second best available option that could significantly improve the inter-comparison of altitude-resolved and altitude-integrated measurements. Several researchers have used this methodology to obtain an indirect estimate of the OH peak altitude by comparing temperatures from two different ground-based instruments where one provides altitude-resolved measurements, and the other one provides altitude-integrated measurements (Dunker, 2018;Zhao et al, 2005). Typically, a Gaussian function is employed as the weighting function where the FWHM and peak altitude of the Gaussian function are the free parameters.…”

Retrieval of intrinsic mesospheric gravity wave parameters using lidar and airglow temperature and meteor radar wind data

“…with c p = 1.005 kJ kg −1 K −1 being the specific heat capacity for air at constant pressure. We calculate the nightly mean of N in the altitude range of 82-91 km based on background temperature profiles which are obtained by low-pass filtering of lidar temperature profiles following Ehard et al (2015). We derive N = 0.0202±0.0016 s −1 and H s = 5.60±0.08 km at OH layer altitudes.…”

A Comparison of Fabry–Perot Interferometer and Meteor Radar Wind Measurements Near the Polar Mesopause Region

“…Although the optical instruments provide several valuable upper atmospheric parameters at relatively low cost, their performance and continuity of data records are limited only to moonless clear night condition over the observation site. Furthermore, most of airglow observations from ground‐based optical instruments rely on the underlying assumption of the fixed height profile of airglow emission layers (Won et al., 1999; Dunker, 2018). The height of hydroxyl (OH) emission layer is assumed to be 87 km with a full width at half maximum (FWHM) of about 8 km (Baker & Stair, 1988) and the height of OI‐green line emission layer is widely known to be 97 km with a FWHM of 7 km (Yee & Abreu, 1987).…”