On the latitudinal distribution of mesospheric temperatures during sudden stratospheric warming events

Abstract

Mesospheric rotational temperatures from O 2 (0-1) and OH(6-2) band nightglow emissions that originate from 94 and 87 km altitudes, respectively, were obtained from a low-latitude location, Mount Abu (24.6°N, 72.8°E), in India using a high spectral resolution grating spectrograph, which showed significant enhancements during the major sudden stratospheric warming (SSW) event of January 2013. To investigate the relationship of these enhancements in the context of SSW occurrences, a detailed study was carried out for 11 SSW events that occurred during 2004-2013 using SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) data. In addition to SABER, Optical Spectrograph and Infrared Imaging System and Solar Occultation For Ice Experiment mesospheric temperatures were also used which showed similar latitudinal behavior as obtained by SABER. The longitudinal mean mesospheric temperatures at different latitudes of Northern and Southern Hemispheres have been derived. It is found that during SSW events the well-known mesospheric cooling over the Northern Hemispheric high latitudes turns to heating over midlatitudes and then reverts to cooling closer to equatorial regions. This trend continues into the Southern Hemisphere as well. These variations in the mesospheric temperatures at different latitudes have been characterized based on northern hemispheric stratospheric temperature enhancements at high latitudes during SSW periods. In comparison with the COSPAR International Reference Atmosphere-86-derived temperatures, the SABER temperatures show an increase/decrease in Southern/Northern Hemisphere. Such a characterization in mesospheric temperatures with respect to latitudes reveals a hitherto unknown intriguing nature of the latitudinal coupling in the mesosphere that gets set up during the SSW events.

Large- and small-scale periodicities in the mesosphere as obtained from variations in O<sub>2</sub> and OH nightglow emissions

“…GWs play an important role in the MLT en-ergetics and dynamics since they act as significant source of momentum and energy flux in this region. Further, the GWs in the mesosphere are significantly affected by tropospheric cyclones, as shown in a recent study by Singh and Pallamraju (2016), wherein unambiguous evidence was obtained for the propagation of waves from the troposphere to the mesosphere during cyclone Nilofar, which occurred in October 2014 in the Arabian Sea, to the west of our optical observational location of Gurushikhar (24.6 • N, 72.8 • E), in India. Therefore, gravity wave studies at various locations over different time durations have formed one of the important topics of investigation (e.g., Fritts and Alexander, 2003).…”

“…NIRIS provides O 2 (0-1) atmospheric and OH(6-2) Meinel band nightglow emission spectra with a spectral resolution of 0.78 nm in a large field of view of around 80 • with a data cadence of 5 min. The details of the NIRIS and the methodology used to obtain nocturnal intensities and of deriving mesospheric temperatures using rotational line ratios of O 2 and OH band emissions can be found elsewhere (Pallamraju et al, 2014;Singh and Pallamraju, 2015). The O 2 and OH emission intensities are determined by integrating the nightglow brightness over 1.2 nm centered at each emission wavelength and are given in arbitrary units.…”

The responses of the nightglow emissions observed by the TIMED/SABER satellite to solar radiation

“…The influence of diurnal tides on the airglows is the strongest in the tropical region [Zhang et al, 2001]. In addition, the planetary wave coupling with the tides can cause the temperature to change with latitude [Singh and Pallamraju, 2015]. This can cause the airglow emission to change with latitude.…”

Effect of cyclone Nilofar on mesospheric wave dynamics as inferred from optical nightglow observations from Mount Abu, India

“…An in‐house built near‐infrared imaging spectrograph (NIRIS) has been used to carry out measurements of O 2 (0–1) and OH(6–2) band nightglow emission intensities which emanate at altitudes of 94 and 87 km, respectively. The details of NIRIS have been reported earlier [ Pallamraju et al , ], and the methodology adopted to derive mesospheric temperatures using rotational line intensity ratios of these band emissions from this instrument has been detailed in Singh and Pallamraju []. The accuracy of temperatures derived by NIRIS is ±3 K with a cadence of 5 min.…”