Investigations of the middle atmospheric thermal structure and oscillations over sub-tropical regions in the Northern and Southern Hemispheres

International audienceThe temperature retrieved from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) onboard Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite during January 2002 to September 2015 are used in this study to delineate the differences of middle atmospheric thermal structure in the Northern Hemisphere (NH) and Southern Hemisphere (SH). Two stations namely Mt. Abu (24.59°N, 72.70°E) in NH and Reunion Island (21.11°S, 55.53°E) in SH are chosen over sub-tropical regions. Temperature climatology from SABER observations suggests that stratopause is warmer, and upper mesosphere is cooler in NH as compared to SH. Three atmospheric models are used to understand the monthly thermal structure differences for different altitudes. Moreover, semi-annual, annual and quasi-biennial oscillations are studied using Lomb Scargle Periodogram and Wavelet transform techniques. Over NH, summer and winter season are warmer (~4 K) and cooler (~3 K) respectively in stratosphere as compared to SH. It is important to note here that Mt. Abu temperature is warmer (~9 K) than Reunion Island in winter but in summer season Mt. Abu temperature is cooler in upper mesosphere and above mesosphere NH shows warming. Results show that annual oscillations are dominated in both hemisphere as compared to semi-annual and quasi-biennial oscillations. In upper mesosphere, strength of annual oscillations is substantial in NH, while semi-annual oscillations are stronger in SH. Wavelet analyses found that annual oscillations are significant in NH near mesopause, while semi-annual oscillations are strengthening in SH

Evaluation of Inter-Hemispheric Characteristics of the Tropopause–Stratopause–Mesopause Over Sub-Tropical Regions

International audienceThe transition regions in thermal structure viz. Tropopause, stratopause and mesopause play a vital role in the vertical coupling of the Earth’s atmosphere. For the first time, interhemispheric characteristics of the transition regions over two subtropical regions are studied using temperature observations from the SABER onboard TIMED satellite and the ERA Interim reanalysis during year 2002 to 2015. Results show that tropopause height is higher over Reunion Island (21.11S, 55.53E) in the Southern Hemisphere (SH) as compared to Mt. Abu region (24.59°N, 72.70°E) in the Northern Hemisphere (NH). Temporal variation of tropopause temperature reveals a decreasing (* 4 K) trend from year 2002 to 2008 and beyond this, an increasing (* 1.5 K) trend is found in tropopause temperature. These features are reinforcing for Mesopause as compared to tropopause temperature. The SH shows stronger variations in Mesopause temperature (* 7 K) compared to NH during year 2002 to 2008.The occurrence frequency of mesopause and stratopause height shows that the maximum occurrence frequency (* 60%) of mesopause at * 100 km in NH, while frequency is found to be * 55% in the SH. Results show that stratopause (mesopause) is cooler (warmer) in NH as compared SH. Moreover, Lomb Scargle Periodogram and wavelet transform techniques are used to investigate the periodicity of mesopause, stratopause and tropopause temperatures and heights. Investigations revealed prominent annual oscillations in the tropopause and stratopause temperatures in both hemispheres. These findings will be of immense use for the vertical and inter-hemispheric atmospheric coupling studies

Analysis of the middle atmospheric ozone using SABER observations: a study over mid-latitudes in the northern and southern hemispheres

International audienceThe present study focuses on the middle atmospheric ozone variability using 14 (2002–2015) years of Sounding of the Atmosphere using Broadband Emission Radiometry onboard Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite observations over the mid-latitude regions of northern and southern hemispheres. It is noted that ozone buildup starts late winter, and peaks during the springtime and gradually decreases in summer to autumn transitional period in both the hemispheres. The time series of ozone indicates the dominant annual and semi-annual oscillations in the middle atmosphere. The annual oscillation (AO) is found to be dominant over both the hemispheres, while the semi-annual oscillation (SAO) peaks at two different altitude regions: 30–60 km and 80–100 km. Further, the amplitude of AO is much significant than SSAO and MSAO. It is also noted another significant oscillation that peaks at ~ 4 months in the altitude range 60–80 km. The strength of these oscillations at different sites is studied by comparing it with the zonal mean spectrum to assess the longitudinal asymmetry. It is found that the longitudinal asymmetry is more significant in the northern hemisphere than the southern hemisphere. This can be attributed to the differences in the land (elevated topographies in the northern hemisphere) and primarily ocean (in southern hemisphere) contrast that further contributes to the differences in the strength of the vertically propagating planetary-scale waves modulating the middle atmospheric ozone