Tropical mesopause: Is it always close to 100 km?

Abstract

[1] Global distribution of mesopause using observations of Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) aboard the Thermosphere-IonosphereMesosphere Energetics and Dynamics satellite is studied with special emphasis on tropical latitudes. Temperature structure of the mesosphere and lower thermosphere over Gadanki (13.5°N, 79.2°E), a tropical latitude location in India, has been studied in detail. The mesopause altitude at Gadanki is observed to be in the range of 87-105 km with a mean of ∼98 km, and the temperature is in the range of 160-205 K with a mean of ∼170 K. A secondary temperature minimum is observed in the height region of 75-80 km with temperature in the range of 175-195 K. Although the mesopause temperature and altitude show pronounced short-term variability, on a seasonal mean basis, the variation in these two parameters is rather small. There is no significant long-term variation in mesopause altitude. The height of the secondary minimum, however, is found to show semiannual variation with a maximum in solstices and a minimum in equinoxes. Thus, the variabilities in the height and temperature of the mesopause and the secondary minimum reported here are different from the two-level mesopause reported previously for middle and high latitudes. Another significant result that comes from the time series analysis of mesopause temperature is a decreasing trend with a rate of ∼0.72 ± 0.05 K/yr. Furthermore, the long-term mean profile of temperature does not show the secondary minimum, providing strong support that it could be due to shorter scale tides and gravity waves. The possible implications of the mesopause temperature structure on various physical processes occurring in the mesosphere and the lower thermosphere are discussed.

The occurrence altitudes of middle atmospheric temperature inversions and mesopause over low-latitude Indian sector

“…2b, d) the mesopause occurs at two distinct altitudes with one occurring at ∼ 75 km and another at ∼ 98 km, which is in agreement with the results obtained by von Zhan (1996) that there are two preferential altitudes for the mesopause occurrences. It is also noted that for the majority of time, the mesopause altitude is near to 95-98 km during night and 98-100 km during daytime with a mean value of total data (including day-night data) of ∼ 98 km which is consistent with the recent reports that mesopause occurs around the 100 km altitudes (Ratnam et al, 2010). It is of importance that the mesopause temperature distributions are different in 2002 and 2008, with the distribution of the latter showing the temperature shifting to lower values.…”

Modes of zonal mean temperature variability 20–100 km from the TIMED/SABER observations

“…The MTI is strong at equinox but rather weak in winter. The time series of PC (3) also exhibit a semiannual cycle, which agrees with ground-based observations at Gadanki (13.5 • N, 79.2 • E) by Venkat Ratnam et al (2010). In the subtropical mesosphere, mirror patterns weaken and elevate to higher latitudes.…”

Trends in the upper atmosphere and ionosphere: Recent progress

“…[22] In the mesopause region of low latitudes, the turnaround of ozone trends resulted in a change from no trend to a mild negative trend in temperature [e.g., Ratnam et al, 2010]. Temperature trends in the mesopause region in general changed from no trend to a negative trend [Beig, 2011].…”