ACP - The semi-annual oscillation (SAO) in the upper troposphere

Abstract. Both the scientific and operational communities are increasingly interested in subseasonal to seasonal variations of weather and climate. The semi-annual oscillation (SAO) has been studied extensively at the surface as well as in the middle atmosphere (upper stratosphere and the lower mesosphere). However, the SAO in the upper troposphere and lower stratosphere (UTLS) has been less discussed. Here we find evident SAO of temperature in the UTLS (250–175 hPa) from the subtropics to middle latitudes (22.5–42.5∘) using high-quality satellite measurements, reanalysis data, and model simulations. We show the mechanism of its formation by an energy budget analysis. The temperature in the Northern Hemisphere (NH) UTLS shows the first peak in February according to the dynamical heating and shows the second peak in July due to the dynamical heating and moist processes. Similar to the NH, the austral winter time maximum temperature in the Southern Hemisphere (SH) is related to dynamical heating and the austral summer time maximum is related to both moisture and dynamical heating in the UTLS. Model simulations indicate that the SAO in the UTLS is partly affected by the existence of an SAO in sea surface temperatures (SSTs) in the SH mid-latitudes and weakly affected by the SAO in SSTs in the NH mid-latitudes.

Semiannual Oscillation - an overview

ACP - Representation of the equatorial stratopause semiannual oscillation in global atmospheric reanalyses

PDF) The semiannual oscillation (SAO) in the tropical middle atmosphere and its gravity wave driving in reanalyses and satellite observations

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ACP - Aeolus wind lidar observations of the 2019/2020 quasi-biennial oscillation disruption with comparison to radiosondes and reanalysis

ACP - Does the coupling of the semiannual oscillation with the quasi-biennial oscillation provide predictability of Antarctic sudden stratospheric warmings?

PDF) The semi-annual oscillation (SAO) in the upper troposphere and lower stratosphere (UTLS)

PDF) Aura/MLS observes and SD-WACCM-X simulates the seasonality, quasi-biennial oscillation and El Niño–Southern Oscillation of the migrating diurnal tide driving upper mesospheric CO primarily through vertical advection

ACP - Representation of the equatorial stratopause semiannual oscillation in global atmospheric reanalyses