SOLA Vol. 13A(2017) No. Special_Edition
: International Symposium on the Whole Atmosphere (ISWA)

Research on the effects of energetic particle precipitation (EPP) on earth's atmosphere is rapidly growing. However, these effects have not been well distinguished from those of other climate forcings. This study extracts EPP effects on the middle atmosphere in the southern hemisphere from the latest reanalysis datasets using multiple regression analysis and composite analysis. Statistically significant temperature anomalies in the winter polar upper stratosphere and lower mesosphere are found, but a simple dynamical signature explaining the anomalies is not evident. On the other hand, it is found that a negative temperature anomaly extending from the polar lower mesosphere to the midlatitude upper stratosphere in July is driven by anomalous Eliassen-Palm flux divergence in the midlatitude lower mesosphere. This result suggests that EPP effects are distinguishable from other climate forcings in the latest reanalysis data.

Abrupt breakdowns of the polar winter stratospheric circulation such as sudden stratospheric warmings (SSWs) are a manifestation of strong two-way interactions between upward propagating planetary waves and the mean flow. The importance of sufficient upward wave activity fluxes from the troposphere and the preceding state of the stratospheric circulation in forcing SSW-like events have long been recognized. Past research based on idealized numerical simulations has suggested that the state of the stratosphere may be more important in generating extreme stratospheric events than anomalous upward wave fluxes from the troposphere. Other studies have emphasized the role of tropospheric precursor events. Here reanalysis data are used to define events of extreme stratospheric mean flow deceleration (SSWs being a subset) and events of extreme lower tropospheric upward planetary wave activity flux. While the wave fluxes leading to SSW-like events ultimately originate near the surface, the anomalous upward wave activity fluxes associated with these events primarily occur within the stratosphere. The crucial dynamics for forcing SSW-like events appear to take place in the communication layer just above the tropopause. Anomalous upward wave fluxes from the lower troposphere may play a role for some events, but seem less important for the majority of them.

The Superconducting Submillimeter-Wave Limb-Emission Sounder 2 (SMILES-2) is a satellite mission that will be proposed to the Japan Aerospace Exploration Agency (JAXA) for a launch after 2023. It will scan the atmospheric limb from the lower stratosphere to the lower thermosphere for retrieving the profiles of temperature between 15 and 160 km, horizontal wind vector (30-160 km), ground state atomic oxygen (90-160 km), and dynamical tracers and ozone-chemistry related species (15-110 km). SMILES-2 is designed to fit the JAXA small satellite and will be equipped with two antennas, three GHz-channel receivers, and one THz receiver. Each receiver has a superconducting device on the front end cooled by a mechanical cryocooler, which is an established technology. Highly sensitive limb observation owing to the superconducting technology has great advantages of satisfactorily measuring all the altitude profiles in a short time of less than 1 min, and of retrieving the main products with sufficient precision on a single profile. Hence, a wind vector profile can be obtained with a precision better than 10 m s⁻¹ with a vertical resolution of 3 km below 100 km and 5 km above 100 km.

We investigated characteristics of mesosphere echoes over Syowa Station (69S) in the Antarctic, which were detected by the Program of the Antarctic Syowa Mesosphere, Stratosphere and Troposphere/Incoherent Scatter (PANSY) radar (47 MHz) and Medium Frequency (MF) radar (2.4 MHz). Winter echoes from the PANSY radar and low altitude MF echoes below approximately 70-75 km mostly coexisted, appearing during the daytime as well as for a few hours post sunset. Summer echoes in the lower height region were absent in both radar observations, suggesting a close relationship in the generation mechanisms of these two radar echoes. High correlation between local K-index and the occurrence of winter echoes suggested that electron density enhancement due to ionized particle precipitation was one of the triggers of echo generation. Angles of arrival of the MF echoes were more isotropic in winter. Because gravity wave activity is much higher in winter over Syowa, higher turbulence energy caused by gravity wave breaking may also be responsible for the generation of the winter echoes and their isotropic behavior. The horizontal wind velocities of the two systems were further compared and agreed well throughout the height region of 60-90 km.

High resolution Whole Atmosphere Community Climate Model (WACCM) simulations are used to study how gravity waves vary during a stratospheric sudden warming (SSW) event from the source region to the lower thermosphere. The variation of zonal mean momentum flux of resolved gravity waves (with zonal wavelengths less than 1600 km) during SSW are qualitatively consistent with those obtained from parameterized studies, mainly caused by the change of filtering by the mean zonal wind. At high latitude in the winter hemisphere, stratospheric and mesospheric momentum fluxes vary rapidly during SSW, and their magnitudes decrease significantly following SSW, agreeing with satellite observations. Gravity waves are also found to vary as wave sources change. At tropical regions (especially in the summer hemisphere), convectively generated gravity waves increase due to enhanced deep convection following SSW. At higher latitudes, orographic waves vary during SSW as the wind changes extend from the stratosphere down into the troposphere. Gravity waves generated from adjustment of the polar jet also undergo significant changes during SSW. These changes lead to strong longitudinal variation of gravity waves.