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The sudden enhancement in the mesospheric neutral metal layers (Ns) has been studied in different latitudes for decades. Specifically, at 23°S, Sodium Ns layers have been analyzed since their first observation at the end of the seventies. Several studies have reported Sodium Ns during events of energetic particle precipitation (EPP) and the formation of auroral-type sporadic E (Esa) layers at high-latitude stations. The Esa layers are also observed in the Brazilian low-latitude sector during the EPP events due to the South American Magnetic Anomaly (SAMA). However, despite extensive studies on the SAMA region, no reports exist about the co-occurrence of the Ns layer and the Esa layer. Therefore, in the present work, for the first time, we observed on 26 April 2023 a peculiar Ns layer event synchronously occurring with the development of the Esa layer in the SAMA region. [ABSTRACT FROM AUTHOR]

The temperature trend in the mesosphere and lower thermosphere (MLT) region can be regarded as an indicator of climate change. Using temperature profiles measured by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument during 2002–2023 and binning them based on yaw cycle, we get continuous dataset with wide local time coverage at 50° S–80° N or 80° S–50° N. The seasonal change of temperature, caused by the forward drift of SABER yaw cycle, is removed by using the climatological temperature of MSIS2.0. The corrected temperature without any waves and is regarded as the mean temperature. At 50° S–50° N, the cooling trends of the mean temperature are significant in the MLT region and are in agreement with previous studies. The novel finding is that the cooling trends of ≥2 K/decade exhibit seasonal symmetric and reach peaks of ≥6 K/decade at highest latitudes around the summer solstice. Moreover, there are warming trends of 1–2.5 K/decade at pressure height range of 10-2–10-3 hPa, specifically at latitudes higher than 55° N in October and December and at latitudes higher than 55° S in April and August. The mesopause temperature (height) in the northern summer polar region is colder (lower) than that in the southern counterpart by ~5–11 K (~1 km) over the past 22 years. The trends of the mesopause temperature are dependent on latitudes and months. But they are negative at most latitudes and reach larger magnitudes at highest latitudes. These results indicate that the temperature in high latitude MLT region is more sensitive to dynamic changes. [ABSTRACT FROM AUTHOR]

The temperature trend in the mesosphere and lower thermosphere (MLT) region can be regarded as an indicator of climate change. Using temperature profiles measured by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument during 2002-2023 and binning them based on yaw cycle, we get continuous dataset with wide local time coverage at 50°S-80°N or 80°S-50°N. The seasonal change of temperature, caused by the forward drift of SABER yaw cycle, is removed by using the climatological temperature of MSIS2.0. The corrected temperature without any waves and is regarded as the mean temperature. At 50°S-50°N, the cooling trends of the mean temperature are significant in the MLT region and are in agreement with previous studies. The novel finding is that the cooling trends of ≥2 K/decade exhibit seasonal symmetric and reach peaks of ≥6 K/decade at highest latitudes around the summer solstice. Moreover, there are warming trends of 1-2.5 K/decade at pressure height range of 10-2-10-3 hPa, specifically at latitudes higher than 55°N in October and December and at latitudes higher than 55°S in April and August. The mesopause temperature (height) in the northern summer polar region is colder (lower) than that in the southern counterpart by ~5-11 K (~1 km) over the past 22 years. The trends of the mesopause temperature are dependent on latitudes and months. But they are negative at most latitudes and reach larger magnitudes at highest latitudes. These results indicate that the temperature in high latitude MLT region is more sensitive to dynamic changes. [ABSTRACT FROM AUTHOR]

Variations of global wind are important in changing the atmospheric structure and circulation, in the coupling of atmospheric layers, in influencing the wave propagations. Due to the difficulty of directly measuring zonal wind from the stratosphere to the lower thermosphere, we derived the global balance wind (BU) from 2002 to 2019 using the gradient wind approximation and SABER temperatures and modified by meteor radar observations at the equator. These capture the main feature of global monthly mean zonal wind and can be used to study the variations (i.e., annual, semiannual, terannual, and linear) of zonal wind and the responses of zonal wind to QBO (quasi-biennial oscillation), ENSO (El Niño/Southern Oscillation), and solar activity. Same procedure is performed on the MERRA2 zonal wind (MerU) to validate BU and its responses below 70 km. The annual, semiannual, terannual oscillations of BU and MerU have similar amplitudes and phases. The semi-annual oscillation of BU has peaks around 80 km, which are stronger in the southern tropical region and coincide with previous satellite observations. The responses to QBO shift from positive to negative and extend from the equator to higher latitudes with the increasing height. The responses to ENSO and F10.7 are strongest (positive and negatively, respectively) in the southern stratospheric polar jet region below 70 km and exhibit hemispheric asymmetry. While above 70 km, the responses of BU to F10.7 and ENSO are mainly positive. Both BU and MerU exhibit similar linear changes, but the negative linear changes of BU at 50°N are absent in MerU during October-January. The discussions on the possible influences of the temporal intervals and sudden stratospheric warmings (SSWs) on the variations and responses of BU illustrate that: (1) the seasonal variations and the responses to QBO are almost independent on the temporal intervals selected; (2) the responses to ENSO and F10.7 are robust but slightly dependent on the temporal intervals; (3) the linear changes of both BU and MerU depend strongly on the temporal intervals; (4) SSWs affect the magnitudes but do not affect the hemispheric asymmetry of the variations and responses of BU at least in the monthly mean sense. The variations and responses of global zonal wind to various factors are based on BU, which is derived from observations, and thus provide a good complementary to model studies and ground-based observations. [ABSTRACT FROM AUTHOR]

Zonal winds in the stratosphere and mesosphere play important roles in the atmospheric dynamics and aeronomy. However, the direct measurement of winds in this height range is difficult. We present a dataset of the monthly mean zonal wind in the height range of 18-100 km and at latitudes of 50°S-50°N from 2002 to 2019, which is derived by the gradient balance wind theory and the temperature and pressure observed by the SABER instrument. The tide alias above 80 km at the equator is replaced by the monthly mean zonal wind measured by a meteor radar at 0.2°S. The dataset (named as BU) is validated by comparing with the zonal wind from MERRA2 (MerU), UARP (UraU), HWM14 empirical model (HwmU), meteor radar (MetU) and lidar (LidU) at seven stations from 53.5°N to 29.7°S. At 18-70 km, BU and MerU have (1) nearly identical zero wind lines, (2) year-to-year variations of the eastward/westward wind jets at middle and high latitudes, (3) the quasi-biennial oscillation (QBO) and semi-annual oscillation (SAO), especially the anormal QBO in early 2016. The comparisons among BU, UraU and HwmU show good agreement in general below 80 km. Above 80 km, the agreements among BU, UraU, HwmU, MetU and LidU are good in general, except some discrepancies at limited heights and months. The BU data are archived as netCDF files and can be available at https://dx.doi.org/10.12176/01.99.00574 (Liu et al., 2021). [ABSTRACT FROM AUTHOR]