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The atmospheric effects of precipitating electrons are not fully understood, and uncertainties are large for electrons with energies greater than ~30 keV. These electrons are underrepresented in modeling studies today, primarily because valid measurements of their precipitating spectral energy fluxes are lacking. This paper compares simulations from the Whole Atmosphere Community Climate Model (WACCM) that incorporated two different estimates of precipitating electron fluxes for electrons with energies greater than 30 keV. The estimates are both based on data from the Polar Orbiting Environmental Satellite Medium Energy Proton and Electron Detector (MEPED) instruments but differ in several significant ways. Most importantly, only one of the estimates includes both the 0° and 90° telescopes from the MEPED instrument. Comparisons are presented between the WACCM results and satellite observations poleward of 30°S during the austral winter of 2003, a period of significant energetic electron precipitation. Both of the model simulations forced with precipitating electrons with energies >30 keV match the observed descent of reactive odd nitrogen better than a baseline simulation that included auroral electrons, but no higher energy electrons. However, the simulation that included both telescopes shows substantially better agreement with observations, particularly at midlatitudes. The results indicate that including energies >30 keV and the full range of pitch angles to calculate precipitating electron fluxes is necessary for improving simulations of the atmospheric effects of energetic electron precipitation. Plain Language Summary: The study presented here investigates the effects from energetic electron precipitation (EEP) in the southern hemisphere winter of 2003. Electron precipitation is common during periods of enhanced geomagnetic activity and can create reactive nitrogen oxides and hydrogen oxides that can destroy ozone. Most global climate models currently do not include precipitating electrons with energies greater than 30 keV. To test whether this deficiency is important, this investigation compares observations with model simulations that included electrons with energies greater than 30 keV, as observed by the Medium Energy Proton and Electron Detector (MEPED) satellite instruments. In addition, one of the EEP data sets used in the simulations included data from just one of the telescopes on the MEPED instruments, whereas the other included data from both of the telescopes. We found that including both of the telescopes is important for capturing chemistry changes at polar and subpolar latitudes. The model simulation that only included only one of the telescopes showed significant improvement compared to a simulation with only low energy electrons. However, it did not perform as well as the model simulation that included both MEPED telescopes. This work is important because it shows that including energies >30 keV and the full range of precipitating electron pitch angles is necessary to show the impact electrons have on the atmosphere and provides an EEP data set for use in future model simulations. Key Points: Effects of energetic electron precipitation in southern hemisphere 2003 simulated with Whole Atmosphere Community Climate ModelSimulations of middle atmosphere chemistry improve significantly by including >30‐keV precipitating electronsIncluding the full range of pitch angles is necessary to capture precipitating electron impacts at subpolar latitudes [ABSTRACT FROM AUTHOR]

We have investigated the coupling between the stratosphere and mesosphere-lower thermosphere (MLT) in the Southern Hemisphere (SH) during 2010 minor sudden stratospheric warmings (SSWs). Three episodic SSWs were noticed in 2010. Mesospheric zonal winds between 82 and 92 km obtained from King Sejong Station (62.22°S, 58.78°W) meteor radar showed the significant difference from usual trend. The zonal wind reversal in the mesosphere is noticed a week before the associated SSW similar to 2002 major SSW. The mesosphere wind reversal is also noticed in 'Specified Dynamics' version of Whole Atmosphere Community Climate Model (SD-WACCM) and Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) simulations. The similar zonal wind weakening/reversal in the lower thermosphere between 100 and 140 km is simulated by GAIA. Further, we observed the mesospheric cooling in consistency with SSWs using Microwave Limb Sounder data. However, the GAIA simulations showed warming between 130 and 140 km after few days of SSW. Thus, the observation and model simulation indicate for the first time that the 2010 minor SSW also affects dynamics of the MLT region over SH in a manner similar to 2002 major SSW. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A minor stratospheric sudden warming (SSW) event was noticed in the southern hemisphere (SH) during September (day 259) 2010 along with two episodic warmings in early August (day 212) and late October (day 300) 2010. Among the three warming events, the signature of mesosphere response was detected only for the September event in the mesospheric wind dataset from both meteor radar and MF radar located at King Sejong Station (62°S, 59°W) and Rothera (68°S, 68°W), Antarctica, respectively. The zonal winds in the mesosphere reversed approximately a week before the September SSW event, as has been observed in the 2002 major SSW. Signatures of mesospheric cooling (MC) in association with stratospheric warmings are found in temperatures measured by the Microwave Limb Sounder (MLS). Simulations of specified dynamics version of Whole Atmosphere Community Climate Model (SD-WACCM) are able to reproduce these observed features. The mesospheric wind field was found to differ significantly from that of normal years probably due to enhanced planetary wave (PW) activity before the SSW. From the wavelet analysis of wind data of both stations, we find that strong 14–16 day PWs prevailed prior to the SSW and disappeared suddenly after the SSW in the mesosphere. Our study provides evidence that minor SSWs in SH can result in significant effects on the mesospheric dynamics as in the northern hemisphere. [ABSTRACT FROM AUTHOR]

The seasonal and interannual variations of the gravity waves (GWs) in the Antarctic mesosphere were examined using horizontal wind data at altitudes of 50-100 km above the medium frequency (MF) radar at Syowa Station (69.0°S, 39.6°E). The climatology of the GW variance reached a maximum in winter over a wide altitude range of 64-90 km, and the interannual variability was large below 80 km in spring and autumn. These features are consistent with observations from previous studies. In addition, we detected a weak but significant maximum in the GW variance in summer from 70-78 km as well as large interannual variability. Moreover, we examined three possible mechanisms underlying the GW interannual variability observed in summer. The first mechanism was modulation by stratospheric sudden warmings in the Arctic through inter-hemispheric coupling, and it was not clearly observed at Syowa Station. The second mechanism was modulation of the vertical filtering of GWs in association with the breakdown of the polar vortex in the Southern Hemisphere, and it was identified as a potential mechanism. The third mechanism was tropical convection and propagation to the Antarctic region, and it was identified as another likely mechanism of interannual variability in the GWs. This result was supported by the consistency between years with strong tropical precipitation and years with large GW variances at Syowa Station. [ABSTRACT FROM AUTHOR]

Abstract: Daily UK Met Office stratospheric assimilated data for the Northern and Southern Hemispheres, accumulated for the period from 2004 to 2012 and pressure range of 1000–0.1hPa, are used in this paper. The paper presents and thoroughly discusses spatial–temporal distributions of stationary planetary wave (SPW) amplitudes and phases, calculated on the basis of geopotential height, temperature, zonal and meridional wind data for zonal wave numbers 1 and 2 (SPW1 and SPW2). The climatological planetary wave amplitudes and phases are calculated by extracting waves from three types of data: daily, monthly mean and climatological monthly mean. It has been established that magnitude of amplitudes and height-latitude distribution of amplitudes of SPW1 and SPW2 depend on data processing method for all parameters. It has also been established that height-latitude distribution amplitudes and phases significantly differ for geopotential height, temperature, zonal and meridional wind and depend on wave number and hemisphere. However, height-latitude distributions of phases are little different from each other for the used methods of data processing. [Copyright &y& Elsevier]

The relationship between polar mesosphere summer echoes (PMSE) and geomagnetic disturbances (represented by magnetic K indices) is examined. Calibrated PMSE reflectivities for the period May 2006-February 2012 are used from two 52.0/54.5MHz radars located in Arctic Sweden (68° N, geomagnetic latitude 65°) and at two different sites in Queen Maud Land, Antarctica (73°/72° S, geomagnetic latitudes 62°/63°). In both the Northern Hemisphere (NH) and the Southern Hemisphere (SH) there is a strong increase in mean PMSE reflectivity between quiet and disturbed geomagnetic conditions. Mean volume reflectivities are slightly lower at the SH locations compared to the NH, but the position of the peak in the lognormal distribution of PMSE reflectivities is close to the same at both NH and SH locations, and varies only slightly with magnetic disturbance level. Differences between the sites, and between geomagnetic disturbance levels, are primarily due to differences in the high-reflectivity tail of the distribution. PMSE occurrence rates are essentially the same at both NH and SH locations during most of the PMSE season when a sufficiently low detection threshold is used so that the peak in the lognormal distribution is included. When the local-time dependence of the PMSE response to geomagnetic disturbance level is considered, the response in the NH is found to be immediate at most local times, but delayed by several hours in the afternoon sector and absent in the early evening. At the SH sites, at lower magnetic latitude, there is a delayed response (by several hours) at almost all local times. At the NH (auroral zone) site, the dependence on magnetic disturbance is highest during evening-to-morning hours. At the SH (sub-auroral) sites the response to magnetic disturbance is weaker but persists throughout the day. While the immediate response to magnetic activity can be qualitatively explained by changes in electron density resulting from energetic particle precipitation, the delayed response can largely be explained by changes in nitric oxide concentrations. Observations of nitric oxide concentration at PMSE heights by the Odin satellite support this hypothesis. Sensitivity to geomagnetic disturbances, including nitric oxide produced during these disturbances, can explain previously reported differences between sites in the auroral zone and those at higher or lower magnetic latitudes. The several-day lifetime of nitric oxide can also explain earlier reported discrepancies between high correlations for average conditions (year-by-year PMSE reflectivities and K indices) and low correlations for minute-to-day timescales. [ABSTRACT FROM AUTHOR]

Abstract: Using data from a meteor radar at Cachoeira Paulista (22.7°S; 45.0°W), the atmospheric lunar semidiurnal tide in the mesosphere and lower thermosphere was studied from January 2000 to October 2008. Monthly tidal amplitudes and phases were estimated using hourly mean winds in seven layers of 4km thickness each. Several amplitude and phase profiles of the lunar semidiurnal tide over Cachoeira Paulista showed characteristics of vertically propagating waves. The mean amplitudes over all heights were greater in the northward wind in January, February, May, June, July, August, November and December, but taken into account the error bars this behavior can be different in certain months. The mean phases presented characteristics appropriate to the Southern Hemisphere throughout the year, except in July. In some aspects, the results presented similarities with the atmospheric lunar semidiurnal tidal model. [Copyright &y& Elsevier]

Abstract: Polar Mesospheric Cloud (PMC) observations from the Aeronomy of Ice in the Mesosphere (AIM) Cloud Imaging and Particle Size (CIPS) experiment are compared to results from the Solar Backscatter UltraViolet (SBUV/2) instrument for two PMC seasons in each hemisphere, from 2007–2009. For these comparisons, a CIPS cloud retrieval algorithm based on a technique similar to that used in the operational SBUV PMC retrievals was developed. CIPS nadir data analyzed this way agree with SBUV data to better than 1% (2%) for PMC occurrence frequency (albedo). Non-nadir, forward scattering CIPS data are also analyzed with the SBUV-type algorithm, enabling an indirect verification of the CIPS operational retrievals. CIPS operational PMC frequencies agree with these CIPS–SBUV-type retrievals to within 0.6% at 80–85° latitude, and are lower by 9.8% at 70–75° latitude. Overall, the comparisons show that the v3.20 CIPS operational cloud retrievals are valid for scientific research. [Copyright &y& Elsevier]

Abstract: Variations in the Southern Hemisphere (SH) winter of 2007, 2008 and 2009 had important consequences on polar mesospheric clouds (PMCs) observed in the corresponding Northern summers. Specifically, the stratospheric SH winter of 2007 was observed to be warmer than in 2008 and 2009. Using the high altitude analysis from the Navy Operational Global Atmospheric Prediction System-Advanced Level Physics High Altitude (NOGAPS-ALPHA) forecast/assimilation system we show that this warmth was linked to similar temperature increases in the high latitude summer mesosphere. These temperature changes led to a dramatic reduction in PMC occurrence (factor of 5–6) recorded by the SHIMMER instrument at sub-arctic latitudes and a factor of 2 decrease in total ice water content in PMCs seen by the SOFIE instrument on the NASA AIM satellite. Microphysical modeling confirms the overall effect of these temperature changes on PMCs at high latitudes; however, a detailed comparison of the cloud occurrence with the SHIMMER data for all three years shows that the clouds are associated with a surprisingly wide range (130–165K) of temperatures. [Copyright &y& Elsevier]

Abstract: An inter-hemispheric asymmetry is found in the characteristics of polar mesosphere summer echoes (PMSE) and upper mesosphere temperatures at conjugate latitudes (∼69°) above Antarctica and the Arctic. The second complete mesosphere–stratosphere–troposphere (MST) radar summer observation season at Davis (68.6°S) revealed that PMSE occur less frequently, with lower strength and on average 1km higher compared with their northern counterparts at Andenes (69.3°N). We consider the thermodynamic state of the mesosphere for conjoining hemispheric summers based on satellite and ground-based radar measurements, and show the mesopause region near ∼80–87km of the Southern Hemisphere (SH) to be up to 7.5K warmer than its Northern Hemisphere (NH) counterpart. We show that this is consistent with our observation of asymmetries in the characteristics of PMSE and demonstrate how the mesosphere meridional wind field influences the existence and strength of the echoes in both hemispheres. [Copyright &y& Elsevier]

The evolution of the tropopause in the past, present, and future climate is examined by analyzing a set of long-term integrations with stratosphere-resolving chemistry climate models (CCMs). These CCMs have high vertical resolution near the tropopause, a model top located in the mesosphere or above, and, most important, fully interactive stratospheric chemistry. Using such CCM integrations, it is found that the tropopause pressure (height) will continue to decrease (increase) in the future, but with a trend weaker than that in the recent past. The reduction in the future tropopause trend is shown to be directly associated with stratospheric ozone recovery. A significant ozone recovery occurs in the Southern Hemisphere lower stratosphere of the CCMs, and this leads to a relative warming there that reduces the tropopause trend in the twenty-first century. The future tropopause trends predicted by the CCMs are considerably smaller than those predicted by the Intergovernmental Panel on Climate Change Fourth Assessment Report (AR4) models, especially in the southern high latitudes. This difference persists even when the CCMs are compared with the subset of the AR4 model integrations for which stratospheric ozone recovery was prescribed. These results suggest that a realistic representation of the stratospheric processes might be important for a reliable estimate of tropopause trends. The implications of these finding for the Southern Hemisphere climate change are also discussed. [ABSTRACT FROM AUTHOR]

Abstract: Polar Mesosphere Summer Echoes (PMSE) were detected above the high-latitude station Davis, Antarctica (68.6°S) using a 55MHz atmospheric radar during the 2003–2004 austral summer. In this paper, we examine the characteristics of southern hemisphere PMSE events observed during the interval 19 November to 16 February 2004. Coincident satellite-SABER temperature measurements and ground-VHF radar backscatter observations revealed that PMSE existed for mesosphere temperatures in the range ∼124.4–134.7K. An examination of the horizontal wind field using collocated VHF and MF radar measurements showed that PMSE also occurred during conditions of westward zonal winds and equatorward meridional winds. A remarkable correlation was evident between the onset (end) of the austral summer PMSE season and equatorward (poleward) flowing meridional mesospheric winds observed for the 19 November 2003 (16 February 2004), respectively. We present evidence of a semidiurnal influence of the meridional and zonal tides on the occurrence, intensity, and altitude of PMSE events. The effects of tidal, gravity and planetary waves on PMSE events are also considered. [Copyright &y& Elsevier]

Whole Atmosphere Community Climate Model simulations are used to investigate the short‐term (<30‐day) temporal variability in the midlatitude and high‐latitude Southern Hemisphere mesosphere. We focus primarily on the short‐term variability in zonal mean gravity wave drag and its influence on the mesosphere circulation and chemistry. The seasonal climatology from 36 years (1979–2014) of specified dynamics Whole Atmosphere Community Climate Model simulations reveals that the short‐term variability of zonal mean gravity wave drag, which is quantified by the standard deviation over a 30‐day window, in the Southern Hemisphere midlatitude mesosphere maximizes during December to March and September to November. The December to March enhancement is related to interhemispheric coupling during Northern Hemisphere sudden stratospheric warming events, and the enhancement during September to November is attributed to variability in the stratosphere and lower mesosphere zonal mean zonal winds that is driven by planetary wave activity in the Southern Hemisphere. Analysis of the simulations demonstrates that the short‐term variability in mesospheric gravity wave drag leads to changes in the residual circulation, which subsequently introduces short‐term variability in atomic oxygen (O) and nitrogen oxides (NOx). Comparison with the Northern Hemisphere reveals that the zonal mean short‐term variability in the Southern Hemisphere during September to November is nearly as large (∼80–85%) as the maximum short‐term variability in the Northern Hemisphere, which occurs during December to March. This demonstrates that although the Southern Hemisphere middle atmosphere is generally considered to be less disturbed than the Northern Hemisphere, there is still substantial short‐term variability in the Southern Hemisphere mesosphere. Key Points: Short‐term (<30‐day) zonal mean gravity wave drag variability in the SH mesosphere is investigatedShort‐term variability in SH is largest during austral winter‐spring and is nearly as large as in the NH during boreal winterGravity wave drag variability leads to short‐term variability in mesosphere circulation and chemistry [ABSTRACT FROM AUTHOR]

The article reports on the new findings of Earth's highest clouds with the use of a satellite called Aeronomy of Ice in the Mesosphere (AIM). It provides information on the noctilucent clouds and reveals that clouds are 10 times brighter and form at a broader range of altitudes. According to James Russell, this all yields critical information to examine why clouds form and vary. Its first AIM data came from the noctilucent clouds over the Arctic and is gathering data on clouds in the Southern Hemisphere.