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The Andes account for the largest source of orographic gravity waves (GWs) in the middle atmosphere. This results from persistent, strong zonal winds at the surface encountering the north‐south mountain chain, producing strong orographic lift, and resulting GWs. Here, we consider GWs in the stratosphere and mesosphere above the Andes as observed by the Cloud Imaging and Particle Size instrument, the Solar Occultation for Ice Experiment on the AIM satellite, and the Sounding of the Atmosphere using Broadband Emission Radiometry instrument onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. GW variability is considered in the context of the location of the stratospheric wintertime westerly jet and planetary wave (PW) amplitude and phase. The occurrence of GWs in the middle and upper atmosphere depends not only on tropospheric sources, like the Andes, but also on the background winds through which they propagate. Results suggest that the propagation of GWs into the mesosphere is well correlated with winds throughout the middle and upper stratosphere. PWs cause the westerly jet to move over the Andes, resulting in an increase in GW amplitude throughout the middle and upper stratosphere. The evolution and variability of GWs are tied closely to the phase of the PW‐1 and are linked to PW‐2 when the PW amplitudes are sufficiently large. GW amplitude, as observed by all three data sets, increases in the upper stratosphere and lower mesosphere when the trough of the PW‐1 in the stratosphere is over the Andes. Plain Language Summary: In the Southern Hemisphere, strong wintertime winds continuously flow west to east at mid‐latitudes (40°–50°S). As these winds flow over surface features like the Andes Mountains, the air is forced upwards, creating waves in the atmosphere that propagate both horizontally and vertically. These gravity waves (GWs) transport energy from the surface to the upper atmosphere, where they break and deposit their momentum, causing either turbulent mixing, an acceleration of the winds, or the generation of additional waves. The energy deposited from GWs has a significant impact on the circulation in the upper atmosphere, so it is important to understand where they break and to characterize sources of variability. As GWs propagate vertically, they encounter horizontal wind shear associated with a band of strong winds in the middle atmosphere, causing them to turn toward the area of strong winds. The latitude where these strong winds occur can change significantly, driven by planetary‐scale waves. This work shows that the occurrence of GWs in the middle atmosphere, observed by several NASA instruments, strongly depends on the amplitude and orientation of the planetary scale waves and the resulting location of the middle atmospheric winds. Key Points: Gravity waves (GWs) at the stratopause show significant variability over the Andes associated with stratospheric winds and planetary wave (PW) phaseEnhanced GW activity follows the trough of the PW‐1 and strong stratospheric winds at mid‐southern latitudesGW activity is enhanced over the Andes when the PW trough and the polar night jet are over the Andes [ABSTRACT FROM AUTHOR]

Satellite data records of stratospheric water vapour have been compared to balloon-borne frost point hygrometer (FP) profiles that are coincident in space and time. The satellite data records of 15 different instruments cover water vapour data available from January 2000 through December 2016. The hygrometer data are from 27 stations all over the world in the same period. For the comparison, real or constructed averaging kernels have been applied to the hygrometer profiles to adjust them to the measurement characteristics of the satellite instruments. For bias evaluation, we have compared satellite profiles averaged over the available temporal coverage to the means of coincident FP profiles for individual stations. For drift determinations, we analysed time series of relative differences between spatiotemporally coincident satellite and hygrometer profiles at individual stations. In a synopsis we have also calculated the mean biases and drifts (and their respective uncertainties) for each satellite record over all applicable hygrometer stations in three altitude ranges (10–30 hPa, 30–100 hPa, and 100 hPa to tropopause). Most of the satellite data have biases <10 % and average drifts <1 % yr -1 in at least one of the respective altitude ranges. Virtually all biases are significant in the sense that their uncertainty range in terms of twice the standard error of the mean does not include zero. Statistically significant drifts (95 % confidence) are detected for 35 % of the ≈ 1200 time series of relative differences between satellites and hygrometers. [ABSTRACT FROM AUTHOR]

The Halogen Occultation Experiment (HALOE) conducted satellite solar occultation measurements for 14 years ending on 21 November 2005. HALOE contained a calibration wheel, which included three neutral density filters that were used to examine response linearity through a combination of ground and on-orbit measurements. Although measurement uncertainties preclude a confident assessment of the true extent of nonlinearity, the on-orbit data lead to the conclusion that any existing response nonlinearity has changed by less than 2% over the mission lifetime. This conclusion eliminates a potentially significant uncertainty when using HALOE data for studies of long-term atmospheric trends. OCIS codes: 040.0040, 040.3060, 010.0280.

We use the Specified Dynamics version of the Whole Atmosphere Community Climate Model Extended (SD-WACCMX) to model the descent of nitric oxide (NO) and other mesospheric tracers in the extended, elevated stratopause phase of the 2013 Sudden Stratospheric Warming (SSW). The dynamics are specified with a high altitude version of the Navy Global Environmental model (NAVGEM-HA). Consistent with our earlier published results, we find that using a high altitude meteorological analysis to nudge WACCMX allows for a realistic simulation of the descent of lower thermospheric nitric oxide down to the lower mesosphere, near 60 km. This is important because these simulations only included auroral electrons, and did not consider additional sources of NO from higher energy particles, for example, medium energy electron precipitation (> 30 keV). This suggests that the so-called energetic particle precipitation indirect effect (EPP-IE) can be accurately simulated, at least in years of low geomagnetic activity, such as 2013, without the need for additional NO production, provided the meteorology is accurately constrained. Despite the general success of WACCMX in simulating mesospheric NO, a detailed comparison of the WACCMX fields with the analyzed NAVGEM-HA H2O and satellite NO and H2O data from the Solar Occultation for Ice Experiment (SOFIE) and the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) reveals significant differences in the latitudinal and longitudinal distributions in the 45-55 km region. This stems from the tendency for WACCMX descent to maximize at sub-polar latitudes and while such sub-polar descent is seen in the NAVGEM-HA analysis, it is more transient than in the WACCMX simulation. These differences are linked to differences in the Transformed Eulerian Mean (TEM) circulation between NAVGEM-HA and WACCMX, most likely arising from small differences in how gravity wave forcing is represented. To attempt to compensate for the differing distributions of model vs. observed NO and to enable us to quantify the total amount of upper atmospheric NO delivered to the stratopause region, we use potential vorticity and equivalent latitude coordinates. Preliminary results suggest both model and observations are generally consistent with NO totals in the range of 0.1-0.25 gigamoles (GM). [ABSTRACT FROM AUTHOR]