Stratospheric Gravity Waves Research Articles

Responses of polar mesospheric cloud brightness to stratospheric gravity waves at the South Pole and Rothera, Antarctica

We present the first observational proof that polar mesospheric cloud (PMC) brightness responds to stratospheric gravity waves (GWs) differently at different latitudes by analyzing the Fe Boltzmann lidar data collected from the South Pole and Rothera (67.5°S, 68.0°W), Antarctica. Stratospheric GW strength is characterized by the root-mean-square (RMS) relative density perturbation in the 30–45 km region and PMC brightness is represented by the total backscatter coefficient (TBC) in austral summer from November to February. The linear correlation coefficient (LCC) between GW strength and PMC brightness is found to be +0.09 with a 42% confidence level at the South Pole and −0.49 with a 98% confidence level at Rothera. If a PMC case potentially affected by a space shuttle exhaust plume is removed from the Rothera dataset, the negative correlation coefficient and confidence level increase to −0.61 and 99%, respectively. The Rothera negative correlation increases when shorter-period waves are included while no change is observed in the South Pole correlation. Therefore, observations show statistically that Rothera PMC brightness is negatively correlated with the stratospheric GW strength but no significant correlation exists at the South Pole. A positive correlation of +0.74 with a confidence level of 99.98% is found within a distinct subset of the South Pole data but the rest of the dataset exhibits a random distribution, possibly indicating different populations of ice particles at the South Pole. Our data show that these two locations have similar GW strength and spectrum in the 30–45 km region during summer. The different responses of PMC brightness to GW perturbations are likely caused by the latitudinal differences in background temperatures in the ice crystal growth region between the PMC altitude and the mesopause. At Rothera, where temperatures in this region are relatively warm and supersaturations are not as large, GW-induced temperature perturbations can drive subsaturation in the warm phase. Thus, GWs can destroy growing ice crystals or limit their growth, leading to negative correlation at Rothera. Because the South Pole temperatures in the mesopause region are much colder, GW-perturbed temperature may never be above the frost point and have less of an impact on crystal growth and PMC brightness. The observed phenomena and proposed mechanisms above need to be understood and verified through future modeling of GW effects on PMC microphysics and ray modeling of GW propagation over the South Pole and Rothera.

Estimation of Gravity Wave Momentum Flux and Phase Speeds from Quasi-Lagrangian Stratospheric Balloon Flights. Part II: Results from the Vorcore Campaign in Antarctica

The stratospheric gravity wave field in the Southern Hemisphere is investigated by analyzing observations collected by 27 long-duration balloons that flew between September 2005 and February 2006 over Antarctica and the Southern Ocean. The analysis is based on the methods introduced by Boccara et al. in a companion paper. Special attention is given to deriving information useful to gravity wave drag parameterizations employed in atmospheric general circulation models. The balloon dataset is used to map the geographic variability of gravity wave momentum fluxes in the lower stratosphere. This flux distribution is found to be very heterogeneous with the largest time-averaged value (28 mPa) observed above the Antarctic Peninsula. This value exceeds by a factor of ∼10 the overall mean momentum flux measured during the balloon campaign. Zonal momentum fluxes were predominantly westward, whereas meridional momentum fluxes were equally northward and southward. A local enhancement of southward flux is nevertheless observed above Adélie Land and is attributed to waves generated by katabatic winds, for which the signature is otherwise rather small in the balloon observations. When zonal averages are performed, oceanic momentum fluxes are found to be of similar magnitude to continental values (2.5–3 mPa), stressing the importance of nonorographic gravity waves over oceans. Last, gravity wave intermittency is investigated. Mountain waves appear to be significantly more sporadic than waves observed above the ocean.

Stratospheric Gravity Waves Generated by Multiscale Tropical Convection

Abstract The generation of gravity waves by multiscale cloud systems evolving in an initially motionless and thermodynamically uniform environment is explored using a two-dimensional cloud-system-resolving model. The simulated convection has similar depth and intensity to observed tropical oceanic systems. The convection self-organizes into preferred horizontal and temporal scales involving weakly organized propagating cloud clusters. The multiscale systems generate a broad spectrum of gravity waves with horizontal scales that range from the cloud-system scale up to the cloud-cluster scale. The gravity waves with the largest horizontal scale play an important role in modifying layered tropospheric inflow and outflow to the cloud systems, which in turn influence the multiscale convective organization. Slower-moving short-scale gravity waves make the strongest individual contribution to the vertical flux of horizontal momentum and cause a robust peak in the momentum flux spectrum that corresponds to the lifetime and spatial scale of the individual cloud systems.

A study of the relationship between stratospheric gravity waves and polar mesospheric clouds at Davis Antarctica

We used a Rayleigh lidar located at Davis station, East Antarctica, to compare Polar Mesospheric Cloud (PMC) and stratospheric gravity wave (GW) strengths in the austral summer 2005–2006. Earlier similar studies from Greenland noted that intervals of large stratospheric GW activity appeared to coincide with reduced PMC strengths. We measure the stratospheric GW strength in the 30–45 km altitude range, for waves of vertical wavelength between ∼2 and ∼10 km, and of periods greater than 1 h. We find little consistency with the Greenland studies, as the occurrence of PMC over Davis appear to have little relationship to observed stratospheric gravity wave activity. Hemispheric differences, in both PMC strength and occurrence and in gravity wave strength, may have a role in explaining our results. Our data suggest that a significant controller of occurrence of PMC over Davis is related to diurnal tidal movement. We also investigate the potential influence of sampling biases in our data set.

COSMIC GPS Observations of Northern Hemisphere winter stratospheric gravity waves and comparisons with an atmospheric general circulation model

COSMIC satellite temperature data are used to derive the 2006/07 winter mean stratospheric Northern Hemisphere potential energy Ep from gravity waves with vertical wavelengths less than 7 km in grid cells of size 10° × 5°; and to study longitudinal and latitudinal variability in cells of size 20° × 5° × 7 days. Large Ep at 17–23 km is mostly associated with the sub‐tropical jet and shows significant longitudinal variability. Some contribution to total Ep from local orographic sources may occur above the Canadian Rockies, Scandinavia and northern Japan, but not above the Himalayas, due to the background wind conditions. Many of the waves are likely to have low ground‐based phase speeds, as observed by filtering around the 0–10 m s−1 background zonal wind. COSMIC results are compared with a T106L60 AGCM, confirming sub‐tropical jet related generation, upward propagation and low phase speeds of the observed gravity waves.

Sensitivity of typhoon‐induced gravity waves to cumulus parameterizations

Sensitivity of typhoon‐induced gravity waves to cumulus parameterizations is examined using a mesoscale model (MM5). For this, Typhoon Rusa (2002) is simulated with four cumulus parameterizations (Kain‐Fritsch, Grell, Anthes‐Kuo, and Betts‐Miller schemes) and the characteristics of typhoon‐induced gravity waves are compared. The experiments show differences in rainband structure and vertical motion, resulting in different forcing spectra for zonal wavelength and period. As a result, induced stratospheric gravity waves are different in amplitude and spectral shape. However, the difference is not as large as that in the forcing spectrum, since a large portion of the waves generated by major forcing components is filtered out by the background wind, which is nearly the same in all the experiments. Instead, variation in zonal wavelength and period of forcing modifies the characteristics of stratospheric gravity waves by changing damping time scale in the nonfiltered region.

Stratospheric gravity wave simulation over Greenland during 24 January 2005

The “Advanced Regional Prediction System” forecast model is extended up to the stratopause and over the entire hemisphere to simulate gravity waves during 24 January 2005. With a 15‐km horizontal resolution, the simulation produces dominant gravity wave features near Eastern Greenland that are associated mainly with orographic forcing by the Greenland terrain. The simulated wave temperature perturbations compare favorably with radiance perturbations from NASA Atmospheric Infrared Sounder observations. In the upper stratosphere (40–50 km), vertical overturning of the isentropes suggests the occurrence of wave breaking just east of Greenland that leads to a tremendous reduction of wave amplitudes. The associated flux divergence produces horizontal flow deceleration of 12–120 m s−1 day−1 and coincides with areas of depleted stratospheric wind speed, suggesting strong interactions between orographic gravity waves and the polar vortex. A simulation using the coarser 50‐km horizontal resolution produces gravity waves of significantly weaker amplitudes.

Ondas de gravidade na estratosfera terrestre inferida através da técnica de rádio ocultação de GPS

Perfis de temperatura obtidos pelo satélite CHAMP nos anos de 2001 a 2005 foram utilizados para determinar a atividade de ondas de gravidade na região da baixa estratosfera sobre a América do Sul. Os resultados encontrados para a energia potencial integrada, entre 24 e 34 km de altitude, mostraram uma variação interanual na atividade de ondas de gravidade, com uma maior atividade de ondas em torno da região equatorial. Para melhor avaliar a variação da atividade de ondas de gravidade, foi determinada a energia potencial média integrada entre (10ºN-10ºS) e (100ºO- 20ºO). Os resultados da energia potencial média mostraram uma variação sazonal da atividade de ondas de gravidade. O inverno foi a estação do ano com a menor atividade de ondas, enquanto que a primavera apresentou um aumento na atividade de ondas. A atividade de ondas de gravidade na baixa estratosfera, inferida através da energia potencial média, apresenta claramente um aumento nos anos de 2002 e 2004 e uma diminuição nos anos de 2003 e 2005.

Seasonal variations of gravity waves revealed in rawinsonde data at Pohang, Korea

Seasonal variations of gravity wave characteristics are investigated using rawinsonde data observed at Pohang observatory, Korea (36°2′N, 129°23′E) during the one-year period of 1998. Analysis is carried out for two atmospheric layers representing the troposphere (2–9 km) and stratosphere (17–30 km). There exist clear seasonal variations in amplitudes of temperature and wind perturbations and wave energy in the stratosphere, with their maxima in wintertime and minima in summertime. A strong correlation is found between the wave activity and the strength of the jet stream, but there is no clear correlation between the wave activity and the vertical gradient of static stability. The intrinsic frequency and vertical and horizontal wavelengths of gravity waves in the stratosphere are 2f–3f, where f is the Coriolis parameter, and 2–3 km and 300–500 km, respectively. The intrinsic phase velocity directs westward in January and northeastward in July. The vertical flux of the stratospheric zonal momentum is mostly negative except in summertime with a maximum magnitude in January. Topography seems to be a major source of stratospheric gravity waves in wintertime. Convection can be a source of gravity waves in summertime, but it is required to know convective sources at nearby stations, due to their intermittency and locations relative to floating balloons.

Mountain Wave–Induced Polar Stratospheric Cloud Forecasts for Aircraft Science Flights during SOLVE/THESEO 2000

Abstract The results of a multimodel forecasting effort to predict mountain wave–induced polar stratospheric clouds (PSCs) for airborne science during the third Stratospheric Aerosol and Gas Experiment (SAGE III) Ozone Loss and Validation Experiment (SOLVE)/Third European Stratospheric Experiment on Ozone (THESEO 2000) Arctic ozone campaign are assessed. The focus is on forecasts for five flights of NASA's instrumented DC-8 research aircraft in which PSCs observed by onboard aerosol lidars were identified as wave related. Aircraft PSC measurements over northern Scandinavia on 25–27 January 2000 were accurately forecast by the mountain wave models several days in advance, permitting coordinated quasi-Lagrangian flights that measured their composition and structure in unprecedented detail. On 23 January 2000 mountain wave ice PSCs were forecast over eastern Greenland. Thick layers of wave-induced ice PSC were measured by DC-8 aerosol lidars in regions along the flight track where the forecasts predicted enhanced stratospheric mountain wave amplitudes. The data from these flights, which were planned using this forecast guidance, have substantially improved the overall understanding of PSC microphysics within mountain waves. Observations of PSCs south of the DC-8 flight track on 30 November 1999 are consistent with forecasts of mountain wave–induced ice clouds over southern Scandinavia, and are validated locally using radiosonde data. On the remaining two flights wavelike PSCs were reported in regions where no mountain wave PSCs were forecast. For 10 December 1999, it is shown that locally generated mountain waves could not have propagated into the stratosphere where the PSCs were observed, confirming conclusions of other recent studies. For the PSC observed on 14 January 2000 over northern Greenland, recent work indicates that nonorographic gravity waves radiated from the jet stream produced this PSC, confirming the original forecast of no mountain wave influence. This forecast is validated further by comparing with a nearby ER-2 flight segment to the south of the DC-8, which intercepted and measured local stratospheric mountain waves with properties similar to those predicted. In total, the original forecast guidance proves to be consistent with PSC data acquired from all five of these DC-8 flights. The work discussed herein highlights areas where improvements can be made in future wave PSC forecasting campaigns, such as use of anelastic rather than Boussinesq linearized gridpoint models and a need to forecast stratospheric gravity waves from sources other than mountains.

Measurement Noise and Stratospheric Gravity Wave Characteristics Obtained from GPS Occultation Data

Tsuda and Hocke (2002) reduce the amount of filtering applied to raw radio occultation data in order to increase the vertical resolution of GPS based temperature retrievals in the stratosphere. The authors discuss gravitywave characteristics obtained from these optimised retrievals, including characteristics of vertical wave number spectra for vertical wavelengths below 2 km, and the meridional distribution of potential energies for such short wavelengths. The filtering of raw data is required because real measurements contain noise. In this note, we discuss the role of measurement noise for gravity wave characteristics obtained from dry temperature retrievals of GPS based radio occultation soundings. We show that for realistic noise levels, temperature fluctuations can be safely interpreted as originating from small scale atmospheric waves in the altitude region below 30 km and for wavelengths greater than 2 km, with the detailed limits depending on noise and retrieval characteristics. An optimising procedure as the one applied by Tsuda and Hocke, however, may raise noise related effects to the level of atmospheric waves for short vertical wavelengths. We further show that conclusions for vertical wavelengths less than 2 km, if at all, can only be drawn after taking the actual noise characteristics of the observations and the details of the filter procedures applied in the retrieval into account.

Interstation correlation of high‐latitude lower‐stratosphere gravity wave activity: Evidence for planetary wave modulation of gravity waves over Antarctica

Four years of operational radiosonde balloon flights, from three Australian stations in eastern Antarctica (Casey, 66.3°S, 110.0°E; Davis, 68.6°S, 78.0°E; and Mawson, 67.6°S, 62.9°E) are analyzed to derive lower‐stratosphere (12–20 km altitude) gravity wave information from perturbations in wind and temperature. Gravity wave activity and seasonal behavior was found to be similar to that seen in earlier studies from Antarctica. Interstation comparisons of zonal wind and gravity wave activity showed very high correlations throughout the entire data set, between Mawson and Davis stations (∼600 km distant), with a lag near 0.5 days. The correlations between Casey and Davis (1400 km apart) were lower but still significant, with a lag near 1 day. There is no significant correlation between stratospheric gravity wave activity and surface winds. Our results suggest a pattern of winds and waves moving eastward over the stations with a speed near 15 m s−1. As this is comparable to planetary wave speeds, we interpret our results as being evidence for a significant planetary wave–induced modulation of the zonal wind and the gravity wave field, although we are unable to identify the mechanism by which this operates. Our work suggests that the high‐latitude lower‐stratosphere gravity wave fields are relatively uniform on spatial scales of 500–1000 km and on timescales of around 0.5–1 days.

Global and Seasonal Variations of Stratospheric Gravity Wave Activity Deduced from theCHAMP/GPS Satellite

Abstract Global analyses of gravity wave (GW) activity in the stratosphere are presented using radio occultation data from the Challenging Minisatellite Payload (CHAMP) satellite. Temperature profiles obtained from CHAMP/ GPS radio occultations are first compared with ground-based instruments. In general, good agreement is found between these different techniques. Monthly mean values of potential energy Ep, being a measure of GW activity, which is estimated with radiosonde observations, are compared with CHAMP/GPS data and it is found that radiosonde-observed Ep values are slightly higher than those estimated with radio occultations. Strong diurnal variation of GW activity has been found. From the global morphology of GW activity, large Ep values are noticed, besides at tropical latitudes, even at midlatitudes during winter, but not during equinoxes. This suggests that wave activity at stratospheric heights is not only modulated due to orography (mountain/lee waves) but mainly depends on seasonal variatio...

Gravity waves and mesospheric clouds in the summer middle atmosphere: A comparison of lidar measurements and ray modeling of gravity waves over Sondrestrom, Greenland

We conducted gravity wave ray‐tracing experiments within an atmospheric region centered near the ARCLITE lidar system at Sondrestrom, Greenland (67°N, 310°E), in efforts to understand lidar observations of both upper stratospheric gravity wave activity and mesospheric clouds during August 1996 and the summer of 2001. The ray model was used to trace gravity waves through realistic three‐dimensional daily‐varying background atmospheres in the region, based on forecasts and analyses in the troposphere and stratosphere and climatologies higher up. Reverse ray tracing based on upper stratospheric lidar observations at Sondrestrom was also used to try to objectively identify wave source regions in the troposphere. A source spectrum specified by reverse ray tracing experiments in early August 1996 (when atmospheric flow patterns produced enhanced transmission of waves into the upper stratosphere) yielded model results throughout the remainder of August 1996 that agreed best with the lidar observations. The model also simulated increased vertical group propagation of waves between 40 km and 80 km due to intensifying mean easterlies, which allowed many of the gravity waves observed at 40 km over Sondrestrom to propagate quasi‐vertically from 40–80 km and then interact with any mesospheric clouds at 80 km near Sondrestrom, supporting earlier experimentally‐inferred correlations between upper stratospheric gravity wave activity and mesospheric cloud backscatter from Sondrestrom lidar observations. A pilot experiment of real‐time runs with the model in 2001 using weather forecast data as a low‐level background produced less agreement with lidar observations. We believe this is due to limitations in our specified tropospheric source spectrum, the use of climatological winds and temperatures in the upper stratosphere and mesosphere, and missing lidar data from important time periods.

Concerning the upper stratospheric gravity wave and mesospheric cloud relationship over Sondrestrom, Greenland

Recent research has shown experimental evidence that upper stratospheric gravity waves observed over Sondrestrom, Greenland (67°N, 310°E) portray a relationship with overlaying mesospheric clouds. It is the purpose of this paper to update the data from these studies with additional observations and reinvestigate the recently proposed hypothesis that suggests an anti-correlation between upper stratospheric gravity wave activity and mesospheric cloud strength. Data collected with the molecular/aerosol lidar at the ARCtic LIdar TEchnology (ARCLITE) facility in Sondrestrom have provided a total of 37 mesospheric cloud and upper stratospheric gravity wave observations from 1995–2001 that lend additional support to this hypothesis. We find a −0.44 linear correlation between the upper stratospheric gravity wave activity and the observed mesospheric cloud brightness within the 95% confidence interval. Even after considering geophysical variability due to observational limits, the linear correlation between the two fields is still −0.35 and also within a 95% confidence interval. These results suggest that there is indeed a statistically significant negative correlation between the upper stratospheric gravity wave activity and the mesospheric clouds. We then present two case studies from July 2001 that indicate that the upper stratospheric gravity wave activity leads the corresponding onset of mesospheric cloud activity with a time lag of ∼1– 4 h . Five additional data sets from 2001, which are not included here, are consistent with these lag values. The results support recent arguments for upper stratospheric gravity wave activity being related to mesospheric cloud characteristics (1) through the associated vertical group velocity propagation, (2) through a phase delay of the gravity wave field, or (3) through a spurious relationship with other gravity waves generated from a related source spectrum. In an effort to show causality, a scenario is proposed that relates the two phenomena and explains the physical nature of the mesospheric cloud–stratospheric gravity wave relationship.

A Global Distribution of the Stratospheric Gravity Wave Activity from GPS Occultation Profiles with SAC-C and CHAMP

We have analysed the gravity wave activity using temperature profiles retrieved from the GPS occultation experiments on board the SAC-C and CHAMP satellites. By dividing the latitude and longitude ranges, here considered in individual cells, the variability of wave energy as a function of altitude observed in both hemispheres during October, November and December 2001 is presented. Some features were repeatedly observed during the three months. Nevertheless, as most available occultations were occurred during November, we begin showing results from this month. Significant differences detected during October are only pointed out at midlatitudes, provided that sufficient number of occultations are available. A significantly larger wave activity at 40-60°N with respect to 40-60°S is detected during this month. Differences between both the hemispheres are discussed and compared with previous results. Wave activity enhancements at equatorial regions above Brazil, Indonesia and India are found to be correlated with outgoing longwave radiation data. Vertical fluctuations with lengths above and below 3.5 km are considered separately, in order to identify the contribution of Kelvin and Rossby-gravity waves. In both cases, for long and short fluctuations and at the upper troposphere as well as at the lower stratosphere, there is a height interval of several kilometers where a systematic enhanced wave activity is observed. Its average height is progressively decreasing with increasing latitude, same as the height variation in the tropopause location. Longitudinal enhancements are also detected mainly around the equator and at midlatitudes. A clear signature is observed locally in the Southern Hemisphere (SH) at midlatitudes and 70-65°W, for vertical wavelengths longer than 3.5 km. It corresponds to mountain waves forced by the Andes Range, observed whenever occultations are available in this cell.

High Arctic observations of mesospheric inversion layers

Rayleigh lidar measurements of middle atmospheric temperatures obtained in the High Arctic at Eureka (80°N, 86°W) are examined for evidence of mesospheric inversion layers with overlying nearly‐adiabatic lapse rates. Inversion layers are identified in 5.4 ± 0.5% of the measurements, a rate considerably lower than is observed at midlatitudes. The altitude distribution for the Arctic inversions is similar to that found at midlatitudes. No phase progression or relationship with stratospheric gravity wave activity was found. The observations have important consequences for theories of the mesospheric inversion layer.

A meridional scan of the stratospheric gravity wave field over the ocean in 2001 (MeSSO2001)

In order to examine gravity wave characteristics over the ocean, we conducted a radiosonde observation campaign to scan the stratosphere meridionally over the middle Pacific with Hakuho‐maru research vessel operated by the Ocean Research Institute, University of Tokyo. Seventy vertical profiles of temperature, winds, and humidity were successfully obtained over a wide latitude range of 28°N to 48°S with an interval of 1 degree. Gravity wave energy and vertical wavenumber spectra were examined as a function of latitude. Gravity wave energy is maximized in the tropical region where the convection is active and in the middle latitude region where the subtropical westerly jet is situated. The wave energy in the tropical region is greater than the climatology based on operational radiosonde observation over land regions. The gravity wave amplitude does not necessarily increase with altitude, in contradiction to simple vertical propagation. The latitudinal distribution of wave energy rather suggests that gravity waves propagate meridionally toward higher latitudes. An interesting feature is that a wave packet having large horizontal wind and temperature amplitudes is observed continuously over 7 days in the latitudinal region extending 26 degrees. Results of hodograph analysis indicate that the wave packet is due to an inertia‐gravity wave with horizontal and vertical wavelengths of about 1800 km and 4–5km, respectively. This inertia‐gravity wave is likely generated in association with vigorous convection in the Intertropical Convergence Zone (ITCZ) in the Northern Hemisphere and propagated southward interhemispherically. The results in this study show that there are strong nonstationary gravity wave sources over the ocean. The importance of meridionally propagating gravity waves is discussed.

MLS observations of atmospheric gravity waves over Antarctica

Stratospheric gravity waves over Antarctica are studied with the radiance variances observed by Upper Atmosphere Research Satellite Microwave Limb Sounder (UARS MLS). Strong wave activities are found during August and September in 1992–1994 over the Drake Passage region (290°–315° longitude and 50°S–70°S latitude), where the enhancement seems associated with the topography of both South America and Antarctic Peninsula tips. During the same period, significant gravity wave activities are also evident along the Antarctic coastal region. The vertical growth of the wave variance shows a scale height of ∼14 km at low altitudes for both Drake Passage and the coastal regions but reduces substantially at high altitudes. The growth rate transition occurs at a lower altitude in the Drake Passage region where the variance is larger. The gravity wave activities observed near the Antarctic may contribute significantly to the formation of polar stratospheric clouds (PSC) because of the overlapping with the vortex edge and with the PSC activities as observed by CLAES (Cryogenic Limb Array Etalon Spectrometer).

A study of stratospheric GW fluctuations and sporadic E at midlatitudes with focus on possible orographic effect of Andes

Longitudinal dependences of stratospheric gravity wave (GW) fluctuations and lower ionospheric irregularities (sporadic E) at midlatitudes are studied by means of radio occultation data of the Global Positioning System/Meteorology Experiment (GPS/MET) satellite mission. The zonal average of temperature variance of GW fluctuations with vertical scales less than 7 km at northern midlatitudes is observed to be similar to that at southern midlatitudes, but there is a significant interhemispheric difference in the longitudinal dependence of GW fluctuations. The GPS/MET data at northern midlatitudes show a rapid change of the gravity wave distribution from 25 to 35 km height, resulting in a broad maximum of temperature variance located over the Atlantic and Eurasia. We only find in the wave distribution at h = 25 km some weak traces of possible orographic effects. On the other hand, the distribution of GW fluctuations at southern midlatitudes has a strong and sharp maximum over Andes, which is obviously due to orographic wave generation by the interaction of surface wind with the Andean mountain ridge. This observation of the new GPS radio occultation technique is in agreement with previous measurements of spaceborne microwave and infrared limb sounders. The amplitude of the average wave field increases with height over Andes, while the amplitude maximum moves westward, against the prevailing wind. The temperature fluctuations have an apparent, dominant vertical wavelength of around 6 km. In situ measurements by a balloon‐borne rawinsonde at Ushuaia, Argentina (54.7°S, 68.1°W) are compared to a simultaneous GPS/MET temperature profile. The balloon observations of temperature and horizontal wind are interpreted by a large amplitude mountain wave propagating to the upper stratosphere. Wave characteristics and atmospheric background conditions are investigated in detail for this mountain wave observation. Finally, the GPS/MET experiment indicates enhanced sporadic E in the lower ionosphere over Southern Andes. We assume that these plasma irregularities are generated by enhanced, upward wave flux due to the possible orographic effect of Andes.