Dominant Vertical Wavelength Research Articles

Strong Gravity Waves Associated With Tonga Volcano Eruption Revealed by SABER Observations

AbstractUsing the Sounding of the Atmosphere using Broadband Emission Radiometry temperature profiles from January 6 to 21 2022, we studied the mesospheric gravity waves (GWs) associated with the Tonga volcano eruption on January 15. We observed that the eruption induced strong GWs in the mesosphere. Detailed analysis shows that there were strong GWs with amplitudes greater than 30 K (twice the usual GWs) on January 15. These GWs have dominant vertical wavelengths of 13.9–25.5 km and horizontal speeds of 44–81 ms−1, and they have intrinsic periods (momentum flux per unit mass) of ∼2–5 hr (4–320 m2s−2). The strong but slow GWs observed here are opposite to the fast GWs observed at different atmospheric layers after the Tonga volcano eruption, and are stronger than the GWs associated with other volcanic eruption and extreme weather events. Such that one can get a more comprehensive picture on GWs excited by a powerful source.

Serendipitous Internal Wave Signals in Deep Argo Data

AbstractSerendipitous measurements of deep internal wave signatures are evident in oscillatory variations around the background descent rates reported by one model of Deep Argo float. For the 10,045 profiles analyzed here, the average root‐mean‐square of vertical velocity variances, , from 1,000 m to the seafloor, is 0.0045 m s−1, with a 5%–95% range of 0.0028–0.0067 m s−1. Dominant vertical wavelengths, λz, estimated from the integrals of lagged autocorrelation sequences have an average value of 757 m, with a 5%–95% range of 493–1,108 m. Both and λz exhibit regional variations among and within some deep ocean basins, with generally larger and shorter λz in regions of rougher bathymetry or stronger deep currents. These correlations are both expected, since larger and shorter λz should be found near internal wave generation regions.

Gravity Wave Activities Associated With Convective Phenomena at a Tropical Location Near Land‐Sea Boundary

AbstractThe seasonal analysis of gravity wave activity has been made for the present tropical location, Kolkata (22.5726°N, 88.3639°E) using radiosonde and European Centre for Medium‐Range Weather Forecasts 60 model level data. Gravity wave generated due to intense tropical cyclone Aila has also been investigated using European Centre for Medium‐Range Weather Forecasts 91 model level data over the Indian region. The gravity wave energy calculated from temperature and wind perturbation profiles show a significant enhancement during convective activities as indicated by a low outgoing longwave radiation. The pattern of zonal and meridional wind shears plays an important role in determining the seasonal variation of gravity wave activities. An intrusion of water vapor into the lower stratosphere over the cyclone affected region is detected from European Centre for Medium‐Range Weather Forecasts 91 model level data. The dominant vertical wavelengths of gravity waves in the range of 2.5–3.2 km are found from spectral analysis of wind and temperature perturbations during the tropical cyclone.

Elliptical Structures of Gravity Waves Produced by Typhoon Soudelor in 2015 near Taiwan

Tropical cyclones (TCs) are complex sources of atmospheric gravity waves (GWs). In this study, the Weather Research and Forecasting Model was used to model TC Soudelor (2015) and the induced elliptical structures of GWs in the upper troposphere (UT) and lower stratosphere (LS) prior to its landfall over Taiwan. Conventional, spectral and wavelet analyses exhibit dominant GWs with horizontal and vertical wavelengths, and periods of 16–700 km, 1.5–5 km, and 1–20 h, respectively. The wave number one (WN1) wind asymmetry generated mesoscale inertia GWs with dominant horizontal wavelengths of 100–300 km, vertical wavelengths of 1.5–2.5 km (3.5 km) and westward (eastward) propagation at the rear of the TC in the UT (LS). It was also revealed to be an active source of GWs. The two warm anomalies of the TC core induced two quasi-diurnal GWs and an intermediate GW mode with a 10-h period. The time evolution of dominant periods could be indicative of changes in TC dynamics. The FormoSat-3/COSMIC (Formosa Satellite Mission-3/Constellation Observing System for Meteorology, Ionosphere, and Climate) dataset confirmed the presence of GWs with dominant vertical wavelengths of about 3.5 km in the UT and LS.

Gravity Wave Propagation from the Stratosphere into the Mesosphere Studied with Lidar, Meteor Radar, and TIMED/SABER

A low-frequency inertial atmospheric gravity wave (AGW) event was studied with lidar (40.5° N, 116° E), meteor radar (40.3° N, 116.2° E), and TIMED/SABER at Beijing on 30 May 2012. Lidar measurements showed that the atmospheric temperature structure was persistently perturbed by AGWs propagating upward from the stratosphere into the mesosphere (35–86 km). The dominant contribution was from the waves with vertical wavelengths λ z = 8 − 10 km and wave periods T ob = 6.6 ± 0.7 h . Simultaneous observations from a meteor radar illustrated that MLT horizontal winds were perturbed by waves propagating upward with an azimuth angle of θ = 247 ° , and the vertical wavelength ( λ z = 10 km ) and intrinsic period ( T in = 7.4 h ) of the dominant waves were inferred with the hodograph method. TIMED/SABER measurements illustrated that the vertical temperature profiles were also perturbed by waves with dominant vertical wavelength λ z = 6 − 9 km . Observations from three different instruments were compared, and it was found that signatures in the temperature perturbations and horizontal winds were induced by identical AGWs. According to these coordinated observation results, the horizontal wavelength and intrinsic phase speed were inferred to be ~560 km and ~21 m/s, respectively. Analyses of the Brunt-Väisälä frequency and potential energy illustrated that this persistent wave propagation had good static stability.

Identification of inertia gravity wave sources observed in the troposphere and the lower stratosphere over a tropical station Gadanki

In the present study, sources for the inertia–gravity waves (IGWs) that are observed in the troposphere and lower stratosphere during different seasons over a tropical station Gadanki (13.5°N, 79.2°E), India, have been identified. For this we have used long-term high resolution radiosonde observations of horizontal winds and temperature during May 2006 to March 2014. The IGW parameters are extracted using Stokes method. Rotary analysis is applied to the wind data to find the vertical direction of propagation. Dominant vertical wavelengths for these waves are obtained from FFT in the altitude domain as well as from apparent frequency method. The vertical and horizontal wavelengths are found to be in the range of 2–5km (1–3km) and 500–1500km (1000–2000km) in the troposphere (stratosphere), respectively. Using Stokes parameter method we have obtained the statistics of the number of the waves which are monochromatic. GROGRAT model with ERA-Interim data as the background atmosphere is used to identify the terminal (and source) points (sources) for the observed waves. In general, 53% of the waves observed over this location have convection as source and for only 38% of the cases vertical shear in the horizontal wind is identified as a source. For the rest of the 9% of the cases, these two sources are not found to be active.

Lidar observations of persistent gravity waves with periods of 3–10 h in the Antarctic middle and upper atmosphere at McMurdo (77.83°S, 166.67°E)

AbstractPersistent, dominant, and large‐amplitude gravity waves with 3–10 h periods and vertical wavelengths ~20–30 km are observed in temperatures from the stratosphere to lower thermosphere with an Fe Boltzmann lidar at McMurdo, Antarctica. These waves exhibit characteristics of inertia‐gravity waves in case studies, yet they are extremely persistent and have been present during every lidar observation. We characterize these 3–10 h waves in the mesosphere and lower thermosphere using lidar temperature data in June from 2011 to 2015. A new method is applied to identify the major wave events from every lidar run longer than 12 h. A continuous 65 h lidar run on 28–30 June 2014 exhibits a 7.5 h wave spanning ~60 h, and 6.5 h and 3.4 h waves spanning 40 and 45 h, respectively. Over the course of 5 years, 323 h of data in June reveal that the major wave periods occur in several groups centered from ~3.5 to 7.5 h, with vertical phase speeds of 0.8–2 m/s. These 3–10 h waves possess more than half of the spectral energy for ~93% of the time. A rigorous prewhitening, postcoloring technique is introduced for frequency power spectra investigation. The resulting spectral slopes are unusually steep (−2.7) below ~100 km but gradually become shallower with increasing altitude, reaching about −1.6 at 110 km. Two‐dimensional fast Fourier transform spectra confirm that these waves have a uniform dominant vertical wavelength of 20–30 km across periods of 3.5–10 h. These statistical features shed light on the wave source and pave the way for future research.

Thermospheric dissipation of upward propagating gravity wave packets

AbstractWe use a nonlinear, fully compressible, two‐dimensional numerical model to study the effects of dissipation on gravity wave packet spectra in the thermosphere. Numerical simulations are performed to excite gravity wave packets using either a time‐dependent vertical body forcing at the bottom boundary or a specified initial wave perturbation. Three simulation case studies are performed to excite (1) a steady state monochromatic wave, (2) a spectrally broad wave packet, and (3) a quasi‐monochromatic wave packet. In addition, we analyze (4) an initial condition simulation with an isothermal background. We find that, in cases where the wave is not continually forced, the dominant vertical wavelength decreases in time, predominantly due to a combination of refraction from the thermosphere and dissipation of the packets' high frequency components as they quickly reach high altitude. In the continually forced steady state case, the dominant vertical wavelength remains constant once initial transients have passed. The vertical wavelength in all simulations increases with altitude above the dissipation altitude (the point at which dissipation effects are greater than the wave amplitude growth caused by decreasing background density) at any fixed time. However, a shift to smaller vertical wavelength values in time is clearly exhibited as high‐frequency, long vertical wavelength components reach high altitudes and dissipate first, to be replaced by slower waves of shorter vertical wavelength. Results suggest that the dispersion of a packet significantly determines its spectral evolution in the dissipative thermosphere.

Characteristics of Gravity Waves over the Tibetan Plateau during the PRC-Japan Cooperative JICA Project in 2008

Using wind and temperature data with high vertical resolution obtained from Global Positioning System (GPS) radiosondes which were launched four times a day at Gerze (32.2°N, 84.4°E) and Litang (30.0°N, 100.3°E) stations during the People’s Republic of China (PRC)-Japan cooperative JICA project in 2008, the characteristics of gravity waves such as vertical energy propagation directions, intrinsic frequencies, vertical wave-lengths, and horizontal propagation directions over the Tibetan Plateau are investigated by hodograph method. The statistic characteristics of the gravity waves show that the activities of the gravity waves over the western and eastern Tibetan Plateau have significant spatial variations except for horizontal propagation directions, and that the gravity waves over the eastern Tibetan Plateau are easier to be triggered. The energy propagates upward for almost half of the observed gravity waves, and the energy propagation is downward for the other half of the gravity waves, indicating that the wave sources in lower and upper troposphere are equally important over the Tibetan Plateau. The dominant gravity wave frequencies lie in the frequency range of 2-2.5 times of Coriolis parameter f at Gerze station, while the dominant gravity wave frequencies are in the range of 1.5-2 times of f at Litang station. The dominant vertical wavelengths are 1.5-2.5 km over Gerze and Litang. For Gerze station, the dominant gravity waves propagate along the west-southwestward directions, while the dominant gravity wave propagating directions are north-northwestward for Litang station.

Vertical fluctuation energy in United States high vertical resolution radiosonde data as an indicator of convective gravity wave sources

Convectively generated internal gravity waves at extratropical latitudes are difficult to identify by climatological analysis of the temperature and horizontal wind fields from radiosonde profiles using traditional analysis methods. Here, we show that, by analyzing ascent rate profiles (we define a new variable, “vertical fluctuation energy (VE)”), we can identify convection sources in climatological analyses. Analysis of a 9‐year time series (1998–2006) of United States high vertical resolution radiosonde data shows that VE maximizes in summer in midlatitudes within the troposphere (2–8.9 km), and peaks at local afternoon–early evening during the summer over most of the contiguous United States. Furthermore, the apparent dominant vertical wavelength based on Fourier analysis of the low‐pass filtered ascent rate fluctuations also increase and decrease with VE, both on diurnal and seasonal timescales. VE in the lower stratosphere, however, does not show this same relationship to convection, but analysis of the vertical wavelength does show some of the features seen in tropospheric VE. Unlike midlatitude stations, VE within both the troposphere and the lower stratosphere over tropical western Pacific island stations is highly correlated with convective precipitation and inversely correlated with outgoing longwave radiation. We interpret this difference by using the 4‐D Gravity Wave Regional or Global Ray Tracer ray‐tracing model with a source spectrum representative of a convection source.

Statistics of gravity wave spectra in the troposphere and lower stratosphere over Beijing

We utilize the temperature profiles with a height resolution of 50-m obtained over the Beijing Observatory in the period between January of 2002 and December of 2002 to study vertical wavenumber spectra of normalized temperature fluctuations in the 1.67–8.02 km and 13.57–19.92 km altitude ranges and compare them with linear saturation model. Results indicate that individual vertical wavenumber spectra reveal a considerable variability in both slope and amplitude. The observed variability is not consistent with the predictions of linear saturation model. However, mean vertical wavenumber spectra in the troposphere measured at different seasons and different local times show great similarities with fairly uniform negative slopes of ~3.0 and amplitudes proportional to N 4 , suggesting that the seasonal mean spectra observed in the troposphere completely obey the linear saturation model and are unique at present. In contrast, while the spectral slopes of the mean vertical wavenumber spectra in the lower stratosphere tend to support the explanation of the observed temperature fluctuations by linear saturation model, the spectral amplitudes diverge significantly from linear saturation model, suggesting that the seasonal mean spectra in the lower stratosphere do not obey the linear saturation model and are unique at present. The dominant vertical wavelengths derived from the observed mean vertical wavenumber spectra are estimated to be ~3.2–~2.1 km in the troposphere and lower stratosphere, which is generally consistent with those reported in the literature. Balloon measurements, temperature and temperature spectra, gravity waves and saturation mode, dominant vertical wavelengths.

Vertical wavenumber spectra of atmospheric ozone measured from ozonesonde observations

Vertical profiles of ozone have been measured at balloon altitudes. Our purpose is to examine the character of vertical wavenumber spectra of ozone fluctuations, to assess the possible roles of gravity wave field in ozone fluctuations, and to determine dominant vertical wavelengths of ozone spectra. Vertical wavenumber spectra of 12 ozone fluctuations obtained during June–August 2003 are presented. Results indicate that mean spectral slopes in the wavenumber range from 4.69 × 10 −4 to 2.50 × 10 −3 cyc/m are about −2.91 in the troposphere and −2.87 in the lower stratosphere, which is close to the slope of −3 predicted by current gravity wave saturation models. The consistency of the observed spectral slopes with the value of −3 predicted by current gravity wave saturation models suggests that the observed ozone fluctuations are due primarily to atmospheric gravity waves. At m = 1/(1000 m) the mean spectral amplitude is over 30 times larger in the lower stratosphere than in the troposphere. Mean vertical wavenumber spectra in area-preserving form reveal dominant vertical wavelengths of ∼2.6 km in the troposphere and ∼2.7 km in the lower stratosphere, which is consistent with the values varying between 1.5 and 3.0 km estimated from the velocity field and temperature field at these heights.

Inertia gravity waves in the upper troposphere during the MaCWAVE winter campaign – Part I: Observations with collocated radars

Abstract. During the {MaCWAVE} campaign, combined rocket, radiosonde and ground-based measurements have been performed at the Norwegian Andøya Rocket Range (ARR) near Andenes and the Swedish Rocket Range (ESRANGE) near Kiruna in January 2003 to study gravity waves in the vicinity of the Scandinavian mountain ridge. The investigations presented here are mainly based on the evaluation of continuous radar measurements with the ALWIN VHF radar in the upper troposphere/ lower stratosphere at Andenes (69.3° N, 16.0° E) and the ESRAD VHF radar near Kiruna (67.9° N, 21.9° E). Both radars are separated by about 260 km. Based on wavelet transformations of both data sets, the strongest activity of inertia gravity waves in the upper troposphere has been detected during the first period from 24–26 January 2003 with dominant vertical wavelengths of about 4–5 km as well as with dominant observed periods of about 13–14 h for the altitude range between 5 and 8 km under the additional influence of mountain waves. The results show the appearance of dominating inertia gravity waves with characteristic horizontal wavelengths of ~200 km moving in the opposite direction than the mean background wind. The results show the appearance of dominating inertia gravity waves with intrinsic periods in the order of ~5 h and with horizontal wavelengths of 200 km, moving in the opposite direction than the mean background wind. From the derived downward energy propagation it is supposed, that these waves are likely generated by a jet streak in the upper troposphere. The parameters of the jet-induced gravity waves have been estimated at both sites separately. The identified gravity waves are coherent at both locations and show higher amplitudes on the east-side of the Scandinavian mountain ridge, as expected by the influence of mountains.

Characteristics of inertia gravity waves over the South Pacific as revealed by radiosonde observations

Using horizontal wind and temperature data with fine vertical resolution obtained by radiosondes, we investigate the characteristics of parameters and propagation properties of inertia gravity waves in the upper troposphere and lower stratosphere in the subtropics and extratropics over the South Pacific where very few observations have so far been done. Components extracted by a band‐pass filter having cutoff vertical wavelengths of 0.5 and 5 km are analyzed as gravity waves. Gravity wave parameters such as intrinsic frequency , vertical and horizontal wavelengths, and phase and group velocities are estimated by hodograph analysis. The statistics on such parameters are presented for both the stratosphere and troposphere for the three latitudinal ranges 17°–24°S, 25°–33°S, and 34°–48°S. The horizontal wavelengths decrease and increases with increasing latitude south. The dominant values for the Coriolis parameter f divided by are ∼0.5 in the lower stratosphere and ∼0.3 in the troposphere, with little dependence on latitude. The dominant vertical wavelengths for upward propagating waves are longer in the troposphere than in the lower stratosphere. The most dominant direction of horizontal propagation is southward, with a little bias toward southeastward. A case study using ray tracing suggests that the major source of such southeastward waves is located in the upper troposphere. Notable northward propagation of gravity waves is also found in the subtropical lower stratosphere. The source of the gravity waves is considered to be a cutoff cyclone developing in the upper troposphere.

Investigation of inertia-gravity waves in the upper troposphere/lower stratosphere over Northern Germany observed with collocated VHF/UHF radars

Abstract. A case study to investigate the properties of inertia-gravity waves in the upper troposphere/lower stratosphere has been carried out over Northern Germany during the occurrence of an upper tropospheric jet in connection with a poleward Rossby wave breaking event from 17-19 December 1999. The investigations are based on the evaluation of continuous radar measurements with the OSWIN VHF radar at Kühlungsborn (54.1 N, 11.8 E) and the 482 MHz UHF wind profiler at Lindenberg (52.2 N, 14.1 E). Both radars are separated by about 265 km. Based on wavelet transformations of both data sets, the dominant vertical wavelengths of about 2-4 km for fixed times as well as the dominant observed periods of about 11 h and weaker oscillations with periods of 6 h for the altitude range between 5 and 8 km are comparable. Gravity wave parameters have been estimated at both locations separately and by a complex cross-spectral analysis of the data of both radars. The results show the appearance of dominating inertia-gravity waves with characteristic horizontal wavelengths of 300 km moving in the opposite direction than the mean background wind and a secondary less pronounced wave with a horizontal wavelength in the order of about 200 km moving with the wind. Temporal and spatial differences of the observed waves are discussed.

Spatial and Temporal Variations of Gravity Wave Parameters. Part I: Intrinsic Frequency, Wavelength, and Vertical Propagation Direction

Abstract Five years (1998–2002) of U.S. high vertical resolution radiosonde data are analyzed to derive important gravity wave parameters, such as intrinsic frequencies, vertical and horizontal wavelengths, and vertical propagation directions in the lower stratosphere and troposphere. Intrinsic frequencies ω̂ increase with increasing latitude, with larger values in the troposphere. In the lower stratosphere, ω̂ is higher in winter than in summer, especially at mid- and high latitudes. Intrinsic frequencies divided by the Coriolis parameter f are ∼4 in the troposphere, and ∼2.4–3 in the lower stratosphere. The lower-stratospheric ω̂/f generally decreases weakly with increasing latitude. The latitudinal distributions of the lower-stratospheric ω̂/f are explained largely by the propagation effects. The seasonal variations of ω̂ in the lower stratosphere are found to be related to the variations of the background wind speeds. Dominant vertical wavelengths decrease with increasing latitude in the lower stratosphere, and maximize at midlatitudes (35°–40°N) in the troposphere. They are generally longer in winter than in summer. The variations of the dominant vertical wavelengths are found to be associated with the similar variations in gravity wave energies. Dominant horizontal wavelengths decrease with increasing latitude, with larger values in the lower stratosphere. Approximately 50% of the tropospheric gravity waves show upward energy propagation, whereas there is about 75% upward energy propagation in the lower stratosphere. The lower-stratospheric fraction of upward energy propagation is generally smaller in winter than in summer, especially at mid- and high latitudes. The seasonal variation of upward fraction is likely an artifice due to the analysis method, although a small part of it may be interpreted by the variations in background wind speeds. Results suggest that propagation effects are much more important than source variations for explaining the large-scale time-average properties of waves observed by radiosondes.

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.

A numerical study of propagation characteristics of gravity wave packets propagating in a dissipative atmosphere

By using a two‐dimensional, full‐implicit‐continuous‐Eulerian (FICE) scheme, we simulated the nonlinear propagation and evolution of gravity wave packets in a compressible, nonisothermal and dissipative atmosphere. The numerical results show that when an upgoing gravity wave packet is generated in the lower mesosphere, it can propagate along its ray path until it reaches lower thermosphere. However, upon reaching the lower thermosphere, the wave packet and associated energy propagate almost horizontally, which departs obviously from the prediction of linear gravity wave theory under WKB approximation in the nondissipative case. Further discussion indicates that the influences of nonlinearity and background temperature are not strong enough to restrict completely the upward energy propagation of the wave packet and that the influence of constant molecular viscosity on the characteristics (energy propagation path and wave parameters) of gravity waves is insignificant. It is the vertical inhomogeneity of molecular viscosity that causes the restriction of upward energy propagation of the gravity wave packet. Moreover, throughout propagation, the dominant vertical wavelength of the wave packet decreases with time, as it is affected by the joint actions of nonlinearity, background temperature, and dissipation. These results indicate that the molecular viscosity, especially the vertical inhomogeneity of molecular viscosity, plays an important role in the nonlinear propagation of gravity wave packets.

Gravity wave characteristics over Tromelin Island during the passage of cyclone Hudah

The time and spatial evolution of gravity‐wave characteristics are analysed using wavelets in vertical profiles of temperature and winds at Tromelin Island (15.53°S, 54.31°E) during the passage of the intense tropical cyclone Hudah in the Southern Ocean Indian Basin in 2000. Inertia‐gravity waves were observed in the upper troposphere and the lower stratosphere with dominant vertical wavelengths of 1.5–3 km, horizontal wavelengths <2000 km and periods of 0.6–1.6 days. Large amounts of gravity‐wave energy were detected during landfalls of the tropical cyclone. The distribution of total energy indicates that mesoscale convective structures such as tropical cyclones are important gravity‐wave sources in the upper troposphere.

Mean characteristics of the spectrum of horizontal velocity in the polar summer mesosphere and lower thermosphere observed by foil chaff

Thirty-three foil chaff rockets were flown at high latitudes during the summers of 1987, 1988, and 1991.Vertical profiles of horizontal wind were obtained at high resolution (25 m) in the 67– 103 km region of the mesosphere and lower thermosphere. This resolution (at that range of altitude) is unique and provides sensitivity to more than two decades of vertical wavenumbers. This study utilizes the unique data set to present observed spectra and their mean characteristics. Average vertical wavenumber spectra indicate that there is excellent agreement with the saturated gravity wave spectral model developed by Dewan and Good (J. Geophys. Res. 91(D3) (1986) 2742) and Smith et al. (J. Atmos. Sci. 44(10) (1987) 1404), which has a slope of −3 and a spectral amplitude proportional to the buoyancy frequency squared. This excellent agreement provides further support for the saturated spectrum theory in a mean sense and suggests that saturation processes are present in the horizontal flow and act to produce turbulence. We can therefore expect that turbulence is enhanced near the polar summer mesopause. Dominant vertical wavelength obtained from the average spectra is estimated to be 12.8 km .