Propagation of short-period gravity waves at high-latitudes during the MaCWAVE winter campaign (original) (raw)
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Annales Geophysicae, 2013
Orography is a well-known source of gravity and inertia-gravity waves in the atmosphere. Other sources, such as convection, are also known to be potentially important but the large amplitude of orographic waves over Scandinavia has generally precluded the possibility to study such other sources experimentally in this region. In order to better understand the origin of stratospheric gravity waves observed by the VHF radar ESRAD (Esrange MST radar) over Kiruna, in Arctic Sweden (67.88 • N, 21.10 • E), observations have been compared to simulations made using the Weather Research and Forecasting model (WRF) with and without the effects of orography and clouds. This case study concerns gravity waves observed from 00:00 UTC on 18 February to 12:00 UTC on 20 February 2007. We focus on the wave signatures in the static stability field and vertical wind deduced from the simulations and from the observations as these are the parameters which are provided by the observations with the best height coverage. As is common at this site, orographic gravity waves were produced over the Scandinavian mountains and observed by the radar. However, at the same time, southward propagation of fronts in the Barents Sea created short-period waves which propagated into the stratosphere and were transported, embedded in the cyclonic winds, over the radar site.
Observations of the breakdown of an atmospheric gravity wave near the cold summer mesopause at 54N
Geophysical Research Letters, 2000
Recently, it was shown from a single set of airglow/lidar observations in Urbana, Illinois (40N) that some small-scale wave-like structure seen in OH airglow images can be associated with the breakdown, via a convective instability, of an atmospheric gravity wave. A second set of simultaneous airglow/lidar observations, showing wave breakdown, has been obtained over Kfihlungsborn, Germany (54N) during a period when noctilucent clouds (NLCs) were also observed. This showed that the wave breakdown process can occur under the same cold, low altitude summer mesopause conditions that support the occurrence of NLCs.
Journal of Geophysical Research, 2003
1] An all-sky charge-coupled device imager capable of measuring wave structure in the OH, O 2 , and O I (557.7 nm) airglow emissions was operated at Cachoeira Paulista, Brazil (23°S, 45°W), for 2 years in collaboration with Utah State University, Logan. The dominant quasi-monochromatic gravity wave components investigated over a 1yearperiod(September1998toOctober1999)havebeenextracted,andtheirseasonalvariationshavebeenmeasured.Atotalof283waveeventsweremeasured,exhibitinghorizontalwavelengthsfrom5to60km,observedperiodsfrom5to35min,andhorizontalphasespeedsofupto1 year period (September 1998 to October 1999) have been extracted, and their seasonal variations have been measured. A total of 283 wave events were measured, exhibiting horizontal wavelengths from 5 to 60 km, observed periods from 5 to 35 min, and horizontal phase speeds of up to 1yearperiod(September1998toOctober1999)havebeenextracted,andtheirseasonalvariationshavebeenmeasured.Atotalof283waveeventsweremeasured,exhibitinghorizontalwavelengthsfrom5to60km,observedperiodsfrom5to35min,andhorizontalphasespeedsofupto80 m s À1 . The large-scale ''band'' wave patterns (horizontal wavelength between 10 and 60 km) exhibited a clear seasonal dependence on the horizontal propagation direction, propagating toward the southeast during the summer months and toward the northwest during the winter. The direction of propagation was observed to change abruptly around the equinox period in mid March and at the end of September. Using a numerical simulation of gravity wave propagation in a seasonally variable climatological wind field, we have determined that the observed anisotropy in the wave propagation directions can be attributed to a strong filtering of the waves in the middle atmosphere by stratospheric winds.
Annales Geophysicae, 2006
We present an experimental and modelling study of a strong gravity wave event in the upper troposphere/lower stratosphere near the Scandinavian mountain ridge. Continuous VHF radar measurements during the MaCWAVE rocket and ground-based measurement campaign were performed at the Norwegian Andoya Rocket Range (ARR) near Andenes (69.3 • N, 16 • E) in January 2003. Detailed gravity wave investigations based on PSU/NCAR Fifth-Generation Mesoscale Model (MM5) data have been used for comparison with experimentally obtained results. The model data show the presence of a mountain wave and of an inertia gravity wave generated by a jet streak near the tropopause region. Temporal and spatial dependencies of jet induced inertia gravity waves with dominant observed periods of about 13 h and vertical wavelengths of ∼4.5-5 km are investigated with wavelet transform applied on radar measurements and model data. The jet induced wave packet is observed to move upstream and downward in the upper troposphere. The model data agree with the experimentally obtained results fairly well. Possible reasons for the observed differences, e.g. in the time of maximum of the wave activity, are discussed. Finally, the vertical fluxes of horizontal momentum are estimated with different methods and provide similar amplitudes. We found indications that the derived positive vertical flux of the horizontal momentum corresponds to the obtained parameters of the jet-induced inertia gravity wave, but only at the periods and heights of the strongest wave activity.
The MaCWAVE program to study gravity wave influences on the polar mesosphere
Annales Geophysicae, 2006
Ascending VErtically) was a highly coordinated rocket, ground-based, and satellite program designed to address gravity wave forcing of the mesosphere and lower thermosphere (MLT). The MaCWAVE program was conducted at the Norwegian Andøya Rocket Range (ARR, 69.3 • N) in July 2002, and continued at the Swedish Rocket Range (Esrange, 67.9 • N) during January 2003. Correlative instrumentation included the ALOMAR MF and MST radars and RMR and Na lidars, Esrange MST and meteor radars and RMR lidar, radiosondes, and TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics) satellite measurements of thermal structures. The data have been used to define both the mean fields and the wave field structures and turbulence generation leading to forcing of the large-scale flow. In summer, launch sequences coupled with groundbased measurements at ARR addressed the forcing of the summer mesopause environment by anticipated convective and shear generated gravity waves. These motions were measured with two 12-h rocket sequences, each involving one Terrier-Orion payload accompanied by a mix of MET rockets, all at ARR in Norway. The MET rockets were used to define the temperature and wind structure of the stratosphere and mesosphere. The Terrier-Orions were designed to measure small-scale plasma fluctuations and turbulence that might be induced by wave breaking in the mesosphere. For the summer series, three European MIDAS (Middle Atmosphere Dynamics and Structure) rockets were also launched from ARR in coordination with the MaCWAVE Correspondence to: R. A. Goldberg (richard.a.goldberg@nasa.gov) payloads. These were designed to measure plasma and neutral turbulence within the MLT. The summer program exhibited a number of indications of significant departures of the mean wind and temperature structures from "normal" polar summer conditions, including an unusually warm mesopause and a slowing of the formation of polar mesospheric summer echoes (PMSE) and noctilucent clouds (NLC). This was suggested to be due to enhanced planetary wave activity in the Southern Hemisphere and a surprising degree of interhemispheric coupling. The winter program was designed to study the upward propagation and penetration of mountain waves from northern Scandinavia into the MLT at a site favored for such penetration. As the major response was expected to be downstream (east) of Norway, these motions were measured with similar rocket sequences to those used in the summer campaign, but this time at Esrange. However, a major polar stratospheric warming just prior to the rocket launch window induced small or reversed stratospheric zonal winds, which prevented mountain wave penetration into the mesosphere. Instead, mountain waves encountered critical levels at lower altitudes and the observed wave structure in the mesosphere originated from other sources. For example, a large-amplitude semidiurnal tide was observed in the mesosphere on 28 and 29 January, and appears to have contributed to significant instability and small-scale structures at higher altitudes. The resulting energy deposition was found to be competitive with summertime values. Hence, our MaCWAVE measurements as a whole are the first to characterize influences in the MLT region of planetary wave activity and related stratospheric warmings during both winter and summer.
Annales Geophysicae, 2008
The Mesosphere and Lower Thermosphere (MLT) winds acquired by medium frequency (MF) radar at Tirunelveli (8.7 • N, 77.8 • E) for the years 1993-2007 are used to study seasonal and interannual variabilities of gravity wave (GW) variances in the altitude region 84-94 km. The GW variances in zonal and meridional winds show semiannual oscillation with maximum variance during March-April and August-September and minimum during June-July and November-December months. The wind variances, in general, are observed to be enhanced during and after the year 1998 and they undergo large interannual variability, in particular, during spring equinox months. An enhancement of GW variances is observed during spring equinox months of the years 2000, 2004 and 2006. These larger GW enhancements, most of the times, coincide with eastward phase of zonally averaged stratospheric QBO at 30 hPa over equator and sudden stratospheric warming occurred at high latitudes. From the zonal and meridional variances, the perturbation ellipses are calculated and they show that the predominant direction of propagation of gravity waves is in SE-NW plane.
Characteristics and sources of gravity waves observed in NLC over Norway
Atmospheric Chemistry and Physics Discussions, 2013
Four years of noctilucent cloud (NLC) images from an automated digital camera in Trondheim and results from a ray tracing model are used to extend the climatology of gravity waves to higher latitudes and to identify their sources at high latitudes during summertime. The climatology of the summertime gravity-waves detected in NLC between 64 • and 74 • N is similar to that observed between 60 • and 64 • N by Pautet et al. (2011). The direction of propagation of gravity waves observed in the NLC north of 64 • N is a continuation of the north and northeast propagation as observed in south of 64 • N. However, a unique population of fast, short wavelength waves propagating towards the SW is observed in the NLC, which is consistent with transverse instabilities generated in-situ by breaking gravity waves (Fritts et al., 2003). The relative amplitude of the waves observed in the NLC Mie-scatter have been combined with ray-tracing results to show that waves propagating from near the tropopause, rather than those resulting from secondary generation in the stratosphere or mesosphere, are more likely to be the sources of the prominent wave structures observed in the NLC. The coastal region of Norway along the latitude of 70 • N is identified as the primary source region of the waves generated near the tropopause. 1 Introduction Gravity waves contribute strongly to the global dynamics, circulation, structure, variability and thermal balance of the atmosphere. They can be generated in the lower atmosphere through topography, convection and wind shear, and propagate upward into the middle and upper atmosphere (Fritts and Alexander, 2003, and reference therein). Their amplitude grows with altitude due to the exponential decrease of the atmospheric density with height. In the mesosphere the waves can become unstable and break, dissipating their energy and depositing their momentum locally (Lindzen,
Trends of mesospheric gravity waves at northern middle latitudes during summer
Journal of Geophysical Research, 2011
Recent investigations of the seasonal variation of the activity of gravity waves in the mesosphere/lower thermosphere (MLT) at middle and high latitudes suggest a semiannual variation with maxima during winter and summer and minima during the equinoxes. It is generally assumed that this annual cycle is determined by filtering processes due to the background winds in the stratosphere and lower mesosphere. On the other side, long-term observations of mesospheric winds at Juliusruh (55°N, 13°E) since 1990 indicate a stable increase of westward directed winds below 80 km (negative trends) during summer, as, e.g., clearly evident in monthly means in July. Here, we are studying how these long-term changes of winds are related to trends of the activity of gravity waves (GW) with periods between 3-6 hours. Our results show that the observed zonal wind trend at about 75 km during July goes along with an enhancement of the GW activity at altitudes above 80 km. Indeed, also the year-to-year variation of maxima of the observed westward directed winds at altitudes near 75 km and the GW activity at about 80 km are significantly correlated. Our results stimulate the further study of long-term wind changes and corresponding gravity wave trends.
Journal of Atmospheric and Terrestrial Physics, 1994
This paper reviews some recent observations of gravity wave characteristics in the middle atmosphere, revealed by co-ordinated observations with the MU radar in Shigaraki (35 'N. 136 E) and ncarbq rocketsondc experiments at Uchinoura (3 I N, I3 I E). We further summarize the results of comparative studies on the latitudinal variations of the gravity wa\c activity, which were detected by additionally employing data obtained with MF radars at Adelaide (35 S. I39 E) and Saskatoon (52 N. I07 W) and lidar observations at Haute Provencc (44 N. 6 E). The seasonal variation of gravity wave activity detected with the MU radar in the lower stratosphere showscd a clear annual variation with a maximum in winter, and coincided with that for the jet-stream intensity, indicating a close relation between the excitation of gravity Raves and jet-stream activity Ott middle latitudes. The long-period (2-2 I h) gravity W;IVCS seemed to be excited near the ground, presumably due to the interactlon of flow with topo!rdphy. and the short-period (5 min 2 h) components had the largest kinetic energy around the peak ofjet-stream.
2021
An intriguing and rare gravity wave event was recorded on the night of 25 April 2017 using a multiwavelength all-sky airglow imager over northern Germany. The airglow imaging observations at multiple altitudes in the mesosphere and lower thermosphere region reveal that a prominent upward-propagating wave structure appeared in O(1 S) and O 2 airglow images. However, the same wave structure was observed to be very faint in OH airglow images, despite OH being usually one of the brightest airglow emissions. In order to investigate this rare phenomenon, the altitude profile of the vertical wavenumber was derived based on colocated meteor radar wind-field and SABER temperature profiles close to the event location. The results indicate the presence of a thermal duct layer in the altitude range of 85-91 km in the southwest region of Kühlungsborn, Germany. Utilizing these instrumental data sets, we present evidence to show how a leaky duct layer partially inhibited the wave progression in the OH airglow emission layer. The coincidental appearance of this duct layer is responsible for the observed faint wave front in the OH airglow images compared O(1 S) and O 2 airglow images during the course of the night over northern Germany.