scholarly journals Characteristics and sources of gravity waves observed in noctilucent cloud over Norway

2014 ◽  
Vol 14 (22) ◽  
pp. 12133-12142 ◽  
Author(s):  
T. D. Demissie ◽  
P. J. Espy ◽  
N. H. Kleinknecht ◽  
M. Hatlen ◽  
N. Kaifler ◽  
...  
Keyword(s):  
Ray Tracing ◽  
Gravity Waves ◽  
Source Region ◽  
Digital Camera ◽  
Coastal Region ◽  
Primary Source ◽  
Noctilucent Cloud ◽  
The North ◽  
The Waves

Abstract. 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 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 and Alexander, 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.

scholarly journals Characteristics and sources of gravity waves observed in NLC over Norway

2013 ◽  
Vol 13 (11) ◽  
pp. 29303-29331
Author(s):  
T. D. Demissie ◽  
P. J. Espy ◽  
N. H. Kleinknecht ◽  
M. Hatlen ◽  
N. Kaifler ◽  
...  
Keyword(s):  
Ray Tracing ◽  
Gravity Waves ◽  
Source Region ◽  
Digital Camera ◽  
Coastal Region ◽  
Primary Source ◽  
Noctilucent Cloud ◽  
The North ◽  
The Waves

Abstract. 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.

scholarly journals Mesospheric gravity waves observed near equatorial and low–middle latitude stations: wave characteristics and reverse ray tracing results

2006 ◽  
Vol 24 (12) ◽  
pp. 3229-3240 ◽  
Author(s):  
C. M. Wrasse ◽  
T. Nakamura ◽  
H. Takahashi ◽  
A. F. Medeiros ◽  
M. J. Taylor ◽  
...  
Keyword(s):  
Ray Tracing ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Source Region ◽  
Phase Speed ◽  
Middle Latitude ◽  
Wave Source ◽  
Middle Latitudes ◽  
Summer Time ◽  
The Waves

Abstract. Gravity wave signatures were extracted from OH airglow observations using all-sky CCD imagers at four different stations: Cachoeira Paulista (CP) (22.7° S, 45° W) and São João do Cariri (7.4° S, 36.5° W), Brazil; Tanjungsari (TJS) (6.9° S, 107.9° E), Indonesia and Shigaraki (34.9° N, 136° E), Japan. The gravity wave parameters are used as an input in a reverse ray tracing model to study the gravity wave vertical propagation trajectory and to estimate the wave source region. Gravity waves observed near the equator showed a shorter period and a larger phase velocity than those waves observed at low-middle latitudes. The waves ray traced down into the troposphere showed the largest horizontal wavelength and phase speed. The ray tracing results also showed that at CP, Cariri and Shigaraki the majority of the ray paths stopped in the mesosphere due to the condition of m2<0, while at TJS most of the waves are traced back into the troposphere. In summer time, most of the back traced waves have their final position stopped in the mesosphere due to m2<0 or critical level interactions (|m|→∞), which suggests the presence of ducting waves and/or waves generated in-situ. In the troposphere, the possible gravity wave sources are related to meteorological front activities and cloud convections at CP, while at Cariri and TJS tropical cloud convections near the equator are the most probable gravity wave sources. The tropospheric jet stream and the orography are thought to be the major responsible sources for the waves observed at Shigaraki.

scholarly journals First tomographic observations of gravity waves by the infrared limb imager GLORIA

2017 ◽  
Vol 17 (24) ◽  
pp. 14937-14953 ◽  
Author(s):  
Isabell Krisch ◽  
Peter Preusse ◽  
Jörn Ungermann ◽  
Andreas Dörnbrack ◽  
Stephen D. Eckermann ◽  
...  
Keyword(s):  
Ray Tracing ◽  
Gravity Wave ◽  
Gravity Waves ◽  
General Circulation ◽  
Wave Packets ◽  
Source Region ◽  
General Circulation Models ◽  
Climate Projections ◽  
Flight Pattern ◽  
The Waves

Abstract. Atmospheric gravity waves are a major cause of uncertainty in atmosphere general circulation models. This uncertainty affects regional climate projections and seasonal weather predictions. Improving the representation of gravity waves in general circulation models is therefore of primary interest. In this regard, measurements providing an accurate 3-D characterization of gravity waves are needed. Using the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA), the first airborne implementation of a novel infrared limb imaging technique, a gravity wave event over Iceland was observed. An air volume disturbed by this gravity wave was investigated from different angles by encircling the volume with a closed flight pattern. Using a tomographic retrieval approach, the measurements of this air mass at different angles allowed for a 3-D reconstruction of the temperature and trace gas structure. The temperature measurements were used to derive gravity wave amplitudes, 3-D wave vectors, and direction-resolved momentum fluxes. These parameters facilitated the backtracing of the waves to their sources on the southern coast of Iceland. Two wave packets are distinguished, one stemming from the main mountain ridge in the south of Iceland and the other from the smaller mountains in the north. The total area-integrated fluxes of these two wave packets are determined. Forward ray tracing reveals that the waves propagate laterally more than 2000 km away from their source region. A comparison of a 3-D ray-tracing version to solely column-based propagation showed that lateral propagation can help the waves to avoid critical layers and propagate to higher altitudes. Thus, the implementation of oblique gravity wave propagation into general circulation models may improve their predictive skills.

scholarly journals Evidence for tropospheric wind shear excitation of high-phase-speed gravity waves reaching the mesosphere using the ray-tracing technique

2015 ◽  
Vol 15 (5) ◽  
pp. 2709-2721 ◽  
Author(s):  
M. Pramitha ◽  
M. Venkat Ratnam ◽  
A. Taori ◽  
B. V. Krishna Murthy ◽  
D. Pallamraju ◽  
...  
Keyword(s):  
Ray Tracing ◽  
Gravity Waves ◽  
High Frequency ◽  
Phase Speed ◽  
Horizontal Wind ◽  
Climatological Model ◽  
Background Temperature ◽  
The Waves ◽  
High Phase ◽  
Mf Radar

Abstract. Sources and propagation characteristics of high-frequency gravity waves observed in the mesosphere using airglow emissions from Gadanki (13.5° N, 79.2° E) and Hyderabad (17.5° N, 78.5° E) are investigated using reverse ray tracing. Wave amplitudes are also traced back, including both radiative and diffusive damping. The ray tracing is performed using background temperature and wind data obtained from the MSISE-90 and HWM-07 models, respectively. For the Gadanki region, the suitability of these models is tested. Further, a climatological model of the background atmosphere for the Gadanki region has been developed using nearly 30 years of observations available from a variety of ground-based (MST radar, radiosondes, MF radar) and rocket- and satellite-borne measurements. ERA-Interim products are utilized for constructing background parameters corresponding to the meteorological conditions of the observations. With the reverse ray-tracing method, the source locations for nine wave events could be identified to be in the upper troposphere, whereas for five other events the waves terminated in the mesosphere itself. Uncertainty in locating the terminal points of wave events in the horizontal direction is estimated to be within 50–100 km and 150–300 km for Gadanki and Hyderabad wave events, respectively. This uncertainty arises mainly due to non-consideration of the day-to-day variability in the tidal amplitudes. Prevailing conditions at the terminal points for each of the 14 events are provided. As no convection in and around the terminal points is noticed, convection is unlikely to be the source. Interestingly, large (~9 m s−1km−1) vertical shears in the horizontal wind are noticed near the ray terminal points (at 10–12 km altitude) and are thus identified to be the source for generating the observed high-phase-speed, high-frequency gravity waves.

scholarly journals Investigation of sources of gravity waves observed in the Brazilian Equatorial region on 08 April 2005

2019 ◽  
Author(s):  
Oluwakemi Dare-Idowu ◽  
Igo Paulino ◽  
Cosme A. O. B. Figueiredo ◽  
Amauri F. Medeiros ◽  
Ricardo A. Buriti ◽  
...  
Keyword(s):  
Ray Tracing ◽  
Gravity Waves ◽  
Spectral Characteristics ◽  
Phase Speed ◽  
Radar Data ◽  
Equatorial Region ◽  
Inter Tropical Convergence Zone ◽  
Wind Profiles ◽  
Ray Path ◽  
The Waves

Abstract. On 08 April 2005, a strong gravity wave activity (more than 3 hours) was observed in São João do Cariri (7.4° S, 36.5° W). These waves propagated to the southeast and presented different spectral characteristics (wavelength, period and phase speed). Using OH airglow images, the parameters of 5 observed gravity waves were calculated; the wavelengths ranged from ~ 90 to 150 km, the periods from ~ 26 to 67 min and the phase speeds from 32 to 71 m/s. A reserve ray-tracing analysis was performed to investigate the likely sources of these waves. The ray-tracing database was composed of temperature profiles from NRLMSISE-00 model and SABER measurements and wind profiles from HWM-14 model and meteor radar data. According to the ray path, the likely source of these gravity waves was the Inter Tropical Convergence Zone with intense convective processes taking place in the northern part of the observatory. Also, the observed preferential propagation direction of the waves to the southeast could be explained using blocking diagrams, i.e., due to the wind filtering process.

2. On the Destructive Effects of the Waves of the Sea on the North-East Shores of Shetland

1862 ◽  
Vol 4 ◽  
pp. 200-201
Author(s):  
Thomas Stevenson
Keyword(s):  
North Sea ◽  
Present Communication ◽  
North East ◽  
The North ◽  
The North Sea ◽  
The One ◽  
The Waves

The author stated, that the present communication might be regarded as supplementary to the one describing the results of his marine dynamometer, which would be found in the 14th volume of the “Transactions.” On the Bound Skerry of Whalsey, which is only exposed to the waves of the North Sea or German Ocean, he had found, on first landing in 1852, masses of rock, weighing 9½ tons and under, heaped together by the action of the waves at the level of no less than 62 feet above the sea; and others, ranging from 6 to 13½ tons, were found to have been quarried out of their positions in situ, at levels of from 70 to 74 feet above the sea.

scholarly journals Seasonal characteristics of small- and medium-scale gravity waves in the mesosphere and lower thermosphere over the Brazilian equatorial region

2018 ◽  
Vol 36 (3) ◽  
pp. 899-914 ◽  
Author(s):  
Patrick Essien ◽  
Igo Paulino ◽  
Cristiano Max Wrasse ◽  
Jose Andre V. Campos ◽  
Ana Roberta Paulino ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Source Region ◽  
Lower Thermosphere ◽  
Atmospheric Composition ◽  
Small Scale ◽  
Wave Source ◽  
Medium Scale ◽  
Seasonal Characteristics ◽  
Mesosphere And Lower Thermosphere ◽  
The Waves

Abstract. The present work reports seasonal characteristics of small- and medium-scale gravity waves in the mesosphere and lower thermosphere (MLT) region. All-sky images of the hydroxyl (NIR-OH) airglow emission layer over São João do Cariri (7.4∘ S, 36.5∘ W; hereafter Cariri) were obtained from September 2000 to December 2010, during a total of 1496 nights. For investigation of the characteristics of small-scale gravity waves (SSGWs) and medium-scale gravity waves (MSGWs), we employed the Fourier two-dimensional (2-D) spectrum and keogram fast Fourier transform (FFT) techniques, respectively. From the 11 years of data, we could observe 2343 SSGW and 537 MSGW events. The horizontal wavelengths of the SSGWs were concentrated between 10 and 35 km, while those of the MSGWs ranged from 50 to 200 km. The observed periods for SSGWs were concentrated around 5 to 20 min, whereas the MSGWs ranged from 20 to 60 min. The observed horizontal phase speeds of SSGWs were distributed around 10 to 60 m s−1, and the corresponding MSGWs were around 20 to 120 m s−1. In summer, autumn, and winter both SSGWs and MSGWs propagated preferentially northeastward and southeastward, while in spring the waves propagated in all directions. The critical level theory of atmospheric gravity waves (AGWs) was applied to study the effects of wind filtering on SSGW and MSGW propagation directions. The SSGWs were more susceptible to wind filtering effects than MSGWs. The average of daily mean outgoing longwave radiation (OLR) was also used to investigate the possible wave source region in the troposphere. The results showed that in summer and autumn, deep convective regions were the possible source mechanism of the AGWs. However, in spring and winter the deep convective regions did not play an important role in the waves observed at Cariri, because they were too far away from the observatory. Therefore, we concluded that the horizontal propagation directions of SSGWs and MSGWs show clear seasonal variations based on the influence of the wind filtering process and wave source location. Keywords. Atmospheric composition and structure (airglow and aurora) – electromagnetics (wave propagation) – history of geophysics (atmospheric sciences)

scholarly journals Comparing Multiple Precipitation Products against In-Situ Observations over Different Climate Regions of Pakistan

2019 ◽  
Vol 11 (6) ◽  
pp. 628 ◽  
Author(s):  
Waheed Ullah ◽  
Guojie Wang ◽  
Gohar Ali ◽  
Daniel Tawia Hagan ◽  
Asher Bhatti ◽  
...  
Keyword(s):  
Primary Source ◽  
Tropical Rainfall Measuring Mission ◽  
Reanalysis Data ◽  
Climate Data ◽  
Satellite Precipitation ◽  
In Situ Data ◽  
The North ◽  
Precipitation Seasonality ◽  
In Situ Observations

Various state-of-the-art gridded satellite precipitation products (GPPs) have been derived from remote sensing and reanalysis data and are widely used in hydrological studies. An assessment of these GPPs against in-situ observations is necessary to determine their respective strengths and uncertainties. GPPs developed from satellite observations as a primary source were compared to in-situ observations, namely the Climate Hazard group Infrared Precipitation with Stations (CHIRPS), Multi-Source Weighted-Ensemble Precipitation (MSWEP), Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Climate Data Record (PERSIANN-CDR) and Tropical Rainfall Measuring Mission (TRMM) multi-satellite precipitation analysis (TMPA). These products were compared to in-situ data from 51 stations, spanning 1998–2016, across Pakistan on daily, monthly, annual and interannual time scales. Spatiotemporal climatology was well captured by all products, with more precipitation in the north eastern parts during the monsoon months and vice-versa. Daily precipitation with amount larger than 10 mm showed significant (95%, Kolmogorov-Smirnov test) agreement with the in-situ data, especially TMPA, followed by CHIRPS and MSWEP. At monthly scales, there were significant correlations (R) between the GPPs and in-situ records, suggesting similar dynamics; however, statistical metrics suggested that the performance of these products varies from north towards south. Temporal agreement on an interannual scale was higher in the central and southern parts which followed precipitation seasonality. TMPA performed the best, followed in order by CHIRPS, MSWEP and PERSIANN-CDR.

scholarly journals First tomographic observations of gravity waves by the infrared limb imager GLORIA

2017 ◽  
Author(s):  
Isabell Krisch ◽  
Peter Preusse ◽  
Jörn Ungermann ◽  
Andreas Dörnbrack ◽  
Stephen D. Eckermann ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Wave Packets ◽  
Regional Climate ◽  
Climate Projections ◽  
Atmospheric Models ◽  
The South ◽  
Flight Pattern ◽  
The North ◽  
The Waves

Abstract. Atmospheric gravity waves are a major cause of uncertainty in global atmospheric models. This uncertainty affects regional climate projections and seasonal weather predictions. Improving the representation of gravity waves in global atmospheric models, is therefore of primary interest. In this regard, measurements providing an accurate 3-D characterization of gravity waves are needed. Using the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA), the first airborne implementation of a novel infrared limb imaging technique, a gravity wave event over Iceland was measured. An air volume disturbed by this gravity wave, was investigated from different angles by encircling the volume with a closed flight pattern. Using a tomographic retrieval approach the measurements of this air mass under different angles allowed for a 3-D reconstruction of the temperature and trace gas structure. The temperature measurements were used to derive gravity wave amplitudes, 3-D wave vectors, and direction-resolved momentum fluxes. These parameters facilitated the backtracing of the waves to their sources on the south coast of Iceland. Two wave packets are distinguished, one stemming from the main mountain ridge in the South of Iceland, a second one from the smaller mountains in the North. The total, area-integrated fluxes of these two wave packets are determined. Following the waves forward with a ray-tracing model highlighted the importance of 3-D propagation, an effect generally neglected in global atmospheric models.

scholarly journals Statistical analysis of thermospheric gravity waves from Fabry-Perot Interferometer measurements of atomic oxygen

2008 ◽  
Vol 26 (1) ◽  
pp. 29-45 ◽  
Author(s):  
E. A. K. Ford ◽  
A. L. Aruliah ◽  
E. M. Griffin ◽  
I. McWhirter
Keyword(s):  
Gravity Waves ◽  
Time Resolution ◽  
Atomic Oxygen ◽  
Source Region ◽  
Auroral Oval ◽  
Wave Activity ◽  
Similar Proportion ◽  
Short Period ◽  
Fabry Perot ◽  
The Waves

Abstract. Data from the Fabry-Perot Interferometers at KEOPS (Sweden), Sodankylä (Finland), and Svalbard (Norway), have been analysed for gravity wave activity on all the clear nights from 2000 to 2006. A total of 249 nights were available from KEOPS, 133 from Sodankylä and 185 from the Svalbard FPI. A Lomb-Scargle analysis was performed on each of these nights to identify the periods of any wave activity during the night. Comparisons between many nights of data allow the general characteristics of the waves that are present in the high latitude upper thermosphere to be determined. Comparisons were made between the different parameters: the atomic oxygen intensities, the thermospheric winds and temperatures, and for each parameter the distribution of frequencies of the waves was determined. No dependence on the number of waves on geomagnetic activity levels, or position in the solar cycle, was found. All the FPIs have had different detectors at various times, producing different time resolutions of the data, so comparisons between the different years, and between data from different sites, showed how the time resolution determines which waves are observed. In addition to the cutoff due to the Nyquist frequency, poor resolution observations significantly reduce the number of short-period waves (<1 h period) that may be detected with confidence. The length of the dataset, which is usually determined by the length of the night, was the main factor influencing the number of long period waves (>5 h) detected. Comparisons between the number of gravity waves detected at KEOPS and Sodankylä over all the seasons showed a similar proportion of waves to the number of nights used for both sites, as expected since the two sites are at similar latitudes and therefore locations with respect to the auroral oval, confirming this as a likely source region. Svalbard showed fewer waves with short periods than KEOPS data for a season when both had the same time resolution data. This gives a clear indication of the direction of flow of the gravity waves, and corroborates that the source is the auroral oval. This is because the energy is dissipated through heating in each cycle of a wave, therefore, over a given distance, short period waves lose more energy than long and dissipate before they reach their target.

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