scholarly journals Intradiurnal wind variations observed in the lower thermosphere over the South Pole

2000 ◽  
Vol 18 (5) ◽  
pp. 547-554 ◽  
Author(s):  
Y. I. Portnyagin ◽  
J. M. Forbes ◽  
E. G. Merzlyakov ◽  
N. A. Makarov ◽  
S. E. Palo
Keyword(s):  
Middle Atmosphere ◽  
Lamb Waves ◽  
Lower Thermosphere ◽  
Winter Season ◽  
Internal Gravity Wave ◽  
Wave Number ◽  
South Pole ◽  
Seasonal Behavior ◽  
Linear Interaction ◽  
Short Period

Abstract. The first meteor radar measurements of meridional winds in the lower thermosphere (about 95 ± 5 km), along four azimuth directions: 0°, 90°E, 180° and 90°W; approximately 2° from the geographic South Pole were made during two observational campaigns: January 19, 1995-January 26, 1996, and November 21, 1996-January 27, 1997. Herein we report analyses of the measurement results, obtained during the first campaign, which cover the whole one-year period, with particular emphasis on the transient nature and seasonal behavior of the main parameters of the intradiurnal wind oscillations. To analyze the data, two complementary methods are used: the well-known periodogram (FFT) technique and the S-transform technique. The most characteristic periods of the intradiurnal oscillations are found to be rather uniformly spread between about 7 h and 12 h. All of these oscillations are westward-propagating with zonal wave number s=1 and their usual duration is confined to several periods. During the austral winter season the oscillations with periods less than 12 h are the most intensive, while during summer season the 12-h oscillations dominate. Lamb waves and internal-gravity wave propagation, non-linear interaction of the short-period tides, excitation in situ of the short period waves may be considered as possible processes which are responsible for intradiurnal wind oscillations in the lower thermosphere over South Pole.Key words: Meteorology and atmospheric dynamics (middle atmosphere dynamics; thermospheric dynamics; waves and tides)

scholarly journals A comparative study of winds and tidal variability in the mesosphere/lower-thermosphere region over Bulgaria and the UK

2000 ◽  
Vol 18 (10) ◽  
pp. 1304-1315 ◽  
Author(s):  
D. Pancheva ◽  
P. Mukhtarov ◽  
N. J. Mitchell ◽  
A. G. Beard ◽  
H. G. Muller
Keyword(s):  
Middle Atmosphere ◽  
Spatial Scales ◽  
Lower Thermosphere ◽  
Planetary Waves ◽  
Wave Number ◽  
Linear Interaction ◽  
Zonal Wave Number ◽  
Tidal Variability ◽  
Cross Wavelet Analysis ◽  
The Uk

Abstract. Meteor radars located in Bulgaria and the UK have been used to simultaneously measure winds in the mesosphere/lower-thermosphere region near 42.5°N, 26.6°E and 54.5°N, 3.9°W, respectively, over the period January 1991 to June 1992. The data have been used to investigate planetary waves and diurnal and semidiurnal tidal variability over the two sites. The tidal amplitudes at each site exhibit fluctuations as large as 300% on time scales from a few days to the intra-seasonal, with most of the variability being at intra-seasonal scales. Spectral and cross-wavelet analysis reveals closely related tidal variability over the two sites, indicating that the variability occurs on spatial scales large compared to the spacing between the two radars. In some, but not all, cases, periodic variability of tidal amplitudes is associated with simultaneously present planetary waves of similar period, suggesting the variability is a consequence of non-linear interaction. Calculation of the zonal wave number of a number of large amplitude planetary waves suggests that during summer 1991 the 2-day wave had a zonal wave number of 3, but that during January–February 1991 it had a zonal wave number of 4.Key words: Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

scholarly journals Forcing mechanisms of the 6 h tide in the mesosphere/lower thermosphere

2018 ◽  
Vol 16 ◽  
pp. 141-147 ◽  
Author(s):  
Christoph Jacobi ◽  
Christoph Geißler ◽  
Friederike Lilienthal ◽  
Amelie Krug
Keyword(s):  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Radar Data ◽  
Radiation Absorption ◽  
Semidiurnal Tide ◽  
Bispectral Analysis ◽  
Solar Forcing ◽  
Linear Interaction ◽  
Non Linear ◽  
Forcing Mechanisms

Abstract. Solar tides such as the diurnal and semidiurnal tide, are forced in the lower and middle atmosphere through the diurnal cycle of solar radiation absorption. This is also the case with higher harmonics like the quarterdiurnal tide (QDT), but for these also non-linear interaction of tides such as the self-interaction of the semidiurnal tide, or the interaction of terdiurnal and diurnal tides, are discussed as possible forcing mechanism. To shed more light on the sources of the QDT, 12 years of meteor radar data at Collm (51.3∘ N, 13∘ E) have been analyzed with respect to the seasonal variability of the QDT at 82–97 km altitude, and bispectral analysis has been applied. The results indicate that non-linear interaction, in particular self-interaction of the semidiurnal tide probably plays an important role in winter, but to a lesser degree in summer. Numerical modelling of 6 h amplitudes qualitatively reproduces the gross seasonal structure of the observed 6 h wave at Collm. Model experiments with removed tidal forcing mechanisms lead to the conclusion that, although non-linear tidal interaction is one source of the QDT, the major forcing mechanism is direct solar forcing of the 6 h tidal components.

scholarly journals MF radar observations of mean winds and tides over Poker Flat, Alaska (65.1° N, 147.5° W)

2002 ◽  
Vol 20 (5) ◽  
pp. 679-690 ◽  
Author(s):  
P. Kishore ◽  
S. P. Namboothiri ◽  
K. Igarashi ◽  
Y. Murayama ◽  
B. J. Watkins
Keyword(s):  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Winter Season ◽  
Wave Model ◽  
Global Scale ◽  
Meridional Winds ◽  
Wind Measurements ◽  
The Mean ◽  
Tidal Characteristics ◽  
Mf Radar

Abstract. MF radar wind measurements in the mesosphere and lower thermosphere over Poker Flat, Alaska (65.1° N, 147.5° W) are used to study the features of mean winds and solar tides. Continuous observation with the newly installed radar is in progress and in the present study we have analyzed a database of the first 27 months (October 1998–December 2000) of observation. The observed mean wind climatology has been compared with previous measurements and the latest empirical model values (HWM93 model). Similarly, the tidal characteristics are described and compared with the Global Scale Wave Model (GSWM00). The mean wind characteristics observed are fairly consistent with previous wind measurements by the Poker Flat MST radar. The main feature of the zonal circulation is the annual variation with summer westward flow and winter eastward flow. The annual mean zonal wind has a west-ward motion at altitudes below 90 km. The annual mean meridional circulation has mainly southward motion at 70–100 km. There is very good agreement between the radar zonal winds and the HWM93 model winds. Comparison of the meridional winds shows some discrepancy. Analysis of two years of data indicated that the year-to-year consistency is preserved in the mean circulation in the mesosphere. Tidal characteristics observed are also consistent with previous measurements. Semidiurnal tides have the largest amplitudes in summer while the weakest amplitude is observed during the winter months. The vertical wavelength is longer during the summer season compared to the winter season. Comparison with the GSWM00 produces mixed results. There is reasonable agreement between the observed and modeled phases. Diurnal tide amplitudes are comparable in magnitude with that of the semidiurnal tide. Seasonal variation is less evident in the amplitudes. Comparison of the observed tidal parameters with the GSWM00 reveals some agreement and discrepancies.Key words. Meteorology and atmospheric dynamics (climatology; middle atmosphere dynamics; waves and tides)

scholarly journals On the longitudinal structure of the transient day-to-day variation of the semidiurnal tide in the mid-latitude lower thermosphere − I. Winter season

2001 ◽  
Vol 19 (5) ◽  
pp. 545-562 ◽  
Author(s):  
E. G. Merzlyakov ◽  
Yu. I. Portnyagin ◽  
C. Jacobi ◽  
N. J. Mitchell ◽  
H. G. Muller ◽  
...  
Keyword(s):  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Winter Season ◽  
Semidiurnal Tide ◽  
Longitudinal Structure ◽  
Transient Behaviour ◽  
Meteorology And Atmospheric Dynamics ◽  
S Transform ◽  
Wind Measurements ◽  
Waves And Tides

Abstract. The longitudinal structure of the day-to-day variations of semidiurnal tide amplitudes is analysed based on coordinated mesosphere/lower thermosphere wind measurements at several stations during three winter campaigns. Possible excitation sources of these variations are discussed. Special attention is given to a nonlinear interaction between the semidiurnal tide and the day-to-day mean wind variations. Data processing includes the S-transform analysis which takes into account transient behaviour of secondary waves. It is shown that strong tidal modulations appear during a stratospheric warming and may be caused by aperiodic mean wind variations during this event.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

scholarly journals STATISTICALLY SIGNIFICANT ESTIMATES OF INFLUENCE OF SOLAR ACTIVITY ON PLANETARY WAVES IN THE MIDDLE ATMOSPHERE OF THE NORTHERN HEMISPHERE AS DERIVED FROM MUAM MODEL DATA

2019 ◽  
Vol 5 (4) ◽  
pp. 64-72
Author(s):  
Andrey Koval
Keyword(s):  
Solar Activity ◽  
Northern Hemisphere ◽  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Planetary Waves ◽  
Wave Number ◽  
Winter Period ◽  
Long Period ◽  
Neutral Gas ◽  
Solar Radio Flux

Numerical simulation has been used to examine the effect of changes in solar activity (SA) in the thermosphere on amplitudes of long-period planetary waves (PW) for the winter period in the Northern Hemisphere. The model of the middle and upper atmosphere (MUAM) is used. It allows simulations of general atmospheric circulation at altitudes 0–300 km. In order to reproduce SA changes, different values of the solar radio flux at a wavelength of 10.7 cm at an altitude of more than 100 km are set in the MUAM radiation block. To take into account the effect of charged particles in the ionosphere on the neutral gas dynamics, ionospheric conductivities for different SA levels are included in MUAM. To improve the statistical reliability of the results, two ensembles of model simulations consisting of 16 runs corresponding to the minimum and maximum SA have been obtained. The statistical confidence of average differences in PW amplitudes between high and low SA has been calculated. The results are shown to be reliable in almost the entire altitude range 0–300 km. Results of the simulations have shown for the first time that statistically significant differences in amplitudes of long-period PWs can reach 10–15 % in the middle atmosphere of the Northern Hemisphere, depending on the zonal wave number. At the same time, reflection of PWs at altitudes of lower thermosphere has a significant effect on the PW structure in the middle atmosphere.

scholarly journals STATISTICALLY SIGNIFICANT ESTIMATES OF INFLUENCE OF SOLAR ACTIVITY ON PLANETARY WAVES IN THE MIDDLE ATMOSPHERE OF THE NORTHERN HEMISPHERE AS DERIVED FROM MUAM MODEL DATA

2019 ◽  
Vol 5 (4) ◽  
pp. 53-59
Author(s):  
Andrey Koval
Keyword(s):  
Solar Activity ◽  
Northern Hemisphere ◽  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Planetary Waves ◽  
Wave Number ◽  
Winter Period ◽  
Long Period ◽  
Neutral Gas ◽  
Solar Radio Flux

Numerical simulation has been used to examine the effect of changes in solar activity (SA) in the thermosphere on amplitudes of long-period planetary waves (PW) for the winter period in the Northern Hemisphere. The model of the middle and upper atmosphere (MUAM) is used. It allows simulations of general atmospheric circulation at altitudes 0–300 km. In order to reproduce SA changes, different values of the solar radio flux at a wavelength of 10.7 cm at an altitude of more than 100 km are set in the MUAM radiation block. To take into account the effect of charged particles in the ionosphere on the neutral gas dynamics, ionospheric conductivities for different SA levels are included in MUAM. To improve the statistical reliability of the results, two ensembles of model simulations consisting of 16 runs corresponding to the minimum and maximum SA have been obtained. The statistical confidence of average differences in PW amplitudes between high and low SA has been calculated. The results are shown to be reliable in almost the entire altitude range 0–300 km. Results of the simulations have shown for the first time that statistically significant differences in amplitudes of long-period PWs can reach 10–15 % in the middle atmosphere of the Northern Hemisphere, depending on the zonal wave number. At the same time, reflection of PWs at altitudes of lower thermosphere has a significant effect on the PW structure in the middle atmosphere.

scholarly journals Intercomparison of Middle Atmospheric Meteorological Analyses for the Northern Hemisphere Winter 2009–2010

2021 ◽  
Author(s):  
John P. McCormack ◽  
V. Lynn Harvey ◽  
Nicholas Pedatella ◽  
Dai Koshin ◽  
Kaoru Sato ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Planetary Waves ◽  
Wave Number ◽  
Physical Mechanisms ◽  
Wide Range ◽  
Zonal Wave Number ◽  
Analysis System ◽  
Hemisphere Winter

Abstract. Detailed meteorological analyses based on observations extending through the middle atmosphere (~15–100 km altitude) can provide key information to whole atmosphere modelling systems regarding the physical mechanisms linking day-to-day changes in ionospheric electron density to meteorological variability near the Earth’s surface. It is currently unclear how middle atmosphere analyses produced by various research groups consistently represent the wide range of proposed linking mechanisms involving migrating and non-migrating tides, planetary waves, gravity waves, and their impact on the zonal mean state in the mesosphere and lower thermosphere (MLT) region. To begin to address this issue, we present the first intercomparison among four such analyses, JAGUAR-DAS, MERRA-2, NAVGEM-HA, and WACCMX+DART, focusing on the Northern Hemisphere (NH) 2009–2010 winter that includes a major stratospheric sudden warming (SSW) in late January. This intercomparison examines the altitude, latitude, and time dependences of zonal mean zonal winds and temperatures among these four analyses over the 1 December 2009–31 March 2010 period, as well as latitude and altitude dependences of monthly mean amplitudes of the diurnal and semidiurnal migrating solar tides, the eastward propagating diurnal zonal wave number 3 nonmigrating tide, and traveling planetary waves associated with the quasi-5 day and quasi-2-day Rossby modes. Our results show generally good agreement among the four analyses up to the stratopause (~50 km altitude). Large discrepancies begin to emerge in the MLT owing to (1) differences in the types of satellite data assimilated by each system and (2) differences in the details of the global atmospheric models used by each analysis system. The results of this intercomparison provide initial estimates of uncertainty in analyses commonly used to constrain middle atmospheric meteorological variability in whole atmosphere model simulations.

scholarly journals Latitudinal variability of the quasi-16-day wave in the middle atmosphere over Brazilian stations

2016 ◽  
Vol 34 (4) ◽  
pp. 411-419 ◽  
Author(s):  
Amitava Guharay ◽  
Paulo Prado Batista ◽  
Barclay Robert Clemesha ◽  
Ricardo Arlen Buriti ◽  
Nelson Jorge Schuch
Keyword(s):  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Reanalysis Data ◽  
Lower Latitude ◽  
Meteor Radar ◽  
Background Wind ◽  
Short Period ◽  
General Preference ◽  
Santa Maria ◽  
Zonal Propagation

Abstract. A comparative study of the quasi-16-day wave (QSDW) in the middle atmosphere using meteor radar observations and reanalysis data from three Brazilian stations, Sao Joao do Cariri (7.4° S, 36.5° W) (CA), Cachoeira Paulista (22.7° S, 45° W) (CP), and Santa Maria (29.7° S, 53.7° W) (SM) has been carried out in the year 2005 to delineate its latitudinal variability characteristics. The broad spectral behavior around 16-day periodicity may indicate multiple modes of the concerned wave component. The wave amplitude shows a number of peaks over the year with the largest one in summer and winter in the case of mesosphere–lower thermosphere (MLT) and stratosphere, respectively. A potential coupling of the concerned wave with other short period planetary waves, especially at CA and CP is evinced. Although zonal propagation exhibits both eastward as well as westward waves there is a general preference of eastward waves at mid-latitude and westward waves at tropical latitudes. The prevailing westerly background wind in the middle atmosphere is conceived to favor the wave filtering of westward propagating Rossby waves at lower latitude.

scholarly journals Statistical characteristics of gravity wave activities observed by an OH airglow imager at Xinglong, in northern China

2011 ◽  
Vol 29 (8) ◽  
pp. 1401-1410 ◽  
Author(s):  
Q. Li ◽  
J. Xu ◽  
J. Yue ◽  
W. Yuan ◽  
X. Liu
Keyword(s):  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Northern China ◽  
Lower Atmosphere ◽  
Statistical Characteristics ◽  
Meridional Direction ◽  
Short Period ◽  
Different Seasons ◽  
One Year ◽  
Almost All

Abstract. An all-sky airglow imager (ASAI) was installed at Xinglong, in northern China (40.2° N, 117.4° E) in November 2009 to study the morphology of atmospheric gravity waves (AGWs) in the mesosphere and lower thermosphere (MLT) region. Using one year of OH airglow imager data from December 2009 to November 2010, the characteristics of short-period AGWs are investigated and a yearlong AGW climatology in northern China is first ever reported. AGW occurrence frequency in summer and winter is higher than that in equinoctial months. Observed bands mainly have horizontal wavelengths from 10 to 35 km, observed periods from 4 to 14 min and observed horizontal phase speeds in the range of 30 to 60 m s−1. Most of the bands propagate in the meridional direction. The propagation directions of the bands show a strong southwestward preference in winter, while almost all bands propagate northeastward in summer. Although the wind filtering in the middle atmosphere may control AGW propagations in the zonal direction, the non-uniform distribution of wave sources in the lower atmosphere may contribute to the anisotropy in the meridional direction in different seasons. Additionally, as an indication of local instability, the characteristics of ripples are also analyzed. It also shows seasonal variations, occurring more often in summer and winter and mainly moving westward in summer and eastward in winter.

scholarly journals The summertime 12-h wind oscillation with zonal wavenumber <i>s</i> = 1 in the lower thermosphere over the South Pole

1998 ◽  
Vol 16 (7) ◽  
pp. 828-837 ◽  
Author(s):  
Y. I. Portnyagin ◽  
J. M. Forbes ◽  
N. A. Makarov ◽  
E. G. Merzlyakov ◽  
S. Palo
Keyword(s):  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Thermal Excitation ◽  
South Pole ◽  
Planetary Scale ◽  
Zonal Wavenumber ◽  
Wind Measurements ◽  
Waves And Tides ◽  
Thermospheric Dynamics

Abstract. Meteor radar measurements of winds near 95 km in four azimuth directions from the geographic South Pole are analyzed to reveal characteristics of the 12-h oscillation with zonal wavenumber one (s=1). The wind measurements are confined to the periods from 19 January 1995 through 26 January 1996 and from 21 November 1996 through 27 January 1997. The 12-h s=1 oscillation is found to be a predominantly summertime phenomenon, and is replaced in winter by a spectrum of oscillations with periods between 6 and 11.5 h. Both summers are characterized by minimum amplitudes (5–10 ms–1) during early January and maxima (15–20 ms–1) in November and late January. For 10-day means of the 12-h oscillation, smooth evolutions of phase of order 4–6 h occur during the course of the summer. In addition, there is considerable day-to-day variability (±5–10 ms–1 in amplitude) with distinct periods (i.e., ~5 days and ~8 days) which suggests modulation by planetary-scale disturbances. A comparison of climatological data from Scott Base, Molodezhnaya, and Mawson stations suggests that the 12-h oscillation near 78°S is s=1, but that at 68°S there is probably a mixture between s=1 and other zonal wavenumber oscillations (most probably s=2). The mechanism responsible for the existence of the 12-h s=1 oscillation has not yet been identified. Possible origins discussed herein include in situ excitation, nonlinear interaction between the migrating semidiurnal tide and a stationary s=1 feature, and thermal excitation in the troposphere.Key words. Meteorology and atmospheric dynamics · Middle atmosphere dynamics · Thermospheric dynamics · Waves and tides

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