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N J Mitchell - One of the best experts on this subject based on the ideXlab platform.
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A link between variability of the Semidiurnal Tide and planetary waves in the opposite hemisphere
Geophysical Research Letters, 2007Co-Authors: Anne K. Smith, D Pancheva, N J Mitchell, Daniel R. Marsh, James M. Russell, Martin G. MlynczakAbstract:[1] Horizontal wind observations over four years from the meteor radar at Esrange (68°N, 21°E) are analyzed to determine the variability of the Semidiurnal Tide. Simultaneous global observations of temperature and geopotential from the SABER satellite instrument are used to construct time series of planetary wave amplitudes and geostrophic mean zonal wind. During Northern Hemisphere summer and fall, the temporal variability of the Semidiurnal Tide at Esrange is found to be well correlated with the amplitude of planetary wavenumber 1 in the stratosphere in high southern latitudes (i.e. in the opposite hemisphere). The correlations indicate that a significant part of the tidal variation at Esrange is due to dynamical interactions in the Southern Hemisphere. A corresponding robust correlation pattern for the Esrange Tides is not apparent at other times of the multiple years analyzed.
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On the day-to-day wind and Semidiurnal Tide variations at heights of the mid-latitude summer mesopause: Zonal wavenumber estimations and its consequences, case-study in 1998
Journal of Atmospheric and Solar-Terrestrial Physics, 2005Co-Authors: E. G. Merzlyakov, Y. I. Portnyagin, N J Mitchell, Ch. Jacobi, B.l. Kashcheyev, A.n. Oleynikov, I. N. Fedulina, A. H. MansonAbstract:Abstract This work presents an analysis of spectra and estimations of zonal wavenumbers for mean wind and Semidiurnal Tide amplitude oscillations observed during July–September 1998 by 3 meteor radars and one MF radar. A number of mean wind and tidal amplitude oscillations are found that are possibly related to the evolution of the summer mesospheric zonal wind jet. The mean zonal wind undergoes several significant variations (“transitions”) during this time interval. These changes were accompanied by a frequency decreasing of the QTDW (quasi-2-day wave) in such a way that oscillations with a period of roughly about 36–44 h at the beginning of the measurements were replaced by strong 48-h waves, which in its turn after the end of the QTDW burst are replaced by a set of 3–6 day oscillations. Before the strong 48-h wave appearance we observe mean zonal wind variations with a temporal scale of 4 days. The set of 3–6 days includes 3–4 day waves with s ∼ 3 and 5–6 day waves with s = 1 . The last wave is absent in the upper stratosphere during the time of observations and suggests to appear in the mesosphere. The both waves could represent a signature of the simultaneous non-linear excitation of a triad of waves. The zonal wind “transitions” also reflected in the Semidiurnal Tide by modulations of the tidal amplitudes with periods of 3–4 days and about 5 days. Some features observed at the end of summer 1998 could be explained by interaction between a zonally averaged wind variation and the Semidiurnal Tide. In a spectral representation, this variation looks like an oscillation, but is not a planetary wave. The strongest long-period modulations of the Semidiurnal Tide were observed during strong geopotential perturbations in the stratosphere of the Southern hemisphere.
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planetary waves and variability of the Semidiurnal Tide in the mesosphere and lower thermosphere over esrange 68 n 21 e during winter
Journal of Geophysical Research, 2004Co-Authors: D Pancheva, N J MitchellAbstract:[1] The main features of the planetary waves and the variability of the Semidiurnal Tide with planetary wave periods observed by meteor radar over Esrange (68°N, 21 °E) have been investigated. The interval of 39 months covering continuous measurements from October 1999 to December 2002 has been examined. The planetary waves most frequently observed by meteor radar measurements in the mesosphere and lower thermosphere (80-100 km) over Esrange are: 5-, 8- to 10-, 16-, and 23-day waves (the quasi-2-day wave is excluded in this study). They are strongly amplified in the winter. Some differences between high- and middle-latitude planetary waves notwithstanding, the 5-, 10-, and 16-day waves are most probably related to the well-known normal mode. There are some reasons to believe that the vertically upward propagating 23-day wave could be generated by solar forcing. The variability of the Semidiurnal Tide with periods of planetary waves has been thoroughly studied as well. It is found that in the winter when the planetary waves are significantly amplified, a very strong periodic variability of the Semidiurnal Tide is observed as well. This result indicates that the most probable mechanism responsible for the periodic tidal variability during winter is in situ nonlinear coupling between Tides and planetary waves. Two winter periods have been examined (1999/2000 and 2001/2002) in order to find strong evidence supporting this suggestion. The validity of the frequency, phase, and vertical wavenumber (wavelength) relationship between the prime (the planetary wave and Semidiurnal Tide) and secondary waves has been established. The novel aspect of this work is that we show for the first time that the calculated vertical structures (vertical wavelengths) of the sum and difference secondary waves, which have very close periods, are actually very different.
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Planetary waves and variability of the Semidiurnal Tide in the mesosphere and lower thermosphere over Esrange (68°N, 21°E) during winter
Journal of Geophysical Research, 2004Co-Authors: D Pancheva, N J MitchellAbstract:[1] The main features of the planetary waves and the variability of the Semidiurnal Tide with planetary wave periods observed by meteor radar over Esrange (68°N, 21 °E) have been investigated. The interval of 39 months covering continuous measurements from October 1999 to December 2002 has been examined. The planetary waves most frequently observed by meteor radar measurements in the mesosphere and lower thermosphere (80-100 km) over Esrange are: 5-, 8- to 10-, 16-, and 23-day waves (the quasi-2-day wave is excluded in this study). They are strongly amplified in the winter. Some differences between high- and middle-latitude planetary waves notwithstanding, the 5-, 10-, and 16-day waves are most probably related to the well-known normal mode. There are some reasons to believe that the vertically upward propagating 23-day wave could be generated by solar forcing. The variability of the Semidiurnal Tide with periods of planetary waves has been thoroughly studied as well. It is found that in the winter when the planetary waves are significantly amplified, a very strong periodic variability of the Semidiurnal Tide is observed as well. This result indicates that the most probable mechanism responsible for the periodic tidal variability during winter is in situ nonlinear coupling between Tides and planetary waves. Two winter periods have been examined (1999/2000 and 2001/2002) in order to find strong evidence supporting this suggestion. The validity of the frequency, phase, and vertical wavenumber (wavelength) relationship between the prime (the planetary wave and Semidiurnal Tide) and secondary waves has been established. The novel aspect of this work is that we show for the first time that the calculated vertical structures (vertical wavelengths) of the sum and difference secondary waves, which have very close periods, are actually very different.
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variability of the Semidiurnal Tide due to fluctuations in solar activity and total ozone
Journal of Atmospheric and Solar-Terrestrial Physics, 2003Co-Authors: D Pancheva, N J Mitchell, H Middleton, H G MullerAbstract:Abstract An attempt was made to investigate some variations of the Semidiurnal Tide observed in the mesosphere/lower thermosphere (MLT) region by meteor radar above the UK in the time interval 1 January 1989–6 May 1993, which are possibly due to the variability in the total ozone and solar activity. The total ozone is used here mainly as a proxy for stratospheric planetary wave information in the extra tropics. A positive correlation between the solar activity and the variability of the Semidiurnal Tide and total ozone was found for the investigated interval. During winter the Semidiurnal amplitude modulations with periods: ∼10, ∼16 and 25–28 days were found to be present simultaneously with similar variations in the total ozone. They strengthen significantly during stratospheric warmings and the amplification of the stratospheric height wave 1. The amplitude modulations of the Semidiurnal Tide observed in the MLT region during winter are mainly produced by non-local coupling between the Semidiurnal Tide and planetary waves in the stratosphere. The influence of the planetary wave activity in the lower stratosphere on the variability of the Semidiurnal Tide observed in the MLT region indicates the non-negligible effects of the tropospheric tidal forcing. A strong response of the total ozone and the Semidiurnal Tide to solar radio flux variations on the time scale of the solar rotation period was found especially in the beginning of 1991. There is some provisional evidence for a response of the Semidiurnal Tide and the total ozone to the variations in the solar radio flux at intermediate periods of 50–80 days.
D. C. Fritts - One of the best experts on this subject based on the ideXlab platform.
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Interannual variability of the nonmigrating Semidiurnal Tide at high latitudes and stationary planetary wave in the opposite hemispheres
Journal of Atmospheric and Solar-Terrestrial Physics, 2014Co-Authors: H. Iimura, Ruth S. Lieberman, D. C. Fritts, Wilbert R. SkinnerAbstract:Abstract The westward propagating zonal wavenumber 1 nonmigrating Semidiurnal Tide (SW1) enhanced at high latitudes during summer in the mesosphere and lower thermosphere (MLT) is believed to originate from the nonlinear interaction between the migrating Semidiurnal Tide (SW2) and the stationary planetary wave zonal wavenumber 1 (SPW1) in the opposite winter hemispheres. This paper presents correlations of the SW1 over the Antarctic and Arctic and the SPW1 in the opposite hemispheres. The SW1 is determined from horizontal wind measurements by the TIMED Doppler Interferometer (TIDI) and the SPW1 is from temperature measurements by the Sounding the Atmosphere using Broadband Emission Radiometry (SABER), both aboard the NASA׳s Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite. We focus on the SW1 over the Antarctic and the SPW1 in the northern hemisphere during an interval from mid-September to mid-November, and the SW1 over the Arctic and the SPW1 in the southern hemisphere during an interval from mid-March to mid-May. Large interannual variations of the SW1 and SPW1 are exhibited in both northern and southern hemispheres. For amplitudes of the SW1 at 90 km and 82.5°S, positive correlations are exhibited with SPW1 amplitudes at ~55 km in the equatorial region, and ~25 km and 55°N. Although zonal SW1 amplitude at 95 km and 86.5°N is positively correlated with SPW1 amplitudes at ~30°S above 35 km, meridional SW1 amplitude is negatively correlated with SPW1 amplitudes equatorward of 30°S. We also present results of a correlation analysis for SW3 amplitudes during an interval from mid-January to mid-March over the Antarctic and from mid-July to mid-September over the Arctic with SPW1 amplitudes.
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drake antarctic agile meteor radar first results configuration and comparison of mean and tidal wind and gravity wave momentum flux measurements with southern argentina agile meteor radar
Journal of Geophysical Research, 2012Co-Authors: D. C. Fritts, H. Iimura, Diego Janches, W K Hocking, J V Bageston, N P LemeAbstract:[1] A new generation meteor radar was installed at the Brazilian Antarctic Comandante Ferraz Base (62.1°S) in March 2010. This paper describes the motivations for the radar location, its measurement capabilities, and comparisons of measured mean winds, Tides, and gravity wave momentum fluxes from April to June of 2010 and 2011 with those by a similar radar on Tierra del Fuego (53.8°S). Motivations for the radars include the “hotspot” of small-scale gravity wave activity extending from the troposphere into the mesosphere and lower thermosphere (MLT) centered over the Drake Passage, the maximum of the Semidiurnal Tide at these latitudes, and the lack of other MLT wind measurements in this latitude band. Mean winds are seen to be strongly modulated at planetary wave and longer periods and to exhibit strong coherence over the two radars at shorter time scales as well as systematic seasonal variations. The Semidiurnal Tide contributes most to the large-scale winds over both radars, with maximum tidal amplitudes during May and maxima at the highest altitudes varying from ∼20 to >70 ms−1. In contrast, the diurnal Tide and various planetary waves achieve maximum winds of ∼10 to 20 ms−1. Monthly mean gravity wave momentum fluxes appear to reflect the occurrence of significant sources at lower altitudes, with relatively small zonal fluxes over both radars, but with significant, and opposite, meridional momentum fluxes below ∼85 km. These suggest gravity waves propagating away from the Drake Passage at both sites, and may indicate an important source region accounting in part for this “hotspot.”
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Nonmigrating Semidiurnal Tide over the Arctic determined from TIMED Doppler Interferometer wind observations
Journal of Geophysical Research, 2010Co-Authors: H. Iimura, Wilbert R. Skinner, D. C. Fritts, Scott PaloAbstract:Received 25 June 2009; revised 30 October 2009; accepted 5 November 2009; published 30 March 2010. [1] The TIMED Doppler Interferometer (TIDI) on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite has been measuring horizontal winds in the mesosphere and lower thermosphere (MLT) since 2002. Because of the high inclination of the TIMED orbit, TIDI measures the horizontal winds from pole to pole every orbit. This paper presents the first assessment of the spatial structure and temporal evolution of the nonmigrating Semidiurnal Tides over the Arctic determined from the TIDI wind measurements and a comparison of the structure of the nonmigrating Semidiurnal Tide between the Arctic and Antarctic. The nonmigrating Semidiurnal Tides were determined as a 60 day average based on the yaw cycles of the spacecraft. The nonmigrating Semidiurnal tidal wind field over the Arctic comprises mainly the westward‐propagating zonal wave numbers1(W1)and3(W3)andstandingzonalwavenumber0(S0)modes.TheW1modeis the most prominent, maximizing above 90 km poleward of 60°N during the yaw interval ranging from mid‐March to mid‐May. While this mode exhibits a slight amplitude increase toward the North Pole during this interval, its phase is nearly constant with latitude. The S0 mode is enhanced over two yaw intervals ranging from mid‐January to mid‐May, but its amplitude decreases toward the North Pole. Compared to the W1 Semidiurnal Tide over the Antarctic, that over the Arctic is smaller in amplitude, of less extended duration, achieves maximum amplitudes at higher altitudes by ∼10 km, and exhibits a weaker amplitude increase toward the pole. These differences likely result from differences in excitation mechanisms and efficiency and/or in propagation conditions in the two responses for the nonmigrating Semidiurnal Tides between the Arctic and Antarctic.
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Source regions for Antarctic MLT non-migrating Semidiurnal Tides
Geophysical Research Letters, 2009Co-Authors: Damian J. Murphy, Robert Hibbins, Adrian Mcdonald, Masaki Tsutsumi, D. M. Riggin, D. C. Fritts, T. Aso, Robert A. VincentAbstract:[1] Source regions for the westward propagating zonal wavenumber one and three components of the Semidiurnal Tide observed in the summer mesosphere and lower thermosphere over Antarctica are identified by correlating local tidal variations with global planetary wave one activity in the stratosphere and lower mesosphere. The advantages of using zonal wavenumber resolved tidal amplitudes for such a study are described. The results support the prediction of a source region in the northern hemisphere.
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Gravity wave propagation through a large Semidiurnal Tide and instabilities in the mesosphere and lower thermosphere during the winter 2003 MaCWAVE rocket campaign
Annales Geophysicae, 2006Co-Authors: B. P. Williams, D. C. Fritts, C. Y. She, R. A. GoldbergAbstract:The winter MaCWAVE (Mountain and convective waves ascending vertically) rocket campaign took place in January 2003 at Esrange, Sweden and the ALOMAR observatory in Andenes, Norway. The campaign combined balloon, lidar, radar, and rocket measurements to produce full temperature and wind profiles from the ground to 105 km. This paper will investigate gravity wave propagation in the mesosphere and lower thermosphere using data from the Weber sodium lidar on 28?29 January 2003. A very large Semidiurnal Tide was present in the zonal wind above 80 km that grew to a 90 m/s amplitude at 100 km. The superposition of smaller-scale gravity waves and the Tide caused small regions of possible convective or shear instabilities to form along the downward progressing phase fronts of the Tide. The gravity waves had periods ranging from the Nyquist period of 30 min up to 4 h, vertical wavelengths ranging from 7 km to more than 20 km, and the frequency spectra had the expected ?5/3 slope. The dominant gravity waves had long vertical wavelengths and experienced rapid downward phase progression. The gravity wave variance grew exponentially with height up from 86 to 94 km, consistent with the measured scale height, suggesting that the waves were not dissipated strongly by the tidal gradients and resulting unstable regions in this altitude range.
Y. I. Portnyagin - One of the best experts on this subject based on the ideXlab platform.
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Height-latitude structure of the vertical component of the migrating Semidiurnal Tide in the upper mesosphere and lower thermosphere region (80–100 km)
Izvestiya Atmospheric and Oceanic Physics, 2011Co-Authors: Y. I. Portnyagin, Plamen Mukhtarov, E. G. Merzlyakov, T. V. Solov’eva, Alexander Pogoreltsev, E. V. Suvorova, D PanchevaAbstract:The height-latitude distributions of parameters of the vertical wind component of the Semidiurnal Tide were calculated for the mesosphere and lower thermosphere (MLT) region (80–100 km) on the basis of empirical height-latitude distributions of the monthly mean parameters of variations in the horizontal wind component of the migrating Semidiurnal Tide. The constructed distributions are compared with the results of a numerical modeling of the migrating Semidiurnal Tide with the aid of a model of global circulation in the middle and upper atmosphere, as well as with the parameters of Semidiurnal temperature variations obtained from the data of satellite measurements. It is shown that different models yield the distributions of parameters of Semidiurnal variations, which agree within the errors of their values. The presence of high-latitude regions of local maximal amplitudes is a specific feature of the distributions of parameters of Semidiurnal variations in the vertical wind constructed in the course of this work. On the whole, at heights of about 90 km and higher, Semidiurnal variations in the vertical wind exceed the prevailing vertical wind in amplitude.
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On the day-to-day wind and Semidiurnal Tide variations at heights of the mid-latitude summer mesopause: Zonal wavenumber estimations and its consequences, case-study in 1998
Journal of Atmospheric and Solar-Terrestrial Physics, 2005Co-Authors: E. G. Merzlyakov, Y. I. Portnyagin, N J Mitchell, Ch. Jacobi, B.l. Kashcheyev, A.n. Oleynikov, I. N. Fedulina, A. H. MansonAbstract:Abstract This work presents an analysis of spectra and estimations of zonal wavenumbers for mean wind and Semidiurnal Tide amplitude oscillations observed during July–September 1998 by 3 meteor radars and one MF radar. A number of mean wind and tidal amplitude oscillations are found that are possibly related to the evolution of the summer mesospheric zonal wind jet. The mean zonal wind undergoes several significant variations (“transitions”) during this time interval. These changes were accompanied by a frequency decreasing of the QTDW (quasi-2-day wave) in such a way that oscillations with a period of roughly about 36–44 h at the beginning of the measurements were replaced by strong 48-h waves, which in its turn after the end of the QTDW burst are replaced by a set of 3–6 day oscillations. Before the strong 48-h wave appearance we observe mean zonal wind variations with a temporal scale of 4 days. The set of 3–6 days includes 3–4 day waves with s ∼ 3 and 5–6 day waves with s = 1 . The last wave is absent in the upper stratosphere during the time of observations and suggests to appear in the mesosphere. The both waves could represent a signature of the simultaneous non-linear excitation of a triad of waves. The zonal wind “transitions” also reflected in the Semidiurnal Tide by modulations of the tidal amplitudes with periods of 3–4 days and about 5 days. Some features observed at the end of summer 1998 could be explained by interaction between a zonally averaged wind variation and the Semidiurnal Tide. In a spectral representation, this variation looks like an oscillation, but is not a planetary wave. The strongest long-period modulations of the Semidiurnal Tide were observed during strong geopotential perturbations in the stratosphere of the Southern hemisphere.
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Longitude variability of the solar Semidiurnal Tide in the lower thermosphere through assimilation of ground‐ and space‐based wind measurements
Journal of Geophysical Research: Space Physics, 2003Co-Authors: K M Cierpik, Jeffrey M. Forbes, A. H. Manson, Yasunobu Miyoshi, A.n. Fahrutdinova, Saburo Miyahara, N. J. Mitchell, Christoph Jacobi, C E Meek, Y. I. PortnyaginAbstract:[1] Wind measurements from the Upper Atmosphere Research Satellite (UARS) and model output from the Middle Atmosphere General Circulation Model (GCM) at Kyushu University are used to investigate the nature of nonmigrating Semidiurnal Tides between 50–55°N using combined space-based (SBM) and ground-based (GBM) wind measurements at 95 km. The GCM is used to create a mock database to test the effects of various sampling scenarios, data gaps, and relative weighting between SBM and GBM, on retrieval of the longitude structure of the Semidiurnal Tide. SB sampling is based upon orbital characteristics of UARS. GB sampling corresponds to hourly radar measurements from Saskatoon (52°N, 107°W), Sheffield (53°N, 4°W), Collm (52°N, 15°E), Obninsk (55°N, 37°E), and Kazan (56°N, 49°E). Results are presented for the month of August when Semidiurnal amplitudes are large and sampling by UARS instruments is good. By compositing over a 5–10 day “fit span,” it is found that the combination of temporal coverage by GB radars and spatial sampling by the satellite is sufficient to allow reasonable recovery of the zonal wave number s = 1, 2, 3 components of the Semidiurnal Tide. Over significantly longer fit spans, the contributions of GBM become less critical. Using actual UARS and GBM during 1–20 August 1993, the Semidiurnal amplitude of eastward wind is found to vary from a minimum value (12 ms−1) at 20°E, to a maximum of 45 ms−1 near 160°E, and a secondary maximum (29 ms−1) at 300°E. The zonal wave number components corresponding to this longitude variation in the Semidiurnal Tide are 7.7 ± 1.9 ms−1, 19.8 ± 1.5 ms−1 and 13.0 ± 1.3 ms−1 for s = 1, 2, 3 (westward), respectively where ±1−σ uncertainties are indicated. These results are in reasonable agreement with those simulated within the Kyushu GCM. However, there is roughly a four- to five-hour phase offset between the phases recovered from the observational data and from the Kyushu GCM, possibly connected with strong model phase gradients in this atmospheric regime.
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longitude variability of the solar Semidiurnal Tide in the lower thermosphere through assimilation of ground and space based wind measurements
Journal of Geophysical Research, 2003Co-Authors: K M Cierpik, A. H. Manson, Yasunobu Miyoshi, A.n. Fahrutdinova, J M Forbes, Saburo Miyahara, N. J. Mitchell, Christoph Jacobi, C E Meek, Y. I. PortnyaginAbstract:[1] Wind measurements from the Upper Atmosphere Research Satellite (UARS) and model output from the Middle Atmosphere General Circulation Model (GCM) at Kyushu University are used to investigate the nature of nonmigrating Semidiurnal Tides between 50–55°N using combined space-based (SBM) and ground-based (GBM) wind measurements at 95 km. The GCM is used to create a mock database to test the effects of various sampling scenarios, data gaps, and relative weighting between SBM and GBM, on retrieval of the longitude structure of the Semidiurnal Tide. SB sampling is based upon orbital characteristics of UARS. GB sampling corresponds to hourly radar measurements from Saskatoon (52°N, 107°W), Sheffield (53°N, 4°W), Collm (52°N, 15°E), Obninsk (55°N, 37°E), and Kazan (56°N, 49°E). Results are presented for the month of August when Semidiurnal amplitudes are large and sampling by UARS instruments is good. By compositing over a 5–10 day “fit span,” it is found that the combination of temporal coverage by GB radars and spatial sampling by the satellite is sufficient to allow reasonable recovery of the zonal wave number s = 1, 2, 3 components of the Semidiurnal Tide. Over significantly longer fit spans, the contributions of GBM become less critical. Using actual UARS and GBM during 1–20 August 1993, the Semidiurnal amplitude of eastward wind is found to vary from a minimum value (12 ms−1) at 20°E, to a maximum of 45 ms−1 near 160°E, and a secondary maximum (29 ms−1) at 300°E. The zonal wave number components corresponding to this longitude variation in the Semidiurnal Tide are 7.7 ± 1.9 ms−1, 19.8 ± 1.5 ms−1 and 13.0 ± 1.3 ms−1 for s = 1, 2, 3 (westward), respectively where ±1−σ uncertainties are indicated. These results are in reasonable agreement with those simulated within the Kyushu GCM. However, there is roughly a four- to five-hour phase offset between the phases recovered from the observational data and from the Kyushu GCM, possibly connected with strong model phase gradients in this atmospheric regime.
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On the longitudinal structure of the transient day-to-day variation of the Semidiurnal Tide in the mid-latitude lower thermosphere ? I. Winter season
Annales Geophysicae, 2001Co-Authors: E. G. Merzlyakov, Y. I. Portnyagin, A. H. Manson, H G Muller, C. Jacobi, N. J. Mitchell, A. N. Fachrutdinova, W. Singer, P. HoffmannAbstract: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)
D Pancheva - One of the best experts on this subject based on the ideXlab platform.
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Height-latitude structure of the vertical component of the migrating Semidiurnal Tide in the upper mesosphere and lower thermosphere region (80–100 km)
Izvestiya Atmospheric and Oceanic Physics, 2011Co-Authors: Y. I. Portnyagin, Plamen Mukhtarov, E. G. Merzlyakov, T. V. Solov’eva, Alexander Pogoreltsev, E. V. Suvorova, D PanchevaAbstract:The height-latitude distributions of parameters of the vertical wind component of the Semidiurnal Tide were calculated for the mesosphere and lower thermosphere (MLT) region (80–100 km) on the basis of empirical height-latitude distributions of the monthly mean parameters of variations in the horizontal wind component of the migrating Semidiurnal Tide. The constructed distributions are compared with the results of a numerical modeling of the migrating Semidiurnal Tide with the aid of a model of global circulation in the middle and upper atmosphere, as well as with the parameters of Semidiurnal temperature variations obtained from the data of satellite measurements. It is shown that different models yield the distributions of parameters of Semidiurnal variations, which agree within the errors of their values. The presence of high-latitude regions of local maximal amplitudes is a specific feature of the distributions of parameters of Semidiurnal variations in the vertical wind constructed in the course of this work. On the whole, at heights of about 90 km and higher, Semidiurnal variations in the vertical wind exceed the prevailing vertical wind in amplitude.
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Global structure, seasonal and interannual variability of the migrating Semidiurnal Tide seen in the SABER/TIMED temperatures (2002-2007)
Annales Geophysicae, 2009Co-Authors: D Pancheva, Plamen Mukhtarov, B. AndonovAbstract:Abstract. The present paper is focused on the global spatial (altitude and latitude) structure, seasonal and interannual variability of the migrating Semidiurnal Tide derived from the SABER/TIMED temperature measurements for 6 years (January 2002–December 2007). The tidal results are obtained by a new analysis method where the Tides (migrating and nonmigrating) and the planetary waves (zonally travelling and stationary) are simultaneously extracted from the satellite data. The strongest migrating Semidiurnal Tide has been derived at tropical latitudes (±20–30°) where it revealed significant amplification between May and August in the lower thermosphere of both hemispheres. On the average, the Semidiurnal temperature Tide is stronger in the SH (32 K) than that in the NH (30 K) and the tidal amplitudes at 110 km height are nearly a factor of 5 larger than those at 90 km. The migrating Semidiurnal Tide in both hemispheres revealed remarkable seasonal behavior at the altitude where it maximizes, ~110 km in the NH and ~115 km in the SH, indicating repeatable each year maxima exactly in May–June and August. However, while the main maximum in the NH is that in August, in the SH it is that in May. The vertical wavelengths indicated seasonal variability being larger in summer (~38–50 km) than in winter (~25–35 km). The seasonal behavior of the Semidiurnal Tide in the middle latitudes (±40°) is dominated by annual variability with a winter maximum in the upper mesosphere (90 km) of both hemispheres and summer one in the lower thermosphere (110 km). The NH summer maximum (June and August peaks) is much stronger than that in the SH (November and March peaks) having amplitudes of ~23 K and ~13–15 K respectively. The vertical wavelengths at both hemispheres indicated slight seasonal changes and a mean vertical wavelength of ~35 km is observed during most of the year. The interannual variability of the Semidiurnal Tide in the midlatitude lower thermosphere is at least partly connected with the stratospheric QBO as this effect is stronger in the NH.
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global structure seasonal and interannual variability of the migrating Semidiurnal Tide seen in the saber timed temperatures 2002 2007
Annales Geophysicae, 2009Co-Authors: D Pancheva, Plamen Mukhtarov, B. AndonovAbstract:Abstract. The present paper is focused on the global spatial (altitude and latitude) structure, seasonal and interannual variability of the migrating Semidiurnal Tide derived from the SABER/TIMED temperature measurements for 6 years (January 2002–December 2007). The tidal results are obtained by a new analysis method where the Tides (migrating and nonmigrating) and the planetary waves (zonally travelling and stationary) are simultaneously extracted from the satellite data. The strongest migrating Semidiurnal Tide has been derived at tropical latitudes (±20–30°) where it revealed significant amplification between May and August in the lower thermosphere of both hemispheres. On the average, the Semidiurnal temperature Tide is stronger in the SH (32 K) than that in the NH (30 K) and the tidal amplitudes at 110 km height are nearly a factor of 5 larger than those at 90 km. The migrating Semidiurnal Tide in both hemispheres revealed remarkable seasonal behavior at the altitude where it maximizes, ~110 km in the NH and ~115 km in the SH, indicating repeatable each year maxima exactly in May–June and August. However, while the main maximum in the NH is that in August, in the SH it is that in May. The vertical wavelengths indicated seasonal variability being larger in summer (~38–50 km) than in winter (~25–35 km). The seasonal behavior of the Semidiurnal Tide in the middle latitudes (±40°) is dominated by annual variability with a winter maximum in the upper mesosphere (90 km) of both hemispheres and summer one in the lower thermosphere (110 km). The NH summer maximum (June and August peaks) is much stronger than that in the SH (November and March peaks) having amplitudes of ~23 K and ~13–15 K respectively. The vertical wavelengths at both hemispheres indicated slight seasonal changes and a mean vertical wavelength of ~35 km is observed during most of the year. The interannual variability of the Semidiurnal Tide in the midlatitude lower thermosphere is at least partly connected with the stratospheric QBO as this effect is stronger in the NH.
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A link between variability of the Semidiurnal Tide and planetary waves in the opposite hemisphere
Geophysical Research Letters, 2007Co-Authors: Anne K. Smith, D Pancheva, N J Mitchell, Daniel R. Marsh, James M. Russell, Martin G. MlynczakAbstract:[1] Horizontal wind observations over four years from the meteor radar at Esrange (68°N, 21°E) are analyzed to determine the variability of the Semidiurnal Tide. Simultaneous global observations of temperature and geopotential from the SABER satellite instrument are used to construct time series of planetary wave amplitudes and geostrophic mean zonal wind. During Northern Hemisphere summer and fall, the temporal variability of the Semidiurnal Tide at Esrange is found to be well correlated with the amplitude of planetary wavenumber 1 in the stratosphere in high southern latitudes (i.e. in the opposite hemisphere). The correlations indicate that a significant part of the tidal variation at Esrange is due to dynamical interactions in the Southern Hemisphere. A corresponding robust correlation pattern for the Esrange Tides is not apparent at other times of the multiple years analyzed.
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planetary waves and variability of the Semidiurnal Tide in the mesosphere and lower thermosphere over esrange 68 n 21 e during winter
Journal of Geophysical Research, 2004Co-Authors: D Pancheva, N J MitchellAbstract:[1] The main features of the planetary waves and the variability of the Semidiurnal Tide with planetary wave periods observed by meteor radar over Esrange (68°N, 21 °E) have been investigated. The interval of 39 months covering continuous measurements from October 1999 to December 2002 has been examined. The planetary waves most frequently observed by meteor radar measurements in the mesosphere and lower thermosphere (80-100 km) over Esrange are: 5-, 8- to 10-, 16-, and 23-day waves (the quasi-2-day wave is excluded in this study). They are strongly amplified in the winter. Some differences between high- and middle-latitude planetary waves notwithstanding, the 5-, 10-, and 16-day waves are most probably related to the well-known normal mode. There are some reasons to believe that the vertically upward propagating 23-day wave could be generated by solar forcing. The variability of the Semidiurnal Tide with periods of planetary waves has been thoroughly studied as well. It is found that in the winter when the planetary waves are significantly amplified, a very strong periodic variability of the Semidiurnal Tide is observed as well. This result indicates that the most probable mechanism responsible for the periodic tidal variability during winter is in situ nonlinear coupling between Tides and planetary waves. Two winter periods have been examined (1999/2000 and 2001/2002) in order to find strong evidence supporting this suggestion. The validity of the frequency, phase, and vertical wavenumber (wavelength) relationship between the prime (the planetary wave and Semidiurnal Tide) and secondary waves has been established. The novel aspect of this work is that we show for the first time that the calculated vertical structures (vertical wavelengths) of the sum and difference secondary waves, which have very close periods, are actually very different.
Keith Makinson - One of the best experts on this subject based on the ideXlab platform.
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diurnal and Semidiurnal Tide induced lateral movement of ronne ice shelf antarctica
Geophysical Research Letters, 2012Co-Authors: Keith Makinson, Matt A King, Keith W Nicholls, Hilmar G GudmundssonAbstract:[1] Recent GPS observations from a spatially extensive network across Ronne Ice Shelf show significant daily ice flow variations. At all sites, the almost-synchronous horizontal displacements occur at diurnal and Semidiurnal tidal periods. During spring Tides, displacements, velocities and strains near the ice front have superimposed oscillations that are 300% of their mean values and occur over a six-hour period, resulting in regular ice shelf flow reversals. Close to ice stream grounding lines, however, the horizontal diurnal and Semidiurnal signals decay and almost vanish. From our analysis, we conclude that ice shelves respond primarily elastically to tidal tilting, thus accounting for the observed diurnal and Semidiurnal flow variations, and their amplification toward the ice shelf front. Our findings suggest that detailed modeling of these data could provide improved ice shelf and ice stream models for correctly simulating ice shelf flow and predicting future ice sheet evolution. Citation: Makinson, K., M. A. King, K. W. Nicholls, and G. Hilmar Gudmundsson (2012), Diurnal and Semidiurnal Tide-induced lateral movement of Ronne Ice Shelf, Antarctica, Geophys. Res. Lett., 39, L10501, doi:10.1029/2012GL051636.
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Diurnal and Semidiurnal Tide‐induced lateral movement of Ronne Ice Shelf, Antarctica
Geophysical Research Letters, 2012Co-Authors: Keith Makinson, Matt A King, Keith W Nicholls, G. Hilmar GudmundssonAbstract:[1] Recent GPS observations from a spatially extensive network across Ronne Ice Shelf show significant daily ice flow variations. At all sites, the almost-synchronous horizontal displacements occur at diurnal and Semidiurnal tidal periods. During spring Tides, displacements, velocities and strains near the ice front have superimposed oscillations that are 300% of their mean values and occur over a six-hour period, resulting in regular ice shelf flow reversals. Close to ice stream grounding lines, however, the horizontal diurnal and Semidiurnal signals decay and almost vanish. From our analysis, we conclude that ice shelves respond primarily elastically to tidal tilting, thus accounting for the observed diurnal and Semidiurnal flow variations, and their amplification toward the ice shelf front. Our findings suggest that detailed modeling of these data could provide improved ice shelf and ice stream models for correctly simulating ice shelf flow and predicting future ice sheet evolution. Citation: Makinson, K., M. A. King, K. W. Nicholls, and G. Hilmar Gudmundsson (2012), Diurnal and Semidiurnal Tide-induced lateral movement of Ronne Ice Shelf, Antarctica, Geophys. Res. Lett., 39, L10501, doi:10.1029/2012GL051636.
