scholarly journals Seasonal variations in the horizontal wind structure from 0–100 km above Rothera station, Antarctica (67° S, 68° W)

2005 ◽  
Vol 5 (4) ◽  
pp. 4291-4310 ◽  
Author(s):  
R. E. Hibbins ◽  
J. D. Shanklin ◽  
P. J. Espy ◽  
M. J. Jarvis ◽  
D. M. Riggin ◽  
...  
Keyword(s):  
Lower Thermosphere ◽  
Model Atmosphere ◽  
Horizontal Wind ◽  
Zero Crossing ◽  
Zonal Winds ◽  
Wind Structure ◽  
Falling Sphere ◽  
Wind Climatology ◽  
Meridional Winds ◽  
Summer Time

Abstract. A medium frequency spaced-antenna radar has been operating at Rothera station, Antarctica (67° S, 68° W) for two periods, between 1997–1998 and since 2002, measuring winds in the mesosphere and lower thermosphere. In this paper monthly mean winds are derived and presented along with three years of radiosonde balloon data for comparison with the HWM-93 model atmosphere and other high latitude southern hemisphere sites. The observed meridional winds are slightly more northwards than those predicted by the model above 80 km in the winter months and below 80 km in summer. In addition, the altitude of the summer time zero crossing of the zonal winds above the westward jet is overestimated by the model by up to 8 km. These data are then merged with the wind climatology obtained from falling sphere measurements made during the PORTA campaign at Rothera in early 1998 and the HWM-93 model atmosphere to generate a complete zonal wind climatology between 0 and 100 km as a benchmark for future studies at Rothera. A westwards (eastwards) maximum of 44 ms−1 at 67 km altitude occurs in mid December (62 ms−1 at 37 km in mid July). The 0 ms−1 wind contour reaches a maximum altitude of 90 km in mid November and a minimum altitude of 18 km in January extending into mid March at 75 km and early October at 76 km.

scholarly journals Seasonal variations in the horizontal wind structure from 0-100 km above Rothera station, Antarctica (67° S, 68° W)

2005 ◽  
Vol 5 (11) ◽  
pp. 2973-2980 ◽  
Author(s):  
R. E. Hibbins ◽  
J. D. Shanklin ◽  
P. J. Espy ◽  
M. J. Jarvis ◽  
D. M. Riggin ◽  
...  
Keyword(s):  
Lower Thermosphere ◽  
Model Atmosphere ◽  
Horizontal Wind ◽  
Zero Crossing ◽  
Zonal Winds ◽  
Wind Structure ◽  
Falling Sphere ◽  
Wind Climatology ◽  
Meridional Winds ◽  
Summer Time

Abstract. A medium frequency spaced-antenna radar has been operating at Rothera station, Antarctica (67° S, 68° W) for two periods, between 1997-1998 and since 2002, measuring winds in the mesosphere and lower thermosphere. In this paper monthly mean winds are derived and presented along with three years of radiosonde balloon data for comparison with the HWM-93 model atmosphere and other high latitude southern hemisphere sites. The observed meridional winds are slightly more northwards than those predicted by the model above 80 km in the winter months and below 80 km in summer. In addition, the altitude of the summer time zero crossing of the zonal winds above the westward jet is overestimated by the model by up to 8 km. These data are then merged with the wind climatology obtained from falling sphere measurements made during the PORTA campaign at Rothera in early 1998 and the HWM-93 model atmosphere to generate a complete zonal wind climatology between 0 and 100 km as a benchmark for future studies at Rothera. A westwards (eastwards) maximum of 44 ms-1 at 67 km altitude occurs in mid December (62 ms-1 at 37 km in mid July). The 0 ms-1 wind contour reaches a maximum altitude of 90 km in mid November and a minimum altitude of 18 km in January extending into mid March at 75 km and early October at 76 km.

scholarly journals Mean winds, temperatures and the 16- and 5-day planetary waves in the mesosphere and lower thermosphere over Bear Lake Observatory (42° N, 111° W)

2012 ◽  
Vol 12 (3) ◽  
pp. 1571-1585 ◽  
Author(s):  
K. A. Day ◽  
M. J. Taylor ◽  
N. J. Mitchell
Keyword(s):  
Zonal Wind ◽  
Lower Thermosphere ◽  
Planetary Waves ◽  
Zonal Winds ◽  
Annual Variability ◽  
Bear Lake ◽  
Meridional Winds ◽  
The Mean ◽  
Mesosphere And Lower Thermosphere ◽  
Wind Shears

Abstract. Atmospheric temperatures and winds in the mesosphere and lower thermosphere have been measured simultaneously using the Aura satellite and a meteor radar at Bear Lake Observatory (42° N, 111° W), respectively. The data presented in this study is from the interval March 2008 to July 2011. The mean winds observed in the summer-time over Bear Lake Observatory show the meridional winds to be equatorward at meteor heights during April−August and to reach monthly-mean velocities of −12 m s−1. The mean winds are closely related to temperatures in this region of the atmosphere and in the summer the coldest mesospheric temperatures occur about the same time as the strongest equatorward meridional winds. The zonal winds are eastward through most of the year and in the summer strong eastward zonal wind shears of up to ~4.5 m s−1 km−1 are present. However, westward winds are observed at the upper heights in winter and sometimes during the equinoxes. Considerable inter-annual variability is observed in the mean winds and temperatures. Comparisons of the observed winds with URAP and HWM-07 reveal some large differences. Our radar zonal wind observations are generally more eastward than predicted by the URAP model zonal winds. Considering the radar meridional winds, in comparison to HWM-07 our observations reveal equatorward flow at all meteor heights in the summer whereas HWM-07 suggests that only weakly equatorward, or even poleward flows occur at the lower heights. However, the zonal winds observed by the radar and modelled by HWM-07 are generally similar in structure and strength. Signatures of the 16- and 5-day planetary waves are clearly evident in both the radar-wind data and Aura-temperature data. Short-lived wave events can reach large amplitudes of up to ~15 m s−1 and 8 K and 20 m s−1 and 10 K for the 16- and 5-day waves, respectively. A clear seasonal and short-term variability are observed in the 16- and 5-day planetary wave amplitudes. The 16-day wave reaches largest amplitude in winter and is also present in summer, but with smaller amplitudes. The 5-day wave reaches largest amplitude in winter and in late summer. An inter-annual variability in the amplitude of the planetary waves is evident in the four years of observations. Some 41 episodes of large-amplitude wave occurrence are identified. Temperature and wind amplitudes for these episodes, AT and AW, that passed the Student T-test were found to be related by, AT = 0.34 AW and AT = 0.62 AW for the 16- and 5-day wave, respectively.

scholarly journals Mean winds in the MLT, the SQBO and MSAO over Ascension Island (8° S, 14° W)

2013 ◽  
Vol 13 (18) ◽  
pp. 9515-9523 ◽  
Author(s):  
K. A. Day ◽  
N. J. Mitchell
Keyword(s):  
Gravity Waves ◽  
Lower Thermosphere ◽  
Strong Support ◽  
Phase Relationship ◽  
Second Phase ◽  
Meteor Radar ◽  
Quasi Biennial Oscillation ◽  
Zonal Winds ◽  
Ascension Island ◽  
Meridional Winds

Abstract. Mean winds in the mesosphere and lower thermosphere (MLT) over Ascension Island (8° S, 14° W) have been measured at heights of approximately 80–100 km by a meteor radar. The results presented in this study are from the interval October 2001 to December 2011. In all years, the monthly-mean meridional winds display a clear annual oscillation. Typically, these winds are found to be southward during April–October, when they reach velocities of up to about −23 m s−1, and northward throughout the rest of the year, when they reach velocities up to about 16 m s−1. The monthly-mean zonal winds are generally westward throughout most of the year and reach velocities of up to about −46 m s−1. However, eastward winds are observed in May–August and again in December at the lower heights observed. These eastward winds reach a maximum at heights of about 86 km with velocities of up to about 36 m s−1, but decay quickly at heights above and below that level. The mesospheric semi-annual oscillation (MSAO) is clearly apparent in the observed monthly-mean zonal winds. The winds in first westward phase of the MSAO are observed to be much stronger than in the second phase. The westward phase of the MSAO is found to maximise at heights of about 84 km with typical first-phase wind velocities reaching about −35 m s−1. These meteor-radar observations have been compared to the HWM-07 empirical model. The observed meridional winds are found to be generally more southward than those of the model during May–August, when at the lower heights observed the model suggests there will be only weakly southward, or even northward, winds. The zonal monthly-mean winds are in generally good agreement, although in the model they are somewhat less westward than those observed. Throughout the observations there were eight occasions in which the first westward phase of the MSAO was observed. Strikingly, in 2002 there was an event in which the westward winds during the first phase of the MSAO were much stronger than normal and reached velocities of about −75 m s−1. This event is explained in terms of a previously proposed mechanism in which the relative phasing of the stratospheric quasi-biennial oscillation (SQBO) and the MSAO allows an unusually large flux of gravity waves of large westward phase speed to reach the mesosphere. It is the dissipation of these gravity waves that then drives the MLT winds to the large westward velocities observed. It is demonstrated that the necessary SQBO–MSAO phase relationship did indeed exist during 2002, but not during the other years observed here. This demonstration provides strong support for the suggestion that extreme zonal-wind events during the MSAO result from the modulation of gravity-wave fluxes.

scholarly journals Global empirical wind model for the upper mesosphere/lower thermosphere. I. Prevailing wind

2000 ◽  
Vol 18 (3) ◽  
pp. 300-315 ◽  
Author(s):  
Y. I. Portnyagin ◽  
T. V. Solovjova
Keyword(s):  
General Circulation ◽  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Systematic Bias ◽  
Prevailing Wind ◽  
Wind Model ◽  
Zonal Winds ◽  
Meridional Winds ◽  
Contour Plots ◽  
Thermospheric Dynamics

Abstract. An updated empirical climatic zonally averaged prevailing wind model for the upper mesosphere/lower thermosphere (70-110 km), extending from 80°N to 80°S is presented. The model is constructed from the fitting of monthly mean winds from meteor radar and MF radar measurements at more than 40 stations, well distributed over the globe. The height-latitude contour plots of monthly mean zonal and meridional winds for all months of the year, and of annual mean wind, amplitudes and phases of annual and semiannual harmonics of wind variations are analyzed to reveal the main features of the seasonal variation of the global wind structures in the Northern and Southern Hemispheres. Some results of comparison between the ground-based wind models and the space-based models are presented. It is shown that, with the exception of annual mean systematic bias between the zonal winds provided by the ground-based and space-based models, a good agreement between the models is observed. The possible origin of this bias is discussed.Key words: Meteorology and Atmospheric dynamics (general circulation; middle atmosphere dynamics; thermospheric dynamics)

scholarly journals FPI observations of nighttime mesospheric and thermospheric winds in China and their comparisons with HWM07

2013 ◽  
Vol 31 (8) ◽  
pp. 1365-1378 ◽  
Author(s):  
W. Yuan ◽  
X. Liu ◽  
J. Xu ◽  
Q. Zhou ◽  
G. Jiang ◽  
...  
Keyword(s):  
Zonal Wind ◽  
Annual Variation ◽  
Middle Atmosphere ◽  
Geomagnetic Latitude ◽  
Meridional Wind ◽  
Central China ◽  
Horizontal Wind ◽  
Zonal Winds ◽  
Meridional Winds ◽  
First Time

Abstract. We analyzed the nighttime horizontal neutral winds in the middle atmosphere (~ 87 and ~ 98 km) and thermosphere (~ 250 km) derived from a Fabry–Perot interferometer (FPI), which was installed at Xinglong station (40.2° N, 117.4° E) in central China. The wind data covered the period from April 2010 to July 2012. We studied the annual, semiannual and terannual variations of the midnight winds at ~ 87 km, ~ 98 km and ~ 250 km for the first time and compared them with Horizontal Wind Model 2007 (HWM07). Our results show the following: (1) at ~ 87 km, both the observed and model zonal winds have similar phases in the annual and semiannual variations. However, the HWM07 amplitudes are much larger. (2) At ~ 98 km, the model shows strong eastward wind in the summer solstice, resulting in a large annual variation, while the observed strongest component is semiannual. The observation and model midnight meridional winds agree well. Both are equatorward throughout the year and have small amplitudes in the annual and semiannual variations. (3) There are large discrepancies between the observed and HWM07 winds at ~ 250 km. This discrepancy is largely due to the strong semiannual zonal wind in the model and the phase difference in the annual variation of the meridional wind. The FPI annual variation coincides with the results from Arecibo, which has similar geomagnetic latitude as Xinglong station. In General, the consistency of FPI winds with model winds is better at ~ 87 and ~ 98 km than that at ~ 250 km. We also studied the seasonally and monthly averaged nighttime winds. The most salient features include the following: (1) the seasonally averaged zonal winds at ~ 87 and ~ 98 km typically have small variations throughout the night. (2) The model zonal and meridional nighttime wind variations are typically much larger than those of observations at ~ 87 km and ~ 98 km. (3) At ~ 250 km, model zonal wind compares well with the observation in the winter. For spring and autumn, the model wind is more eastward before ~ 03:00 LT but more westward after. The observed nighttime zonal and meridional winds on average are close to zero in the summer and autumn, which indicates a lack of strong stable tides. The consistency of FPI zonal wind with model wind at ~ 250 km is better than the meridional wind.

scholarly journals Climatological lower thermosphere winds as seen by ground-based and space-based instruments

2004 ◽  
Vol 22 (6) ◽  
pp. 1931-1945 ◽  
Author(s):  
J. M. Forbes ◽  
Yu. I. Portnyagin ◽  
W. Skinner ◽  
R. A. Vincent ◽  
T. Solovjova ◽  
...  
Keyword(s):  
Lower Thermosphere ◽  
Meteor Radar ◽  
Hemispheric Differences ◽  
Phase Retardation ◽  
Meridional Component ◽  
Zonal Winds ◽  
Doppler Imager ◽  
Meridional Winds ◽  
Role Based ◽  
Mf Radar

Abstract. Comparisons are made between climatological dynamic fields obtained from ground-based (GB) and space-based (SB) instruments with a view towards identifying SB/GB intercalibration issues for TIMED and other future aeronomy satellite missions. SB measurements are made from the High Resolution Doppler Imager (HRDI) instrument on the Upper Atmosphere Research Satellite (UARS). The GB data originate from meteor radars at Obninsk, (55° N, 37° E), Shigaraki (35° N, 136° E) and Jakarta (6° S, 107° E) and MF spaced-antenna radars at Hawaii (22° N, 160° W), Christmas I. (2° N, 158° W) and Adelaide (35° S, 138° E). We focus on monthly-mean prevailing, diurnal and semidiurnal wind components at 96km, averaged over the 1991-1999 period. We perform space-based (SB) analyses for 90° longitude sectors including the GB sites, as well as for the zonal mean. Taking the monthly prevailing zonal winds from these stations as a whole, on average, SB zonal winds exceed GB determinations by ~63%, whereas meridional winds are in much better agreement. The origin of this discrepancy remains unknown, and should receive high priority in initial GB/SB comparisons during the TIMED mission. We perform detailed comparisons between monthly climatologies from Jakarta and the geographically conjugate sites of Shigaraki and Adelaide, including some analyses of interannual variations. SB prevailing, diurnal and semidiurnal tides exceed those measured over Jakarta by factors, on the average, of the order of 2.0, 1.6, 1.3, respectively, for the eastward wind, although much variability exists. For the meridional component, SB/GB ratios for the diurnal and semidiurnal tide are about 1.6 and 1.7. Prevailing and tidal amplitudes at Adelaide are significantly lower than SB values, whereas similar net differences do not occur at the conjugate Northern Hemisphere location of Shigaraki. Adelaide diurnal phases lag SB phases by several hours, but excellent agreement between the two data sources exists for semidiurnal tidal phases throughout the year. These results are consistent with phase retardation effects in the MF radar technique that are thought to exist above about 90km. Prevailing and tidal amplitudes from Shigaraki track year-to-year variations in SB fields, whereas in the Southern Hemisphere poorer agreement exists. The above hemispheric differences are due in part to MF vs. meteor radar techniques, but zonal asymmetries and day-to-day variability, combined with inadequate sampling, may also be playing a role. Based on these results, some obvious recommendations emerge that are relevant to combined GB/SB studies as part of TIMED and other future aeronomy missions.

scholarly journals Mean winds of the mesosphere and lower thermosphere at 52° N in the period 1988–2000

2002 ◽  
Vol 20 (1) ◽  
pp. 81-91 ◽  
Author(s):  
H. R. Middleton ◽  
N. J. Mitchell ◽  
H. G. Muller
Keyword(s):  
General Circulation ◽  
Lower Thermosphere ◽  
Correlation Coefficients ◽  
Atmospheric Dynamics ◽  
Meridional Component ◽  
Zonal Winds ◽  
Meridional Winds ◽  
Middle Atmospheric Dynamics ◽  
The Uk ◽  
Mlt Region

Abstract. A meteor radar in the UK (near 52° N) has been used to measure the mean winds of the mesosphere/lower-thermosphere (MLT) region over the period 1988–2000. The seasonal course and interannual variability is characterised and comparisons are made with a number of models. Annual mean wind trends were found to be + 0.37 ms-1 yr-1 for the zonal component and + 0.157 ms-1 yr-1 for the meridional component. Seasonal means revealed significant trends in the case of meridional winds in spring ( + 0.38 ms-1 yr-1) and autumn ( + 0.29 ms-1 yr-1), and zonal winds in summer ( + 0.48 ms-1 yr-1) and autumn ( + 0.38 ms-1 yr-1). Significant correlation coefficients, R, between the sunspot number and seasonal mean wind are found in four instances. In the case of the summer zonal winds, R = + 0.732; for the winter meridional winds, R = - 0.677; for the winter zonal winds, R = - 0.472; and for the autumn zonal winds R = + 0.508.Key words. Meteorology and atmospheric dynamics (climatology; general circulation; middle atmospheric dynamics)

scholarly journals Climatology of thermospheric neutral winds over Oukaïmeden Observatory in Morocco

2017 ◽  
Vol 35 (1) ◽  
pp. 161-170 ◽  
Author(s):  
Mohamed Kaab ◽  
Zouhair Benkhaldoun ◽  
Daniel J. Fisher ◽  
Brian Harding ◽  
Aziza Bounhir ◽  
...  
Keyword(s):  
Dissociative Recombination ◽  
Horizontal Wind ◽  
Wind Model ◽  
Neutral Winds ◽  
Zonal Winds ◽  
Early Evening ◽  
Atlas Mountains ◽  
Fabry Perot ◽  
Meridional Winds ◽  
High Atlas Mountains

Abstract. In order to explore coupling between the thermosphere and ionosphere and to address the lack of data relating to thermospheric neutral winds and temperatures over the African sector, a new system of instruments was installed at the Oukaïmeden Observatory located in the high Atlas Mountains, 75 km south of Marrakesh, Morocco (31.206° N, 7.866° W, 22.84° N magnetic). In this work we present the first multi-year results of the climatology of meridional and zonal winds obtained during the period from January 2014 to February 2016, including observations from 648 nights. The measurements are obtained using an imaging Fabry–Pérot interferometer, which measures the 630.0 nm emissions caused by dissociative recombination of O2+. The basic climatology of the winds is as expected, showing zonal winds that are strongly eastward in the early evening just after sunset with a speed of 50 to 100 m s−1 decreasing in magnitude, and reversing directions in the local summer months, towards sunrise. The meridional winds are slightly poleward in the early evening during the local winter, before reversing directions around 21:00 LT. In the local summer months, the meridional winds are equatorward for the entire night, reaching a maximum equatorward speed of 75 m s−1. We compare the observed climatologies of neutral winds to that provided by the recently updated Horizontal Wind Model (HWM14) in order to validate that model's predictions of the thermospheric wind patterns over the eastern portion of Africa. The model captures much of the features in the observational climatologies. The most notable exception is for the zonal winds during local summer, when the maximum eastward wind in the observations occurs approximately 4 h later than seen in the model results.

scholarly journals The two-day wave in the Antarctic and Arctic mesosphere and lower thermosphere

2009 ◽  
Vol 9 (2) ◽  
pp. 10271-10301 ◽  
Author(s):  
V. M. Tunbridge ◽  
N. J. Mitchell
Keyword(s):  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Zonal Flow ◽  
Radar Data ◽  
The Arctic ◽  
Horizontal Wind ◽  
Height Range ◽  
Zonal Winds ◽  
The Antarctic ◽  
Full Height

Abstract. There have been comparatively few studies reported of the 2-day planetary wave in the middle atmosphere at polar latitudes. Here we report studies made using high-latitude meteor radars at Rothera in the Antarctic (68° S, 68° W) and Esrange in Arctic Sweden (68° N, 21° E). Observations from 2005–2008 are used for Rothera and from 1999–2008 for Esrange. Data were recorded for heights of 80–100 km. The radar data reveal distinct summertime and wintertime 2-day waves. The Antarctic summertime wave occurs with significant amplitudes in January–February at heights between about 88–100 km. Horizontal wind monthly variances associated with the wave exceed 160 m2 s−2 and the zonal component has larger amplitudes than the meridional. In contrast, the Arctic summertime wave occurs for a longer duration, June–August and has meridional amplitudes larger than zonal. The Arctic summertime wave is weaker than that in the Antarctic and maximum monthly variances are typically 60 m2 s−2. In both hemispheres the summertime wave reaches largest amplitudes in the strongly sheared eastward zonal flow above the zero wind line and is largely absent in the westward flow below. The observed differences in the summertime wave is probably due to the differences in the background zonal winds in the two hemispheres. The Antarctic and Arctic wintertime waves have very similar behavior. The Antarctic wave has significant amplitudes in May–August and the Arctic wave in November–February. Both are evident across the full height range observed.

scholarly journals Mean winds, SAO and QBO in the stratosphere, mesosphere and lower thermosphere over Ascension Island (8° S 14° W)

2013 ◽  
Vol 13 (3) ◽  
pp. 6779-6805
Author(s):  
K. A. Day ◽  
N. J. Mitchell
Keyword(s):  
Lower Thermosphere ◽  
Strong Support ◽  
Phase Relationship ◽  
Phase Speed ◽  
Zonal Flow ◽  
Quasi Biennial Oscillation ◽  
Zonal Winds ◽  
Ascension Island ◽  
Meridional Winds ◽  
Mesosphere And Lower Thermosphere

Abstract. Mean winds in the mesosphere and lower thermosphere (MLT) over Ascension Island (8° S and 14° W) have been investigated using meteor radar wind observations. The results presented in this study are from the interval October 2001 to December 2011. There is a clear annual oscillation in the monthly-mean meridional winds. The monthly-mean meridional winds observed over Ascension Island at meteor heights are found to be southward during April–October, reaching velocities up to about −23 m s−1 and northward the rest of the year, reaching velocities up to about 16 m s−1. The monthly-mean zonal winds are generally westward through most of the year, reaching velocities up to about −46 m s−1. However, there are eastward winds in May–August and again in December in the lower heights that the radar observes. These winds maximises at heights of about 86 km reaching velocities up to about 36 m s−1 and decays quickly above and below. The Mesospheric Semi-Annual Oscillation (MSAO) is clearly observed in the monthly-mean zonal winds. The first westward phase of the winds is much stronger than the second. The first westward phase of the MSAO was found to maximise at heights of about 84 km and to in general reach amplitudes of about −35 m s−1. We have compared the HWM-07 model to our observations. Our observed meridional winds are generally more southward than those of the model at meteor heights in the southern hemispheric winter, whereas HWM-07 suggests that in this season only weakly southward, or even northward flows occur at the lower heights. The zonal monthly-mean winds are in general agreement but somewhat less westward than observed by the radar. In one of the eight events in which the first westward phase of the MSAO was observed, the strongest westward winds reached about −75 m s−1, compared to the mean of about −35 m s−1 for other events. We explain this observation in terms of a mechanism which has been previously proposed by others. In this the relative phasing of the Stratospheric Quasi-Biennial Oscillation (SQBO) and the MSAO allow an unusually large flux of gravity waves with westward phase speed to reach the mesosphere. The dissipation of these waves then drives the MLT winds to large westward velocities. We demonstrate that the necessary phase relationship existed during the event we observed in 2002 and not during other times. This provides strong support for the suggestion that those extremes in zonal flow are a~result of modulated gravity-wave fluxes.

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