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1.
Data about the variations of mesopause temperature (～87 km) obtained from ground-based spectrographic measurements of the OH emission (834.0 nm, band (6-2)) at Irkutsk and Zvenigorod observatories were compared with satellite data on vertical temperature distribution in the atmosphere from Aura MLS v3.3. We analyzed MLS data for two geopotential height levels: 0.005 hPa (～84 km) and 0.002 hPa (～88 km) as the closest to OH height (～87 km). We revealed that Aura MLS temperature data have lower values than ground-based (cold bias). In summer periods, that difference increases. Aura cold biases compared with OH(6-2) at Irkutsk and Zvenigorod were calculated. For the 0.002 hPa height level, the biases are 10.1 and 9.4 K, and for 0.005 hPa they are 10.5 and 10.2 K at Irkutsk and Zvenigorod, respectively. When the bias is accounted for, an agreement between Aura MLS and OH(6-2) data obtained at both Irkutsk and Zvenigorod is remarkable.  相似文献   

2.
Based on observations of mesopause emissions, namely, emissions of hydroxyl (band (6-2)) and molecular oxygen (band (0-1) of the atmospheric system), their systematic nighttime and seasonal variations are determined at Zvenigorod Observatory in 2000–2008. It is shown that the intensity of hydroxyl emission decreases during the entire night or first half-night, probably due to the influence of the chemical sink of atomic oxygen on the nighttime behavior of hydroxyl emission. The nighttime behavior of the intensity of molecular oxygen emission is explained by the action of atmospheric tides. The seasonal behavior of emissions is characterized by two minima, in April–May and December; it is caused by the annual behavior of the atomic oxygen content, temperature, and atmospheric density in the emitting layer. Based on the emission data, we determined the seasonal variations of atomic oxygen at heights of ∼87 km (maximum of hydroxyl emission) and ∼95 km (maximum of molecular oxygen emission).  相似文献   

3.
Semidiurnal tidal features have been examined in the Mesosphere and Lower Thermosphere (MLT) from the long-term (2002–2007) meteor wind data over Maui (20.75°N, 156.43°W). Amplitude and phase obtained from the harmonic analysis exhibit large day to day variability. Mean amplitude obtained from the monthly mean data over the observation period is found to vary within ～8–28 m/s and 10–32 m/s for the zonal and meridional winds, respectively. The amplitude has revealed clear semiannual oscillation (SAO) pattern with maxima during solstices and altitudinal growth in both wind components. Significant resemblance in its variability with other observations carried out from the low latitude sites all over the globe is obtained. Vertical wavelength estimated from the phase gradients exposes large values (>90 km) in all seasons. Contribution of the semidiurnal tide to the total tidal variability in the MLT is found to vary over wide range throughout the year with generally higher influence during winter season over diurnal and terdiurnal components.  相似文献   

4.
The seasonal dependences of the response of the hydroxyl ((6–2) band) and molecular oxygen O2(b 1Σ g + ) ((0–1) band) emission intensities, temperature, and density indicator in the region of the hydroxyl emission maximum (87 km) to solar activity have been obtained based on the spectral observations of the mesopause emissions at Zvenigorod observatory during 2000–2007. The ratio of the OH (7–3) and (9–4) band intensities, characterizing the behavior of the vibrational temperature, has been used as an indicator of density. It has been established that the response of the studied mesopause characteristics to solar activity is positive in all seasons. In winter the response is maximal in the intensities and temperature and is minimal in the density indicator. The main mechanisms by which solar activity affects the mesopause characteristics have been considered. The behavior of the internal gravity waves with periods of 0.33–7 h depending on solar activity has been studied. It has been noted that these waves become more active at a minimum of the 11-year solar cycle.  相似文献   

5.
Based on the horizontal winds measured using SKiYMET meteor wind radar during the period of June 2004–May 2007, the seasonal and interannual variability of the diurnal and semidiurnal amplitudes and phases in the mesospheric and lower thermospheric (MLT) region over a low-latitude station Trivandrum (8.5°N) are investigated. The monthly values of amplitudes and phases are calculated using a composite day analysis. The zonal and meridional diurnal tidal amplitudes exhibit both annual and semiannual oscillations. The zonal and meridional components of semidiurnal tide show a significant annual oscillation. The phase values of both diurnal and semidiurnal tides exhibit annual oscillation above 90 km. The effect of background wind in the lower atmosphere on the strength of diurnal tidal amplitudes in the MLT region is studied. The effect of diurnal tides on the background wind in the lower thermosphere is also discussed.  相似文献   

6.
The lunar semidiurnal tide in winds measured at around 90 km altitude has been isolated with amplitudes observed up to 4 m s–1. There is a marked amplitude maximum in October and also a considerable phase variation with season. The average variation of phase with height indicated a vertical wavelength of more than 80 km but this, and other results, needs to be viewed in the light of the considerable averaging required to obtain statistical significance. Large year-to-year variations in both amplitude and phase were also found. Some phase comparisons with the GSWM model gave reasonable agreement but the model amplitudes above a height of 100 km were much larger than those measured. An attempt to make a comparison with the lunar geomagnetic tide did not yield a statistically significant result.  相似文献   

7.
Regular measurements of the velocity and direction of the horizontal wind in the mesosphere/lower thermosphere (MLT) region at a height of ∼95 km have been conducted since 1975 over Eastern Siberia (Badary observatory near Irkutsk), using the spaced-diversity reception method in the LF range. The accumulated database of measurement results (for more than 20 years, from 1974 to 1996) makes it possible to get information on the impact on wind in the MLT region from both below (stratospheric warmings) and above (geomagnetic storms as a consequence of magnetospheric disturbances) with sufficient statistical reliability. Effects of stratospheric warmings and strong geomagnetic storms in the prevailing wind and amplitude of the semidiurnal tide are evaluated by the superposed epoch method. It is shown that the effects of stratospheric warmings depend on the type (intensity) of stratospheric warming and on the phase of quasi-biennial oscillations of the wind in the equatorial stratosphere at the 30 hPa level. The response of MLT winds to external impacts is different for the 21st and 22nd cycles of solar activity. Effects of geomagnetic storms (A p > 100) are manifested in the decrease in the eastward prevailing wind and increase in the semidiurnal tide amplitude.  相似文献   

8.
The mesopause kinetic temperature at an altitude of 87 km measured with a SABER broadband radiometer installed on the TIMED satellite and the hydroxyl molecule rotational temperature measured with a ground-spectrograph installed in high-latitude eastern Siberia (Maimaga optical station; φ = 63°N, λ = 129.5°E) are compared. The data of the observations performed from 2002 to 2006 have been analyzed. The temperatures measured during the satellite passes at distances not larger than 300 km from the intersection of the spectrograph sighting line with the hydroxyl emitting layer (∼87 km) have been compared. An analysis of 130 cases of coincident measurements indicated that the average hydroxyl molecule rotational temperatures are systematically lower than the average kinetic temperature at an altitude of the hydroxyl layer measured with SABER by 4.4 K (with a standard deviation of 11.4 K). A seasonal dependence is observed regarding the difference between the ground-based and satellite measurements. The difference decreases from 10 K in January to zero towards March. However, the time variations in the temperature obtained with the ground-based device and on the satellite are similar. Based on the performed analysis, it has been concluded that a series of hydroxyl rotational temperatures can be used to study temperature variations on different time scales, including long-term trends at the temperature emission altitude (∼87 km).  相似文献   

9.
The method for determining the rotational temperature of the hydroxyl emission of the upper atmosphere is analyzed. It is shown that a discrepancy of up to 14 K appears in the temperature values determined for the region of OH emission (～87 km) since different researchers use the intensity factors (line strengths) of the lines of the rotational structure of hydroxyl bands based on various theoretical calculations. This discrepancy considerably exceeds the error (2–3 K) of direct temperature measurements. The use of the set of such data in the analysis of the time and spatial temperature regime can lead to a distortion of the character of the long-term changes in the mesopause temperature. Analytical expressions are obtained making it possible to calculate a systematic correction for the temperatures determined with the use of various intensity factors. One should also take into account considerable seasonal variations in the dependence of rotational temperature values on the level of the hydroxyl vibrational excitation.  相似文献   

10.
Twelve years of horizontal wind data from the Scott Base MF radar and the Halley SuperDARN radar recorded between January 1996 and December 2007 are analysed to study the interannual variability of the migrating (S=2) and non-migrating (S=1) components of the semidiurnal tide around 78°S in the Antarctic upper mesosphere. Significant quasi-biennial modulation of the summer time S=1 component is observed. During early summer the amplitude of the component is up to 4 ms?1 stronger during the easterly phase of the equatorial stratospheric quasi-biennial oscillation (QBO) measured at 30 hPa. No statistically significant effect is seen in amplitude of the migrating component of the tide, or in the phase (time of maximum) of either component. These results are discussed in the light of previous observations of the interannual variability of the semidiurnal tide.  相似文献   

11.
The Islas Quemadas dome in Lake Ilopango, El Salvador, was extruded during December 1879 to March 1880. The eruption took place in six distinct periods, five of which began near fortnightly minima in the amplitude of the semidiurnal solid earth tide. An earthquake swarm preceded dome extrusion. Felt earthquakes were carefully recorded during a two-day period preceding a destructive main shock that occurred on December 27, 1879. During this foreshock sequence the periods of highest earthquake activity occurred at times of maxima and minima in semidiurnal solid-earth tide. The four largest earthquakes, including the main shock, occurred at maxima in the semidiurnal tide.  相似文献   

12.
With the launch of the TIMED satellite in December 2001, continuous temperature and wind data sets amenable to MLT tidal analyses became available. The wind measuring instrument, the TIMED Doppler Interferometer (TIDI), is operating since early 2002. Its day- and nighttime capability allows to derive tidal winds over a range of MLT altitudes. This paper presents climatologies (June 2002–June 2005) of monthly mean amplitudes and phases for six nonmigrating semidiurnal tidal components between 85 and 105 km altitude and between 45°S and 45°N latitude (westward propagating wave numbers 4, 3, 1; the standing oscillation s0; and eastward propagating wave numbers 1, 2) in the zonal and meridional wind directions.Amplitude errors are 15–20% (accuracy) and 0.8 m/s (precision). The phase error is 2 h. The TIDI analysis agrees well with 1991–1994 UARS results at 95 km. During boreal winter, amplitudes of a single component can reach 10 m/s at latitudes equatorward of 45°. Aggregate effects of nonmigrating tides can easily reach or exceed the amplitude of the migrating tide. Comparisons with the global scale wave model (GSWM) and the thermosphere–ionosphere–mesosphere–electrodynamics general circulation model (TIME-GCM) are partly inconclusive but they suggest that wave–wave interaction and latent heat release in the tropical troposphere both play an important role in forcing the semidiurnal westward 1, westward 3, and standing components. Latent heat release is the leading source of the eastward propagating components.  相似文献   

13.
Long-term wind measurements carried out at 6 northern midlatitude sites (Saskatoon, Sheffield, Juliusruh, Collm, Obninsk, Kazan) are investigated to establish a climatology of the semidiurnal tide in the mesopause region for the narrow latitudinal range between 52°N and 56°N. Comparison of zonal and meridional components shows that in general the horizontal components are circularly polarized. Intercomparison of amplitudes and phases generally shows good agreement between the results from the different measuring systems. The results are compared with an empirical model of the semidiurnal tide. The longitudinal variation of the semidiurnal tide is small in summer, but the tidal amplitudes in winter are larger at Saskatoon and Kazan, compared with the results from the other sites. The possible influence of wave–tidal interaction in the stratosphere on the interannual variability of this difference is discussed.  相似文献   

14.
Abstract

Tidal pressures and currents were measured with self‐contained capsules dropped to the sea floor for one month at distances of 175, 190, and 500 nautical miles from San Diego. These observations, together with a one‐week bottom pressure record by Filloux at 750 n miles, and three half‐week bottom current records by Isaacs et al, at intermediary distances, were analyzed for tidal components by cross‐correlation with a noise‐free reference time series. (For short records this method has some merit over classical tide analysis.) It was found that the tide decays seaward to e‐1 times the coastal amplitude over a distance of order 1000 km for the semidiurnal species, slower for the diurnal species. Tidal currents turn counterclockwise, and are polarized with maximum flow parrallel to shore in the direction of tidal propagation (320°T) at local high tide. The current amplitude is roughly 2 cm/sec for the semidiurnal component, 1 cm/sec for the diurnal component. Superimposed baroclinic tidal currents lead to poor signal: noise ratios (between 1:1 and 10:1) for the barotropic currents. In contrast, the ratio is typically 1000:1 for the bottom pressures and generally exceeds that for coastal tide stations of comparable duration. Published I.H.B. tidal constants for exposed California coastal stations indicate “upshore” (towards 320°T) propagation at 140 m/sec for semidiurnal tides. 214 m/sec for diurnal tides.

To interpret these diverse observations, we have computed the dispersion laws for all possible rotationally‐gravitationally trapped waves against a straight coast with shelf. Trapped solutions are conveniently portrayed in terms of a parameter μ such that ? = sin μ = iu/v and f = ‐ cos μ = η/v define the ellipticity and impedance of the wave motion, η, u and v being off‐shelf dimensionless elevation, normal‐to‐shore and longshore components of velocity, respectively. We then attempt to fit the observations by a superposition of the possible wave classes, all of the same tidal frequency: (a) a free Kelvin‐like edge wave with small μ (mostly trapped by rotation, but somewhat slowed by the shelf); (6) a free Poincare‐like leaky wave; and (c) a forced wave (the distortion of the sea bottom by the tide producing forces plays a significant role). The mod el can account for the main features of the observed tidal heights, and gives relative amplitudes at the coast of 54:16:4 cm for components a:b:c in the case of the semidiurnal tides, 21:24:9 cm for the diurnal tides. The results place a semidiurnal amphidrome about midway between San Diego and Hawaii. Tidal currents are not well fitted by the model, and there are problems associated with the separation of barotropic and baroclinic modes, and with the benthic boundary layer. Coastal energy dissipation is small in the sea under investigation, but a “ capacitive “ phase delay appears to be associated with Northern California harbors and inland waters.  相似文献   

15.
Observations of semidiurnal internal tidal currents from three moorings deployed on the continental shelf off central Chile during summer and winter of 2005 are reported. The spectra of the baroclinic currents showed large peaks at the semidiurnal band with a dominant counterclockwise rotation, which was consistent with internal wave activity. The amplitude of the barotropic tidal currents varied according to the spring–neap cycle following the sea level fluctuations. In contrast, the amplitudes of the internal tide showed high spatial-temporal variability not directly related to the spring–neap modulation. Near the middle of the continental shelf and near the coast (San Vicente Bay) the variance of the semidiurnal baroclinic current is larger than the variance of its barotropic counterpart. The vertical structure of the baroclinic tidal current fluctuations was similar to the structure of the first baroclinic internal wave mode. In general, in the three study sites the variance of the baroclinic current was larger near the surface and bottom and tended to show a minimum value at mid depths. Kinetic energy related to semidiurnal internal waves was larger in winter when stratification of the water column was stronger. During summer, upwelling and the decrease of freshwater input from nearby rivers reduced the vertical density stratification. The amplitude of the semidiurnal internal tide showed a tendency to be enhanced with increasing stratification as observed in other upwelling areas. The continental shelf break and submarine canyons, which limit the continental shelf in the alongshore direction, represent near-critical slopes for the semidiurnal period and are suggested to be the main internal tide generation sites in the study region.  相似文献   

16.
Among 2187 nights of airglow observations of the OH(6-2) and O2b(0-1) bands from Argentina (mainly from El Leoncito, 32°S 69°W), 132 show airglow brightness jumps (ABJs) of short duration (16 min median). ABJs are supposed to be related to mesospheric bores or similar nonlinear waves. Several occurrence patterns were identified, which a successful explanation must take into account. ABJs occur preferably in the OH layer at 87 km, and are less likely in the O2 layer at 95 km, maybe because ducts prefer lower altitudes. The seasonal distribution of nights when ABJs are observed only in the OH layer clearly shows a winter maximum centered around solstice, and equinox minima. In contrast, the seasonal distribution of ABJ nights in O2 is flat. Most ABJs simultaneously present in OH and O2 show anticorrelated variation between both layers. ABJ nights tend to occur in clusters lasting several days, which probably reflects duct lifetime.  相似文献   

17.
During the multiband wave Pc1 event on March 7, 2001 the EISCAT UHF and VHF incoherent scatter radars operated simultaneously covering an exceptionally wide altitude range of the ionosphere ～90—2000 km. This made possible to test the ionospheric Alfvén resonator (IAR) model over a large altitude range. The three lowest IAR eigenfrequencies, where the most of the Pc1 pulsation signal bands occur, were selected for the spatial analysis of the standing wave electromagnetic fields, applying the full-wave numerical simulation method. The altitude spread of amplitude maxima and nodes together with polarization characteristics of oscillation maxima in the horizontal plane are presented. The comparison of the standing wave oscillations on the altitude profile with the signal amplitude observed on the ground is also presented.  相似文献   

18.
The parameters of internal gravity waves detected based on the variations in the hydroxyl molecule emission are statistically analyzed. The wave structures were registered with an all-sky infrared camera at Maimaga optical station (? = 63° N, λ = 129.5° E). The data obtained in the winter period of 1998–2002 are analyzed. In total, 162 waves, the majority of which propagated westward, were recorded. The wavelengths vary from 15.4 to 100 km (the average value is ～31 km); the observed horizontal phase velocities change from 19 to 166 m/s (the average value is ～60 m/s), and the estimated periods are 9–90 min (the average value is ～11 min). The statistical characteristics of the waves do not differ from those of similar waves at middle and low latitudes. The azimuthal dependence of the wave propagation direction is consistent with the theory of wave filtration by a background wind in the middle atmosphere. Probable sources of the waves are mountain ranges located at a distance of 200 km east of the observation site. Somewhat greater values of the mean wavelength and wave propagation velocities than those recorded at lower latitudes may be due to the lower loss of energy and velocity of the waves during their propagation from the source to the mesosphere, although other causes are not ruled out. Ripple-type waves have the same direction of propagation as band-type waves.  相似文献   

19.
Horizontal winds in the mesosphere and lower thermosphere over the Antarctic have been measured by a meteor radar at Rothera (67.5°S, 68.0°W) and MF radar at Davis (68.6°S, 78.0°E). Data from Rothera recorded over a 20-month interval in 2005–2006 and data from Davis recorded over the 13-year interval 1994–2006 are examined to investigate the monthly mean behaviour of the lunar semidiurnal tide. Both data sets show a clear signal of the 12.42-h lunar semidiurnal (M2) tide. The amplitude reaches values as large as 8 m s−1. The vertical wavelengths of the tide vary seasonally from 10 to 65 km. Comparisons of the phase of the tide measured over the two sites reveals that it does not purely consist of a migrating wavenumber 2 mode. This suggests that other, non-migrating, modes are likely to be present.  相似文献   

20.
Seasonal variations in the auroral E-region neutral wind for different solar activity periods are studied. This work is based on neutral wind data obtained over 56 days between 95–119 km altitude under geomagnetic quiet conditions (Ap<16) during one solar cycle by the European Incoherent Scatter radar located in northern Scandinavia. In general, the meridional mean wind shifts northward, and the zonal mean wind increases in eastward amplitude from winter to summer. The zonal mean wind blows eastward in the middle and lower E-region for each season and for each solar condition except for the equinox, where the zonal mean wind blows westward at and below 104 km. Solar activity dependence of the mean wind exists during the winter and equinox seasons, while in summer it is less prominent. Under high solar activity conditions, the altitude profiles of the horizontal mean winds in winter and the equinoxes tend to resemble those in summer. The horizontal diurnal tide is less sensitive to solar activity except during summer when the meridional amplitude increases by ∼10 m s−1 and the corresponding phase shifts to a later time period (1–2 h) during high solar activity. Seasonal dependence of the semidiurnal tide is complex, but is found to vary with solar activity. Under low solar activity conditions the horizontal semidiurnal amplitude shows seasonal dependence except at upper E-region heights, while under high solar activity conditions it becomes less sensitive to seasonal effects (except for the meridional component above 107 km). Comparisons of mean winds with LF and UARS observations are made, and the driving forces for the horizontal mean winds are discussed for various conditions.  相似文献   

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