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1.
利用为期一年的卫星遥感温度（SABER/TIMED）资料重建了120°E子午圈内中间层和低热层大气潮汐各主要频率分量（周日、半日和8小时潮汐）.这些主要频率分量随高度振幅增大，在97 km高度达到显著的振幅；其中迁移性周日潮汐在97 km高度出现极大振幅，然后随高度衰减.本文从考察迁移性成分和非迁移性成分各自在总潮汐中贡献角度出发，着重讨论了那些对形成该子午圈中97 km高度上整体潮汐扰动起控制作用的潮汐成分.结果显示，对周日和半日频率这两种潮汐而言，迁移性成分控制了它们的总体时空分布.在春分季节，迁移性周日潮的控制作用最显著，决定了赤道和两半球热带的活动中心；其中北半球副热带地区的季节变化形势与以往利用武汉（30°N，114°E）流星雷达风测量资料开展分析得到的结果是一致的；其他季节受非迁移性成分明显影响，例如，在本文关注的2005年中，夏至季节受（1，0）模、（1，-3）模和（1，-2）模的共同影响形成了从赤道向南延伸的活动中心，极值中心位于赤道附近，振幅达到了20 K以上，是全年的最大值.受迁移性成分控制，半日潮活动主要出现在两半球热带地区，北半球活动中心位于秋分季节（振幅达到13 K），南半球活动中心位于春分和夏至之间.其他季节受非迁移成分的影响，形成若干分布在两半球的活动中心.在本文关注的40°S～40°N范围内，与周日潮和半日潮相比，8小时潮汐具有显著较低的振幅；另外，虽然迁移性成分在一年中的大部分时间系统地分布在两半球热带地区，但是非迁移成分具有与迁移性成分相当或更大的振幅，在整体上控制了这种潮汐的时空分布.  相似文献   

2.
The ionospheric electron gas can be heated artificially by a powerful radio wave. According to our modeling, the maximum effect of this heating occurs in the D-region where the electron temperature can increase by a factor of ten. Ionospheric plasma parameters such as Ne,Te and Ti are measured by EISCAT incoherent scatter radar on a routine basis. However, in the D-region the incoherent scatter echo is very weak because of the low electron density. Moreover, the incoherent scatter spectrum from the D-region is of Lorentzian shape which gives less information than the spectrum from the E- and F-regions. These make EISCAT measurements in the D-region difficult. A combined EISCAT VHF-radar and heating experiment was carried out in November 1998 with the aim to measure the electron temperature increase due to heating. In the experiment the heater was switched on/off at 5 minute intervals and the integration time of the radar was chosen synchronously with the heating cycle. A systematic difference in the measured autocorrelation functions was found between heated and unheated periods.  相似文献   

3.
We performed a statistical and spectral analysis of variations in two main parameters of the ionospheric F2 layer: critical frequency (f 0F2) and peak height (h m F2), recorded at an ionospheric station in Irkutsk (52.5°N, 104.0°E) in the period from December 1, 2006, to January 31, 2008, under low solar activity conditions. It was found that the f 0F2 and h m F2 variations contained quasi-harmonic oscillations with periods T n = 24/n h (n = 1−7). We studied the seasonal changes in the mean and median values of monthly f 0F2 and h m F2 time series, their spectra, as well as the amplitudes and phases of the diurnal (n = 1) and semidiurnal (n = 2) variations. It is shown that the amplitude of the diurnal f 0F2 variations was maximal in October–March 2007 and minimal in May–August 2007. The diurnal f 0F2 variations were maximal at noon in the winter months and at 1600 LT in the summer months. The semidiurnal f 0F2 variations had two maxima: a primary maximum in December and January and a secondary maximum in May–July. The maxima of semidiurnal f 0F2 variations were shifted from 0000 and 1200 LT in winter to 0900 and 2100 LT in summer.  相似文献   

4.
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5.
This study examines connections between mean sea level (MSL) variability and diurnal and semidiurnal tidal constituent variations at 17 open-ocean and 9 continental shelf tide gauges in the western tropical Pacific Ocean, a region showing anomalous rise in MSL over the last 20 years and strong interannual variability. Detrended MSL fluctuations are correlated with detrended tidal amplitude and phase fluctuations, defined as tidal anomaly trends (TATs), to quantify the response of tidal properties to MSL variation. About 20 significant amplitude and phase TATs are found for each of the two strongest tidal constituents, K1 (diurnal) and M2 (semidiurnal). Lesser constituents (O1 and S2) show trends at nearly half of all gauges. Fluctuations in MSL shift amplitudes and phases; both positive and negative responses occur. Changing overtides suggest that TATs are influenced by changing shallow water friction over the equatorial Western Pacific and the eastern coast of Australia (especially near the Great Barrier Reef). There is a strong connection between semidiurnal TATs at stations around the Solomon Islands and changes in thermocline depth, overtide generation, and the El Niño Southern Oscillation (ENSO). TATs for O1, K1, and M2 are related to each other in a manner that suggests transfer of energy from M2 to the two diurnals via resonant triad interactions; these cause major tidal variability on sub-decadal time scales, especially for M2. The response of tides to MSL variability is not only spatially complex, it is frequency dependent; therefore, short-term responses may not predict long-term behavior.  相似文献   

6.
Common programme observations by the EISCAT UHF radar revealed an extended interval, post geomagnetic local noon on 03 April 1992, during which the F-region ion velocity orthogonal to the geomagnetic field was significantly enhanced, to values exceeding 2 km s−1 corresponding to a perpendicular electric field of some 100 mV m−1. Observations from this interval are used to illustrate a method by which estimates of the E-region ion-neutral collision frequency may be derived in the presence of enhanced electric field. From both the rotation of the ion velocity vector and the reduction in the ion velocity magnitude relative to that in the F-region, independent estimates of the normalised ion-neutral collision frequency are made at the UHF E-region tristatic altitudes; the derived values are, in general, lower than model predictions. Although initial calculations assume a stationary neutral atmosphere, first-order estimates of the E-region neutral wind are subsequently employed to calculate revised estimates of the normalised ion-neutral collision frequency; these neutral winds are derived by attributing the difference between predicted and observed enhancements in field-parallel ion temperature to thermospheric motion. The inclusion of neutral winds, which are themselves not inconsiderable, appears to have only a limited effect on the normalised collision frequencies derived.  相似文献   

7.
Currents in the northern Bay of La Paz were examined using an 8-month Acoustic Doppler Current Profiler (ADCP) record collected in the upper 185 m of the water column during 2007. Flow variability was dominated by tidal motions, which accounted for 43% (33% diurnal, 10% semidiurnal) of the total kinetic energy. The tidal motions had a pronounced vertical structure dominated within a shallow (∼30 m thick) surface layer by intense counterclockwise (CCW) rotary S1 diurnal radiational currents that were highly coherent with the counterclockwise seabreeze. Motions within the semidiurnal frequency band were primarily associated with significant counterclockwise S2 radiational tidal currents, which were also coherent with the seabreeze. Both S1 and S2 tidal ellipses in the upper layer were aligned perpendicular to the bay entrance with mean semi-major axes of 55 and 20 cm/s, respectively. Below the surface layer, tidal currents decayed rapidly to relatively weak, clockwise rotary barotropic motions. In contrast to those for radiational harmonics, tidal ellipses of the gravitational constituents (M2, K1 and O1) were oriented cross-bay. Energy within the diurnal frequency band in the surface layer was dominated by a coherent component (barotropic, phase-locked baroclinic and radiational), which accounted for roughly 65% (59% from S1 alone) of the total diurnal kinetic energy. Of the remaining diurnal band energy, 18% was associated with an incoherent baroclinic component and 17% with a background noise component. Below 30 m depth, the corresponding estimates are 40%, 32% and 28%, respectively. The persistent, surface-intensified CCW rotary currents observed at the mooring site are assumed to be forced by strong CCW seabreeze winds in the presence of a “slippery” low-density surface layer. This response may be further augmented by topographic narrowing at the bay entrance and by the close proximity of the diurnal and inertial frequency bands in the region.  相似文献   

8.
Interactions of tidal constituents and the transfer of energy from the tidal frequencies to other frequencies are investigated using 3-D tidal simulations for the Indonesian seas, focusing on an area of active internal tides. Semidiurnal tides strongly affect diurnal tides; however, semidiurnal tides are essentially unaffected by diurnal tides. The semidiurnal and diurnal constituents interact with each other through non-linear interference, both destructive and constructive. Semidiurnal tides generate harmonics at nearly the diurnal frequency and higher vertical wavenumbers. In Ombai Strait, these harmonics are out of phase with the diurnal tides and interact destructively with the diurnal tides, effectively negating the diurnal response in some locations. However, this is not a general response, and interactions differ between locations. Energy is also transferred from both semidiurnal and diurnal tides to other frequencies across the spectrum, with more energy originating from semidiurnal tides. These energy transfers are not homogeneous, and the spectral responses differ between the Makassar and Ombai Straits, with the region east of Ombai showing a more active surface response compared to a more intense benthic response in Makassar. In deep water away from topography, velocity spectra generally follow the Garrett–Munk (GM) relation. However, in areas of internal tide generation, spectral density levels exceed GM levels, particularly between 4 and 8 cycles per day (cpd), indicating increased non-linear interactions and energy transfer through resonant interactions. The model indicates strong surface trapping of internal tides, with surface velocity spectra having significantly higher energy between 4 and 8 cpd even 100 km away from the prominent sill generating the internal tides.  相似文献   

9.
Near-earth plasma parameters were calculated using a global numerical self-consistent and time-dependent model of the thermosphere, ionosphere and protonosphere (GSM TIP). The model results are compared with experimental data of different origin, mainly EISCAT measurements and simultaneous satellite data (Ne and ion composition). Model runs with varying inputs of auroral FAC distributions, temperature of vibrationally excited nitrogen and photoelectron energy escape fluxes are used to make adjustments to the observations. The satellite data are obtained onboard Active and its subsatellite Magion –2 when they passed nearby the EISCAT station around 0325 and 1540 UT on 31 July 1990 at a height of about 2000 and 2200 km, respectively. A strong geomagnetic disturbance was observed two days before the period under study. Numerical calculations were performed with consideration of vibrationally excited nitrogen molecules for high solar-activity conditions. The results show good agreement between the incoherent-scatter radar measurements (Ne, Te, Ti) and model calculations, taking into account the excited molecular nitrogen reaction rates. The comparison of model results of the thermospheric neutral wind shows finally a good agreement with the HWM93 empirical wind model.  相似文献   

10.
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   

11.
A numerical model has been developed which is capable of simulating all phases of the life cycle of metallic ions, and results are described and interpreted herein for the typical case of Fe+ ions. This cycle begins with the initial deposition of metallics through meteor ablation and sputtering, followed by conversion of neutral Fe atoms to ions through photoionization and charge exchange with ambient ions. Global transport arising from daytime electric fields and poleward/downward diffusion along geomagnetic field lines, localized transport and layer formation through descending convergent nulls in the thermospheric wind field, and finally annihilation by chemical neutralization and compound formation are treated. The model thus sheds new light on the interdependencies of the physical and chemical processes affecting atmospheric metallics. Model output analysis confirms the dominant role of both global and local transport to the ions life cycle, showing that upward forcing from the equatorial electric field is critical to global movement, and that diurnal and semidiurnal tidal winds are responsible for the formation of dense ion layers in the 90–250 km height region. It is demonstrated that the assumed combination of sources, chemical sinks, and transport mechanisms actually produces F-region densities and E-region layer densities similar to those observed. The model also shows that zonal and meridional winds and electric fields each play distinct roles in local transport, whereas the ion distribution is relatively insensitive to reasonable variations in meteoric deposition and chemical reaction rates.  相似文献   

12.
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   

13.
The results of coordinated EISCAT and TV-camera observations of a prebreakup event on 15 November 1993 have been considered. The variations of the luminosity of two parallel auroral arcs, plasma depletion on the poleward edge of one of these arcs as well as electron and ion temperatures in front of a westward travelling surge were studied. It was found that a shortlived brightening of a weak zenith arc before an auroral breakup was accompanied by fading of an equatorial arc and, vice versa. A plasma depletion in the E region was detected by the EISCAT radar on the poleward edge of the zenith arc just before the auroral breakup. The plasma depletion was associated with an enhancement of ion (at the altitudes of 150–200 km) and electron (in E region) temperatures. During its occurrence, the electric field in the E-region was extremely large (150 mV/m). A significant increase in ion temperature was also observed 1 min before the arrival of a westward travelling surge (WTS) at the radar zenith. This was interpreted as the existence of an extended area of enhanced electric field ahead of the WTS.  相似文献   

14.
In the first part of this paper (Deshcherevskii and Sidorin, 2012b), the spectra and periodograms of time series of earthquakes in Greece were studied for various magnitude ranges and five calendar epochs. As the main result, the stable diurnal (24-h) and semidiurnal (12-h) periodicities of earthquakes were revealed. Periodicities of small amplitude related to tidal waves M2 and O1 were also revealed in some samplings. This part of the paper deals with the problems of searching for tidal effects in seismicity with traditional techniques. An alternative approach of the task is applied. The time series of earthquakes with various magnitude and representativity (magnitude of completeness) were formed. Correlation coefficients of all the time series of earthquakes were calculated with the following theoretical tide parameters: volume deformation, strain rate, module of strain rate, and smoothed diurnal tidal amplitude. Stable significant correlation of seismicity was revealed with some tidal parameters. However, it can be a result of coincidence in periods of subharmonics of diurnal seismicity rhythm with the solar tidal waves. It means that the correlation discovered could be simply caused with coincidence of two regular components in variations of the compared processes but not with gravitational tide.  相似文献   

15.
面向大气热力潮汐结构分析的Hough函数计算   总被引：1，自引：1，他引：0       下载免费PDF全文
作为一种刻画行星尺度大气波动基本结构的函数,Hough函数为开展有关大气潮汐全球结构的分析提供了具有物理基础的手段,它们也被作为一种数值工具应用于大气模式中以提高数值积分的效率.本文介绍了我们以拉普拉斯潮汐方程为基础,在发展求取Hough函数方面取得的进展,包括对有关计算方案和详细步骤的说明.针对39种分别具有三种主要频率,即周日、半日和1/3日,与此同时纬向波数落在[6,6]区间的潮汐成份,通过计算得到了与每一种成份对应的本征值、本征函数（Hough函数）集合.作为计算结果的示例,本文给出了针对迁移性周日潮和迁移性半日潮开展计算取得结果.这些结果说明这些函数具有正确的空间结构,与此同时还说明相关的本征值计算结果都达到了相当准确的水平.所有这些结果显示当前计算结果已经可以满足普通的应用.  相似文献   

16.
The tropospheric zenith total delay (ZTD) derived from very long baseline interferometry (VLBI) is an important parameter of the atmosphere, reflecting various atmosphere-related processes and variations. In this paper, ZTD time series of the IVS rapid combined tropospheric product (2002–2006) with a 1-h resolution are used for the first time to investigate the diurnal and semidiurnal oscillations. Significant diurnal and semidiurnal variations of ZTD are found at all VLBI stations. The amplitude of the diurnal cycle S1 is 0.6–1.2 mm at most of the VLBI stations, and the amplitude of the semidiurnal cycle S2 is 0.2–1.9 mm, which nearly accord with the surface pressure tides S1/S2 and co-located GPS estimated S1/S2. The results indicate that the S1 and S2 behaviors are mainly dominated by the hydrostatic component, namely pressure tides. In general, the semidiurnal S2 amplitudes are slightly larger than the diurnal S1. While S1 shows no clear dependency on site altitude, S2 has a regular distribution with VLBI site altitude. The results are in accordance with predictions of the classic tidal theory [Chapman, S., Lindzen, R.S., 1970. Atmospheric Tides, Gordon and Breach, New York].  相似文献   

17.
The last of a cycle of three papers aimed at searching for the influence of the gravitational tide on regional Greece seismicity using different techniques is presented. Twenty-five nonintersecting samplings of earthquakes in Greece compiled from events with different energy and time intervals were studied in the two previous papers (Desherevskii and Sidorin, 2012d, 2014). Stable diurnal and semidiurnal periodicities (24:00 and 12:00 h) were revealed in the seismicity spectra. Periodicities with a small amplitude with periods close to M2 and O1 tidal waves were also found in some samples. The correlation coefficients of all time series of earthquakes were calculated with the following theoretical tide parameters: volume deformation, strain rate, of strain rate modulus, and smoothed diurnal tidal amplitude. As the main result, stable significant correlation of seismicity was revealed with some tidal parameters. However, this could be the result of coincidence in periods of sub-harmonics of the diurnal seismicity rhythm with solar tidal waves. This means that the discovered correlation could simply be caused by the coincidence of two regular components in variations of the compared processes, but not with the gravitational tide. Correlations of seismic activity with solar and lunar tides are studied separately in this paper. This makes possible to separate the influence of gravitational and nongravitational factors. Strong correlation of seismicity was observed only with the solar tide. No stable correlation of seismicity with the lunar tide was revealed. The results can be considered evidence for the nongravitational origin of seismic activity variations that correlate with the tidal parameters. This means that tidal seismicity variations, if they are real, should have a much smaller amplitude in comparison with diurnal solar variations of nongravitational origin. Similar effects could cause wrong conclusions on the tidal influence on seismicity in some studies.  相似文献   

18.
Results are presented from a multi-instrument investigation of the signatures of equatorial reconnection in the summer, sunlit ionosphere. Well-established ion dispersion signatures measured during three DMSP satellite passes were used to identify footprints in ionospheric observations made by radio tomography, and both the EISCAT ESR and mainland radars. Under the prevalent conditions of southward IMF with the Bz component increasing in magnitude, the reconnection footprint was seen to move equatorward through the ESR field-of-view. The most striking signature was in the electron temperatures of the F2 region measured by the EISCAT mainland radar that revealed significantly enhanced temperatures with a steep equatorward edge, in general agreement with the leading edge of the ion dispersion. It is suggested that this sharp transition in the electron temperature may be an indicator of the boundary, mapping from the reconnection site, between closed geomagnetic field lines and those opened along which magnetosheath ions precipitate.  相似文献   

19.
In this paper we investigate the tidal triggering evidence on the earthquakes of the seismic area of the Hellenic Arc using the Hist(ogram)Cum(mulation) method. We analyze the series of the earthquakes occurred in the area which is confined by the longitudes 22° and 28°E and latitudes 34° and 36°N in the time period from 1964 to 2012. In this time period 16,137 shallow and of intermediate depth earthquakes with ML up to 6.0 and 1,482 deep earthquakes with ML up to 6.2 occurred. The result of the this analysis indicate that the monthly variation of the frequencies of earthquake occurrence is in accordance with the period of the tidal lunar monthly variations, and the same happens with the corresponding daily variations of the frequencies of earthquake occurrence with the diurnal luni-solar (K1) and semidiurnal solar (S2) tidal variations. These results are in favor of a tidal triggering process on earthquakes when the stress in the focal area is near the critical level.  相似文献   

20.
平流层爆发性增温(SSW)期间,低层大气温度场和风场等的剧烈变化会直接影响潮汐和风剪切作用.此举可能会导致电离层Es的相应变化.本文以2009年1月事件为例,分析了SSW期间Es层的响应.首先,在排除太阳活动和地磁活动对Es层影响的前提下,分析了昆明站附近MLT区域行星波和潮汐波的波动特性,发现此期间存在显著的2日行星波,并伴有日潮汐减弱和半日潮汐增强等波动现象;随后,分析相应时间段内Es层的变化特性发现,重庆和昆明站附近Es层强度明显减弱,且其高度显著抬升.这一现象与低层大气的波动变化具有同步性.最后,通过模拟经典风剪切理论下Es层金属离子的汇聚过程和运动轨迹,再现了SSW期间Es层与低层大气波动的耦合演化过程.该分析结果为研究低层-中层-高层大气的耦合过程提供了一种新的思路.  相似文献   

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