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1.
We study the solar dependence of the thermospheric dynamics based on more than 20 years Fabry–Perot interferometer O 6300 Å emission observation of polar cap thermospheric wind from three stations: Thule (76.53°N, 68.73°W, MLAT 86N), Eureka (80.06°N, 86.4°W, MLAT 89N), and Resolute (74.72°N, 94.98°W, MLAT 84N) in combination with the National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model (NCAR-TIEGCM). All three stations showed a dominant diurnal oscillation in both the meridional and zonal components, which is a manifestation of anti-sunward thermospheric wind in the polar cap. The three-station observations and the TIEGCM simulation exhibit varying degree of correlations between the anti-sunward thermospheric wind and solar F10.7 index. The diurnal oscillation is stronger at Eureka (∼150 m/s) than that at Resolute (∼100 m/s) according to both observations and TIEGCM simulation. The semidiurnal oscillation is stronger at Resolute (∼20 m/s) than that at Eureka based (∼10 m/s) on data and model results. These results are consistent with a two-cell convection pattern in the polar cap thermospheric winds. The Thule results are less consistent between the model and observations. The simulated meridional wind diurnal and semidiurnal oscillations are stronger than those observed.  相似文献   

2.
The variation of plasmaspheric electron content (PEC) is an important parameter for studying the effects of space weather events in the low latitude ionosphere. In the present study, the vertical TEC (VTEC) measurements obtained from co-located dual-frequency Global Positioning System (GPS) and Coherent Radio Beacon Experiment (CRABEX) systems have been used. The daytime PEC variations under different geophysical conditions have been estimated (around the magnetic equator) over the Indian sector, for the first time. The first observations of the nighttime PEC variations over the Indian sector are also estimated from the simultaneous measurements of Faraday rotation, differential Doppler and modulation phase delay made using the CRABEX system on-board the Indian geostationary satellite GSAT2. The study shows that the PEC varies over a range of 10–22% (of the total electron content (TEC)) during daytime of magnetically quiet period. There is an increase in PEC with latitude during magnetically quiet period. During a magnetically disturbed period of 9 November 2004, the PEC increased to ∼30% of the TEC over the magnetic equatorial location of Trivandrum (8.5°N, 76.9°E, dip 0.5°N), while at Bangalore (13°N, 78°E, dip 10°N) it showed a large depletion. The implications of the new observations are discussed.  相似文献   

3.
Resonance lidar observations of sodium density in the upper mesosphere region over Gadanki (13.5°N, 79.2°E) rarely show complex structures with rapid enhancements of sodium density, completely different from normal sporadic sodium structures. The hourly averaged meteor radar zonal winds over Trivandrum (8.5°N, 76.5°E) show an eastward shear with altitude during the nights, when these events are formed. As suggested by Kane et al. [2001. Joint observations of sodium enhancements and field-aligned ionospheric irregularities. Geophysical Research Letters 28, 1375–1378], our observations show that the complex structures may be formed due to Kelvin–Helmholtz instability, which can occur in the region of strong wind shear.  相似文献   

4.
本文介绍了国家气候中心发展的一个全球海洋碳循环环流模式,并分析评估了该模式的基本性能.该模式是在美国地球物理流体动力学实验室(GFDL,Geophysical Fluid Dynamics Laboratory)的全球海洋环流模式MOM4(Modular Ocean Model Version 4)基础上发展的一个垂直方向40层、包含生物地球化学过程的全球三维海洋碳循环环流模式,简称为MOM4_L40(Modular Ocean Model Version 4 With 40Levels).该模式在气候场强迫下长期积分1000年,结果分析表明,与观测相比,模式较好地模拟了海洋温度、盐度、总二氧化碳、总碱、总磷酸盐的表面和垂直分布特征.模拟的海洋总二氧化碳分布与观测基本相符,表层为低值区,其下为高值区,高值区域位于10°S—60°N之间,但2000m以上模拟值较观测偏小,2000m以下模拟值较观测偏大.总体来说,MOM4_L40模式是一个可信赖的海洋碳循环过程模拟研究工具.  相似文献   

5.
The Cloud Imaging and Particle Size (CIPS) instrument on the Aeronomy of the Ice in the Mesosphere (AIM) spacecraft is a 4-camera nadir pointed imager with a bandpass centered at 265 nm and a field of view of 120°×80°. CIPS observes polar mesospheric clouds (PMCs) against the sunlit Rayleigh-scattered background. At individual polar locations approximately 5 km×5 km in area, CIPS observes the same volume of air seven times over a range of scattering angles from about 35° to 150°. These multi-angle observations allow the identification and extraction of the PMC scattered radiance from the Rayleigh-scattered background. We utilize the fact that the former has a highly asymmetric phase function about 90° scattering angle, while the latter has a phase function that is symmetric. The retrieved PMC phase function can then be interpreted to obtain PMC particle size distributions. We describe a technique for identification of PMCs in the CIPS observations through the separation of the Rayleigh and PMC radiances. PMC phase function results are shown for the first season of CIPS observations. Assuming the particles are oblate spheroids with an axial ratio of 2, and a Gaussian distribution of width 14 nm, we find the phase functions are consistent with mean radii between 50 and 60 nm. These results are similar to those discussed by Hervig et al. [2009. Interpretation of SOFIE PMC measurements: cloud identification and derivation of mass density, particle shape, and particle size. J. Atmos. Sol. Terr. Phys., in review.] in this issue from the Solar Occultation for Ice Experiment (SOFIE) which also flies on the AIM satellite.  相似文献   

6.
The results of the ground-based optical observations of sunlit auroras, performed at Lovozero and Apatity observatories on April 10 (event 1) and April 27, 2007(event 2), are presented. The observations were performed in the (OI) 557.7 nm emission, using a new equipment based on a Fabry-Pérot interferometer connected to a PhotonMAX CCD camera. During event 1, the observations were performed in the Harang discontinuity region at a low magnetic disturbance. It has been indicated that an auroral arc was located in the polar part of the eastward electrojet, and the arc position coincides with the equatorward boundary of structured precipitation (b2e). During event 2, auroras were observed within the average statistical boundaries of the auroral oval and the region of structured precipitation under the conditions of rather high geomagnetic activity. However, during the period of low geomagnetic activity, discrete auroras were registered at a geomagnetic latitude of ~64° on that day, which is 3°—4° equatorward of the structured precipitation region. Such a low latitudinal position of auroras can be explained by the effect of a high solar wind velocity, which was ~580 km/s during the period of observations.  相似文献   

7.
The water exchange between the subpolar and subtropical gyres of the North Pacific is demonstrated by the simulation of chlorofluorocarbon (CFC) using an ocean general circulation model. The simulated CFC concentration in the North Pacific is in good agreement with observations. The water exchange is clearly illustrated by the tongues of CFC concentration. The subpolar waters with high CFC are transported southward into the eastern subtropical gyre, whereas the subtropical waters with low CFC are transported northward into the western subpolar gyre. The simulated exchange transport along 42°N in the layer of σθ< 26.8 indicates that the northward mass transport is about 15 Sv (1 Sv = 106 m3·s-1) west of 165°E, and about 5 Sv between 175°W and 150°W. The southward mass transport is about 5 Sv between 165°E and 175°W, and about 2 Sv east of 150°W.  相似文献   

8.
The accuracy of daily mean 2 meter air temperatures from five reanalyses are assessed against in-situ observations from Automatic Weather Stations in East Antarctica for 2005 to 2008.The five reanalyses all explain more than 70%of the average variance,and have annual root mean square errors(RMSE)between 3.4 and 6.9°C.The NOAA reanalyses,NCEP-1,NCEP-2and 20CRv2,have cool biases of 2.5,1.4 and 1.5°C,respectively.The ERA Interim and JCDAS reanalyses have warm biases of 1.7 and 2.0°C.All reanalyses generally perform better in the austral spring and worse in winter and autumn.They also show the best performance at an inland plateau site at 2800 m elevation,but are worst at Dome A,the summit of the East Antarctic ice sheet.In general,ERA Interim is superior to the other reanalyses,probably because of its 4D assimilation scheme.The three NOAA reanalyses perform worst;Their assimilation scheme is more constrained by limited observations and 20CRv2has less input data,assimilating only surface pressure observations.Despite deficiencies and limitations,the reanalyses are still powerful tools for climate studies in the Antarctic region.However,more in-situ observations are required,especially from the vast interior of Antarctica.  相似文献   

9.
On the basis of the data of ground-based spectrometric observations in Zvenigorod (55.7°N, 36.8°E) and published results of measurements of the intensity of the Infrared Atmospheric system of molecular oxygen obtained at other stations, empirical relations describing variations in the intensity of the 1.58-μm emission for various solar and geophysical conditions are calculated.  相似文献   

10.
Results of fractal analysis of ultra-low-frequency (ULF) emissions registered at a low-latitude observatory, Guam (geomagnetic coordinates Φm=9°N, Λm=225°), and at a high-latitude drifting station, North Pole-30 (Φm=75°N, Λm=172°), are presented. The first set of data covers a long period of observations (20 months) including the strong (Ms=8) Guam earthquake of 8 August 1993. The second set of data covers a short period of observations (21 days) in April 1989 during the preparation phase of the big magnetic storm of 25 April 1989. Definite peculiarities in the behavior of ULF emission scaling (fractal) characteristics have been found, which are discussed on the basis of the self-organized criticality concept. The principal common peculiarity for magnetosphere–ionosphere and lithosphere systems is detection of flicker noise (β∼1, D0∼2) in a certain frequency range on the preparation phase of strong magnetospheric and seismic events.  相似文献   

11.
The occurrence frequency of SAR arcs during 1997–2006 has been analyzed based on the photometric observations at the Yakutsk meridian (Maimaga station, corrected geomagnetic coordinates: 57° N, 200° E). SAR arcs appeared in 114 cases (～500 h) during ～370 nights of observations (～3170 h). The occurrence frequency of SAR arcs increases to 27% during the growth phase of solar activity and has a clearly defined maximum ～36% at a decline of cycle 23. The SAR arc registration frequency corresponds to the variations in geomagnetic activity in this solar cycle. The dates, UT, and geomagnetic latitudes of photometric observations are presented for 1997–2006.  相似文献   

12.
The International Seismological Centre (ISC) treats reports of the earliest observed core phase arrivals from earthquakes as PKIKP observations and provides residuals based on Jeffreys-Bullen PKIKP times. An analysis of some 30 000 such data from ISC bulletins for the year 1967 has shown that the data include, in addition to PKIKP, many observations of PKP1 and precursors to PKP. By the use of simple truncation and trimming techniques, travel-time curves (expressed as differences from JB), with standard errors, have been obtained for PKIKP in the ranges 110 to 139° and 152 to 173°, and for PKP1 in the range 144 to 154°. The PKIKP curve in these ranges agrees quite closely with the curve obtained by Cleary and Hales, and with one derived from model 1066B of Gilbert and Dziewonski, except that the Cleary-Hales curve is up to 0.7 s earlier at distances below 120°, and the 1066B curve is up to 1 s later beyond 152°. The PKP1 curve is in good agreement with that derived from 1066B.A plot of the number of observations in each 1° distance interval has been used to estimate the positions of the cusps B, C and D on the PKP curve as 144, 152.5 and 115°, again in reasonable agreement with 1066B.  相似文献   

13.
The results of the observations, using partial reflections, of the lower ionosphere over Tumannyi station in the Murmansk region (69.0° N, 35.7° E) during strong solar flares on January 15–20, 2005, are presented. The structure of the D region of the polar ionosphere and the effects of X-ray flares and fluxes of high energy protons on this region are considered. The anomalous values of electron density in the lower part of the D region, unusually low values of the height of the lower ionospheric boundary, complete or partial absorption of short and medium radiowaves, and bursts of the meter cosmic radio emission were detected during solar disturbances.  相似文献   

14.
A statistical analysis of observations of large-scale undulations during the 23rd cycle of solar activity was performed using optical data from two stations: Tixie (71.6°N, 128.9°E) and Zhigansk (66.8°N, 123.4°E). The total number of events recorded was 54 (43 events at Tixie and 11 at Zhigansk). The complete list of observed events is presented. The occurrence frequency of eveningside (17–23 LT) undulations during the solar activity growth (1999) and decline (2003–2005) phases tends to increase. Large-scale undulations were shown to be generated both on the equatorward boundary of the diffuse auroral zone and inside the diffuse zone, which does not necessarily occur during magnetic storms.  相似文献   

15.
本文利用位于我国中南部电离层闪烁监测台网2012年至2015年的观测数据,比较分析了GPS（Global Positioning System）信号闪烁与周跳的统计特征以及太阳活动和地磁扰动对闪烁与周跳的影响.结果表明,闪烁活动与周跳出现随地方时、月份、太阳活动和地磁扰动变化的统计特征类似,且周跳出现的可能性随S4指数增高显著增大,说明闪烁与周跳存在密切的关联,是引起周跳的一种重要因素.一天之中,闪烁和周跳主要出现在日落后至黎明前,午夜前出现最频繁,白天仅偶尔出现.在赤道异常峰及其邻近区域,一年之中,闪烁和周跳主要出现在春秋季,春季闪烁活动和周跳出现明显比秋季频繁,呈现春秋不对称性,冬夏季节闪烁和周跳都很少出现.闪烁活动与周跳出现的逐年变化显著依赖太阳活动水平,随太阳活动水平升高而增强,而地磁扰动与闪烁活动与周跳出现呈负相关,地磁扰动对闪烁活动与周跳出现整体上起抑制作用.平均而言,越靠近磁赤道的台站闪烁活动越频繁,随纬度升高,闪烁活动频次逐渐降低,且闪烁活动的开始时间随纬度升高而滞后,暗示引起GPS信号闪烁的电离层不规则结构主要起源于磁赤道区.此外,分析还发现,闪烁活动与周跳出现的空域有相当好的一致性,主要分布在观测点上空仰角55°以下、方位角150°~240°的空域内.  相似文献   

16.
The results of instrumental observations of geomagnetic variations at the Mikhnevo midlatitudinal observatory of Institute of Geosphere Dynamics of the Russian Academy of Sciences (54.9595° N; 37.7664° E) are presented and discussed. The main periodicities of the local background variations of geomagnetic field are determined. Variations of ~ 27 days have been registered, as well as periodicities with periods of ~6–9, 12–14, 60 days, and a semiannual periodicity. It has been shown that the background geomagnetic variation periodicities have a sporadic and scaling character. An alternating effect of increasing and degradation periods in geomagnetic variation intensity (the intermittency effect) is found.  相似文献   

17.
Long-term series of midnight temperature in the mesopause region have been obtained from spectral observations of hydroxyl airglow emission (OH(6-2) λ840 nm band) at the Tory station (52° N, 103° E) in 2008–2016 and Zvenigorod (56° N, 37° E) station in 2000–2016. On their basis, the Lomb-Scargle spectra of the variations in the period range from ~12 days to ~11 years have been determined. Estimates of the amplitudes of statistically significant temperature fluctuations are made. The dominant oscillations are the first and second harmonics of the annual variation, the amplitudes of which are 23–24 K and 4–7 K, respectively. The remaining variations, the number of which was 16 for the Tory and 22 for Zvenigorod stations, have small amplitudes (0.5–3 K). Oscillations with combinational frequencies, which arise from modulation of the annual variation harmonics, are observed in a structure of the variation spectra in addition to interannual oscillations (periods from ~2 to ~11 years) and harmonics of the annual variation (up to its tenth harmonic).  相似文献   

18.
This paper reports differences in the occurrence statistics of global positioning system (GPS) L-band scintillations at observational sites located in the inner regions of the northern and southern crests of the equatorial ionization anomaly. Ground-based GPS data acquired at the closed magnetically aligned stations of Manaus (3.1°S; 59.9°W; dip lat. 6.2°N) and Cuiabá (15.5°S; 56.1°W; dip. lat. 6.2°S), Brazil, from December 2001 to February 2007 are used in the analysis. The drift dynamics of Fresnel-scale ionospheric irregularities at the southern station of Cuiabá are also investigated. Only geomagnetically quiet days with the sum of daily Kp < 24 were used in the analysis statistics and in the irregularity drift studies. The results reveal a clear dependence of the scintillation occurrence with the solar activity, but there exists an asymmetry in the percentage of scintillation occurrence between the two stations throughout the period analyzed. The nocturnal occurrence of the scintillations over Cuiabá is predominantly larger than over Manaus, but this scenario seems to change with the decline in the solar activity (mainly during local post-midnight hours). A broad minimum and maximum in the scintillation occurrence appears to occur over both the stations, respectively, during the June solstice (winter) and December solstice (summer) months. The dynamics of the Fresnel-scale irregularities, as investigated from the estimations of the mean zonal drift velocities, reveals that the amplitude of the eastward drifts tends to reduce with the decline in the solar activity. The magnitude of the zonal drift velocities during the December solstice months is larger than during the equinoxes, with the differences being more pronounced at solar maximum years. Other relevant aspects of the observations, with complementary data from a low-latitude ionospheric model, are highlighted and discussed.  相似文献   

19.
Two cases when Pc5 geomagnetic pulsations were registered at the IMAGE Scandinavian network of stations and with STARE radars in the afternoon sector (1700–1800 MLT) during the recovery phase of the moderate magnetic storm are analyzed in detail. Using the ground-based observations, it has been indicated that classical quasimonochromatic resonance Pc5 pulsations were observed in the first case (on October 12, 1999; Kp = 5); in this case the maximal amplitude of the spectral maximum at a frequency of 2.5 mHz was registered at Φ ～ 65°. Two maximums were observed in the spectrum in the second case (on October 13, 1999; Kp = 4): ～2.5 mHz (the same maximum) and 2.9 mHz; in this case the maximal oscillation amplitude (2.5 mHz) shifted to Φ > 67°. These results were compared with the echo signal intensity simultaneously registered with the STARE Finland radar on a beam oriented along the 105° geomagnetic meridian. The spatial-temporal maps of the Pc5 pulsation amplitude latitudinal distribution (“keograms”), constructed based on the radar measurements in the wide range of geomagnetic latitudes (63°–70°) where the resolution was substantially higher than that of the ground-based observations, made it possible to detect two regions spaced in latitude (Φ ～ 65° and Φ ～ 67°–68°) with the simultaneous excitation of oscillations (double resonance?), between which the plasmapause projection was supposedly located.  相似文献   

20.
Long period variations in the mesosphere wind have been observed for some time by ground-based radars. These planetary scale disturbances have reoccurring periods at or near 5–7, 10, and 16 days and at times dominate the wind field at mesospheric heights. Recently, due to the continuous operation of several of the MLT radars and the availability of measurements from the UARS satellite, it has been possible to compare observations during periods of large planetary wave activity. Wind measurements from four MLT radars; the meteor radars at Durham, NH (43°N,71°W) and Sheffield, UK (53°N,2°W) and MF radars at Urbana, IL (40°N,88°W) and Saskatoon, Canada (52°N,107°W) were compared with the HRDI measurements during intervals when 7-d planetary waves were present. Wind data from the HRDI instrument on UARS has been processed to show the latitudinal structure and the seasonal variation of the planetary scale wind variation. The phases and amplitudes of the waves as determined by both the satellite and the radars are in good agreement. The ground-based measurements show large modulation of tides by these long period components, and also show comparable responses of these low frequency components over thousands of kilometers. The satellite and the ground-based results both indicate a preponderance of wave occurrence during the equinoxes and at preferred latitudes.  相似文献   

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