共查询到20条相似文献，搜索用时 31 毫秒
1.
使用COSMIC掩星提供的NmF2数据,利用傅里叶分析方法,研究全球F2层峰值电子密度的周年和半年分布特征,分析2010年LT12：00 14：00 NmF2周年和半年变化幅度及2008-2011年年平均值变化.结果显示,电离层NmF2周年和半年变化幅度在中高纬地区相对较大;在赤道和低纬地区相对较小,且NmF2以半年变化为主.太阳活动增强期间,NmF2年平均值增大. 相似文献
2.
用北半球陆地上48个地面电离层垂测站资料，以及国际参考电离层IRI 90模式，考察1985年1月6～7日F2层电子密度最大值日变化的纬度剖面和经度效应. 结果表明，在亚洲地区的20°N～30°N内，F2层赤道异常“喷泉效应”产生的NmF2“北驼峰”最高，其最大值出现在中午，或稍迟时间. 30°N ～50°N区域内，NmF2的白天峰值幅度逐渐下降，峰值时间移至午前约10:00 LT. 更高纬度(50°N～62°N )台站上，中午前后NmF2出现双峰，傍晚有谷值，夜间又再次抬升. 欧、美地区的低纬台站很少，但借助IRI 90模式分析可发现，在270°E经圈上，“喷泉效应”造成的“北驼峰”幅度最小，而且随纬度增大时，NmF2白天幅度下降也不明显，即纬度剖面的经度效应非常显著. 对中国、日本地区台站资料的小范围经度差异分析表明，在驼峰区的90°E～140°E内，各站NmF2无明显差别；但在中纬地区30°N～50°N内，中国西部上空NmF2白天变化幅度较大，且较为陡直，而中国东部和日本台站上空则相对平缓. 相似文献
3.
《Journal of Atmospheric and Solar》2008,70(1):184-192
We analyze Jicamarca ionograms to study the quiet-condition variations in the peak electron density (NmF2), its height (hmF2), and F2-layer thickness parameter (B0) of the equatorial F2 layer during solar minimum. The sunrise peak is found in hmF2 and B0 for all months. During daytime and nighttime, the variation in the hmF2 value is mainly responsible for that in NmF2 and B0. The sunset peaks of hmF2 and B0 exist in the equinoctial months, but not in the winter months. Moreover, the observed values of hmF2, NmF2, and B0 are generally similar to the modeled values of IRI-2001. 相似文献
4.
Saskatoon (52° N, 107°W) medium frequency (MF) radar data from 1979 to 1993 have been analyzed to investigate the climatology of irregular wind components in the height region 60–100 km. This component is usually treated in terms of internal gravity waves (IGW). Three different band-pass filters have been used to separate the intensities of IGWs having periods 0.2-2.5; 1.5-6 and 2–10 h, respectively. Height, seasonal and inter-annual variations of IGW intensities, anisotropy and predominant directions of propagation are investigated. Mean over 14 years’ seasonal variation of the intensity of long-period IGWs shows a dominant annual component with winter maximum and summer minimum. Seasonal variations of the intensity of short-period waves have a strong semi-annual component as well, which forms a secondary maximum in summer. Predominant azimuths of long-period IGWs are generally zonal, though they vary with season. For short-period IGWs, the predominant azimuth is closer to the meridional direction. Anisotropy of IGW intensity is larger in summer, winter and at lower altitudes. The IGW intensity shows apparent correlation with both solar and geomagnetic activity. In most cases, this correlation appears to be negative. The variations versus solar activity is larger for longer-period IGW. Possible reasons and consequences of the observed climatological variations of IGW intensity are discussed. 相似文献
5.
Total electron content (TEC) and foF2 ionosonde data obtained at Tucumán (26.9°S; 65.4°W) from April 1982 to March 1983 (high solar activity period) are analyzed to show the seasonal variation of TEC, NmF2 (proportional to square of foF2) and the equivalent slab thickness EST. Bimonthly averages of the monthly median for January–February, April–May, July–August and October–November have been considered to represent summer, autumn, winter and spring seasons, respectively. The results show that the higher values of TEC and maximum electron density of F2-layer NmF2 are observed during the equinoxes (semiannual anomaly). During daytime, both in TEC and in NmF2 the seasonal or winter anomaly can be seen. At nighttime, this effect is not observed. Also, the observed NmF2 values are used to check the validity of International Reference Ionosphere (IRI) to predict the seasonal variability of this parameter. In general, it is found that averaged monthly medians (obtained with the IRI model) overestimate averaged monthly median data for some hours of the day and underestimate for the other hours. 相似文献
6.
利用太阳活动高年（2000年）IGS提供的全球TEC数据，采用傅里叶展开的方法，分析了白天电离层TEC周年和半年变化的全球特征.结果显示：电离层TEC周年变化幅度在南北半球中高纬度地区较大、赤道和低纬地区很小.半年变化的幅度在“远极地区”（远离地球南北地磁极点的东北亚和南美地区） 比“近极地区”（靠近地球南北地磁极点的北美和澳大利亚）大得多.进一步的统计显示，全球大部分地区TEC在春秋月份出现最大值，北半球近极地区最大值在冬季出现.南半球的南美和澳大利亚部分地区，最大值出现在夏季.同样，采用傅里叶方法分析了中性大气模式MSIS90计算的全球大气原子分子浓度比值（［O/N2］）的数据，发现在南北半球中高纬度地区，中性成分［O/N2］周年变化幅度较大且有明显的冬季异常现象，依据Rishbeth等提出的理论，我们认为大气成分［O/N2］可能对TEC周年变化的产生有重要作用，并且也是TEC在近极地区出现冬季异常现象的主要原因.TEC半年变化的全球分布特征形成的原因较复杂，我们初步分析可能是由于中性成分［O/N2］、太阳天顶角控制的电离层光化学产生率变化共同作用而产生的. 相似文献
7.
We use the measurements of the Jicamarca digisonde to examine the variations in F2 layer peak electron density (NmF2), its height (hmF2), and the F2 layer thickness parameter (B0) near the dip equator. The hourly ionograms during geomagnetic quiet-conditions for a 12-month period close to the maximum solar activity, April 1999–March 2000, are used to calculate the monthly averages of these parameters, for each month. The averages are compared with the International Reference Ionosphere (IRI)-2001 model values. The results show that the higher hmF2 values during daytime, associated with the upward velocity, are mainly responsible for the greater values of NmF2 and B0; while the nighttime lower hmF2, related to the downward velocity, are responsible for the smaller NmF2 and B0. For daytime, hmF2 and NmF2 are correlated with the solar activity in the equinoctial and summer months. The hmF2 and B0 peaks at sunset with an associated sharp decrease in NmF2 are presented in the equinoctial and summer months, but not in the winter months. Comparison of the measured hmF2 values with the International Radio Consultative Committee (CCIR) maps used in IRI-2001 (IRI-CCIR) reveals an IRI overestimate in hmF2 during daytime. The most significant discrepancy is that the IRI-CCIR does not model the post-sunset peak in hmF2. For the NmF2 comparison, the values obtained from both the CCIR and URSI maps are generally close to the observed values. For the B0 comparison, the highest discrepancy between the observation and the Gulyaeva option (IRI-Gulyaeva) is the location of the annual maximum for the daytime values, also the winter daytime predictions are too low. Additionally, the significant negative difference between the observation and the B0-table option (IRI-B0-table) provides a slightly better prediction, except for 0400–1000 LT when the model significantly overestimates. The post-sunset peak in B0 at some months is predicted by neither the IRI-Gulyaeva nor the IRI-B0-table options. 相似文献
8.
《Journal of Atmospheric and Solar》2007,69(8):947-954
The GPS-derived total electron content (TEC) and NmF2 are measured at the Chung-Li ionosonde station (24.9°N, 121°E) in order to study the variations in slab thickness (τ) of the ionosphere at low-latitudes ionosphere during 1996–1999, corresponding to half of the 23rd solar cycle. This study presents the diurnal, seasonal, and solar flux variations in τ for different solar phases. The seasonal variations show that the average daily value is greater during summer and the reverse is true during equinox in the equatorial ionization anomaly (EIA) region. Moreover, the τ values are greater during the daytime (0800–1600 LT) and nighttime (2000–0400 LT) for summer and winter, respectively. The diurnal variation shows two abnormal peaks that appear during the pre-sunrise and post-sunset hours. The peak values decrease as the sunspot number increases particularly for the pre-sunrise peak. Furthermore, the variation in the F-peak height (hpF2) indicates that a thermospheric wind toward the equator leads to an increase in hpF2 and an enhancement in τ during the pre-sunrise period. Furthermore, the study shows the variations of τ values for different geophysical conditions such as the geomagnetic storm and earthquake. A comprehensive discussion about the relation between τ and the geophysical events is provided in the paper. 相似文献
9.
本文利用2005-2009年的全球网格化Argo数据,分别采用温度判据和密度判据计算了全球大洋混合层深度(Mixed Layer Depth, MLD),讨论了障碍层(Barrier Layer, BL)和补偿层(Compensated Layer, CL)对混合层深度计算的影响,得到了合成的混合层深度,并研究了其时空变化特征. 研究表明:(1)在赤道西太平洋(10°S -5°N,150°E-150°W),孟加拉湾,热带西大西洋(10°N-20°N,30°W-60°W)是障碍层高发区域. 冬季的北太平洋副热带区域(30°N附近)以及东北大西洋(40°N-60°N,0°-30°W)是补偿层发生的区域. (2) 在各个半球的夏季MLD都比较浅,在各个半球的冬季MLD则普遍比较深. 北太平洋和北大西洋的MLD的分布和变化比较相似,印度洋MLD受季风影响显著,呈现半年周期变化. 太平洋和大西洋的MLD 的经向分布大致呈现出"两端深,中间浅"的拱形特点. (3)混合层深度距平场EOF第一模态时间变化为周期的年信号,北太平洋和北大西洋、南大洋(尤其是南极绕流区)都是MLD变化剧烈的海域,第二模态显示全球大洋混合层深度距平存在着一个半年的变化周期. 相似文献
10.
This paper presents results from the TIME-GCM-CCM3 thermosphere–ionosphere–lower atmosphere flux-coupled model, and investigates how well the model simulates known F2-layer day/night and seasonal behaviour and patterns of day-to-day variability at seven ionosonde stations. Of the many possible contributors to F2-layer variability, the present work includes only the influence of ‘meteorological’ disturbances transmitted from lower levels in the atmosphere, solar and geomagnetic conditions being held at constant levels throughout a model year.In comparison to ionosonde data, TIME-GCM-CCM3 models the peak electron density (NmF2) quite well, except for overemphasizing the daytime summer/winter anomaly in both hemispheres and seriously underestimating night NmF2 in summer. The peak height hmF2 is satisfactorily modelled by day, except that the model does not reproduce its observed semiannual variation. Nighttime values of hmF2 are much too low, thus causing low model values of night NmF2. Comparison of the variations of NmF2 and the neutral [O/N2] ratio supports the idea that both annual and semiannual variations of F2-layer electron density are largely caused by changes of neutral composition, which in turn are driven by the global thermospheric circulation.Finally, the paper describes and discusses the characteristics of the F2-layer response to the imposed ‘meteorological’ disturbances. The ionospheric response is evaluated as the standard deviations of five ionospheric parameters for each station within 11-day blocks of data. At any one station, the patterns of variability show some coherence between different parameters, such as peak electron density and the neutral atomic/molecular ratio. Coherence between stations is found only between the closest pairs, some 2500 km apart, which is presumably related to the scale size of the ‘meteorological’ disturbances. The F2-layer day-to-day variability appears to be related more to variations in winds than to variations of thermospheric composition. 相似文献
11.
Ionospheric electron content (IEC) observed at Delhi (geographic co-ordinates: 28.63°N, 77.22°E; geomagnetic co-ordinates: 19.08°N, 148.91E; dip Latitude 24.8°N), India, for the period 1975/80 and 1986/89 belonging to an ascending phase of solar activity during first halves of solar cycles 21 and 22 respectively have been used to study the diurnal, seasonal, solar and magnetic activity variations. The diurnal variation of seasonal mean of IEC on quiet days shows a secondary peak comparable to the daytime peak in equinox and winter in high solar activity. IECmax (daytime maximum value of IEC, one per day) shows winter anomaly only during high solar activity at Delhi. Further, IECmax shows positive correlation with F10.7 up to about 200 flux units at equinox and 240 units both in winter and summer; for greater F10.7 values, IECmax is substantially constant in all the seasons. IECmax and magnetic activity (Ap) are found to be positively correlated in summer in high solar activity. Winter IECmax shows positive correlation with Ap in low solar activity and negative correlation in high solar activity in both the solar cycles. In equinox IECmax is independent of Ap in both solar cycles in low solar activity. A study of day-to-day variations in IECmax shows single day and alternate day abnormalities, semi-annual and annual variations controlled by the equatorial electrojet strength, and 27-day periodicity attributable to the solar rotation. 相似文献
12.
《Journal of Atmospheric and Solar》2007,69(15):1864-1870
The ionospheric slab thickness, the ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2), is closely related to the shape of the ionospheric electron density profile Ne (h) and the TEC. Therefore, the ionospheric slab thickness is a significant parameter representative of the ionosphere. In this paper, the continuous GPS observations in South Korea are firstly used to study the equivalent slab thickness (EST) and its seasonal variability. The averaged diurnal medians of December–January–February (DJF), March–April–May (MAM), June–July–August (JJA) and September–October–November (SON) in 2003 have been considered to represent the winter, spring, summer and autumn seasons, respectively. The results show that the systematic diurnal changes of TEC, NmF2 and EST significantly appeared in each season and the higher values of TEC and NmF2 are observed during the equinoxes (semiannual anomaly) as well as in the mid-daytime of each season. The EST is significantly smaller in winter than in summer, but with a consistent variation pattern. During 14–16 LT in daytime, the larger EST values are observed in spring and autumn, while the smaller ones are in summer and winter. The peaks of EST diurnal variation are around 10–18 LT which are probably caused by the action of the thermospheric wind and the plasmapheric flow into the F2-region. 相似文献
13.
A statistical analysis of two peaks (pre-midnight and post-midnight) occurrence in NmF2 daily variations was made on a latitudinal chain of four ionosonde stations in the Eurasian longitudinal sector. Overall 6182 cases of the first and 5600 cases of the second peak occurrence were analyzed using all available foF2 observations for the years of solar maximum and minimum. Well-pronounced and systematic variations with season and solar activity were revealed in the occurrence probability of the peaks, their amplitude and timing. The pattern of both peaks occurrence is similar during winter and equinoxes for midlatitude stations implying one and the same mechanism of their formation. The pre-midnight summer peak shows specific variations in particular during solar maximum pointing to a different mechanism controlling its appearance. Possible mechanisms of both peaks formation are discussed. 相似文献
14.
K. Parameswaran Bijoy V. Thampi S.V. Sunilkumar 《Journal of Atmospheric and Solar》2010,72(13):1024-1035
The altitude profiles of particulate extinction in the upper troposphere and lower stratosphere (UTLS) obtained from SAGE-II in the latitude region 0–30°N over the Indian longitude sector (70–90°E) are used to study the latitudinal variation of its annual pattern in this region during the volcanically quiescent period of 1998–2003. The SAGE-II data is compared with the lidar measurements from Gadanki (13.5°N, 79.2°E) when the satellite had an overhead occultation pass over a small geographical grid centered at this location. The particulate optical depth (τp) in the UT region shows a general decrease with increase in latitude and a pronounced summer–winter contrast with relatively low values during winter and high values during summer. In general, these variations are in accordance with the latitudinal variation of convective available potential energy (CAPE) and thunderstorm activity, which are good representative indices of tropospheric convection. While the particulate extinction (and τp) in the 18–21 km (LS1) region is relatively low in the equatorial region up to 15°N, it shows an increase in the off-equatorial region, beyond 15°N. While the annual variation of τp in the LS1 region is almost insignificant near the equator, it is rather well pronounced in latitude region between 10 and 15°N with relatively high values during winter and low values during summer. Beyond 20°N, this shows a prominent peak during summer. At a higher altitude, the 21–30 km (LS2) region, the latitude variation of τp shows a different pattern with high values near the equator and low values in the off-equatorial region confirming the existence of a stratospheric aerosol reservoir. Low values of τp at lower regime (LS1) near the equator could be due to rapid transport of particulates from the near equatorial region to higher latitudes, while the equatorial high at upper regime (LS2) could be due to lofting and subsequent accumulation. 相似文献
15.
Arecibo (18.4 N, 66.7 W) incoherent scatter (IS) observations of electron density N(h) are compared with the International Reference Ionosphere (IRI-95) during midday (10/14 h), for summer, winter and equinox, at solar maximum (1981). The N(h) profiles below the F2 peak, are normalized to the peak density NmF2 of the F region and are then compared with the IRI-95 model using both the standard B0 (old option) and the Gulyaeva-B0 thickness (new option). The thickness parameter B0 is obtained from the observed electron density profiles and compared with those obtained from the IRI-95 using both the options. Our studies indicate that during summer and equinox, in general, the values of electron densities at all the heights given by the IRI model (new option), are generally larger than those obtained from IS measurements. However, during winter, the agreement between the IRI and the observed values is reasonably good in the bottom part of the F2 layer but IRI underestimates electron density at F1 layer heights. The IRI profiles obtained with the old option gives much better results than those generated with the new option. Compared to the observations, the IRI profiles are found to be much thicker using Gulyaeva-B0 option than using standard B0. 相似文献
16.
本文使用Athens站2001—2005年间电离层GPS/TEC和foF2数据,分析了TEC、NmF2和电离层板厚τ日变化、季节变化特征以及与太阳活动的统计关系,得到以下结论:电离层TEC和NmF2具有相似的日变化特征,最大值出现在14∶00LT;TEC在2001和2002年白天出现"冬季异常"现象,NmF2在2001—2005年白天均出现该现象;电离层板厚τ主要分布在200~600 km,存在黎明峰和日落峰双峰结构,黎明峰一般出现在5∶00—6∶00LT,日落峰结构一般从日落后开始出现,在午夜前达到极大值;14∶00LT和2∶00LT时刻TEC、NmF2同太阳活动的关系呈现"线性"、"饱和"以及"放大"趋势,而τ则出现正、负及不明显的线性关系;最后,我们分析认为黎明峰归因于电离层TEC增加以及NmF2的减少,而日落峰主要是由TEC减少速度低于NmF2造成的. 相似文献
17.
E. L. Afraimovich Ya. F. Ashkaliev V. M. Aushev A. B. Beletsky V. V. Vodyannikov L. A. Leonovich O. S. Lesyuta Yu. V. Lipko A. V. Mikhalev A. F. Yakovets 《Journal of Atmospheric and Solar》2002,64(18)
Basic properties of the mid-latitude traveling ionospheric disturbances (TIDs) during the maximum phase of a major magnetic storm of 6–8 April 2000 are shown. Total electron content (TEC) variations were studied by using data from GPS receivers located in Russia and Central Asia. The nightglow response to this storm at mesopause and termospheric altitudes was also measured by optical instruments FENIX located at the observatory of the Institute of Solar-Terrestrial Physics (51.9°N,103.0°E), and MORTI located at the observatory of the Institute of Ionosphere (43.2°N, 77.0°E). Observations of the O (557.7 and 630.0 nm) emissions originating from atmospheric layers centered at altitudes of 90 and 250 km were carried out at Irkutsk and of the O2(b1∑g+−X3∑g−) (0-1) emission originating from an atmospheric layer centered at altitude of 94 km was carried out at Almaty. Our radio and optical measurement network observed a storm-induced solitary large-scale wave with duration of 1 h and a wave front width of no less than 5000 km, while it traveled equatorward with a velocity of 200 m/s from 62°N to 38°N geographic latitude. The TEC disturbance, basically displaying an electron content depression in the maximum of the F2 region, reveals a good correlation with growing nightglow emission, the temporal shift between the TEC and emission variation maxima being different for different altitudes. A comparison of the auroral oval parameters with dynamic spectra of TEC variations and optical 630 nm emissions in the frequency range 0.4–4 mHz (250–2500 s periods) showed that as the auroral oval expands into mid-latitudes, also does the region with a developed medium-sale and small-scale TEC structure. 相似文献
18.
Annual and seasonal variations in the low-latitude topside ionosphere are investigated using observations made by the Hinotori satellite and the Sheffield University Plasmasphere Ionosphere Model (SUPIM). The observed electron densities at 600 km altitude show a strong annual anomaly at all longitudes. The average electron densities of conjugate latitudes within the latitude range ±25° are higher at the December solstice than at the June solstice by about 100% during daytime and 30% during night-time. Model calculations show that the annual variations in the neutral gas densities play important roles. The model values obtained from calculations with inputs for the neutral densities obtained from MSIS86 reproduce the general behaviour of the observed annual anomaly. However, the differences in the modelled electron densities at the two solstices are only about 30% of that seen in the observed values. The model calculations suggest that while the differences between the solstice values of neutral wind, resulting from the coupling of the neutral gas and plasma, may also make a significant contribution to the daytime annual anomaly, the E × B drift velocity may slightly weaken the annual anomaly during daytime and strengthen the anomaly during the post-sunset period. It is suggested that energy sources, other than those arising from the 6% difference in the solar EUV fluxes at the two solstices due to the change in the Sun-Earth distance, may contribute to the annual anomaly. Observations show strong seasonal variations at the solstices, with the electron density at 600 km altitude being higher in the summer hemisphere than in the winter hemisphere, contrary to the behaviour in NmF2. Model calculations confirm that the seasonal behaviour results from effects caused by transequatorial component of the neutral wind in the direction summer hemisphere to winter hemisphere. 相似文献
19.
Summary The seasonal variation of the Earth's rotation is studied by the method of demodulation of a non-stationary sequence. The variations of the amplitudes and phases of the annual and semi-annual fluctuation of time UT1 — TAI in the years 1963 – 1976 have been calculated. 相似文献
20.
K. Mohanakumar 《Annales Geophysicae》1994,12(5):448-456
A study on the variability of temperature in the tropical middle atmosphere over Thumba (8 32’ N, 76 52’ E), located at the southern part of India, has been carried out based on rocket observations for a period of 20 years, extending from 1970 to 1990. The rocketsonde-derived mean temperatures over Thumba are corrected prior to 1978 and then compared with the middle atmospheric reference model developed from satellite observations and Solar Mesosphere Explorer (SME) satellite data. Temperature variability at every 1 km interval in the 25–75 km region was analysed. The tropical stratosphere is found to be highly stable, whereas considerable variability is noted in the middle mesosphere. The effect of seasonal cycle is least in the lower stratosphere. Annual and semi-annual oscillations in temperature are the primary oscillations in the tropical middle atmosphere. Annual temperature oscillations are dominant in the mesosphere and semi-annual oscillations are strong in the stratosphere. The stratopause region is noted to be the part of the middle atmosphere least sensitive to the changes in solar activity and long-term variability. 相似文献