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1.
Summary This paper describes a study of the fluctuations in total atmospheric ozone amount as measured with a Dobson Spectrophotometer during the summer season over three north Indian stations, using the technique of power spectrum analysis. In all 19 spectra have been constructed. The long term trend was removed by applying a high pass filter. The main conclusions are: (1) The nature of the spectrum at a station generally differs from year to year. (2) Spectra of different stations during the same year, are generally different. (3) From the significance study of the spectral peaks, most of the spectra revealed the presence of two types of periodicities. One of these is in the range of 10–17 days while the other is found to have a range of 4.5–8.3 days. (4) It has been suggested that the former periodicity may be closely linked to the index cycle, while the latter may be related to the long waves in the Westerlies.  相似文献   

2.
A search for Pc3–4 wave activity was performed using data from a trans-Antarctic profile of search-coil magnetometers extending from the auroral zone through cusp latitudes and deep into the polar cap. Pc3–4 pulsations were found to be a ubiquitous element of ULF wave activity in all these regions. The diurnal variations of Pc3 and Pc4 pulsations at different latitudes have been statistically examined using discrimination between wave packets (pulsations) and noise. Daily variations of the Pc3–4 wave power differ for the stations at the polar cap, cusp, and auroral latitudes, which suggests the occurrence of several channels of propagation of upstream wave energy to the ground: via the equatorial magnetosphere, cusp, and lobe/mantle. An additional maximum of Pc3 pulsations during early-morning hours in the polar cap has been detected. This maximum, possibly, is due to the proximity of the geomagnetic field lines at these hours to the exterior cusp. The statistical relation between the occurrence of Pc3–4 pulsations and interplanetary parameters has been examined by analyzing normalized distributions of wave occurrence probability. The dependences of the occurrence probability of Pc3–4 pulsations on the IMF and solar wind parameters are nearly the same at all latitudes, but remarkably different for the Pc3 and Pc4 bands. We conclude that the mechanisms of high-latitude Pc3 and Pc4 pulsations are different: Pc3 waves are generated in the foreshock upstream of the quasi-parallel bow shock, whereas the source of the Pc4 activity is related to magnetospheric activity. Hourly Pc3 power has been found to be strongly dependent on the season: the power ratio between the polar summer and winter seasons is 8. The effect of substantial suppression of the Pc3 amplitudes during the polar night is reasonably well explained by the features of Alfven wave transmission through the ionosphere. Spectral analysis of the daily energy of Pc3 and Pc4 pulsations in the polar cap revealed the occurrence of several periodicities. Periodic modulations with periods 26, 13 and 8–9 days are caused by similar periodicities in the solar wind and IMF parameters, whereas the 18-day periodicity, observed during the polar winter only, is caused, probably, by modulation of the ionospheric conductance by atmospheric planetary waves. The occurrence of the narrow-band Pc3 waves in the polar cap is a challenge to modelers, because so far no band-pass filtering mechanism on open field lines has been identified.  相似文献   

3.
The north-south asymmetry of the Fe XIV 530.3 nm coronal emission line (the green corona) over cycle 22 was investigated. The green corona line brightness was dominant in the southern hemisphere during cycle 22 (A = –0.07), except for short periods of the ascending phase of the activity cycle. The asymmetry of the semi-annual mean over the period 1940 – 1996 was also studied. The asymmetry, during these years, reached its maximum in 1962 – 1966, and then decreased. Important periodicities of the asymmetry in cycle 22, e.g., 158 and 350 days, 2.39 years were found. Similar periodicities were also detected in the years 1940 – 1996. An FFT analysis was used to detect these periodicities.  相似文献   

4.
Ground-based GPS finds potential applications in many atmospheric studies such as spatial distribution of columnar water vapor as well as the tidal oscillations in the atmosphere. The zenith tropospheric delay (ZTD) derived from GPS data at two Indian IGS stations are used to establish its potential for studying the atmospheric tidal, intra-seasonal and planetary oscillations. The major tidal oscillations observed in ZTD data are diurnal, semi-diurnal and their harmonics. Prominent intra-seasonal oscillations observed in ZTD are reported for the first time in this context. These intra-seasonal oscillations are Madden–Julian Oscillation (30–70 days, 60–90 days, 100–120 days) and planetary waves (like 27, 16 and 5–10 days periodicities). Quantification of these periodicities will provide a useful handle to improve the empirical models employed in the estimation of tropospheric delay.  相似文献   

5.
Results of studies of the wave structure of the critical frequencies of the ionospheric F2 layer with periods of planetary waves for two Asian stations—Irkutsk and Wuhan (China)—are presented. Estimates of the appearance frequency, amplitudes, and the lifetime of oscillations with periods typical of planetary waves (2–25 days) are obtained. It is shown that these characteristics depend on the season and place of observation. The appearance of joint periodicities in the critical frequencies at both stations, as well as in the planetary index of geomagnetic activity Ap, is noted.  相似文献   

6.
Summary The technique for evaluating the natural illumination of direct solar radiation introduced byÅngström andDrummond [1]2) has been applied by the authors to the pyrheliometric observations in India and the values of natural illumination derived at eight representative stations are presented in this paper. The dirunal and seasonal variations of the illumination fluxes have been discussed. —In general, illumination fluxes in India show a maximum during summer season except at Madras, where the maximum occurs during winter. The illumination fluxes at various stations vary within the range 80–110 kilolux throughout the year. However, at Calcutta, it varies within a rather narrow range of 65–85 kilolux. Both in summer and winter, the illumination flux during forenoon hours is usually more than that during afternoon hours. An increase in daylight illumination is observed with height of the station above sea level.  相似文献   

7.
United States cloudiness data for 1950–1992 show quasi-biennial (QBO) and quasi-triennial (QTO) oscillations which match partly with the QBO and QTO of the Southern Oscillation (SO) index (the Tahiti minus Darwin pressure), but not with the QBO of the 50-mb equatorial zonal wind. Cloudiness also shows significant periodicities near 4.2 and 7.5 years, and probably a sunspot cycle effect (periodicities 11–14 years), with minimum cloudiness at or soon after sunspot minima, though this could also be due to periodicities of 10 and 17 years observed in the SO index. During 1955-1970, cloudiness increased by about 1%. Thereafter, it remained almost steady for the eastern and central parts of the USA, but continued to rise until about 1980 for the western USA.  相似文献   

8.
The foF2 data obtained at Alma-Ata and Observatorio Del Ebro during the winter/spring of 2003–2004 are analyzed to compare and investigate the upper ionosphere variability at the two selected sites. The geomagnetic activity and the middle stratosphere dynamics, involving planetary wave (PW) activity, are analyzed for understanding the physical conditions and processes that can explain the observed ionospheric variability. By applying the same method of wavelet analysis to the data sets and doing a direct comparison of the results, two types of foF2 disturbances were found. The first type is 2–7-day oscillations, which appeared during periods of increased geomagnetic activity. The second type is oscillations arising from PW activity in the lower atmosphere. These consist of (1) 6–11-day oscillations arising from PW activity in lower atmospheric regions developed during the final stratosphere warming and indicating the timing of the transition from the winter to the summer circulation and (2) 9–13-day and 8–10-day oscillations mostly during the quiet level of geomagnetic activity, indicating a likely close relation with those in the geopotential height at the 1 hPa level for westward-propagating waves at 40°N, which strengthened during stratosphere warming events in January 2004. The time delay of the oscillations in the ΔfoF2 with respect to those in the geopotential height is about 10 days and it seems that the assumed ionosphere response can occur under weakened eastward zonal wind or relatively weak westward zonal wind (V<30 m s−1).  相似文献   

9.
The minimum winter temperature series for the United States Gulf Coast for 1799–1988 (190 values) was subjected to Maximum Entropy Spectral Analysis. Significant periodicities in the QBO region (T-2–3 years) and atT=3.7, 4.5, 5.5, 6.5, 7.5, 12.9, 15.5 and 22 years were detected. Some of these were present in the first half only (1799–1893) while others in the latter half only (1894–1988), indicating a transient nature. Also, more than 50% of the variance was random. Many of the significant periodicities are seen in other geophysical parameters. Some may be harmonics of the 11-year sunspot cycle and the 22-year Hale magnetic sunspot cycle.  相似文献   

10.
Day-time Pc 3–4 (≃5–60 mHz) and night-time Pi 2 (≃5–20 mHz) ULF waves propagating down through the ionosphere can cause oscillations in the Doppler shift of HF radio transmissions that are correlated with the magnetic pulsations recorded on the ground. In order to examine properties of these correlated signals, we conducted a joint HF Doppler/magnetometer experiment for two six-month intervals at a location near L = 1.8. The magnetic pulsations were best correlated with ionospheric oscillations from near the F region peak. The Doppler oscillations were in phase at two different altitudes, and their amplitude increased in proportion to the radio sounding frequency. The same results were obtained for the O- and X-mode radio signals. A surprising finding was a constant phase difference between the pulsations in the ionosphere and on the ground for all frequencies below the local field line resonance frequency, independent of season or local time. These observations have been compared with theoretical predictions of the amplitude and phase of ionospheric Doppler oscillations driven by downgoing Alfvén mode waves. Our results agree with these predictions at or very near the field line resonance frequency but not at other frequencies. We conclude that the majority of the observations, which are for pulsations below the resonant frequency, are associated with downgoing fast mode waves, and models of the wave-ionosphere interaction need to be modified accordingly.  相似文献   

11.
Wavelet and cross-wavelet analysis are used to identify and describe spatial and temporal variability in Canadian seasonal precipitation, and to gain further insights into the dynamical relationship between the seasonal precipitation and the dominant modes of climate variability in the Northern Hemisphere. Results from applying continuous wavelet transform to seasonal precipitation series from 201 stations selected from Environment Canada Meteorological Network reveal striking climate-related features before and after the 1940s. The span of available observations, 1900–2000, allows for depicting variance and covariance for periods up to 12 years. Scale-averaged wavelet power spectra are used to simultaneously assess the temporal and spatial variability in each set of 201 seasonal precipitation time series. The most striking feature, in the 2–3-year period and in the 3–6-year period—the 6–12-year period is dominated by white noise and is not considered further—is a net distinction between the timing and intensity of the temporal variability in autumn, winter and spring–summer precipitation. It is found that the autumn season exhibits the most intense activity (or variance) in both the 2–3 year and the 3–6 year periods. The winter season corresponds to the least intense activity for the 2–3 year period, but it exhibits more activity than the spring–summer for the 3–6 year period.Cross-wavelet analysis is provided between the seasonal precipitation and four selected climatic indices: the Pacific North America (PNA), the North Atlantic Oscillation (NAO), the Northern Hemisphere Annular Mode (NAM) originally called the Arctic Oscillation, and the sea surface temperature series over the Niño-3 region (ENSO). The wavelet cross-spectra revealed coherent space–time variability of the climate–precipitation relationship throughout Canada. It is shown that strong climate/precipitation activity (or covariance) in the 2–6 year period starts after 1940 whatever the climatic index and the season. Prior to year 1940, only local and weaker 2–6 year activity is revealed in western Canada essentially in winter and autumn, but overall a non-significant precipitation/climate relationship is observed prior to 1940. Correlation analysis in the 2–6 year band between the seasonal precipitation and the selected climatic indices revealed strong positive correlations with the ENSO, the NAO, and the NAM in eastern and western Canada for the post-1940 period. For the period prior to 1940, the correlation tend be negative for all the indices whatever the region. A particular feature in the correlation analysis results is the consistently stronger and positive NAM–precipitation correlations in all the regions since 1940. The cross-wavelet spectra and the correlation analysis in the 2–6 year band suggest the presence of a change point around 1940 in Canadian seasonal precipitation—that is found to be more likely related to NAM dynamics.  相似文献   

12.
Summary Characteristic features of long-periodic oscillations in the general atmospheric circulation may be deduced from the correlation existing between the monthly, the three-monthly, the six-monthly and the twelve-monthly figures of the barometric pressure at two distant stations and from the autocorrelation of the same figures at each station.It is shown that the monthly figures of the barometric pressure at Easter Island and those at Djakarta during the six years 1950–1955 have, when plotted as a function of time, one oscillation in common, whereas further these figures have both their own rhythms and their own noise. The period of the common oscillation is 28.6 months, while the phase difference between both stations amounts to 180°. The r.m.s. value of the noise is 0.76 times the value of the amplitude of the oscillation. The rhythms differ in wave length, amplitude and phase.It is also shown that the monthly figures of the barometric pressure at Ponta Delgada and those at Stykkisholm have, when plotted as a function of time, a whole spectrum of oscillations jointly, while all oscillations have the same phase difference (238°) between both stations. These features are deduced from observations during 40 years (1896–1915 and 1921–1940). If yearly figures are used instead of monthly ones, then the greater part of the spectrum of oscillations is smoothed away and only a few common oscillations are left. The first common oscillation has a wave length of 26.5 months and the second one has a wave length of 38.7 months.  相似文献   

13.
The 16-day planetary wave in the mesosphere and lower thermosphere   总被引：3，自引：0，他引：3  
A meteor radar located at Sheffield in the UK has been used to measure wind oscillations with periods in the range 10–28 days in the mesosphere/lower-thermosphere region at 53.5°N, 3.9°W from January 1990 to August 1994. The data reveal a motion field in which wave activity occurs over a range of frequencies and in episodes generally lasting for less than two months. A seasonal cycle is apparent in which the largest observed amplitudes are as high as 14 ms−1 and are observed from January to mid-April. A minimum in activity occurs in late June to early July. A second, smaller, maximum follows in late summer/autumn where amplitudes reach up to 7–10 ms−1. Considerable interannual variability is apparent but wave activity is observed in the summers of all the years examined, albeit at very small amplitudes near mid summer. This behaviour suggests that the equatorial winds in the mesopause region do not completely prevent inter-hemispheric ducting of the wave from the winter hemisphere, or that it is generated in situ.  相似文献   

14.
The effect of the 11-year solar cycle on the response of planetary wavenumbers 1 and 2 at 10 and 30 hPa in winter to solar activity oscillations on the time scale of the Sun's rotation (27.2 day) is discussed in terms of statistical spectral analysis. The three oscillations studied are the 27.2 d (period of the Sun's rotation), 25.3 d (periodicity caused by modulation of the 27.2 d stratospheric response by annual atmospheric variation), and 54.4 d (doubled period of the solar rotation). A significant effect of the 11-year solar cycle is found for the 54.4 d periodicity in planetary wavenumber 1, and for the 27.2 and 25.3 d periodicities in planetary wavenumber 2. The effect of the 11-year solar cycle is expressed in the evident differences between the amplitudes of responses of planetary waves at maximum and minimum of the solar cycle: the amplitudes are much larger at high than at low solar activity. The 11-year modulation of planetary wave activity is most pronounced at mid-latitudes, mainly at 40–60°N, where the observed variability of planetary waves is large. The results obtained are in good agreement with results of the recent modeling study by Shindell et al. (Science 284 (1999) 305).  相似文献   

15.
Abstract

The spatio-temporal variability of daily precipitation series was investigated in a semiarid region of central Macedonia in northern Greece, Ten years of daily rainfall records for seven stations in the region constituted the data base. The spatial characteristics were examined by drawing composite correlation diagrams for the cool (October-March) season and the warm (April-September) season, and the results confirmed the regional homogeneity of the data sets. Furthermore, the temporal analysis indicated that the non-rainy days constituted the major portion of days throughout the year at all the stations. Similarly, light rainfall represented the majority of rainy days. Moreover, the annual rainfall variation showed high values in March, April and November with low values occurring in the summer and autumn. A sharp increase of rainfall between the 185th and the 195th day of the year must be taken into account when the harvest is scheduled. Harmonic and Power Spectrum analyses applied to the annual variation of rain depths using 5-day intervals revealed significant periodicities of 26, 122, 365 and 55 days. Finally the analysis of the annual variation of rain occurrences. revealed periodicities of 365 and 122 days.  相似文献   

16.
Meteor radar measurements of winds near 95 km in four azimuth directions from the geographic South Pole are analyzed to reveal characteristics of the 12-h oscillation with zonal wavenumber one (s = 1). The wind measurements are confined to the periods from 19 January 1995 through 26 January 1996 and from 21 November 1996 through 27 January 1997. The 12-h s = 1 oscillation is found to be a predominantly summertime phenomenon, and is replaced in winter by a spectrum of oscillations with periods between 6 and 11.5 h. Both summers are characterized by minimum amplitudes (5–10 ms–1) during early January and maxima (15–20 ms–1) in November and late January. For 10-day means of the 12-h oscillation, smooth evolutions of phase of order 4–6 h occur during the course of the summer. In addition, there is considerable day-to-day variability (±5–10 ms–1 in amplitude) with distinct periods (i.e., 5 days and 8 days) which suggests modulation by planetary-scale disturbances. A comparison of climatological data from Scott Base, Molodezhnaya, and Mawson stations suggests that the 12-h oscillation near 78°S is s = 1, but that at 68°S there is probably a mixture between s = 1 and other zonal wavenumber oscillations (most probably s = 2). The mechanism responsible for the existence of the 12-h s = 1 oscillation has not yet been identified. Possible origins discussed herein include in situ excitation, nonlinear interaction between the migrating semidiurnal tide and a stationary s = 1 feature, and thermal excitation in the troposphere.  相似文献   

17.
Summary Observations of days with thunderstorm at twelve stations in the Alpine and Pre-Alpine region have been used to look for trends and periodicities in the thunderstorm activity in this area. The annual number of days with thunderstorms was represented by negative binomial distributions, then by means of a non-parametric trend test, parts of the series were found in which the numbers of days with thunderstorm were increasing, decreasing or uniform at the various stations. A variance spectrum analysis showed the existence of long-periodic waves and of short-periodic waves superposed on the background red noise or white noise spectrum. Partitioning the series of observations yielded that these periodicities are not stable.  相似文献   

18.
Ground temperature, pressure and wind speed monthly averages in the area of the Italian Station at Terra Nova Bay, Antarctica, were analyzed for the period 1987–1991 by means of a network of nine AWS (automatic weather stations). Spatial configurations of temperature show a well-defined, relatively warm island in the area of Terra Nova Bay, between Drygalsky and Campbell ice tongues, throughout the year. A second warm island is present to the north along the coast, between Aviator and Mariner ice tongues, for most of the year. From February to March a rapid drop in temperature is observed at all stations. A strong thermal gradient develops during February, March, April and October, November, December, between the coastal region and inner highlands. The baric configuration follows the elevation of the area. Annual average pressure and temperature as functions of stations altitude show linear trends. Severe katabatic wind episodes are recorded at all stations, with wind speed exceeding 25 ms–1 and direction following the orographic features of the inner areas. Co-occurrences of these episodes were observed for stations located along stream lines of cold air drainage. The autocorrelation function of maximum wind speed time series shows wind persistence of 2–3 days and wind periodicity of about one week.  相似文献   

19.
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20.
Summary Measurements of the total incoming solar radiation on a horizontal surface have been recorded since 1967 at a network of actinometric stations in Iraq. The instrument used at each of these stations is a bimetallic actinograph of the Robitzsch type. The stations at Mosul, Baghdad and Nasiriya have been selected, to represent respectively the northern, central and southern climatic zones of Iraq.This paper examines from the available records at these stations, until August 1973, the differnt aspects of radiation climatology which are important in solar energy utilizations. The mean annual, monthly and daily radiation; the number of days in which the radiation has exceeded certain given limits and the periods of successive days having radiation less than 100 and 250 cal cm–2 day–1 have been studied and presented in tabular and graphical forms suitable for direct application.To architects and engineers interested in the availability of solar radiation on vertical and inclined surfaces, the hourly radiation values for Baghdad have been studied for the different months of the year and the corresponding isopleths on the horizontal have been drawn.  相似文献   

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