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1.
Night-time F-region vertical electrodynamic drifts at the magnetic equatorial station, Trivandrum are obtained for a period of 2 years, 1989 and 1990 (corresponding to solar cycle maximum epoch), using ionosonde h‘F data. The seasonal variation of the vertical drift is found to be associated with the longitudinal gradients of the thermospheric zonal wind. Further, the seasonal variation of the prereversal enhancement of the vertical drift is associated with the time difference between the sunset times of the conjugate E-regions (magnetic field line linked to F-region) which is indicative of the longitudinal gradients of the conductivity (of the E-region). The vertical drifts and the causative zonal electric fields at Trivandrum are compared with those at Jicamarca and F-region zonal electric field models. It is seen that the night-time downward drift (as also the causative westward electric field) at Jicamarca is greater than that at Trivandrum. The prereversal enhancement of the drift is greater at Jicamarca than at Trivandrum during the summer and the equinoxes, whereas during the winter the opposite is the case.  相似文献   

2.
T. Ogawa 《Annales Geophysicae》1997,14(12):1454-1461
We briefly overview the radar observations that have been made for 30 years at Syowa Station, Antarctica for studying small-scale electron-density irregularities in the southern high-latitude E- and F-region ionosphere. Some observational results (i.e., long-term variations of radio aurora, Doppler spectra with narrow spectral widths and low Doppler velocities, and simultaneous observations of radar and optical auroras) from VHP radars capable of detecting 1.3- to 3-m scale irregularities are presented. A new 50-MHz radar system equipped with phased-antenna arrays began operation in February 1995 to observe two-dimensional behaviors of E-region irregularities. An HF radar experiment also began in February 1995 to explore decameter-scale E- and F-region irregularities in the auroral zone and polar cap. These two radars will contribute to a better understanding of the ionospheric irregularities and ionospheric physics at southern high latitudes.  相似文献   

3.
Summary The present paper contains studies of the nocturnal radiation at some Indian Stations (Madras, Waltair, Nagpur, New Delhi and Poona) with the help of the Ångström compensation Pyrgeometer. The technique of measurement is also described briefly. A study of the mean monthly variation of sky radiation during clear as well as all nights has been discussed. A comparitive study of mean monthly values of sky and other nocturnal radiation components at these stations is also presented. Ångström, [4]2) expressed the dependence of sky radiationS—on water vapour pressuree (mm of mercury) at the earth's surface and air temperatureT (degrees absolute), near the instrument to be given byS=T 4 (0.75–0.32×10–0.069e ) cal/cm2/min. According to this semi-empirical relationship, the calculated values of sky radiation for clear nights are smaller than the observed values of sky radiation at all the above stations. It is for this reason the authors obtained a new formula with different constants using nine years observed data at all the stations. To investigate the value of the constant, the mean annual observations presented for nine years from clear skies were analysed for correlations betweenB (black body radiation) versesS (sky radiation),N (net radiation) andE (absolute error) and obtained a good correlation co-efficients 0.90, 1 and 0.98 respectively. The new suggested formula isS=T 4 (0.88–0.32×10–0.069e ) cal/cm2/min, 267° A<T<313° A. It is also verified using with observed data of different years of the stations. The agreement between the computed values with the new formula of sky radiation and observed sky radiation is found to be good.  相似文献   

4.
We present a statistical study of the diurnal variations of the E-region backscatter occurrence observed by 15 SuperDARN radars over 3 years. The diurnal variation of echo occurrence observed by each radar is examined for three levels of geomagnetic activity. It is found that the E-region echo occurrence for individual radars exhibits very similar diurnal variations for low geomagnetic activity, with the differences between radars increasing with activity. This indicates that local processes become more important in the generation of the E-region echoes during disturbed periods. It is also shown that the majority of E-region backscatter structures take the form of diffuse echo bands rather than discrete echo patches, with the dominance of diffuse echoes increasing with activity. Finally, a hypothesis that the echo occurrence is controlled by the radar's coverage of the auroral oval is tested using the electron and ion oval models derived from the DMSP satellite observations.  相似文献   

5.
We have developed a lidar to study the temperature structure of the nighttime mesopause region over the Arecibo Observatory (18.35°N, 66.75°W) by measuring the lineshape of the fluorescence spectrum of atomic potassium that is deposited in the mesosphere and lower thermosphere (MLT) by meteors. To demonstrate how the potassium lidar can enhance MLT studies at Arecibo, we show recent results for: (1) comparisons with airglow temperature measurements; (2) simultaneous operations with stratospheric and mesospheric temperature profiling by Rayleigh lidar; (3) simultaneous observations of K, Ca+, and E-region electron density profiles; and (4) occurrences of sporadic K layers, and relationships to sporadic E layers.  相似文献   

6.
This paper presents more data on the properties of type-1 irregularities in the nighttime midlatitude E-region ionosphere. The measurements were made with a 50-MHz Doppler radar system operating in Crete, Greece. The type-1 echoes last from several seconds to a few minutes and are characterized by narrow Doppler spectra with peaks corresponding to wave phase velocities of 250–350 m/s. The average velocity of 285 m/s is about 20% lower than nominal E-region ion-acoustic speeds, probably because of the presence of heavy metallic ions in the sporadic-E-layers that appear to be associated with the mid-latitude plasma instabilities. Sometimes the type-1 echoes are combined with a broad spectrum of type-2 echoes; at other times they dominate the spectrum or may appear in the absence of any type-2 spectral component. We believe these echoes are due to the modified two-stream plasma instability driven by a polarization electric field that must be larger than 10 mV/m. This field is similar in nature to the equatorial electrojet polarization field and can arise when patchy nighttime sporadic-E-layers have the right geometry.  相似文献   

7.
Ionospheric two-stream waves and gradientdrift waves nonlinearly drive a large-scale (D.C.) current in the E-region ionosphere. This current flows parallel to, and with a comparable magnitude to, the fundamental Pedersen current. Evidence for the existence and magnitude of wave-driven currents derives from a theoretical understanding of E-region waves, supported by a series of nonlinear 2D simulations of two-stream waves and by data collected by rocket instruments in the equatorial electrojet. Wave-driven currents will modify the large-scale dynamics of the equatorial electrojet during highly active periods. A simple model shows how a wave-driven current appreciably reduces the horizontally flowing electron current of the electrojet. This reduction may account for the observation that type-I radar echoes almost always have a Doppler velocity close to the acoustic speed, and also for the rocket observation that electrojet regions containing gradientdrift waves do not appear also to contain horizontally propagating two-stream waves. Additionally, a simple model of a gradient-drift instability shows that wavedriven currents can cause nonsinusoidal electric fields similar to those measured in situ.  相似文献   

8.
Summary The variations of the initialh E s height are investigated in the solar cycle 1957–1968, deriving the regressive dependency:h E s =121.4–6·10–2 R referring to the median monthly values at a solar zenith angle =75°. The similar variations ofh E s (R) during the day and night are interpreted as a domination of the sporadic layer formation from a redistribution of the day-time ionization and secondary participation of nightly ionizing sources. The analogous cyclich E s andh E variations confirm this conclusion while the seasonal variations in the state of the sporadic layer show outlined dynamical effects. The comparatively not big cyclic variation in the spatial state of theE-region are considered to confirm the predominating ionizing action of the ultraviolet range (933–1038 Å) in the lower part of theE-region, while the soft X-radiation influences mainly the near maximum part of this region.  相似文献   

9.
Summary History and results of a 41/2-years-expedition to Argentine. A determination of the sun's «temperature» can only be given by the laws ofBoltzmann-Stefan andWien, because the temperature of the different layers is different. In the measurements of the sun's radiation the law ofBoltzmann-Stefan was introduced (T 4, where is a constant, andT the Kelvin-Temperature) while in the passed 100 years the difference between the sun's and the instruments radiation was taken as radiation, although this difference was arbitrariously variable with the instruments temperature. The effect of the vertical exchange of airmasses, on the radiation of the sun and the radiation of the air between the sun and the instrument was cleared. With these corrections one can not receive more as the difference between the so called solar constant and the albedo of the atmosphere. If the highest values are used (smallest albedo) the approximated value of the solar constant becomes 2.4, corresponding well to the value, derived from the supposed temperature of the sun.  相似文献   

10.
Evaporation from the forest floor (EFF) in a deciduous broadleaf forest was measured using microlysimeter and closed‐chamber systems. The microlysimeter was used at six points in the experimental basin, and measurements gave different EFF values at different points. This could be attributed to the local photoenvironment of each sampling point, rather than to litter conditions, if the spatial variation in air temperature (Ta) or vapour pressure deficit (VPD) at the forest floor was small within this basin. A detachable microlysimeter measured condensation in the litter layer during the night, indicating that the litter layer, as well as the mulch layer, played a role in preventing evaporation from the soil layer. The closed‐chamber system made it possible to continuously measure long‐term EFF. EFF was closely related to VPD; even during the night, when solar radiation was zero, EFF amounted to 14·0% of the daily EFF. The daily EFF was 0·20 ± 0·13 mm day?1 during the study period, with two seasonal peaks: in late spring (0·31 mm day?1 in April) and early fall (0·22 mm day?1 in September). The former peak has been reported from two deciduous forests in Japan and is strongly related to the solar radiation reaching the forest floor when the trees are dormant. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

11.
In the theory of E-region plasma instabilities, the ambient electric field and electron density gradient are both included in the same dispersion relation as the key parameters that provide the energy for the generation and growth of electrostatic plasma waves. While there exist numerous measurements of ionospheric electric fields, there are very few measurements and limited knowledge about the ambient electron density gradients, Ne, in the E-region plasma. In this work, we took advantage of the EISCAT CP1 data base and studied statistically the vertical electron density gradient length, Lz = Ne/(dNe/dz), at auroral E-region heights during both eastward and westward electrojet conditions and different ambient electric field levels. Overall, the prevailing electron density gradients, with Lz ranging from 4 to 7 km, are found to be located below 100 km, but to move steadily up in altitude as the electric field level increases. The steepest density gradients, with Lz possibly less than 3 km, occur near 110 km mostly in the eastward electrojet during times of strong electric fields. The results and their implications are examined and discussed in the frame of the linear gradient drift instability theory. Finally, it would be interesting to test the implications of the present results with a vertical radar interferometer.  相似文献   

12.
Zusammenfassung Es werden einfache halbempirische Formeln zur Berechnung der Globalstrahlung angegeben. Die Abhängigkeit der Globalstrahlung von den meteorologischen Parametern Trübungsgrad (Linke'scher TrübungsfaktorT g) sowie Bewölkungsart und-bedeckung wurde empirisch aus Messungen in Frankfurt (Main) und Potsdam ermittelt. Die nach diesen Formeln berechnete Globalstrahlungsleistung in ly min–1 und die 24-stündige Globalstrahlungsenergiesumme in ly wird mit Messergebnissen anderer Autoren in den Tropen, bzw. in Polargebieten, verglichen, wobei sich eine sehr gute Übereinstimmung zeigt.
Summary Simple halfempirical formulas for the calculation of the global radiation are presented. The dependence of global radiation on the meteorological parameters: turbidity (turbidity factorT g afterLinke) and type and amount of cloud was find empirically from the measurements in Frankfurt (Main) and Potsdam. The flux of global radiation (in ly min–1) and the daily sum of global radiation energy, calculated by these formulas, was compared with measured values of other authors in the tropics and in polar regions, respectively, and shows satisfactory agreement.
  相似文献   

13.
Summary Second derivative coefficients for various grid systems are derived followingPeters' andElkins' approaches. Two simple formulae, one for three dimensional bodies and the other for two dimensional bodies are also suggested. These utilise the average of the anomalies around a single circle and the anomaly at the central point.All the coefficient sets and the proposed simple formulae are applied to gravity fields of spheres and cylinders. Coefficients ofElkins' type derived with a weightage of 1/r 4 to all the circles gave excellent results in both the cases of spheres and cylinders, whereasPeters' coefficients without any weightage to the circles gave reliable results in case of cylinders only. The simple formulae suggested gave more accurate results than any of the above coefficient sets.  相似文献   

14.
Pan evaporation (Ep) is an important indicator of water and energy and the decline of Ep has been reported in many regions over the last decades. The climate and Ep are dependent on each other. In this study, the temporal trends of Ep and main Ep drivers, namely mean air temperature (Ta), wind speed (u), global solar radiation (Rs), net long‐wave radiation(Rnl) and vapour pressure deficit (D) from 1970 to 2012, were calculated on the basis of 26 meteorological stations on the Tibetan Plateau. The arithmetic average of Ep from 26 stations decreased with the rate of ?11.91 mm a?2; the trends of Rs, Rnl, Ta, u and D were ?1.434 w m?2 decade?1, 0.2511 w m?2 decade?1, 0.3590°C decade?1, ?0.2376 m s?1 decade?1 and 9.523 Pa decade?1, respectively. The diffuse irradiance is an essential parameter to model Ep and quantify the contribution of climatic factors to changing Ep. 60 724 observations of Rs and diffuse solar irradiance (Rd) from seven of the 26 stations were used to develop the correlation between the diffuse fraction (Rd/Rs), and the clearness index (Rs/Ro). On the basis of the estimation of the diffuse component of Rs and climatic data, we modified the PenPan model to estimate Chinese micro‐pan evaporation (Ep) and assess the attribution of Ep dynamics using partial derivatives. The results showed that there was a good agreement between the observed and calculated daily Ep values. The observed decrease in Ep was mostly due to declining wind speed (?13.7 mm a?2) with some contributions from decreasing solar irradiance (?3.1 mm a?2); and the increase of temperature had a large positive effect (4.55 mm a?2) in total whilst the increase of Rnl had insignificant effect (0.35 mm a?2) on Ep rates. The change of Ep is the net result of all the climatic variables. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

15.
Checking the predictive worth of an environmental model inevitably includes a goodness of fit metric to quantify the degree of matching to recorded data, thereby giving a measure of model performance. Considerable analysis and discussion have taken place over fit indices in hydrology, but a neglected aspect is the degree of communicability to other disciplines. It is suggested that a fit index is best communicated to colleagues via reference to models giving unbiased predictions, because unbiased environmental models are a desirable goal across disciplines. That is, broad recognition of a fit index is aided if it simplifies in the unbiased case to a familiar and logical expression. This does not hold for the Nash–Sutcliffe Efficiency E which reduces to the somewhat awkward unbiased expression E = 2 – 1/r2, where r2 is the coefficient of determination. A new goodness of fit index V is proposed for model validation as V = r2/(2‐E), which simplifies to the easily communicated V = r4 in the unbiased case. The index is defined over the range 0 ≤ V ≤ 1, and it happens that V < E for larger values of E. Some synthetic and recorded data sets are used to illustrate characteristics of V in comparison to E. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

16.
An overview of studies of the ionospheric E-region using artificial periodic inhomogeneities (API) is presented. Generation of the electron density API is considered theoretically. Methods of measurements of the electron density profile and neutral atmosphere temperature, density and vertical velocity are outlined and illustrated by experimental results. Some suggestions concerning investigations of the atmospheric turbulence using API are presented.  相似文献   

17.
The large-scale terms in the vorticity equation are evaluated usingKrishnamurti's (1971a, b) summer mean winds at 200 mb for a global belt from 25°S to 45°N. The production of vorticity by the divergent wind field is found to be imbalanced over all of the tropical and subtropical belt. As a result there is a requirement for a sub-grid scale (space or time) mechanism which removes negative vorticity from the regions of strong divergence (Tibetan and Mexican highlands) and removes positive vorticity from the regions of strong convergence (mid-oceanic troughs) at 200 mb during northern summer at a rate of approximately 4×10–10 sec–2. As suggested byHolton andColton (1972), in regions of strong and persistent convection, such as the Tibetan Plateau, deep cumulus clouds can account for this transport. However, the mechanism for removing positive vorticity in the vicinity of the upper tropospheric mid-oceanic troughs is still an intriguing and open question.On leave-of-absence at the National Science Foundation, Climate Dynamics Research Section.  相似文献   

18.
Theoretical and experimental aspects of the production, transformation, diffusion and loss of N2 in the upper atmosphere are considered. The N2-CO2 near-resonant system in theD andE regions is taken into account. We describe our understanding of the methods necessary to find the vibrational populations of N2 and CO2 (asymmetric mode of CO2). The calculations of the vibrational temperatures in theD, E, andF regions for the mid-latitude ionosphere and an aurora are presented. The connection between the excited species and the 4.26-m radiation intensities is considered. The models for the rate coefficient of the reaction of O+ with N2 and the electron density decrease resulting from N2 in the F region are discussed.  相似文献   

19.
In this study, we examined the year 2011 characteristics of energy flux partitioning and evapotranspiration of a sub‐alpine spruce forest underlain by permafrost on the Qinghai–Tibet Plateau (QPT). Energy balance closure on a half‐hourly basis was H + λE = 0.81 × (Rn ? G ? S) + 3.48 (W m?2) (r2 = 0.83, n = 14938), where H, λE, Rn, G and S are the sensible heat, latent heat, net radiation, soil heat and air‐column heat storage fluxes, respectively. Maximum H was higher than maximum λE, and H dominated the energy budget at midday during the whole year, even in summer time. However, the rainfall events significantly affected energy flux partitioning and evapotranspiration. The mean value of evaporative fraction (Λ = λE/(λE + H)) during the growth period on zero precipitation days and non‐zero precipitation days was 0.40 and 0.61, respectively. The mean daily evapotranspiration of this sub‐alpine forest during summer time was 2.56 mm day?1. The annual evapotranspiration and sublimation was 417 ± 8 mm year?1, which was very similar to the annual precipitation of 428 mm. Sublimation accounted for 7.1% (30 ± 2 mm year?1) of annual evapotranspiration and sublimation, indicating that the sublimation is not negligible in the annual water balance in sub‐alpine forests on the QPT. The low values of the Priestley–Taylor coefficient (α) and the very low value of the decoupling coefficient (Ω) during most of the growing season suggested low soil water content and conservative water loss in this sub‐alpine forest. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

20.
There are differences between existing models of solar EUV with < 1050 Å and between laboratory measurements of the O+ + N2 – reaction rate coefficient, both parameters being crucial for the F2-region modeling. Therefore, indirect aeronomic estimates of these parameters may be useful for qualifying the existing EUV models and the laboratory measured O+ + N2 – rate coefficient. A modified self-consistent method for daytime F2-region modeling developed by Mikhailov and Schlegel was applied to EISCAT observations (32 quiet summer and equinoctial days) to estimate the set of main aeronomic parameters. Three laboratory measured temperature dependencies for the O+ + N2 – rate coefficient were used in our calculations to find self-consistent factors both for this rate coefficient and for the solar EUV flux model from Nusinov. Independent of the rate coefficient used, the calculated values group around the temperature dependence recently measured by Hierl et al. in the 850–1400 K temperature range. Therefore, this rate coefficient may be considered as the most preferable and is recommended for aeronomic calculations. The calculated EUV flux shows a somewhat steeper dependence on solar activity than both, the Nusinov and the EUVAC models predict. In practice both EUV models may be recommended for the F2-region electron density calculations with the total EUV flux shifted by ±25% for the EUVAC and Nusinov models, correspondingly.  相似文献   

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