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1.
Obtaining an accurate, value for total ozone under a cloudy sky, especially when the sun is not high, is a major remaining problem associated with total ozone measurements. The Toronto spectrophotometer has been designed with this in mind. It has been fitted with a polarizing prism, and measures light at four wavelengths simultaneous which makes it possible to obtain two independent double ratios. Clouds produce two effects on ozone measurements; the first is purely an optical effect which causes an apparent increase in ozone, the second is most likely a real increase in ozone associated with large cumulus-type clouds. By considering the three following points it is possible to distinguish between these two cloud effects and probably measure the true total ozone for solar zenith angles less than 80°: 1. The multiply scattered component of polarized light is used to reduce optical cloud variance. This makes all skies appear like thick coulds. 2. A double difference similar to the AD method is used but the two ratios of the double difference are weighted inversely with(= 1 - 2 for a pair). This further reduces the optical effects of clouds. 3. Real ozone increases due to large clouds are verified by comparing the increase of ozone obtained from one double difference to that of another. Differences between this multiply, polarized curve and the direct sun curve will be given, and a technique to obtain an accurate value of total ozone under all sky conditions, provided that the solar zenith angle is less than 80°, will be given.  相似文献   

2.
The Global Ozone Monitoring Experiment (GOME) onboard the ERS-2 satellite has been in operation since July 1995. The Norwegian ground-based total ozone network has played an important role both in the main validation during the commissioning phase and in the validation of upgraded versions of the analysis algorithms of the instrument. The ground-based network consists of various spectrometer types (Dobson, Brewer, UV filter instruments). The validation of the second algorithm version used until January 1998 reveals a very good agreement between GOME and ground-based data at solar zenith angles <60° and deviations of GOME total ozone data from ground-based data of up to ±60 DU (∼20%) at zenith angles ≥60°. The deviations strongly depend on the season of the year, being negative in summer and positive in winter/spring, The deviations furthermore show a considerable scattering (up to ±25 DU in monthly average values of 5° SZA intervals), even in close spatial and temporal coincidence with ground-based measurements, especially in the high Arctic. The deviations are also dependent on the viewing geometry/ground pixel size with an additional negative offset for the large pixels used in the backswath mode and at solar zenith angles ≥85°, compared to forward-swath pixels.  相似文献   

3.
Erythemal ultraviolet (UVER; 280–400 nm) and total shortwave (SW; 305–2800 nm) solar irradiances were recorded from 2000 to 2009 in Valladolid, Spain. UVER and SW values under cloudless conditions are simulated by radiative transfer (TUV 4.6) and empirical models. These model estimations are tested with experimental measurements showing a great agreement (root mean square error around 7%). The aerosol effect on UVER irradiance is determined through a model study. UVER radiation and total ozone column (TOC) temporal evolutions show a negative relationship. TOC accounts for 80% of UVER variance and its radiation amplification factor is 1.1 at zenith of 65°. Cloud effects on solar radiation are shown and quantified by the cloud modification factor. Moreover the enhancement effect cases are analysed. SW radiation proves more sensitive to clouds than UVER. Clouds are seen to attenuate and enhance solar radiation by up to 93% and 22% in the UVER range, respectively.  相似文献   

4.
On the basis of measurements of the intensity of 1.58-μm emissions of the Infrared Atmospheric System of molecular oxygen (IRAO2) conducted at the Zvenigorod scientific station of the Institute of Atmospheric Physics of the Russian Academy of Sciences (φ = 55.7°N, λ = 36.8°E), seasonal variations are estimated for various solar zenith angles. Their amplitude has the maximum value at the solar zenith angles χ S ∼ 105–110°. It decreases at χ S ∼ 125–130° and tends to zero at χ S ∼ 80–85°. The comparison of currently measured values of the 1.58-μm emission intensity of the Infrared Atmospheric System of molecular oxygen with published data on the intensity of this emission obtained in 1961–1966 reveals their decrease over approximately 50 years. This fact is in good agreement with similar behavior of the emission intensity of atomic oxygen (557.7 nm) over the period considered.  相似文献   

5.
The effects of cloud shadowing, channelling, cloud side illumination and droplet concentration are investigated with regard to the reflection of shortwave solar radiation. Using simple geometric clouds, coupled with a Monte Carlo model the transmission properties of idealized cloud layers are found. The clouds are illuminated with direct solar radiation from above. The main conclusion reached is that the distribution of the cloud has a very large influence on the reflectivity of a cloud layer. In particular, if the cloud contains vertical gaps through the cloud layer in which the liquid water content is zero, then, smaller more numerous gaps are more influential on the radiation than fewer, larger gaps with equal cloud fraction. At very low solar zenith angles channelling of the radiation reduces the reflection expected on the basis of the percentage cloud cover. At high solar zenith angles the illumination of the cloud edges significantly increases the reflection despite the shadowing of one cloud by another when the width of the gaps is small. The impact of droplet concentration upon the reflection of cloud layers is also investigated. It is found that at low solar zenith angles where channelling is important, the lower concentrations increase the transmission. Conversely, when cloud edge illumination is dominant the cloud distribution is found to be more important for the higher concentrations.  相似文献   

6.
Polar stratospheric clouds (PSCs) are often observed in the Kiruna region in northern Sweden, east of the Scandinavian mountain range, during wintertime. PSC occurrence can be detected by ground-based optical instruments. Most of these require clear tropospheric weather. By applying the zenith-sky colour index technique, which works under most weather conditions, the data availability can be extended. The observations suggest that PSC events, especially of type II (water PSCs) may indeed more common than predicted by synoptic models, which is expected because of the frequent presence of mountain-induced leewaves. However, it will be of importance to increase the density of independent observations.  相似文献   

7.
Summary The 272 kHz ionospheric absorption has been measured at the Prhonice Observatory by the A3 method (oblique incidence) for a long period. The results of the comparison of these absorption data with indices of solar, geomagnetic and cosmic ray activity are presented for large solar zenith angles. The day-time absorption (x 75° – 85°) is described well by these indices and appears to be affected particularly by direct solar Lyman- radiation. The night-time absorption (x>100°), however, is not described sufficiently by the indices used.  相似文献   

8.
Through their multiple interactions with radiation, clouds have an important impact on the climate. Nonetheless, the simulation of clouds in climate models is still coarse. The present evolution of modeling tends to a more realistic representation of the liquid water content; thus the problem of its subgrid scale distribution is crucial. For a convective cloud field observed during ICE 89, Landsat TM data (resolution: 30m) have been analyzed in order to quantify the respective influences of both the horizontal distribution of liquid water content and cloud shape on the Earth radiation budget. The cloud field was found to be rather well-represented by a stochastic distribution of hemi-ellipsoidal clouds whose horizontal aspect ratio is close to 2 and whose vertical aspect ratio decreases as the cloud cell area increases. For that particular cloud field, neglecting the influence of the cloud shape leads to an over-estimate of the outgoing longwave flux; in the shortwave, it leads to an over-estimate of the reflected flux for high solar elevations but strongly depends on cloud cell orientations for low elevations. On the other hand, neglecting the influence of cloud size distribution leads to systematic over-estimate of their impact on the shortwave radiation whereas the effect is close to zero in the thermal range. The overall effect of the heterogeneities is estimated to be of the order of 10 W m−2 for the conditions of that Landsat picture (solar zenith angle 65○, cloud cover 70%); it might reach 40 W m−2 for an overhead sun and overcast cloud conditions.  相似文献   

9.
Using the MU radar at Shigaraki, Japan (34.85°N, 136.10°E), we measure the power distribution pattern of VHF radar echoes from the mid-troposphere. The large number of radar beam-pointing directions (320) allows the mapping of echo power from 0° to 40° from zenith, and also the dependence on azimuth, which has not been achieved before at VHF wavelengths. The results show how vertical shear of the horizontal wind is associated with a definite skewing of the VHF echo power distribution, for beam angles as far as 30° or more from zenith, so that aspect sensitivity cannot be assumed negligible at any beam-pointing angle that most existing VHF radars are able to use. Consequently, the use of VHF echo power to calculate intensity of atmospheric turbulence, which assumes only isotropic backscatter at large beam zenith angles, will sometimes not be valid.  相似文献   

10.
We report on the development and current capabilities of the ALOMAR Rayleigh/Mie/Raman lidar. This instrument is one of the core instruments of the international ALOMAR facility, located near Andenes in Norway at 69°N and 16°E. The major task of the instrument is to perform advanced studies of the Arctic middle atmosphere over altitudes between about 15 to 90 km on a climatological basis. These studies address questions about the thermal structure of the Arctic middle atmosphere, the dynamical processes acting therein, and of aerosols in the form of stratospheric background aerosol, polar stratospheric clouds, noctilucent clouds, and injected aerosols of volcanic or anthropogenic origin. Furthermore, the lidar is meant to work together with other remote sensing instruments, both ground- and satellite-based, and with balloon- and rocket-borne instruments performing in situ observations. The instrument is basically a twin lidar, using two independent power lasers and two tiltable receiving telescopes. The power lasers are Nd:YAG lasers emitting at wavelengths 1064, 532, and 355 nm and producing 30 pulses per second each. The power lasers are highly stabilized in both their wavelengths and the directions of their laser beams. The laser beams are emitted into the atmosphere fully coaxial with the line-of-sight of the receiving telescopes. The latter use primary mirrors of 1.8 m diameter and are tiltable within 30° off zenith. Their fields-of-view have 180 rad angular diameter. Spectral separation, filtering, and detection of the received photons are made on an optical bench which carries, among a multitude of other optical components, three double Fabry-Perot interferometers (two for 532 and one for 355 nm) and one single Fabry-Perot interferometer (for 1064 nm). A number of separate detector channels also allow registration of photons which are produced by rotational-vibrational and rotational Raman scatter on N2 and N2+O2 molecules, respectively. Currently, up to 36 detector channels simultaneously record the photons collected by the telescopes. The internal and external instrument operations are automated so that this very complex instrument can be operated by a single engineer. Currently the lidar is heavily used for measurements of temperature profiles, of cloud particle properties such as their altitude, particle densities and size distributions, and of stratospheric winds. Due to its very effective spectral and spatial filtering, the lidar has unique capabilities to work in full sunlight. Under these conditions it can measure temperatures up to 65 km altitude and determine particle size distributions of overhead noctilucent clouds. Due to its very high mechanical and optical stability, it can also employed efficiently under marginal weather conditions when data on the middle atmosphere can be collected only through small breaks in the tropospheric cloud layers.  相似文献   

11.
For calculating photolysis rates and solar heating in the atmosphere, the radiation field has to be calculated very accurately. Previous investigations have shown that for large solar zenith angles a solution of the radiation equation which accounts for the Earth\’s curvature is needed. A new simplified version of the 3D radiation equation in spherical geometry allowing for anisotropic scattering is presented. The horizontal variation of physical quantities, the variation of the solar zenith angle with different longitude and latitude for the scattering calculation for one vertical column of air and any effects of refraction are neglected. A numerical model is introduced which efficiently solves this new 3D radiation equation accurately. The effects of anisotropic scattering are shown to be very important for the directional dependence of the scattered intensity. Anisotropic scattering by aerosols and air molecules can change the intensity in certain directions by up to 180% and 25%, respectively. However, most of these changes cancel each other out when averaged over all angles, so that the effect of anisotropic scattering for large solar zenith angles on the mean intensity (actinic flux) is much smaller, i.e. less than 10%. For the heating rates, the effect of anisotropic scattering for large solar zenith angles is even smaller, being less than a few percent. Generally, the effects of anisotropic scattering and the effects of including aerosols are the larger on higher altitudes the larger the solar zenith angle is. Results of the model are shown to compare well with results of previous investigations, including the independent work of Dahlback and Stamnes. The agreement is especially good in the case of isotropic scattering by air molecules and neglecting the effects of aerosols.  相似文献   

12.
A refined empirical model of the Dynamics Explorer-1 far-ultraviolet (FUV) imaging photometer’s response to Earth’s quiet time FUV dayglow has been developed for thermospheric studies. The mean photometer response is based upon FUV observations in 156 images obtained during the first five months of imager operations (September 1981–January 1982) and is determined as a function of solar and satellite zenith angles, observational azimuth and solar clock angles, and solar radio flux. Variations with each parameter are characterized and, where possible, fitted with an appropriate function. The fitted response, based on the n-th power of the cosine of the solar zenith angle, is within 10% of actual mean values at all observed solar and satellite zenith angles and is consistent with the results of a first-principles calculation. Subtraction of the model background from other DE-1 images indirectly reveals the enhancement or diminution of thermospheric O/N2 column density ratios due to transport and Joule heating effects. An analysis of summer storm-time images from the Southern Hemisphere demonstrates the use of the model in revealing these effects. The technique developed here is readily applicable to other FUV data sets.  相似文献   

13.
A high-resolution spectrometer (0.0014 nm at 313 nm) has been developed at the University of L’Aquila (Italy) for atmospheric spectroscopic studies. The layout, optics and software for the instrument control are described. Measurements of the mercury low-pressure lamp lines from 200 to 600 nm show the high performances of the spectrometer. Laboratory measurements of OH and NO2 spectrums demonstrate that the system could be used for cross-section measurements and to detect these species in the atmosphere. The first atmospheric application of the system was the observation of direct solar and sky spectrums that shows a filling-in of the sky lines due to rotational Raman scattering. The measurements have been done with clear and cloudy sky and in both there was a strong dependence of the filling-in from the solar zenith angle whereas no dependence from the wavelengths was evident at low solar zenith angles (less than 85°).  相似文献   

14.
Rocket-borne ultraviolet photometers operating at =0.31 m have been used at Thumba (8°33N, 76°52E) to make measurements of atmospheric scattering at tropospheric and lower stratospheric altitudes. Measurements could be made of the amplitude of the scattered fluxes and the angular distribution up to an altitude of about 24 km on three rocket flights conducted as part of the 16 February 1980 solar eclipse campaign. These measurements have been used to study the size distribution as well as the number densities of aerosols in the troposphere and lower stratosphere over Thumba.  相似文献   

15.
A statistical study of underestimates of wind speeds by VHF radar   总被引：1，自引：0，他引：1  
Comparisons are made between horizontal wind measurements carried out using a VHF-radar system at Aberystwyth (52.4°N, 4.1°W) and radiosondes launched from Aberporth, some 50 km to the southwest. The radar wind results are derived from Doppler wind measurements at zenith angles of 6° in two orthogonal planes and in the vertical direction. Measurements on a total of 398 days over a 2-year period are considered, but the major part of the study involves a statistical analysis of data collected during 75 radiosonde flights selected to minimise the spatial separation of the two sets of measurements. Whereas good agreement is found between the two sets of wind direction, radar-derived wind speeds show underestimates of 4–6% compared with radiosonde values over the height range 4–14 km. Studies of the characteristics of this discrepancy in wind speeds have concentrated on its directional dependence, the effects of the spatial separation of the two sets of measurements, and the influence of any uncertainty in the radar measurements of vertical velocities. The aspect sensitivity of radar echoes has previously been suggested as a cause of underestimates of wind speeds by VHF radar. The present statistical treatment and case-studies show that an appropriate correction can be applied using estimates of the effective radar beam angle derived from a comparison of echo powers at zenith angles of 4.2° and 8.5°.  相似文献   

16.
Study of sporadic-E clouds by backscatter radar   总被引：1，自引：0，他引：1  
It is shown that swept-frequency backscatter ionograms covering a range of azimuths can be used to study the dynamics of sporadic-E clouds. A simple technique based on analytic ray tracing can be used to simulate the observed narrow traces associated with Es patches. This enables the location and extent of the sporadic-E clouds to be determined. The motion of clouds can then be determined from a time sequence of records. In order to demonstrate the method, results are presented from an initial study of 5 days of backscatter ionograms from the Jindalee Stage B data base obtained during March-April 1990. Usually 2–3 clouds were observed each day, mainly during the evening and up to midnight. The clouds lasted from 1–4 h and extended between 30°–80° in azimuth and 150–800 km in range. The clouds were mostly stationary or drifted generally westward with velocities of up to 80 ms–1. Only one cloud was observed moving eastward.  相似文献   

17.
This paper studies the ionospheric and geomagnetic response to an X6.2 solar flare recorded at 14:30 UT on December 13, 2001, in quiet geomagnetic conditions which allow the variations in the geomagnetic field and ionosphere measurements to be easily related to the solar flare radiation.By using measurements from the global positioning system (GPS) and geomagnetic observatories, the temporal evolution of ionospheric total electron content variation, vTECV, and geomagnetic field variations, δB, as well as their rates of variation, were obtained around the subsolar point at different solar zenith angles. The enhancement of both parameters was recorded one to three minutes later than the Geostationary Operational Environmental Satellite (GOES) programme recording; such delay tends to depend on the latitude, longitude, and solar zenith angle of the observatory's observations.The vTECV is related to the local time and the δB to the intensity and position of the ionospheric currents.The vTECV′s maximum value is always recorded later than the maximum values reached by δB and the X-ray intensity. The maximum δB is larger in the local morning than in the afternoon.The rates of vTECV and δB have two maximum values at the same time as the maximum values recorded by Hα (for each ribbon).This work shows the quantitative and qualitative relations between a solar flare and the ionospheric and geomagnetic variations that it produces.  相似文献   

18.
The seasonal variation of gravity wave activity at altitudes around 95 km is investigated using digital measurements of low-frequency nighttime radiowave absorption at Prhonice (50°N, 15°E) between 1989 and 1993. The analysis of 5 years of data allows two conclusions to be drawn: (1) under high solar activity conditions, there is no clearly detectable seasonal variation of gravity wave activity; (2) under medium solar activity conditions (1992, 1993), there is a tendency to a pronounced summer maximum.  相似文献   

19.
A new optical sensor, the airborne Polar Nephelometer, is described. The sensor is designed to measure the optical and microphysical parameters of clouds containing either water droplets or ice crystals or a mixture of these particles ranging in size from a few micrometers to about 500 m diameter. The probe measures the scattering phase function of an ensemble of cloud particles intersecting a collimated laser beam near the focal point of a paraboloïdal mirror. The light scattered from polar angles from 3.49° to 169° is reflected onto a circular array of 33 photodiodes. The signal processing electronics and computer storage can provide one measurement of the scattering phase function every 100 ms or every 0.2 ms. The first part of the paper describes the theoretical design of a prototype version of the probe.  相似文献   

20.
A new parameterization for atmospheric transmission and O2 photodissociation in the Schumann-Runge band region has been developed and tested with a 1D radiative-photochemical model. The parameterization is based on the O2-column along the line of sight to the Sun and the local temperature. Line-by-line calculations have served as a benchmark for testing this method and several other, commonly used, parameterizations. The comparisons suggest that differences between the line-by-line calculations and currently accepted parameterizations can be reduced significantly by using the new method, particularly at large solar zenith angles. The production rate of O-atoms computed with this method shows less than 6% deviation compared to the line-by-line calculations at any altitude, all solar zenith angles and in all seasons. The largest errors are found toward the shorter wavelengths in the Schumann-Runge region at low altitudes. Transmittance is approximated to better than 4% at any altitude and/or solar zenith angle. The total O-production rate above 20 km is approximated to better than 2%. The new parameterization is easily implemented in existing photochemical models and in many cases it may simply replace the existing algorithm. The computational effort exceeds that of other parameterizations but in view of the total computation time needed for the actual calculation of the parameterized Schumann-Runge bands this should not lead to significant performance degeneration. The first 14 coefficients of the parameterization are included in this study. Both the complete sets of coefficients and a simple algorithm can be obtained by contacting the authors. A photochemical model study shows the largest effect of the parameterization method is on odd hydrogen concentrations. Subsequent interaction with an odd oxygen family causes differences in the ozone concentrations between the different parameterizations of more than 10% at selected altitudes. Although it is already established that deficiencies in the treatment of Schumann-Runge band absorption are unlikely to explain the current underestimation of ozone concentration at the stratopause in a variety of photochemical models, this study does show that the choice of parameterization has a large impact on the accuracy of the results at large solar zenith angles and in different seasons.  相似文献   

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