Ground-based Method Research Articles

Comparison of the characteristic energy of precipitating electrons derived from ground-based and DMSP satellite data

Abstract. Energy maps are important for ionosphere-magnetosphere coupling studies, because quantitative determination of field-aligned currents requires knowledge of the conductances and their spatial gradients. By combining imaging riometer absorption and all-sky auroral optical data it is possible to produce high temporal and spatial resolution maps of the Maxwellian characteristic energy of precipitating electrons within a 240240 common field of view. These data have been calibrated by inverting EISCAT electron density profiles into equivalent energy spectra. In this paper energy maps produced by ground-based instruments (optical and riometer) are compared with DMSP satellite data during geomagnetic conjunctions. For the period 1995-2002, twelve satellite passes over the ground-based instruments' field of view for the cloud-free conditions have been considered. Four of the satellite conjunctions occurred during moderate geomagnetic, steady-state conditions and without any ion precipitation. In these cases with Maxwellian satellite spectra, there is 71% agreement between the characteristic energies derived from the satellite and the ground-based energy map method.

Measurement of solute diffusivities. Part III. From solutal convection dominated transport to quasi-diffusive transport

This paper presents an analytical and experimental investigation of the new ground-based method for diffusion measurements in liquid metals presented in the two companion papers [Int. J. Heat Mass Transfer 17 (2001) 1639] and [Int. J. Heat Mass Transfer 44 (2001) 3345]. The configuration under consideration is a horizontal capillary tube submitted to a vertical steady magnetic field; the temperature field is assumed isothermal. The aim of this third part is to introduce a single description of transport in a diffusion experiment over a wide range of parameters (namely magnetic field intensity and experimental duration), which overlaps both the two asymptotic models previously presented. The experimental results, obtained in two different apparatus, are in good agreement with the analytical model and exhibit a fair repeatability. The impurity diffusion coefficient of Bi in Sn is measured at 275 °C and near the fusion point, in good agreement with recent microgravity data.

Comparison of Ground-Based and Airborne Snow Depth Measurements with Georadar Systems, Case Study

Snow depth measurements with the help of georadar (Ground Penetrating Radar, GPR) were investigated for almost two decades in Scandinavia. For the first tests in the early 1980s, results were of poor quality. Later, data quality improved when different systems were developed. In Norway, emphasis was put on ground-based snow measurements of scientific character; few attempts for operational use were undertaken. In Sweden, airborne, operational snow measurements with georadar were performed since 1986. A helicopter, flying near to the ground, was used as platform. The objective of the presented study was to compare results from ground-based and airborne snow measurements. The radar control units used were comparable, but the antenna configuration and frequencies differed. Also radar data interpretation and the conversion of radar signal travel time into snow depth values varied. Measurements were made at common snow courses. The comparison showed in general high correlation between radar results from both methods. Differing results were found for shallow snow and bare areas. Here, the ground-based method indicated zero or close-to-zero snow depth, whereas the airborne method rarely detected zero snow depth. This phenomenon seemed to be connected to the bigger footprint size of the airborne radar and to the different radar data interpretation methods. On average, the airborne measurements indicated shallower snow depths than ground-based measurements, 4% less in open terrain and 7% less in forest. Comparing snow depth as grid cell values, the best agreement, less than 1% difference, was obtained for the 10 m resolution.

Ground-based method for measuring thermal infrared effective emissivities: Implications and perspectives on the measurement of land surface temperature from satellite data

Thermal infrared emissivity is an important parameter for surface characterization and for determining surface temperature. The field-based measurements for ground and vegetation emissivities in 8-14 w m waveband were performed with an emissivity box. A theoretical analysis was carried out using the box and a correcting factor has been determined. The average value for thermal band emissivity of the exposed bare soil was found to be around 0.909; the average value measured for most of the varieties of vegetation present were in the range of 0.980-0.985. A theoretical model is used for obtaining effective emissivity in the 8-14 w m region from Advanced Very High Resolution Radiometer (AVHRR) data considering the proportion of vegetation cover in a pixel and the field-measured emissivity values. The error of the methodology is found to be within 1.5%. Narrow band emissivities for AVHRR channels 4 and 5 have been derived from the emissivity values in the 8-14 w m waveband. The surface temperature has been derived from AVHRR data using a split-window algorithm as a function of emissivities derived in narrow bands. The split-window algorithm accounted for absorption effects of the atmosphere by incorporating the water vapour concentration measured in the campaign. A good agreement was obtained between the satellite-derived surface temperature and the in situ observations. The result suggest that the methodology allows us to derive land surface temperature with an accuracy better than 1.5° C provided the surface emissivity is known. The paper describes the field-based emissivity measurement and approach for deriving surface temperature over land surface.

Remote sensing of the heliospheric solar wind using radio astronomy methods and numerical simulations

The ground-based radio astronomy method of interplanetary scintillations (IPS) and spacecraft observations have shown, in the past 25 years, that while coronal holes give rise to stable, reclining high speed solar wind streams during the minimum of the solar activity cycle, the slow speed wind seen more during the solar maximum activity is better associated with the closed field regions, which also give rise to solar flares and coronal mass ejections (CME’s). The latter events increase significantly, as the cycle maximum takes place. We have recently shown that in the case of energetic flares one may be able to track the associated disturbances almost on a one to one basis from a distance of 0.2 to 1 AU using IPS methods. Time dependent 3D MHD models which are constrained by IPS observations are being developed. These models are able to simulate general features of the solar-generated disturbances. Advances in this direction may lead to prediction of heliospheric propagation of these disturbances throughout the solar system.

Remote Sensing of the Heliospheric Solar Wind using Radio Astronomy Methods and Numerical Simulations

AbstractThe ground-based radio astronomy method of interplanetary scintillations (IPS) and spacecraft observations have shown, in the past 25 years, that while coronal holes give rise to stable, recurring high speed solar wind streams during the minimum of the solar activity cycle, the slow speed wind seen more during the solar maximum activity is better associated with the closed field regions, which also give rise to solar flares and coronal mass ejections (CME’s). The latter events increase significantly, as the cycle maximum takes place. We have recently shown that in the case of energetic flares one may be able to track the associated disturbances almost on a one to one basis from a distance of 0.2 to 1 AU using IPS methods. Time dependent 3D MHD models which are constrained by IPS observations are being developed. These models are able to simulate general features of the solar-generated disturbances. Advances in this direction may lead to prediction of heliospheric propagation of these disturbances throughout the solar system.

Solar Corona Investigation by the Coronal Line Photometer at Lomnický Peak

AbstractThis paper deals with a possibility to use the ground-based method of observation in order to solve basic problems connected with the solar corona research. Namely:1.heating of the solar corona2.course of the global cycle in the corona3.rotation of the solar corona and development of active regions.There is stressed a possibility of high-time resolution of the coronal line photometer at Lomnický Peak coronal station, and use of the latter to obtain crucial observations.

A comparison between protein crystals grown with vapor diffusion methods in microgravity and protein crystals using a gel liquid-liquid diffusion ground-based method

Crystals of human serum albumin have been successfully grown in a variety of gels using crystallization conditions otherwise equivalent to those utilized in the popular hanging-drop vapor-equilibration method. Preliminary comparisons of gel grown crystals with crystals grown by the vapor diffusion method via both ground-based and microgravity methods indicate that crystals superior in size and quality may be grown by limiting solutal convection. Preliminary X-ray diffraction statistics are presented.

Solar astrometry by photolithography

Observed temporal variations of shape and size of the solar disk as viewed from Earth may act as constraints for theories of the interior of the Sun. In addition to existing programs of solar diameter measurements we investigate a ground-based photographic method.

Distribution of energetic particles near interplanetary shocks

The acceleration of charged particles by collisionless shocks is a process of considerable importance in astrophysics, but the physical mechanism is not yet understood in detail. Energetic particles near interplanetary shocks may be studied in situ by spacecraft, but little is known about their distribution across the shock surface because of inadequate knowledge of the location of the sampling point in relation to the whole disturbance. A ground-based method has been developed2 which enables shock-associated disturbances to be mapped in three dimensions, and we have used it, in combination with near-Earth spacecraft measurements, to study how the particle flux varies for shocks travelling at different angles to the Sun–Earth line. We have observed a pronounced east–west asymmetry which indicates that the inclination of the interplanetary magnetic field to the shock surface must be a potent factor in the acceleration process.

First measurements of thermospheric winds in Antarctica by an optical ground-based method

The installation of a Fabry–Perot interferometer at Halley (75.5° S, 26.8° W; L = 4.2), Antarctica, has now allowed the first comparison to be made between Southern Hemisphere ground-based thermospheric wind measurements and the predictions of a three-dimensional time-dependent thermospheric global circulation model. Because some terms of the thermospheric momentum equation are more dependent on geomagnetic than geographic latitude, the large separation of these that exists at Halley provides a distinct contrast to the dynamic behaviour observed in the more frequently studied northern polar thermosphere. Although the initial results from the experiment are in general agreement with the model, some consistent and significant differences between the observed wind field and that predicted are evident in the morning sector. These may be related to uncertainties in mapping magnetospheric boundaries to ionospheric heights in the Southern Hemisphere.

Observing interplanetary disturbances from the ground

The scintillation of celestial radio sources due to small-scale turbulence along lines of sight through the interplanetary medium provides a convenient, ground-based method of monitoring disturbances in interplanetary space. With the sensitive 3.6-hectare Array at Cambridge we have carried out a new programme in which ∼900 sources were observed each day for more than 1 yr. When the long-term average scintillation behaviour of each source had been accurately determined we found that transient disturbances could be clearly distinguished. We detected large clouds of enhanced turbulence moving out from the Sun and were able to track them to distances beyond the Earth's orbit. Our observations differ from recent work elsewhere1 in that we used a larger grid of sources and observed them more continuously over a wider range of solar elongations. To illustrate the information that is now being obtained we present observations for 10–21 December 1978, a period of considerable solar activity for which spacecraft and other data are also available.

Structure of the uranian upper atmosphere

Although the occultations of relatively bright stars by planets are rare events, they provide an important ground-based method for determining temperature, pressure and number density profiles of planetary upper atmospheres1. The technique is particularly valuable for planets in the outer Solar System, whose atmospheres have not yet been probed by spacecraft missions. Since the atmosphere of Uranus had not yet been investigated by the occultation technique, we have observed and report here the occultation of the star SAO158687 by Uranus on 10 March 1977 (refs 2, 3).

Atmospheric Temperature Measurement Using Raman Backscatter

A ground-based method of measuring atmospheric vertical temperature profiles using Raman backscatter from N(2) is discussed. Experimental measurement of temperature fluctuations at tower heights is described.