High Frequency Capacitance Probe Research Articles

Rocket observations of propagating waves in the night time equatorial F-region over Brazil

A Brazilian SONDA III rocket carrying plasma diagnostic experiments was launched from the Brazilian rocket launching stations in Alcântara (2.31°S, 44.4°W Geog. Lat.) to measure the height profiles of electron density, electron temperature and the ambient electric field. High frequency capacitance probe was used to measure the height profile of the electron density and the Langmuir probe was used to measure the electron density and the spatial structures of plasma irregularities. An electric field double probe was used to measure the electric field fluctuations associated with the F-region plasma irregularities. Spectral analysis of the fluctuations in electron density and electric field indicated the presence of propagating waves in the night time F-region over a large height range. The electron temperatures estimated from the LP data showed abnormally high values in the base of the F-region during the upleg of the rocket and practically normal values in the same height region during the downleg. A brief study of the characteristic features of the spectra of electron density and electric field fluctuations and the associated electron temperature variations are presented and discussed here.

Spectral features of E- and F-region plasma irregularities as observed by rocket-borne electron density probes from Brazil

The height variation of the ionospheric electron density was measured with rocket-borne electron density probes from Alcˆ (2.31 ◦ S; 35.2 ◦ W) in Brazil. A Black Brant X sounding rocket was launched on 14-th October 1994 at 19h55min (LT) to investigate the phenomenon of high-altitude equatorial spread-F events. Ground equipments were operated during the campaign to ensure that the rocket was launched under conditions favorable for the generation of plasma bubbles in the F-region. The electron density was measured by three different types of probes. A High Frequency Capacitance probe (HFC) gave density data with low height resolution, while a conventional Langmuir Probe (LP) and a Plasma Frequency Probe (PFP) measured the electron density and the spatial fluctuations in it. The k -spectra of the plasma irregularities were obtained by the spectral analysis of the electron density fluctuation data. An important feature observed was the continuous presence of plasma irregularities of a large range of vertical scale sizes in the altitude range of 340 km to 817 km. The electron number density varied considerably in these spatial structures, for example a decrease by a factor of 2.6 in a vertical extension of 1 km near the altitude of 497 km. Near 535 km altitude the electron density increased by a factor of 1.8 within a height range of 2.7 km. Density structures of vertical scale sizes in the range of hundreds of meters also were observed superposed on the large-scale structures. During the rocket upleg two height regions of intense irregularities were observed, one between 366 and 480 km and the other between 684 and 812 km. The Langmuir Probe (LP) could make measurements of irregularities of vertical scale sizes more than 8 m in these height ranges, while the Plasma Frequency Probe, could make measurements of irregularities of vertical scale sizes as small as 0.5 m. Spectral features of these irregularities as observed by the two plasma probes at different height regions are presented and discussed here.

On the deviations of measured electron density profiles from IRI predictions for low latitudes

In situ electron density profiles obtained from the equatorial stations in Brazil using conventional Langmuir probes and High Frequency Capacitance probes are compared with the IRI predictions in the light of the spectral distribution of the plasma density irregularities observed. Plasma instability mechanisms, especially the Rayleigh-Taylor and the Cross-Field instability mechanisms are considered responsible for the generation of the plasma irregularities observed at different height regions along the electron density profile, in the post sunset ionosphere. A comparative study of the observed characteristics of the plasma irregularities with those expected from the theories can give us information on the reliability of the observed profiles. This reliability estimate is all the more important because of the fact that the techniques used for the measurement of electron density are known to be associated with some inherent problems. The presence or absence of plasma irregularities in a given height region can, therefore, give us information as to whether the deviations of the observed electron density profiles from the IRI predictions are genuine or not. From this comparative study one can also obtain information as to what are the physical parameters responsible for the observed deviations in the profiles and thereby suggest some possible improvements in the methods used for IRI predictions for low latitudes.

In-situ measurement of ionospheric plasma density by two different techniques—a comparison

Night-time ionospheric plasma density profiles over the equatorial station Natal, Brazil, measured simultaneously using a rocket-borne Langmuir Probe (LP) and a High Frequency Capacitance Probe (HFC) on two occasions, show considerable differences, especially above the F-region peak. In this height region, the electron density values estimated from the LP ion currents are considerably less than those estimated from the HFC data, while below the F-region peak, the LP electron densities seem to be slightly greater than the HFC electron densities. From considerations of the basic principles of the two experiments it is seen that while the higher LP electron densities at lower heights are probably due to an increase in the effective sensor surface area caused by the sheath formation, in the region above the F-peak the relative lower plasma density obtained from LP current seems to be caused by (a) a change in the floating potential of the rocket, (b) a decrease in the thickness of the plasma sheath, and (c) an increase in the mean ion thermal velocity relative to the rocket velocity.

Rocket observation of equatorial plasma bubbles over Natal, Brazil, using a high‐frequency capacitance probe

In situ measurement of electron density height profile of the equatorial nighttime ionosphere, under a developing spread F event, was carried out using a dual mode high frequency capacitance (HFC) probe that was flown on board a SONDA‐III rocket launched from Natal on December 11, 1985. This represents the first measurement of plasma bubble characteristics using an HFC probe. A series of plasma bubbles in varying degrees of their growth phase was detected mostly during the upleg of the flight. A somewhat detailed discussion, and comparative studies, of the measurements at the two probe frequencies (6.17 MHz and 11.75 MHz) are presented in this paper. Among the important findings from the present study is an evidence of electron temperature enhancement in the plasma bubble possibly caused by electron heating from energetic particle precipitation in the South Atlantic magnetic anomaly.

Rocket-borne measurements of equatorial ionospheric electron densities and their comparison with IRI-10 predictions

Three experiments were conducted using high frequency capacitance probes carried on board SONDA III rockets launched off the coast of Natal (6° S, 36\\dgW), Brasil. Electron-density height profiles from two of the experiments, one daytime, and one nighttime, are representative of quiet equatorial ionospheric conditions whereas for the third experiment the rocket was launched into a nighttime ionosphere that was disturbed by a developing plasma hubble event. Agreement between experimental results and the IRI predictions for the quiet day and night densities varies with height. Comparisons are also made with electron densities obtained from the semi-empirical Low Latitude Ionospheric Model (SLIM).

The Difficulties of Measuring the Water Saturation and Porosity of Snow

AbstractLiquid saturation and porosity control most of the important material properties of wet snow, hence accurate measurements of these two parameters is of the utmost importance for both field research and glaciological applications. For example, the movement of liquid water through snow is highly sensitive to the volume of water present and accurate measurements of the water saturation are necessary in order to infer the temporal and spatial variations in the flow field. Nevertheless, most of the instruments in use are not capable of making accurate determinations of saturation.An error analysis shows that only direct measurements of the liquid volume can provide accurate values of water saturation, hence the melting calorimeter is inherently inaccurate. While centrifuges extract some of the liquid for direct measurement, there is always some residual liquid left depending on the grain size and structural parameters of the ice matrix. Therefore, some uncertainty exists over the interpretation of the data obtained from centrifuges. High-frequency capacitance probes can be used either in situ or on the surface and are very sensitive to the volume of liquid present. Capacitance probes are by far the best of the available devices. Remote-sensing techniques, like the active microwave system, require more development for use in operational forecasting schemes and as research tools.

Uniform Stratified Layers in the Equatorial E-region

A CENTAURE rocket carrying a high frequency capacitance probe was launched from the Thumba Equatorial Rocket Launching Station, India (geographic coordinates 8° 32′N, 76° 51′ E), at 1530 IST (1000 UT), on February 26 ,1969. In this communication we present some interesting preliminary results on the electron density observations in the E-region. A more detailed article will be published elsewhere.