Density structures inside the plasmasphere: Cluster observations

Abstract. The electron density profiles derived from the EFW and WHISPER instruments on board the four Cluster spacecraft reveal density structures inside the plasmasphere and at its outer boundary, the plasmapause. We have conducted a statistical study to characterize these density structures. We focus on the plasmasphere crossing on 11 April 2002, during which Cluster observed several density irregularities inside the plasmasphere, as well as a plasmaspheric plume. We derive the density gradient vectors from simultaneous density measurements by the four spacecraft. We also determine the normal velocity of the boundaries of the plume and of the irregularities from the time delays between those boundaries in the four individual density profiles, assuming they are planar. These new observations yield novel insights about the occurrence of density irregularities, their geometry and their dynamics. These in-situ measurements are compared with global images of the plasmasphere from the EUV imager on board the IMAGE satellite.

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Analysis of plasmaspheric plumes: CLUSTER and IMAGE observations

Annales Geophysicae ◽

10.5194/angeo-24-1737-2006 ◽

2006 ◽

Vol 24 (6) ◽

pp. 1737-1758 ◽

Cited By ~ 28

Author(s):

F. Darrouzet ◽

J. De Keyser ◽

P. M. E. Décréau ◽

D. L. Gallagher ◽

V. Pierrard ◽

...

Keyword(s):

High Time Resolution ◽

Total Electron Density ◽

Density Profiles ◽

Total Electron ◽

In Situ Data ◽

Spacecraft Potential ◽

Point Analysis ◽

Boundary Velocity ◽

Electron Density Profiles

Abstract. Plasmaspheric plumes have been routinely observed by CLUSTER and IMAGE. The CLUSTER mission provides high time resolution four-point measurements of the plasmasphere near perigee. Total electron density profiles have been derived from the electron plasma frequency identified by the WHISPER sounder supplemented, in-between soundings, by relative variations of the spacecraft potential measured by the electric field instrument EFW; ion velocity is also measured onboard these satellites. The EUV imager onboard the IMAGE spacecraft provides global images of the plasmasphere with a spatial resolution of 0.1 RE every 10 min; such images acquired near apogee from high above the pole show the geometry of plasmaspheric plumes, their evolution and motion. We present coordinated observations of three plume events and compare CLUSTER in-situ data with global images of the plasmasphere obtained by IMAGE. In particular, we study the geometry and the orientation of plasmaspheric plumes by using four-point analysis methods. We compare several aspects of plume motion as determined by different methods: (i) inner and outer plume boundary velocity calculated from time delays of this boundary as observed by the wave experiment WHISPER on the four spacecraft, (ii) drift velocity measured by the electron drift instrument EDI onboard CLUSTER and (iii) global velocity determined from successive EUV images. These different techniques consistently indicate that plasmaspheric plumes rotate around the Earth, with their foot fully co-rotating, but with their tip rotating slower and moving farther out.

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Greenland annual accumulation along the EGIG line, 1959–2004, from ASIRAS airborne radar and detailed neutron-probe density measurements

The Cryosphere Discussions ◽

10.5194/tcd-9-6791-2015 ◽

2015 ◽

Vol 9 (6) ◽

pp. 6791-6828

Author(s):

T. B. Overly ◽

R. L. Hawley ◽

V. Helm ◽

E. M. Morris ◽

R. N. Chaudhary

Keyword(s):

Mesoscale Model ◽

Snow Accumulation ◽

Accumulation Rates ◽

Radar Altimeter ◽

Density Profiles ◽

Density Measurements ◽

Fifth Generation ◽

Neutron Probe ◽

Airborne Sar

Abstract. We report annual snow accumulation rates from 1959 to 2004 along a 250 km segment of the Expéditions Glaciologiques Internationales au Groenland (EGIG) line across central Greenland using Airborne SAR/Interferometric Radar Altimeter System (ASIRAS) radar layers and detailed neutron-probe (NP) density profiles. ASIRAS-NP accumulation rates are not statistically different (C.I. 95 %) from in situ EGIG accumulation measurements from 1985 to 2004. Below 3000 m elevation, ASIRAS-NP increases by 20 % for the period 1995 to 2004 compared to 1985 to 1994. Above 3000 m elevation, accumulation increases by 13 % for 1995–2004 compared to 1985–1994. Model snow accumulation results from the calibrated Fifth Generation Mesoscale Model modified for polar climates (Polar MM5) underestimate mean annual accumulation by 16 % compared to ASIRAS-NP from 1985 to 2004. We test radar-derived accumulation rates sensitivity to density using modelled density profiles in place of detailed NP data. ASIRAS radar layers combined with Herron and Langway (1980) model density profiles (ASIRAS-HL) produce accumulation rates within 3.5 % of ASIRAS-NP estimates. We suggest using Herron and Langway (1980) density profiles to calibrate radar layers detected in dry snow regions of ice sheets lacking detailed in situ density measurements, such as those observed by the IceBridge campaign.

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Greenland annual accumulation along the EGIG line, 1959–2004, from ASIRAS airborne radar and neutron-probe density measurements

The Cryosphere ◽

10.5194/tc-10-1679-2016 ◽

2016 ◽

Vol 10 (4) ◽

pp. 1679-1694 ◽

Cited By ~ 17

Author(s):

Thomas B. Overly ◽

Robert L. Hawley ◽

Veit Helm ◽

Elizabeth M. Morris ◽

Rohan N. Chaudhary

Keyword(s):

Climate Models ◽

Regional Climate ◽

Regional Climate Models ◽

Snow Accumulation ◽

Accumulation Rates ◽

Radar Altimeter ◽

Density Profiles ◽

Density Measurements ◽

Neutron Probe

Abstract. We report annual snow accumulation rates from 1959 to 2004 along a 250 km segment of the Expéditions Glaciologiques Internationales au Groenland (EGIG) line across central Greenland using Airborne SAR/Interferometric Radar Altimeter System (ASIRAS) radar layers and high resolution neutron-probe (NP) density profiles. ASIRAS-NP-derived accumulation rates are not statistically different (95 % confidence interval) from in situ EGIG accumulation measurements from 1985 to 2004. ASIRAS-NP-derived accumulation increases by 20 % below 3000 m elevation, and increases by 13 % above 3000 m elevation for the period 1995 to 2004 compared to 1985 to 1994. Three Regional Climate Models (PolarMM5, RACMO2.3, MAR) underestimate snow accumulation below 3000 m by 16–20 % compared to ASIRAS-NP from 1985 to 2004. We test radar-derived accumulation rates sensitivity to density using modeled density profiles in place of NP densities. ASIRAS radar layers combined with Herron and Langway (1980) model density profiles (ASIRAS-HL) produce accumulation rates within 3.5 % of ASIRAS-NP estimates in the dry snow region. We suggest using Herron and Langway (1980) density profiles to calibrate radar layers detected in dry snow regions of ice sheets lacking detailed in situ density measurements, such as those observed by the Operation IceBridge campaign.

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Dynamical features of Venus ionosphere from comparative study of theoretical and in-situ measured electron density profiles

Advances in Space Research ◽

10.1016/0273-1177(90)90164-u ◽

1990 ◽

Vol 10 (5) ◽

pp. 41-44 ◽

Cited By ~ 1

Author(s):

Hari Om Upadhyay ◽

R.N. Singh

Keyword(s):

Comparative Study ◽

Electron Density ◽

Density Profiles ◽

Dynamical Features ◽

Electron Density Profiles

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Deviations from model predictions in measured electron density profiles for low latitudes: A critique

Geofísica Internacional ◽

10.22201/igeof.00167169p.2004.43.2.167 ◽

2004 ◽

Vol 43 (2) ◽

pp. 165-172

Author(s):

P. Muralikrishna ◽

L. P. Vieira ◽

M. A. Abdu ◽

E. R. De Paula

Keyword(s):

Electron Density ◽

Density Profiles ◽

Model Predictions ◽

Low Latitudes ◽

Electron Density Profiles

Se comparan los perfiles obtenidos in situ de las estaciones ecuatoriales de Brasil, usando pruebas de Langmuir y de Frecuencia de Alta Capacitancia, con las predicciones del modelo IRI, en el contexto de las distribuciones espectrales de las irregularidades observadas en la densidad del plasma. Se asume que las inestabilidades de Rayleigh-Taylor y la de Campo Cruzado, son las responsables de la generación de las irregularidades observadas en el plasma, y con ellas se estima el tiempo de crecimiento y el tamaño mínimo de las irregularidades que se observan en diferentes alturas para el perfil de densidad electrónica. Para ello se usan aproximaciones polinomiales simples para representar el perfil observado. La comparación entre las características de las irregularidades observadas del plasma con las esperadas a partir de la teoría nos puede dar información sobre la confiabilidad del perfil observado. La confiabilidad se vuelve particularmente importante de estimar debido a que las técnicas de medición de densidad electrónica se asocian a algunos problemas. Entonces se puede ver que si las desviaciones observadas del perfil comparadas con el modelo IRI son reales o no. De este estudio comparativo uno puede saber cuáles son los parámetros físicos responsables por las desviaciones observadas y sugerir mejoras en los métodos usados en las predicciones de IRI a bajas latitudes.

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Mars’ ionopause characterization based on MAVEN and Mars Express observations

10.5194/epsc2020-208 ◽

2020 ◽

Author(s):

Beatriz Sanchez-Cano ◽

Clara Narvaez ◽

Mark Lester ◽

Michael Mendillo ◽

Majd Mayyasi ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Magnetic Fields ◽

Electron Density ◽

Dynamic Pressure ◽

Solar Wind Dynamic Pressure ◽

Thermal Pressure ◽

Density Profiles ◽

Electron Density Profiles

<p>The ionopause is a tangential discontinuity in the ionospheric thermal plasma density profile that marks the upper boundary of the ionosphere for unmagnetized planets. Since only Venus and Mars have no global &#8220;dipole&#8221; magnetic fields, ionopauses are unique to those planets. For Venus, the ionopause formation is well characterized because the thermal pressure of the ionosphere is usually larger than the solar wind dynamic pressure. For Mars, however, the maximum thermal pressure of the ionosphere is usually insufficient to balance the total pressure in the overlying magnetic pileup boundary. Therefore, the Martian ionopause is not always formed, and when it does, it is highly structured and is located at different altitudes. In this study, we characterise the Martian ionopause formation from the point of view of the electron density and electron temperature, as well as the thermal, magnetic and dynamic pressures. The objective is to investigate under which circumstances the Martian ionopause is formed, both over and far from crustal magnetic fields, and compare to the Venus&#8217; case. We use several multi-plasma and magnetic field in-situ observations from the three deep dip campaigns of the MAVEN mission that occurred on the dayside of Mars (near subsolar point), as well as in-situ solar wind plasma observations from the Mars Express mission. We find that that 36% of the electron density profiles over strong crustal magnetic field regions had an ionopause event in contrast to the 54% of electron density profiles far from strong crustal magnetic field regions. We also find that the topside ionosphere is typically magnetized at mostly all altitudes. The ionopause, if formed, occurs where the total ionospheric pressure (magnetic+thermal) equals the upstream solar wind dynamic pressure.</p>

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In Situ Measurement of Solar Pond Density Profiles

Journal of Solar Energy Engineering ◽

10.1115/1.3266396 ◽

1983 ◽

Vol 105 (4) ◽

pp. 380-382 ◽

Cited By ~ 1

Author(s):

J. Langeliers ◽

C. G. Stojanoff

Keyword(s):

Hydrostatic Pressure ◽

Density Gradient ◽

Experimental Results ◽

Design Parameters ◽

Density Profiles ◽

Solar Pond ◽

Vertical Density ◽

The Stability ◽

Prototype Instrument

The stability of a solar pond is critically dependent upon the maintenance of a suitable vertical density gradient, but rapid, inexpensive methods of profiling the density gradient do not presently exist. A method for obtaining in situ density profiles through measurement of hydrostatic pressure differential is described and investigated. Design parameters and experimental results are presented for a prototype instrument.

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