D. Alcaydé

Bio: D. Alcaydé is an academic researcher from Hoffmann-La Roche. The author has contributed to research in topics: Ionosphere & Incoherent scatter. The author has an hindex of 19, co-authored 36 publications receiving 2119 citations.

First multispacecraft ion measurements in and near the Earth's magnetosphere with the identical Cluster ion spectrometry (CIS) experiment

Abstract: . On board the four Cluster spacecraft, the Cluster Ion Spectrometry (CIS) experiment measures the full, three-dimensional ion distribution of the major magnetospheric ions (H+, He+, He++, and O+) from the thermal energies to about 40 keV/e. The experiment consists of two different instruments: a COmposition and DIstribution Function analyser (CIS1/CODIF), giving the mass per charge composition with medium (22.5°) angular resolution, and a Hot Ion Analyser (CIS2/HIA), which does not offer mass resolution but has a better angular resolution (5.6°) that is adequate for ion beam and solar wind measurements. Each analyser has two different sensitivities in order to increase the dynamic range. First tests of the instruments (commissioning activities) were achieved from early September 2000 to mid January 2001, and the operation phase began on 1 February 2001. In this paper, first results of the CIS instruments are presented showing the high level performances and capabilities of the instruments. Good examples of data were obtained in the central plasma sheet, magnetopause crossings, magnetosheath, solar wind and cusp measurements. Observations in the auroral regions could also be obtained with the Cluster spacecraft at radial distances of 4–6 Earth radii. These results show the tremendous interest of multispacecraft measurements with identical instruments and open a new area in magnetospheric and solar wind-magnetosphere interaction physics. Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetopheric configuration and dynamics; solar wind - magnetosphere interactions)

Mapping electrodynamic features of the high-latitude ionosphere from localized observations: Combined incoherent-scatter radar and magnetometer measurements for January 18-19, 1984

Abstract: The large-scale electric potential patterns, describing ionospheric convection, are estimated for northern high latitudes during January 18-19, 1984, from combined incoherent-scatter radar and ground magnetometer observations, using the technique of Richmond and Kamide (this issue). The patterns usually have a dominant two-cell characteristic, although the intensities, orientations and shapes of the cells undergo considerable changes with time. Often evident during substorm expansive phases is a “tongue” of low electric potential extending toward the east along the low-latitude edge of the high potential cell at night. Time-series plots of the maximum and minimum electric potentials show that they can respond rapidly to changes in the interplanetary magnetic field Bz component. Total estimated potential drops for this 2-day period range from about 15 kV up to 108 kV. The influence of the different types of data on the resultant estimated electric potential patterns is analyzed. Where available, the direct electric field observations by the radars primarily control the characteristics of the estimated potential patterns, while the magnetometer data have their greatest influence in regions where direct electric field measurements are unavailable. We also employ the statistical electric potential model of Foster et al. (1986) to help fill in the patterns in datasparse regions. For the present study, data coverage is often good enough that the statistical model plays only a secondary role in determining the estimated convection patterns. The ionospheric electrical conductance observations from the Sondrestrom and EISCAT radars are very important in helping modify the statistical conductance model of Fuller-Rowell and Evans (1987) to yield modified conductance distributions suitable for interrelating the electric fields, currents, and magnetic perturbations. Analysis of the statistical uncertainty in the estimated large-scale electric field patterns shows the uncertainty to exceed 50% in the polar cap and sub auroral regions and to be less than 20% only in the vicinity of the radar electric field observations.

Global measures of ionospheric electrodynamic activity inferred from combined incoherent scatter radar and ground magnetometer observations

Abstract: An analysis of several global measures of high-latitude ionospheric electrodynamic activity is undertaken on the basis of results obtained from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure applied to incoherent scatter radar and ground magnetometer observations for January 18–19, 1984. Different global measures of electric potentials, currents, resistances, and energy transfer from the magnetosphere show temporal variations that are generally well correlated. We present parameterizations of these quantities in terms of the AE index and the hemispheric power index of precipitating auroral particles. It is shown how error estimates of the mapped electric fields can be used to correct the estimation of Joule heating. Global measures of potential drop, field-aligned current, and Joule heating as obtained by the AMIE procedure are compared with similar measures presented in previous studies. Agreement is found to within the uncertainties inherent in each study. The mean potential drop through which field-aligned currents flow in closing through the ionosphere is approximately 28% of the total polar cap potential drop under all conditions during these 2 days. We note that order-of-magnitude differences can appear when comparing different global measures of total electric current flow and of effective resistances of the global circuit, so that care must be exercised in choosing characteristic values of these parameters for circuit-analogy studies of ionosphere-magnetosphere electrodynamic coupling.

Convection electric fields and electrostatic potential over 61°<λ<72° invariant latitude observed with the European incoherent scatter facility 1. Initial results

Abstract: Convection electric fields are observed with the European Incoherent Scatter Common Program CP-3 which probes the F2 region of the auroral ionosphere between 61° and 72° invariant latitude for 24-hour runs. Several examples of convection fields are discussed, corresponding to various levels of magnetospheric activity. The principal characteristics of the convection drifts are discussed in the light of indices of magnetospheric activity level. It is shown that depending on the level of magnetospheric activity as revealed by the Kp index, the two-cell convection pattern is more or less present in the field of view of the radar and that the convection velocities around dawn and dusk increase with increasing activity. A method is described which assumes that the 24-hour convection pattern is due to a steady state potential viewed by the radar rotating with the earth under its ionospheric induced structures; as this assumption can be wrong, in some extreme circumstances of very high and unsteady magnetospheric activity, a test is proposed to ascertain the validity of the method. Inferred potential distributions are then discussed; it is shown in particular that the potential drop from dawn to dusk increases with the magnetospheric activity index Kp. A preliminary analysis of the shapes and positions of the two convection cells is then presented.

Seasonal dependence of high-latitude electric fields

Abstract: The seasonal dependence of the high-latitude electric field was investigated using Sondrestrom incoherent scatter radar data. Average E{times}B drifts were derived from 5 years of measurements centered around solar minimum. The electrostatic potentials that best fit the observed average electric field were calculated. It was found that the large-scale convection pattern significantly changes with season. This change involves the overall shape of the convection pattern, as well as the electric field intensity, and thus the total dawn-dusk potential across the polar cap. The cross polar cap potential drop is largest in fall, followed by winter, spring and summer. The small difference found between the summer and winter cross polar cap potential can be attributed to differing field-aligned potential drops. In view of the well-known relationship between field-aligned currents and parallel potential drop, this is consistent with the observations that Birkeland currents are larger in the summer than in winter. Changes in the overall shape of the convection pattern are consistent with the simple notion that the whole pattern is shifted toward the nightside as well as, to a lesser extent, toward the dawnside in summer as compared to winter. This assumption is based on the following observed effects: (1) Themore » rotation of the overall convection pattern toward earlier local times with respect to the noon-midnight direction is maximum for summer on the dayside. (2) On the nightside, the Harang discontinuity is typically located within the radar field of view ({Lambda}=67 to 82) in the winter averaged patterns, but it is equatorward of the field of view in summer. (3) The line that joins the dawn and dusk potential maxima is shifted toward the midnight sector in summer as compared to winter by about 5{degree}. (4) In the dawn cell, the latitude of the convection reversal is the lowest during summer; in the dusk cell the latitude of the reversal is the lowest during winter.« less

Extension of the MSIS Thermosphere Model into the middle and lower atmosphere

Abstract: The MSIS-86 empirical model has been revised in the lower thermosphere and extended into the mesosphere and lower atmosphere to provide a single analytic model for calculating temperature and density profiles representative of the climatological average for various geophysical conditions. Tabulations from the Handbook for MAP 16 are the primary guide for the lower atmosphere and are supplemented by historical rocket and incoherent scatter data in the upper mesosphere and lower thermosphere. Low-order spherical harmonics and Fourier series are used to describe the major variations throughout the atmosphere including latitude, annual, semiannual, and simplified local time and longitude variations. While month to month details cannot be completely represented, lower atmosphere temperature data are fit to an overall standard deviation of 3 K and pressure to 2%. Comparison with rocket and other data indicates that the model represents current knowledge of the climatological average reasonably well, although there is some conflict as to details near the mesopause.

First multispacecraft ion measurements in and near the Earth's magnetosphere with the identical Cluster ion spectrometry (CIS) experiment

Abstract: . On board the four Cluster spacecraft, the Cluster Ion Spectrometry (CIS) experiment measures the full, three-dimensional ion distribution of the major magnetospheric ions (H+, He+, He++, and O+) from the thermal energies to about 40 keV/e. The experiment consists of two different instruments: a COmposition and DIstribution Function analyser (CIS1/CODIF), giving the mass per charge composition with medium (22.5°) angular resolution, and a Hot Ion Analyser (CIS2/HIA), which does not offer mass resolution but has a better angular resolution (5.6°) that is adequate for ion beam and solar wind measurements. Each analyser has two different sensitivities in order to increase the dynamic range. First tests of the instruments (commissioning activities) were achieved from early September 2000 to mid January 2001, and the operation phase began on 1 February 2001. In this paper, first results of the CIS instruments are presented showing the high level performances and capabilities of the instruments. Good examples of data were obtained in the central plasma sheet, magnetopause crossings, magnetosheath, solar wind and cusp measurements. Observations in the auroral regions could also be obtained with the Cluster spacecraft at radial distances of 4–6 Earth radii. These results show the tremendous interest of multispacecraft measurements with identical instruments and open a new area in magnetospheric and solar wind-magnetosphere interaction physics. Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetopheric configuration and dynamics; solar wind - magnetosphere interactions)

Empirical high-latitude electric field models

Abstract: The present analysis of electric field measurements from the Dynamics Explorer 2 satellite, which extends previous empirical models, emcompasses much data from polar crossings entering and exiting the high latitudes in all magnetic local time zones. The goal is to represent the typical distributions of convective electric fields with a minimum number of characteristic patterns. Significant large-scale revisions of the OGO 6 dawn-dusk measurement models are made. The deformations of the two-cell patterns lead to sunward convection in dayside polar regions, while maintaining the integrity of the nightside convection pattern.

DARN/SUPERDARN : A global view of the dynamics of high-latitude convection

Abstract: The Dual Auroral Radar Network (DARN) is a global-scale network of HF and VHF radars capable of sensing backscatter from ionospheric irregularities in the E and F-regions of the high-latitude ionosphere. Currently, the network consists of the STARE VHF radar system in northern Scandinavia, a northern-hemisphere, longitudinal chain of HF radars that is funded to extend from Saskatoon, Canada to central Finland, and a southern-hemisphere chain that is funded to include Halley Station, SANAE and Syowa Station in Antarctica. When all of the HF radars have been completed they will operate in pairs with common viewing areas so that the Doppler information contained in the backscattered signals may be combined to yield maps of high-latitude plasma convection and the convection electric field. In this paper, the evolution of DARN and particularly the development of its SuperDARN HF radar element is discussed. The DARN/SupperDARN network is particularly suited to studies of large-scale dynamical processes in the magnetosphere-ionosphere system, such as the evolution of the global configuration of the convection electric field under changing IMF conditions and the development and global extent of large-scale MHD waves in the magnetosphere-ionosphere cavity. A description of the HF radars within SuperDARN is given along with an overview of their existing and intended locations, intended start of operations, Principal Investigators, and sponsoring agencies. Finally, the operation of the DARN experiment within ISTP/GGS, the availability of data, and the form and availability of the Key Parameter files is discussed.

Ionospheric Electrodynamics Using Magnetic Apex Coordinates.

Abstract: The equations of ionospheric electrodynamics are developed for a geomagnetic field of general configuration, with specific application to coordinate systems based on Magnetic Apex Coordinates. Two related coordinate systems are proposed: Modified Apex Coordinates, appropriate for calculations involving electric fields and magnetic-field-aligned currents; and Quasi-Dipole Coordinates, appropriate for calculations involving height-integrated ionospheric currents. Distortions of the geomagnetic field from a dipole cause modifications to the equations of electrodynamics, with distortion factors exceeding 50% at some geographical locations. Under the assumption of equipotential geomagnetic-field lines, it is shown how the field-line-integrated electrodynamic equations can be expressed in two dimensions in magnetic latitude and longitude, and how the height-integrated and field-aligned current densities can be calculated. Expressions are derived for the simplified calculation of magnetic perturbations above and below the ionosphere associated with the three-dimensional current system. It is shown how the base vectors for the Modified Apex coordinate system can be applied to map electric fields, plasma-drift velocities, magnetic perturbations, and Poynting fluxes along the geomagnetic field to other altitudes, automatically taking into account changes in magnitude and direction of these vector quantities along the field line. Similarly, it is shown how Quasi-Dipole coordinates are useful for expressing horizontal ionospheric currents, equivalent currents, and ground-level magnetic perturbations. A computer code is made available for efficient calculation of the various coordinates, base vectors, and related quantities described in this article.