The Radio Plasma Imager investigation on the IMAGE spacecraft

Radio plasma imaging uses total reflection of electromagnetic waves from plasmas whose plasma frequencies equal the radio sounding frequency and whose electron density gradients are parallel to the wave normals. The Radio Plasma Imager (RPI) has two orthogonal 500-m long dipole antennas in the spin plane for near omni-directional transmission. The third antenna is a 20-m dipole along the spin axis. Echoes from the magnetopause, plasmasphere and cusp will be received with the three orthogonal antennas, allowing the determination of their angle-of-arrival. Thus it will be possible to create image fragments of the reflecting density structures. The instrument can execute a large variety of programmable measuring options at frequencies between 3 kHz and 3 MHz. Tuning of the transmit antennas provides optimum power transfer from the 10 W transmitter to the antennas. The instrument can operate in three active sounding modes: (1) remote sounding to probe magnetospheric boundaries, (2) local (relaxation) sounding to probe the local plasma frequency and scalar magnetic field, and (3) whistler stimulation sounding. In addition, there is a passive mode to record natural emissions, and to determine the local electron density, the scalar magnetic field, and temperature by using a thermal noise spectroscopy technique.     

The Galaxy Cluster Mass Scale and Its Impact on Cosmological Constraints from the Cluster Population

Space Science Reviews - The QB50 mission is a satellite constellation designed to carry out measurements at between 200–380 km altitude in the ionosphere. The multi-needle Langmuir probe...     

Post-midnight equatorial irregularity distributions and vertical drift velocity variations during solstices

Longitudinal distributions of post-midnight equatorial ionospheric irregularity occurrences observed by ROCSAT-1 (1st satellite of the Republic of China) during moderate to high solar activity years in two solstices are studied with respect to the vertical drift velocity and density variations. The post-midnight irregularity distributions are found to be similar to the well-documented pre-midnight ones, but are different from some published distributions taken during solar minimum years. Even though the post-midnight ionosphere is sinking in general, longitudes of frequent positive vertical drift and high density seems to coincide with the longitudes of high irregularity occurrences. Large scatters found in the vertical drift velocity and density around the dip equator in different ROCSAT-1 orbits indicate the existence of large and frequent variations in the vertical drift velocity and density that seem to be able to provide sufficient perturbations for the Rayleigh-Taylor (RT) instability to cause the irregularity occurrences. The need of seeding agents such as gravity waves from atmospheric convective clouds to initiate the Rayleigh-Taylor instability may not be necessary.     

Assessment of thin cirrus and low cloud over snow by means of the maximum likelihood method

Cirrus clouds and low clouds over snow are sometimes difficult to assess by common retrieval methods. In the case of cirrus the reason is the highly variable optical depth while low clouds have approximately the same temperature and reflection properties as snow covered mountains (or plains). An empirical interactive method is described, which allows to classify with great detail clouds of the described types and to determine the fractional coverage of each cloud type as seen from the satellite. The statistical properties of the cloud classes are determined by analyzing small areas of uniform cloudiness. The algorithms applied to pairs of spectral images is the standard maximum likelihood method.     

A comparison of semi-empirical models in the lower thermosphere

Semi-empirical models are derived predominantly from satellite-borne observations. The nature of these observations restricts the applicability of the models mainly to the atmospheric regions sampled, i.e. the upper thermosphere. Current models are only capable of reproducing a zero-order approximation of the structure of the lower thermosphere. Based on selected examples, the progress in atmospheric research since CIRA-72 as well as the continuing deficiencies are demonstrated.     

The Venus ionosphere

Physical properties of the Venus ionosphere obtained by experiments on the US Pioneer Venus and the Soviet Venera missions are presented in the form of models suitable for inclusion in the Venus International Reference Atmosphere. The models comprise electron density (from 120 km), electron and ion temperatures, and relative ion abundance in the altitude range from 150 km to 1000 km for solar zenith angles from 0° to 180°. In addition, information on ion transport velocities, ionopause altitudes, and magnetic field characteristics of the Venus ionosphere, are presented in tabular or graphical form. Also discussed is the solar control of the physical properties of the Venus ionosphere.     

A Three-Dimensional Simulation of Collisional-Interchange-Instability in the Equatorial-Low-Latitude Ionosphere

We present a three-dimensional simulation of collisional-interchange-instability in the equatorial-low-latitude F region of ionosphere. The instability is responsible for the generation of large plasma density depletion or bubble. General 3D potential and continuity equations are derived to simulate the phenomena. To understand the linear aspect of the instability, the general 3D linear growth rate is derived using 3D potential equation. The linear growth characteristics are compared with earlier field-aligned-integrated growth analyses. The numerical simulation of bubble in the 3D spherical polar geometry is finally presented. Distinct evolution characteristics of bubble in 3D and 2D simulation are further discussed.     

Detection of suprathermal ionospheric O+ ions inside the plasmasphere

The plasma diagnostic experiments on the AUREOL-3 satellite have revealed flows of low energy 0⁺ ions deep inside the night plasmasphere during a large substorm. Flux gradients of the 0⁺ ions were accompanied by enhancements of ELF electric field noise. The appearance of suprathermal ions at $\text{L ? 2.5 – 3}$ is interpreted within the framework of electrostatic ion-cyclotron acceleration of ionospheric ions in the diffuse auroral zone /12/ followed by a radial displacement of these ions inside the plasmasphere driven by azimuthal electric fields during substorm activity. Electrostatic oscillations observed inside the plasmasphere are apparently associated with gradient instability at the sharp boundaries of suprathermal ion flows.     

Classification of solar wind structures and intense geomagnetic storm alarms with self-organizing maps

Intense geomagnetic storms (D_st < −100 nT) usually occur when a large interplanetary duskward-electric field (with Ey > 5 mV m⁻¹) lasts for more than 3 h. In this article, a self-organizing map (SOM) neural network is used to recognize different patterns in the temporal variation of hourly averaged Ey data and to predict intense storms. The input parameters of SOM are the hourly averaged Ey data over 3 h. The output layer of the SOM has a total of 400 neurons. The hourly Ey data are calculated from solar wind data, which are provided by NSSDC OMNIWeb and ACE spacecraft and contain information on 143 intense storms and a fair number of moderate storms, weak storms and quiet periods between September 3, 1966 and June 30, 2002. Our results show that SOM is able to classify solar wind structures and therefore to give timely intense storm alarms. In our SOM, 21 neurons out of 400 are identified to be closely associated with the intense storms and they successfully predict 134 intense storms out of the 143 ones selected. In particular, there are 14 neurons for which, if one or more of them are present, the occurrence probability of intense storms is about 90%. In addition, several of these 14 neurons can predict big magnetic storm (D_st  −180 nT). In summary, our method achieves high accuracy in predicting intense geomagnetic storms and could be applied in space environment prediction.     

Mesospheric ozone densities deduced from solar occultation measurements

Quartz-UV occultation measurements by the satellite Interkosmos-16 have been used to calculate ozone densities at altitudes between 50 and 90 km for the period August to October 1976. Below 65 km densities agree well with the Krueger-Minzner-model. Mesopause densities have been studied in some detail. A certain percentage of the profiles show close correlation with the model of Shimazaki and Laird (with a pronounced minimum below the mesopause) while others fit better to the Park and London model (no minimum). This variability of the ozone density may be caused by different processes in the photo-chemistry of ozone. Two possible causes, the temperature dependent rate coefficients and the odd hydrogen processes are discussed in greater detail.