The high-latitude sections of the Wideband ionospheric scintillation model (WBMOD) have been upgraded extensively, based on analysis of scintillation data from the Defense Nuclear Agency Wideband, HiLat, and Polar BEAR satellite-beacon experiments. Data collected at Sondre Stromfjord, Greenland; Tromso, Norway; Fort Churchill, Canada; and Bellevue, Washington (United States) over a 4-year period were analyzed, and the results of these analyses were used to construct a completely new model for the behavior of the height-integrated irregularity-strength parameter (CkL) at high latitudes. The new high-latitude CkL model includes variations with sunspot number, geomagnetic activity (Kp), latitude, local time, longitude, and season. The new WBMOD CkL models (equatorial and high-latitude) have been implemented in a more versatile code, denoted SCINTMOD, which has the capability to generate a wide range of user-controlled maps of scintillation effects over large spatial areas. Examples of the types of graphical output that SCINTMOD can generate are presented.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97RS00453

High-latitude upgrade to the Wideband ionospheric scintillation model

There is a growing body of evidence that energetic heavy ions observed at one or more earth radii over the polar cap originate from the dayside ionosphere in the vicinity of the dayside cleft. The ions, consisting mostly of O(+), are often characterized by conic pitch-angle distributions, suggesting that they have undergone acceleration transverse to geomagnetic field lines. This process of ion injection from a latitudinally localized source region in the dayside auroral oval followed by dispersal throughout the entire polar cap has been called the 'cleft ion fountain'. Here, results are presented of upward thermal-ion flows measured at 800-km altitude in the dayside polar ionosphere by the Hilat satellite. The characteristics of these thermal-ion upwellings (TIU) are described and shown to be closely associated with the cleft ion fountain. It is shown that TIU events are latitudinally confined and spatially collocated with cleft electron precipitation, upward field-aligned currents, and velocity gradients in magnetospheric convection.

Dayside observations of thermal‐ion upwellings at 800‐km Altitude: An ionospheric signature of the cleft ion fountain

This paper describes the latest edition of the NASA Propagation Effects Handbook for Satellite Systems Design and presents a summary of application of the handbook information to satellite link design and performance. NASA, which has supported a large part of the experimental work in radiowave propagation on space communications links, recognized the need for a reference handbook of this type, and initiated a program in the late 1970's to develop and update a document that will meet this need. The Fifth Edition provides, in a single document, an update to two previous NASA handbooks; the fourth edition of a handbook which focused on propagation effects from 10 to 100 GHz (Ippolito, 1989), and the second edition of a companion handbook which covered propagation effects on satellite systems at frequencies below 10 GHz (Flock, 1987). This Fifth Edition covers the full range of radiowave frequencies that are in use or allocated for space communications and services, from nominally 100 MHz up to 100 GHz.

/pdf/propagation-effects-handbook-for-satellite-systems-design-difwfqg31f.pdf

Propagation Effects Handbook for Satellite Systems Design

Efforts continue to update and improve empirical models of the mean morphological behavior of ionospherically produced scintillation. While often intended for engineering application, these models also can be scientifically useful to the extent that they describe not only the signal fluctuations but also the plasma density irregularities that cause them. Such a model is contained in the computer code called WBMOD, which employs the phase screen propagation theory to calculate the power law spectral index and strength (at a fluctuation frequency of 1 Hz) of phase scintillation and the standard deviation of phase, for a user-specified system. Explicit provision is made for an ionospheric outer scale, but the relevant phase spectrum is cut off by a system parameter in most applications. The intensity scintillation index S, is calculated from weak-scintillation theory and corrected for the saturating effect of multiple scatter on the basis of Rice statistics. The irregularity model in WBMOD describes threedimensionally anisotropic (sheetlike) irregularities on the nightside of the high-latitude scintillation zone and axially symmetric (rodlike) irregularities elsewhere. The current status of WBMOD, which is undergoing continued refinement, is described in this paper for all latitude regimes. Plans for future development of its irregularity model are stated, and it is suggested that such models should now move in the direction of incorporating irregularity dynamics.

/pdf/modeling-and-scientific-application-of-scintillation-results-5amdw5wyaf.pdf

Modeling and scientific application of scintillation results

This report presents the first successful global-scale auroral images in full daylight. The vacuum ultraviolet (VUV) imager on board the recently launched HILAT satellite has demonstrated that clear images of the global auroral display over the local summer polar region under full sunlight conditions can be obtained, indicating that the earth’s albedo and dayglow background are not formidable obstacles to the global auroral imaging at the VUV wavelengths (135.6 ± 1.5 nm and 149.3 ± 1.5 nm). Some of the images of dayglow and auroras in daylight are presented and discussed.

Ultraviolet imaging from space of the aurora under full sunlight

On June 27, 1983, USAF satellite P83-1 was launched from Vandenberg Air Force Base carrying the five ionospheric-effects and diagnostic payloads of DNA's HiLat satellite mission. A Scout launch vehicle placed the satellite in an 800-km circular orbit at an inclination of 82°. The HiLat experiments are as follows: (1) a VHF/UHF/L band coherent radio beacon for observing complex-signal scintillation and total electron content; (2) a three-instrument cold-plasma package for measuring number density and temperature, their spatial fluctuations, and plasma convection velocity and its fluctuations; (3) an electron spectrometer for detection of precipitating and upwelling electrons with energies between 20 eV and 20 keV; (4) a three-axis magnetometer; and (5) an optical assembly for imagery and spectrophotometry in the vacuum-ultraviolet spectrum and for photometry at two visual wavelengths. With the exception of partial launch damage to the electron sensor (Langmuire probe) in the coldplasma package, all payloads initially operated as designed. After approximately 40 orbits of data collection, however, the imaging spectrophotometer failed. In spite of this failure, the optical instrument proved the concept of imaging the aurora, at vacuum-ultraviolet wavelengths, under conditions of full sunlight. Its visual-wavelength photometers continue to perform well, as do the other four HiLat payloads. This paper presents early observations from HiLat.

The HiLat satellite mission

The HILAT satellite is scheduled to be launched June 1983 into a circular, 830-km-altitude orbit with an 82.2° inclination. This spacecraft is a modified U.S. Navy TRANSIT navigation satellite and will conduct a unique combination of experiments: (1) transmissions of radio signals from the spacecraft to surface stations for measurements of ionospheric scintillations and total electron content (TEC), (2) in situ measurements of plasma density, electric fields, magnetic fields, and soft electron fluxes, and (3) visible photometric measurement and UV imaging of aurora and airglow. The objective of this mission is to provide definition information on the formation, development, transport, and decay of plasma density irregularities in the high-latitude ionosphere; the relationship of these plasma processes to auroral and polar cap current systems, electric fields, convective flow patterns, and low-energy electron distributions; and the relationship of these plasma processes to the global distribution of auroral phenomena during quiet and substorm periods and during various interplanetary conditions.

C.-I. Meng

Papers

The HiLat satellite mission

The HILAT program