We have operated a very long baseline interferometer array at a northern midlatitude site, illuminated by VHF radio beacons from two geosynchronous satellites, quasi‐continuously for over a year. The array can detect and measure the trace velocity of traveling ionospheric disturbances (TIDs) via their signatures in the line‐of‐sight total electron content (TEC). The system noise level is of the order of 1013 m−2 in the TEC, so that even very weak perturbations can be studied. We have used the year‐long TID detection/velocimetry data set to describe local time and seasonal dependences of the wave parameters. The most striking finding is that the preferred azimuths of TIDs in the data set tend to belong to either of two modes: The first mode, strongest at midday and in the early afternoon, particularly around winter equinox, propagates southward. The second mode, strongest in the evening, especially during summer solstice through autumn equinox, propagates west‐northwestward. The two modes are disposed in local time such as to suggest the agency of clockwise rotation of the TID preferred azimuths versus time, as expected by wind filtering in the thermospheric diurnal tide. However, there is a gap between the two modes' azimuth bands. Moreover, the two modes exist in all trace‐speed quartiles of the data set TIDs, a finding which is at variance with the hypothesis of wind filtering being the primary explanation of these modes.

The main engine burn (MEB) of the Space Shuttle deposits ∼2×1012 joules of explosive energy and ∼3×105 kg of exhaust in almost horizontal flight at 105–110 km altitude during the period 300–550 s into the ascent. This extremely robust perturbation provides a potential active‐excitation source for a variety of geophysical processes, including (1) the effects of aurora‐like localized heating on the generation of gravity waves in the thermosphere, (2) the ducting mechanisms for long‐period infrasound in the upper atmosphere, (3) dynamo effects associated with transient charge separation, (4) interactions with ambient midlatitude current systems at E‐layer heights, and (5) effects in the Earth‐ionosphere waveguide of transient electron‐density perturbations in the D‐region. The sine qua non of such an agenda is to gain a quantitative understanding of the near‐field behavior of the MEB exhaust‐plume's quasi‐cylindrical expansion, which generates a blast wave propagating away from the explosion. We report on observed electron‐density signatures of this blast wave as manifested on lines‐of‐sight (LOSs) from a very‐long‐baseline interferometer (VLBI) illuminated by 137‐MHz beacon signals from the MARECS‐B satellite. We also compare the observations to a preliminary three‐dimensional neutral‐air acoustic model coupled to the ionospheric electron density.

Orbital elements are given for the spectroscipic binary HD 21242, (6 qi 5, G5 V). The period is 6^4. The cooler component has strong Ca n emission with the same velocities as its absorption lines and is slightly more massive than the G5 star. HD 21242 is a noneclipsing counterpart of a sizable group of eclipsing binaries.

The Semi-Arid Land-Surface-Atmosphere Program (SALSA) is a multi-agency, multinational research effort that seeks to evaluate the consequences of natural and human-induced environmental change in semi-arid regions. The ultimate goal of SALSA is to advance scientific understanding of the semi-arid portion of the hydrosphere-biosphere interface in order to provide reliable information for environmental decision making. SALSA approaches this goal through a program of long-term, integrated observations, process research, modeling, assessment, and information management that is sustained by cooperation among scientists and information users. In this preface to the SALSA special issue, general program background information and the critical nature of semi-arid regions is presented. A brief description of the Upper San Pedro River Basin, the initial location for focused SALSA research follows. Several overarching research objectives under which much of the interdisciplinary research contained in the special issue was undertaken are discussed. Principal methods, primary research sites and data collection used by numerous investigators during 1997-1999 are then presented. Scientists from about 20 US, five European (four French and one Dutch), and three Mexican agencies and institutions have collaborated closely to make the research leading to this special issue a reality. The SALSA Program has served as a model of interagency cooperation by breaking new ground in the approach to large scale interdisciplinary science with relatively limited resources. Published by Elsevier Science B.V.

A radio‐interferometer array illuminated by 136‐MHz beacons of several geosynchronous satellites has been used to study small (≥ 1013 m−2) transient disturbances in the total electron content along the lines of sight to the satellites. High‐frequency (ƒ> 3 mHz) electron content oscillations are persistently observed, particularly during night and particularly during geomagnetically disturbed periods. The oscillations move across the array plane at speeds in the range 200–2000 m/s, with propagation azimuths that are strongly peaked in lobes toward the western half‐plane. Detailed analysis of this azimuth behavior, involving comparison between observations on various satellite positions, indicates compellingly that the phase oscillations originate in radio refraction due to geomagnetically aligned plasma density perturbations in the inner plasmasphere. The motion of the phase perturbations across the array plane is caused by E × B drift of the plasma medium in which the irregularities are embedded. We review the statistics of 2.5 years of around‐the‐clock data on the local time, magnetic disturbance, seasonal, and line‐of‐sight variations of these observed irregularities. We compare the irregularities' inferred electrodynamic drifts to what is known about midlatitude plasma drift from incoherent scatter. Finally, we show in detail how the observation of these irregularities provides a unique and complementary monitor of inner plasmasphere irregularity incidence and zonal drift.