Astronomical data analysis software and systems

In this paper, our current understanding and recent advances in the study of ionospheric storms is reviewed, with emphasis on the F2-region. Ionospheric storms represent an extreme form of space weather with important effects on ground- and space-based technological systems. These phenomena are driven by highly variable solar and magnetospheric energy inputs to the Earth's upper atmosphere, which continue to provide a major difficulty for attempts now being made to simulate the detailed storm response of the coupled neutral and ionized upper atmospheric constituents using increasingly sophisticated global first principle physical models. Several major programs for coordinated theoretical and experimental study of these storms are now underway. These are beginning to bear fruit in the form of improved physical understanding and prediction of ionospheric storm effects at high, middle, and low latitude.

Ionospheric Storms — A Review

A prototype system has been developed to monitor the instantaneous global distribution of ionospheric irregularities, using the worldwide network of Globa Positioning System (GPS) receivers. Case studies in this pape indicate that GPS receiver loss of lock of signal tracking may be associated with strong phase fluctuations. It is shown that a network-based GPS monitoring system will enable us to study the generation and evolution of ionospheric irregularities continuously around the globe under various solar and geophysical conditions, which is particularly suitable for studies of ionospheric storms, and for space weather research and applications.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97GL02273

Monitoring of global ionospheric irregularities using the Worldwide GPS Network

We use radar observations from the Jicamarca Observatory from 1968 to 1992 to study the effects of the F region vertical plasma drift velocity on the generation and evolution of equatorial spread F The dependence of these irregularities on season, solar cycle, and magnetic activity can be explained as resulting from the corresponding effects on the evening and nighttime vertical drifts In the early night sector, the bottomside of the F layer is almost always unstable The evolution of the unstable layer is controlled by the history of the vertical drift velocity When the drift velocities are large enough, the necessary seeding mechanisms for the generation of strong spread F always appear to be present The threshold drift velocity for the generation of strong early night irregularities increases linearly with solar flux The geomagnetic control on the generation of spread F is season, solar cycle, and longitude dependent These effects can be explained by the response of the equatorial vertical drift velocities to magnetospheric and ionospheric disturbance dynamo electric fields The occurrence of early night spread F decreases significantly during equinox solar maximum magnetically disturbed conditions due to disturbance dynamo electric fields which decrease the upward drift velocities near sunset The generation of late night spread F requires the reversal of the vertical velocity from downward to upward for periods longer than about half an hour These irregularities occur most often at ∼0400 local time when the prompt penetration and disturbance dynamo vertical drifts have largest amplitudes The occurrence of late night spread F is highest near solar minimum and decreases with increasing solar activity probably due to the large increase of the nighttime downward drifts with increasing solar flux

/pdf/effects-of-the-vertical-plasma-drift-velocity-on-the-2m25kbykcc.pdf

Effects of the vertical plasma drift velocity on the generation and evolution of equatorial spread F

Within the field of spectral imaging, the vast majority of instruments used are scanning devices. Recently, several snapshot spectral imaging systems have become commercially available, providing new functionality for users and opening up the field to a wide array of new applications. A comprehensive survey of the available snapshot technologies is provided, and an attempt has been made to show how the new capabilities of snapshot approaches can be fully utilized.

https://www.spiedigitallibrary.org/journals/optical-engineering/volume-52/issue-9/090901/Review-of-snapshot-spectral-imaging-technologies/10.1117/1.OE.52.9.090901.pdf

Review of snapshot spectral imaging technologies

The problem of day-to-day variability in the occurrence of equatorial spread F (ESF) is addressed using multidiagnostic observations and semiempirical modeling. The observational results are derived from a two-night case study of ESF onset conditions observed at Kwajalein Atoll (Marshall Islands) using the ALTAIR incoherent scatter radar and all-sky optical imaging techniques. The major difference between nights when ESF instabilities did not occur (August 14, 1988) and did occur (August 15, 1988) in the Kwajalein sector was that the northern meridional gradient of 6300-A airglow was reduced on the night of limited ESF activity. Modeling results suggest that this unusual airglow pattern is due to equatorward neutral winds. Previous researchers have shown that transequatorial thermospheric winds can exert a control over ESF seasonal and longitudinal occurrence patterns by inhibiting Rayleigh-Taylor instability growth rates. Evidence is presented to suggest that this picture can be extended to far shorter time scales, namely, that 'surges' in transequatorial winds acting over characteristic times of a few hours to a day can result in a stabilizing influence upon irregularity growth rates. The seemingly capricious nature of ESF onset may thus be controlled, in part, by the inherent variability of low-latitude thermospheric winds.

/pdf/onset-conditions-for-equatorial-spread-f-3rev4fmon3.pdf

Onset conditions for equatorial spread F

A new low-light-level, all-sky, 6300 A airglow imaging system has been developed for ground-based studies of the optical signatures of equatorial plasma depletions. The system was designed for narrowband interference filters (6 A full width at half power) with interchangeable all-sky (180°) and narrow-field (60°) lenses and records images photographically by using a standard 35 mm camera. A field test of the apparatus was conducted on Ascension Island (8.0°S, 14.4°W) from January 24 to February 10, 1981. The photographs were analyzed for broad morphological characteristics by using simple overlay techniques augmented by digital image processing methods to extract more quantitative detail. The initial results to come from these observations show that airglow depletions occur most often during the 2030–2330 LT period, often covering one-fourth of the visible sky; they extend from the magnetic equator to beyond the crest of the equatorial anomaly, with east-west cross sections of ∼100 km to several hundred kilometers; they are usually not aligned with magnetic meridians, showing a progressive skewness to the west at further distances from the equator; several cases of apparently twisting, overlapping, and bifurcating depletions were observed; the depletions drifted to the east with speeds that decreased from ∼190 m/s at 2100 LT to ∼80 m/s at 0100 LT; the airglow intensities within depletions were typically 40–50% of the background levels, and the western walls of the depletions usually had a steeper gradient than the corresponding eastern walls.

Airglow characteristics of equatorial plasma depletions

Pilot observations were conducted at Arecibo, Puerto Rico, using an all-sky, image-intensified CCD camera system in conjunction with radar, ionosonde, and Global Positioning System (GPS) diagnostic systems during the periods January 19–28, 1993, and February 21 to August 22, 1995. These represent the first use of campaign mode operations of an imager at Arecibo for extended periods of F region observations. The January 1993 period (the so-called “10-day run”) yielded a rich data set of gravity wave signatures, perhaps the first case of direct imaging of thermospheric wave train properties in the F region. The 6-month 1995 campaign revealed two additional optical signatures of F region dynamics. A brightness wave in 6300 A passing rapidly through the field of view (FOV) has been linked to meridional winds driven by the midnight temperature maximum (MTM) pressure bulge. On May 3, 1995, during a period of geomagnetic activity, a 6300-A airglow depletion pattern entered the Arecibo FOV. Such effects represent the optical signatures of equatorial spread F instabilities that rise above the equator to heights near 2500 km, thereby affecting Arecibo's L = 1.4 flux tube.

/pdf/investigations-of-thermospheric-ionospheric-dynamics-with-463xwv2j97.pdf

Investigations of thermospheric-ionospheric dynamics with 6300-Å images from the Arecibo Observatory

[1] All-sky imagers located at Tucuman, Argentina (26.9°S, 65°W, 14.2°S dip latitude), and Arequipa, Peru (16.5°S, 71.5°W, 2.7°S dip latitude), are used to track 630 nm airglow depletion motions in the first use of multisite airglow imagers for studies of low-latitude plasma dynamics. A new image analysis technique yields a consistent determination of nighttime zonal plasma drifts from all-sky images of the depletion motions. The observed eastward plasma drifts are smaller at Arequipa than at Tucuman in the postsunset period. During the postmidnight hours, the opposite pattern occurs. These observations are interpreted using the simple plasma drift model and coupled ionosphere-electric field model of Eccles [1998a, 1998b]. The observed zonal plasma drifts result from low-latitude electrodynamics with a mix of influences from E and F region conductivities and neutral wind shears in altitude and latitude. Analysis of the observations suggests that postsunset zonal drifts near the magnetic equator (Arequipa) are strongly influenced by the E region dynamo, while the F region dynamo is the main cause of zonal drifts observed closer to the Equatorial Ionization Anomaly (Tucuman). The observed altitude-latitude behavior of the plasma drifts gives the first two-dimensional evidence for the so-called F region plasma vortex's influence at equatorial and low latitudes obtained using optical imaging techniques. With this framework a synthesis is offered for seemingly inconsistent zonal drift observations in the published literature.

/pdf/latitude-dependence-of-zonal-plasma-drifts-obtained-from-1jp2iwk0fs.pdf

Latitude dependence of zonal plasma drifts obtained from dual‐site airglow observations

THE detection of a cloud of neutral sodium near Jupiter's moon Io1 has led to the use of sodium as a tracer of processes in the jovian environment. Although relatively rare in the Io–Jupiter system, sodium atoms are easily detected because of their high efficiency for scattering sunlight at wavelengths of ∼5,890 A. Direct imaging of the sodium cloud2 has suggested that sodium atoms are a common feature close to Io (at distances of about six Io radii, RIo) and detection of high-speed sodium jets3 suggested that sodium is present only sporadically at ∼30/RIo (ref. 4). Sodium emission has been reported at greater distances5, even as far as 60RIo (ref. 6) but these observations have been controversial in view of suggestions7 that the detection of sodium beyond ∼10RIo was implausible on theoretical grounds and probably indistinguishable from terrestrial sodium airglow. Here we report on the detection of sodium to distances beyond ∼400 RI, an observation that requires the ejection rate of sodium atoms to be increased. By relating the shape of this great nebula to conditions in the plasma torus surrounding Jupiter, we show that ground-based imaging techniques can provide information about distant planetary magnetospheres.

Jeffrey Baumgardner

Papers

Onset conditions for equatorial spread F

Airglow characteristics of equatorial plasma depletions

Investigations of thermospheric-ionospheric dynamics with 6300-Å images from the Arecibo Observatory

Latitude dependence of zonal plasma drifts obtained from dual‐site airglow observations

The extended sodium nebula of Jupiter