Richard A. Goldberg

Electrical structure of PMSE and NLC regions during the DROPPS Program

The electrical structure of NLC/PMSE regions was investigated by different rocket-borne in situ probe techniques as part of the DROPPS program. Gerdien condenser measurements of very small mobility values suggest concentrations of positively charged aerosols/dust comparable to the density of more mobile positive ions at PMSE/NLC altitudes. Relative electron density values and associated large- and small-scale vertical structure measured by DC Langmuir probes revealed very deep (by a factor of 50) biteouts in PMSE/NLC regions. These biteouts were seen during strong and weak NLC conditions when PMSEs were either present or absent.

Satellite and rocket studies of relativistic electrons and their influence on the middle atmosphere

Abstract Magnetospheric electrons from hundreds of keV to over 10MeV in energy have been systematically measured at geostationary altitude (6.6 R E ) for well over a decade. We find evidence of significant diurnal, solar-rotational (27-day), annual, and solar-cycle (11-yr) variations in the fluxes of the relativistic electron component. We have also used low-altitude satellite data and sounding rocket measurements to characterize the location and strength of the relativistic electron precipitation into the atmosphere. We conclude that the magnetospheric electrons, when dumped into the middle atmosphere, represent a very significant ionization source which affects the pattern of conductivity, electric fields, and atmospheric chemistry. These measurements—when combined with global atmospheric modeling—suggest that relativistic electrons provide a robust coupling mechanism to impose long-term solar wind and magnetospheric variability onto the Earths deep atmospheric regions. A strong 11-yr cycle of relativistic electron effects is found in available atmospheric data sets.

Do meteor showers significantly perturb the ionosphere

More than 40 rocket flights through the main meteoric ionization layer, which peaks near 95 km, have sampled the meteoric metallic ion concentrations. Five of these flights were conducted during or near the peak times of a meteor shower. In each of the latter studies the observed meteoric ion concentrations were assumed to be a consequence of the shower. These measurements were not complemented by baseline observations made for similar ionospheric conditions immediately before the shower and no rigorous quantitative comparisons were made using average non-shower distributions. In order to further investigate the impact of the shower on the ionosphere, all published ion concentration altitude profiles obtained from sounding rockets in the meteoric ionization regime have been scanned to develop a digital data base of meteoric ion concentrations. These data are used to provide the first empirical altitude profile of the metallic ions. The average observed Mg+ concentrations are lower than those yielded by the most comprehensive model to date (McNeil et al., 1996). This compiled ensemble of data provides supporting evidence that meteor showers do have a significant impact on the average ionosphere composition. Although there is much variability in the observed meteoric layers, the peaks in the total metallic ion concentrations at mid-latitudes, on the dayside, observed during meteor showers had concentrations comparable to, or exceeding, the highest concentrations measured in the same altitude regions during non-shower periods.

DROPPS: A study of the polar summer mesosphere with rocket, radar and lidar

DROPPS (The Distribution and Role of Particles in the Polar Summer Mesosphere) was a highly coordinated international study conducted in July, 1999 from the Norwegian rocket range (Andoya, Norway). Two sequences of rockets were launched. Each included one NASA DROPPS payload, containing instruments to measure the electrodynamic and optical properties of dust/aerosol layers, accompanied by European payloads (MIDAS, Mini-MIDAS, and/or Mini-DUSTY) to study the same structures in a complementary manner. Meteorological rockets provided winds and temperature. ALOMAR lidars and radars (located adjacent to the launch site) monitored the mesosphere for noctilucent clouds (NLCs) and polar mesosphere summer echoes (PMSEs), respectively. EISCAT radars provided PMSE and related information at a remote site (Tromso, Norway). Sequence 1 (5–6 July) was launched into a strong PMSE with a weak NLC present; sequence 2 (14 July) occurred during a strong NLC with no PMSE evident. Here we describe program details along with preliminary results.

Evidence for charged aerosols and associated meter‐scale structure in identified PMSE/NLC regions

Evidence for the existence of negatively charged aerosols/dust in PMSE/NLC regions has been obtained by the unique combination of rocket probes flown during the DROPPS Program. Simultaneous current measurements of charged aerosols, ions, and electrons were accomplished by using a configuration of blunt probes, Gerdien condenser, and DC Langmuir probe. The two blunt probes, with different fixed-bias voltages to discriminate the collection of mobile charge carriers, consistently demonstrated the presence of impacting negatively charged aerosols. Their occurrence coincided with an electron bite-out, thus confirming the associated loss process as aerosol attachment.

An overview of NLC‐91: A rocket/radar study of the polar summer mesosphere

In late July and early August of 1991, a major suborbital scientific campaign (NLC-91) involving scientists from eight countries was conducted at ESRANGE, Kiruna, Sweden and at Heiss Island, Russia. The purpose of the program was to investigate the chemical, dynamical, and electrodynamical properties of the polar summer mesosphere. Thirty one rocket flights were coordinated with two coherent radar facilities, EISCAT and CUPRI, and with other ground-based observatories and facilities. This permitted direct comparison between the in situ measurements and those obtained by remote sensing of the mesosphere via continuous ground-based monitoring. The primary objectives of the campaign were to study noctilucent clouds (NLCs) and polar mesospheric summer echoes (PMSEs), including their possible relationship to local aerosols and/or small scale turbulence. This overview describes the scientific program, discusses the geophysical conditions during launch activities, and reviews some of the preliminary results. More detailed results can be found in the papers which follow.

Middle atmospheric electrodynamics : status and future

Abstract Middle atmospheric electrodynamics is a field stimulated by the recent discovery that large electric fields may occasionally exist in the mesosphere and upper stratosphere. The measurements suggest V m −1 magnitudes for these fields, which have been reported to occur in both horizontal and vertical configurations. Since they are usually confined within bounded height regions, they might be of local origin. Although the measurements are still considered controversial, the implications of such fields, if real, could be important. Should these fields persist in both space and time, they could perturb the global electric circuit with a component subject to modulation by phenomena related to solar activity. This might help explain the numerous correlations which exist for tropospheric electrical response to solar and geomagnetic activity. Further work is now required to validate the earlier findings and determine the morphology and extent of the large electric fields. Experiments must also be derived and conducted to determine the physical origin of such fields and their relationships to external influences, such as magnetospheric electric fields and tropospheric thunderstorms. The current status of results regarding V m −1 fields in the middle atmosphere is reviewed in perspective with the more widely accepted electric field structure established for this region from balloon and rocket data. Other factors such as ion conductivity, ion mobility and aerosols are also considered for their potential influence on the middle atmospheric electrical environment.

Electron and positive ion density altitude distributions in the equatorial D-region.

Simultaneous measurements of D-region ionization sources and electron and ion densities have been made in one day aboard three rockets. Electron density profiles for solar zenith angles of 53.2, 27.8 and 48.3° are displayed. The profiles are found to be quite similar to those reported for midlatitudes under non-winter quiet conditions. Simultaneous measurement of the X-ray flux together with NO ionization estimates based on recent measurements of NO by Meira (1971) and O2(1Δg) ionization rates by Huffmanet al. (1971), are used to compute the ion-pair production rate. It is demonstrated that the charged particle distribution can be explained using this production rate and an effective recombination coefficient compatible with recent laboratory measurements of the dissociative recombination coefficient for electrons with hydrated cluster ions.

Direct observation of magnetospheric electron precipitation stimulated by lightning

Abstract Plasmaspheric electron precipitation bursts stimulated by observed lightning flashes have been studied using in situ rocket techniques under night-time conditions at Wallops Island, Virginia, on 23 August 1984. In one case, the rocket-observed ligntning flash was located by a ground-based network to be off the coast of Virginia at 74.8°W, 35.9°N, which was approximately 200km southeast of the rocket. Electron precipitation (> 40 keV) caused by simultaneous 21.4 kHz coded transmissions from a VLF radio transmitter at Annapolis, Maryland, was found to be negligible compared with the observed fluxes and energies of precipitating electrons stimulated by lightning. The results confirm that lightning (which can occur up to 100 times per second globally) can activate ionizing radiation sources within the magnetosphere, and that these may affect local middle atmospheric electrical structure in a measurable way.

Large electric potential perturbations in PMSE during DROPPS

Comprehensive vector electric field detectors were flown during the DROPPS rocket experiment to study electrodynamic processes near the mesopause. This paper will discuss the first DROPPS rocket flight, which penetrated a strong polar mesosphere summer echo (PMSE) event that also included a weak noctilucent cloud (NLC) layer. During this flight, strong potential perturbations were observed which at first appeared to be caused by large geophysical electric fields. However, as shown here, the potential perturbations resulted from the rocket wake, and were not caused by an environmental electric field. This result strongly differs from other previous in-situ experiments, which have reported large electric fields in PMSE regions.