Charles L. Croskey

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.

The Millimeter Wave Atmospheric Sounder (MAS): a shuttle-based remote sensing experiment

The Millimeter Wave Atmospheric Sounder (MAS) will be launched in the spring of 1992 as part of the ATLAS 1 (Atmospheric Laboratory for Application and Science) mission. Using passive limb-scanning millimeter-wave radiometry, it will sense the thermal emission produced by ozone at 184 GHz, water vapor at 183 GHz, chlorine monoxide at 204 GHz, and oxygen (for retrieval of temperature and pressure) at 60 GHz. From these observations, concentration profiles of these gases throughout the middle atmosphere will be made. The fundamentals of the measurements, the design of the radiometers, and the approaches used for the data analysis are described. >

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.

Measurements of O3, H2O and ClO in the Middle Atmosphere Using the Millimeter-Wave Atmospheric Sounder (MAS)

The Millimeter-Wave Atmospheric Sounder (MAS) is a shuttle-based limb-sounding instrument designed for global spectroscopic studies of O3, and constituents important in O3 photochemistry, in the middle atmosphere. It is part of the NASAs Atmospheric Laboratory for Applications and Science (ATLAS) spacelab shuttle mission. This paper presents an overview of the instrument, operation, and data analysis. In addition, as an example of the results, we present zonal average retrievals for O3, H2O and ClO obtained in ATLAS 1. The MAS O3 and H2O measurements are shown to agree well with simultaneous observations made with the UARS MLS instrument.

Intense turbulence observed above a mesospheric temperature inversion at equatorial latitude

[1] Results from a sounding rocket experiment launched on September 19, 2004 from Kwajalein Atoll, Marshall Islands are reported. A large modulation of the temperature profile in the upper mesosphere was observed with a local maximum at 92 km, 40 K warmer than 2 km below. The temperature gradient between 92 and 102 km was near-adiabatic, suggesting strong mixing. Turbulence was observed in the lower part of the mixed layer, as evidenced by neutral and plasma density fluctuations on both the upleg and downleg portions of the flight. The plasma density gradient was less steep in the mixed region. The turbulent energy dissipation rate was found to be 170 mW/kg. The thermal structure can be described as an upper mesospheric inversion layer, possibly caused by enhanced wave breaking or turbulent heat transport.

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.

THE ELECTRODYNAMIC RESPONSES OF THE ATMOSPHERE AND IONOSPHERE TO THE LIGHTNING DISCHARGE

Abstract The purpose of this study was to use the complete set of Maxwell’s equations to simulate the electromagnetic response of the atmosphere and the ionosphere during and after the lightning discharge. A three-dimensional numerical model is used to calculate the quasistatic electric field over the 10 ms–2 s range. The model contains an isotropic conductivity profile below 70 km and an anisotropic conductivity profile from 70 km–150 km (different latitudes, day/night conditions have been considered), a time-varying charge distribution (representing the thunderstorm source function), and a perfectly conducting ground surface. Both vertical and horizontal transient electric fields and upward Maxwell currents in the ionosphere have been calculated for a vertical discharge. The results show that the relaxation time of the electric field due to the lightning discharge, which is no longer than e0/σ, will decrease with an increase of the altitude of observation and have little change with the horizontal distance from the lightning discharge. It also shows that the Maxwell current from the thundercloud spreads out to the ionosphere during a time interval of several milliseconds following the lightning discharge. This current flows along directions both parallel and perpendicular to the geomagnetic field lines and mainly propagates horizontally above 70 km. A good agreement between the simulation results and the measurement data has been achieved. These results show the importance of the use of the complete set of Maxwell’s equations and the inclusion of an anisotropic ionospheric conductivity in the lightning response simulation. The conclusion of this paper also may help to explain some of the long-standing controversies between measurements and theoretical predictions.

Equatorial dynamics observed by rocket, radar, and satellite during the CADRE/MALTED campaign: 1. Programmatics and small‐scale fluctuations

In August 1994, the Mesospheric and Lower Thermospheric Equatorial Dynamics (MALTED) Program was conducted from the Alcântara rocket site in northeastern Brazil as part of the International Guara Rocket Campaign to study equatorial dynamics, irregularities, and instabilities in the ionosphere. This site was selected because of its proximity to the geographic (2.3°S) and magnetic (∼0.5°S) equators. MALTED was concerned with planetary wave modulation of the diurnal tidal amplitude, which exhibits considerable amplitude variability at equatorial and subtropical latitudes. Our goals were to study this global modulation of the tidal motions where tidal influences on the thermal structure are maximum, to study the interaction of these tidal structures with gravity waves and turbulence at mesopause altitudes, and to gain a better understanding of dynamic influences and variability on the equatorial middle atmosphere. Four (two daytime and two nighttime) identical Nike-Orion payloads designed to investigate small-scale turbulence and irregularities were coordinated with 20 meteorological falling-sphere rockets designed to measure temperature and wind fields during a 10-day period. These in situ measurements were coordinated with observations of global-scale mesospheric motions that were provided by various ground based radars and the Upper Atmosphere Research Satellite (UARS) through the Coupling and Dynamics of Regions Equatorial (CADRE) campaign. The ground-based observatories included the Jicamarca radar observatory near Lima, Peru, and medium frequency (MF) radars in Hawaii, Christmas Island, and Adelaide. Since all four Nike-Orion flights penetrated and overflew the electrojet with apogees near 125 km, these flights provided additional information about the electrodynamics and irregularities in the equatorial ionospheric E region and may provide information on wave coupling between the mesosphere and the electrojet. Simultaneous with these flights, the CUPRI 50-MHz radar (Cornell University) provided local sounding of the electrojet region. A description of the campaign logistics and the measurements performed with the Nike-Orion instrumentation and their implications for turbulence due to gravity waves and tidal instability in the mesosphere and lower thermosphere (MLT) are presented here. From a study of electron density fluctuations measured by rocket probes, we have found evidence for equatorial mesospheric neutral-atmospheric turbulence between 85 and 90 km. Furthermore, falling-sphere data imply that gravity wave breaking was a source for this turbulence. Mean motions and the various planetary, tidal, and gravity wave structures and their coherence and variability are the subjects of a companion paper.

MAS measurements of the latitudinal distribution of water vapor and ozone in the mesosphere and lower thermosphere

We present measurements of the latitudinal variation of nighttime O3 and H2O in the mesosphere and (for O3) lower thermosphere obtained with the Millimeter-wave Atmospheric Sounder (MAS) instrument during the ATLAS 2 mission (8–15 April 1993). These are the first such measurements that have ever been reported. They indicate an O3 mixing ratio minimum at mid-latitudes in the upper mesosphere, with maxima in the tropics and at high latitudes. The H2O retrievals indicate H2O mixing ratios decreasing toward the poles in both hemispheres in the upper mesosphere. We also present measurements of the diurnal variation of O3 at southern mid-latitudes, at higher vertical resolution than has ever been reported previously. The results are generally consistent with previous measurements and modeling studies.