M. Friedrich

FIRI: A semiempirical model of the lower ionosphere

An empirical model of the lower, nonauroral ionosphere is presented which is exclusively based on radio wave propagation data from rocket soundings. The very limited number of available profiles provides an empirical correction to a simple theoretical model. This analytical correction, which can be of a very low mathematical order, is determined individually for each pressure surface. An inclusion of this model in tabulated form into the international reference ionosphere (IRI) is foreseen, and electron density profiles for the conditions required by the user can be obtained by interpolation.

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.

High-latitude plasma densities and their relation to riometer absorption

Abstract A large number of D- and E-region electron density profiles from high latitudes have been analysed. These were derived from rocket-borne wave propagation experiments and—after careful screening—arranged according to riometer absorption. Statistical profiles for various degrees of absorption, including 0 dB, were established both for day and night. Furthermore, the height region predominantly contributing to the absorption has been identified. Finally a mean variation of the density of negative ions has been derived.

Tests of an ion-chemical model of the D- and lower E-region

Abstract A relatively simple steady-state ion-chemical model for the non-auroral D - and lower E -regions is presented. Solar fluxes and the neutral atmospheric constituents are taken from up-to-date literature. The model results are systematically compared to measurements, namely: ion composition, electron density vs solar zenith angle, solar activity, season and latitude. Although the agreement is not always good, it is believed to exceed that of purely statistical models.

Rocket-borne in situ measurements of meteor smoke: Charging properties and implications for seasonal variation

Rocket-borne observations of meteoric smoke particles (MSPs) are presented from three campaigns at polar latitudes (69 degrees N) in September 2006, and in the summers of 2007 and 2008. MSPs are detected using a novel technique based on photoelectron emission from the particles after stimulation by UV photons emitted by a xenon flashlamp. Resulting photoelectron currents are shown to be proportional to particle volume density. September results match model predictions qualitatively at altitudes from 65 to 85 km while measurements at higher altitudes are contaminated by photoelectrons from NO and O-2((1)Delta(g)). Contamination below this altitude can be excluded based on concurrent satellite observations. The observations show a large variability from flight to flight. Part of this variability can be attributed to differences in the charging of MSPs during day and night. Finally we find that MSP volume density in summer can exceed that during September. Analyzing model simulations of the global transport and microphysics of these particles, we show that our observations are in agreement with the model predictions, even though number densities of particles with radii >1 nm, which have long been thought to be suitable condensation nuclei for mesospheric ice particles, show the opposite behavior. It is shown that this discrepancy is caused by the fact that even larger particles (similar to 3 nm) dominate the volume density and that transport affects these different particle sizes in different ways. These results reinforce previous model findings according to which seasonal MSP variability is mainly driven by the global circulation and corresponding transport.

Electron density measurements in the lower D-region

Abstract Model calculations of the Faraday rotation and the absorption in the lower ionosphere are presented and the practical limits of this technique to determine the electron density are discussed. With a model and a rocket flight it is shown that probing frequencies slightly below the electron gyro-frequency are the most sensitive for measurements in the lower D -region.

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.

Collision frequencies in the high-latitude D-region

Abstract D -region collision frequencies derived from rocket flights are subjected to a harmonic seasonal analysis. The proportionality between collision frequency and pressure has been derived and found to be in excellent agreement with laboratory data. Some implications of the results are discussed.

Positive ion depletion in a noctilucent cloud

With a Mattauch-Herzog type of mass spectrometer the positive ion composition was measured in the mesosphere between 80 and 98.4 km over Kiruna, Sweden, in summer 1993. During the rocket flight an intense noctilucent cloud (NLC) was present and detected by a particle impact sensor at 83.0–83.6 km and 82.5–85.6 km on ascent and descent, respectively. For the first time a significant depletion of the main positive proton hydrates was observed on ascent and a complete disappearance of these ions on descent in the entire NLC-layer. The observation is associated with an atypical low ion production of 0.01–0.1 cm−3s−1, which favors the ion loss by particle attachment and/or vertical transport. In order to explain the loss of mobile charge a second population of at least 105 cm−3 1–2 nm ice particles is required in the NLC.

Potential observations of an electron-emitting rocket payload and other related plasma measurements

Abstract Observations of plasma effects due to an energetic electron beam near a rocket payload are summarized and an attempt is made to outline the basic processes in the plasma such as beam plasma discharge (BPD). The experiment had some unique features such as a high apogee and low background plasma density. The measurements covered most parameters relevant for the study of plasma effects, as well as payload potential, optical and radio emissions, energetic charged particles and plasma densities. Among the noteworthy observations are radio emissions up to VHP frequencies and very high payload potentials which even exceeded the gun voltage. The observed features are interpreted as BPD at low altitudes and as discharges in the E × B field at other heights.