K. Cierpka

Direct observation of lunar pick-up ions near the Moon

Measurements made with the Suprathermal Ion Spectrometer (STICS) on the WIND spacecraft during 17 lunar fly-bys which took place between 1995 and 1997 allow the direct observations of lunar pick-up ions (PUIs) on the earthwards side of the Moon as close as 17 lunar radii. The composition measurements reveal an O+, an Al+, Si+ and possibly a P+ component.

High‐latitude ground‐based observations of the thermospheric ion‐drag time constant

From previous studies, it has been conclusively demonstrated that F-region thermospheric winds follow, but generally lag behind, the ion drift pattern of magnetospheric convection. Analysis of the ion-neutral momentum exchange equation shows that ion-drag and thermal pressure are the major contributors to neutral momentum forcing at F-region heights with relatively minor effects from coriolis, advection and viscous forces. An ion-neutral coupling time constant (e-folding time) has been defined which describes the time taken for the neutral gas velocity to approach the ion velocity after a step change in convection. In this study, F-region ion drift and neutral winds have been observed by the EISCAT tristatic incoherent scatter facility and a ground-based Fabry-Perot interferometer, respectively, from northern Scandinavia. The e-folding time varies in the range 0.5 - 6.5 hours, with an average of 1.8 and 3.3 hours for a geomagnetically active and quiet period, respectively, which compares well with previous satellite measurements of 0.5 - 3.5 hours.

A comparison of thermospheric winds and temperatures from Fabry-Perot interferometer and EISCAT radar measurements with models

Abstract During the nights of 8–9 and 9–10 February 1997, Fabry-Perot interferometers were operated from the EISCAT radar site at Ramfjord (69.59° N, 19.23° E) and Skibotn (69.35° N, 20.36° E). From Ramfjord, horizontal neutral winds were measured in the lower and upper thermosphere using the auronal/airglow emissions at 557.7 and 630 nm, respectively. From Skibotn, thermospheric neutral temperatures were measured using the same wavelengths. The EISCAT radar measured ion temperatures up the local magnetic field line in the height range 90 – 580 km during the first night. Neutral winds are compared to the HWM-90 and CTIP-200 models with poor agreement. Neutral temperatures are compared to the MSISE-90 and CTIP-200 models as well as EISCAT ion temperatures with good agreement.

A comparison of vertical thermospheric winds from Fabry-Perot interferometer measurements over a 50 km baseline

Abstract During the nights of 8–9 and 9–10 February 1997, Fabry-Perot interferometers were operated from Ramfjord and Skibotn, Norway, a longitudinal baseline of ∼45 km. From Skibotn, thermospheric vertical winds were measured in the lower and upper thermosphere on both nights using the auroral/airglow emissions at 557.7 and 630 nm, respectively. From Ramfjord, neutral winds were measured, using the same wavelengths, parallel to the local magnetic field line on the first night and in the local zenith on the second night. Vertical neutral winds in both height ranges show essentially no correlation between the two stations. Some correlation between the vertical wind in the upper and lower thermosphere over individual stations does exist.

Novel Fabry-Perot interferometer measurements of F-region ion temperature

Novel optical measurements of F-region ion temperatures have been made in conjunction with thermospheric neutral temperatures. A ground-based Fabry-Perot interferometer has been used to observe high-latitude F-region ion temperatures using the O+(2P) auroral emission at 732 nm, and upper-thermospheric neutral temperatures using the O(1D) airglow emission at 630 nm. Dual wavelength measurements were made during February 2001 and clearly show that the ion temperature is equal to or greater than the neutral temperature, as expected. EISCAT radar measurements show that there is good agreement between the incoherent scatter and optical Doppler broadening methods of inferring ion temperature.

Direct Calculation of F-Region Joule Heating from Simultaneous Ion and Neutral Measurements at High Latitudes

Abstract We study a set of simultaneous and coincident ionospheric and thermospheric measurements made by the EISCAT incoherent scatter radar and a nearby Fabry-Perot interferometer, located within the Scandinavian auroral zone. Combined observations of ion and neutral temperatures as well as ion drifts and neutral winds in the F-region are presented for the geomagnetically active night (Kp = 5 − -7 − ) of 9–10 November 1998 and the following quiet night (Kp = 0-0+) of 10–11 November 1998. These data enable a direct calculation of ion temperature enhancements over the neutral temperature, resulting from Joule heating effects, which can be compared directly with the observation. The importance of the neutral wind contribution to the total electric field and Joule heating rates, often assumed to be insignificant, is estimated. Furthermore, MSISE-90 model predictions for neutral temperature are compared to the measurements.

Combined EISCAT and Fabry-Perot interferometer measurements of ionospheric-thermospheric coupling

Abstract Neutral winds and temperatures in the thermosphere and mesosphere are obtained with the help of a Fabry-Perot interferometer (FPI) located at Skibotn (69.35° N, 20.36° E), in close proximity to the EISCAT radar, which measures several ionospheric parameters. During the night of 8–9 February 1997, simultaneous measurements between the two instruments were performed. It is shown that the coupling between ion and neutral velocities decreases with increasing altitude. The horizontal neutral winds in the upper thermosphere are affected by ion drag and solar pressure forcing, depending on geomagnetic activity. A comparison between neutral and ion temperatures indicates the effects of Joule heating.

Composition of low energy solar particles (0.5-225 keV/e) measured by the WIND-S/C during impulsive and gradual flares

The composition of 6 impulsive or 3He rich and 4 gradual solar particle events was studied at the low energy end of their spectrum using SMS-WIND measurements to access an energy range not accessible to date by other experiments. The investigated events were found to have mostly a cutoff energy for 3He ions at ∼30–225 keV/e, but H+, 4He++, 4He+, CNO and sometimes 56Fe10+ ions could be detected during both types of flares in that energy/charge range. The 4He++H+ ratio of impulsive flares increased between Eq = 6.5 – 225 keV/e and 30 – 225 keV/e in most examples, indicating that 4He++ is preferentially accelerated whereas during gradual flares that ratio showed no big variations. The 3He and Fe-enrichment observed at higher energies and the acceleration of 1H+ and 4He++ can be explained by selective gyroresonance processes as proposed e.g. by Miller and Vinas (1993). The flux decrease of 3He at low energies would be caused by a temperature decrease in the flare region at the end of the active flare phase. The density increase in the flare region removes then 3He by coulomb collision from the resonance process with H+-ion cyclotron waves, whereas H+ and 4He++ ions are further accelerated by X-mode waves.

Lower cut-off energy of 3He-rich solar particle events ?

Two 3He- and Fe-rich impulsive solar particle events, measured by the SMS-experiment on the WIND-S/C., were studied at the low energy end of their spectrum (0.5- 225 keV/e) which could not be reached by other experimenters. It could be confirmed that during such events H+, 4He++ and all other ions are accelerated in some tens of seconds to the MeV-range. The SMS measurements showed as a new result that the 3He/4He ratio becomes very small at the low energy end of its spectrum (E < 75 keV/amu). From the two impulsive solar particle events it can be concluded that during the particle acceleration either the 3He content of the source region becomes exhausted or the acceleration process needs a certain injection energy. The model for the acceleration of impulsive solar particle events must simultaneously explain that H+ and 4He++ ions are detectable in the energy/charge range ∼30 – 225 keV/e.