Deriving the normalised ion-neutral collision frequency from EISCAT observations
Common programme observations by the EISCAT UHF radar revealed an extended interval, post geomagnetic local noon on 03 April 1992, during which the F-region ion velocity orthogonal to the geomagnetic field was significantly enhanced, to values exceeding 2 km s−1 corresponding to a perpendicular electric field of some 100 mV m−1. Observations from this interval are used to illustrate a method by which estimates of the E-region ion-neutral collision frequency may be derived in the presence of enhanced electric field. From both the rotation of the ion velocity vector and the reduction in the ion velocity magnitude relative to that in the F-region, independent estimates of the normalised ion-neutral collision frequency are made at the UHF E-region tristatic altitudes; the derived values are, in general, lower than model predictions. Although initial calculations assume a stationary neutral atmosphere, first-order estimates of the E-region neutral wind are subsequently employed to calculate revised estimates of the normalised ion-neutral collision frequency; these neutral winds are derived by attributing the difference between predicted and observed enhancements in field-parallel ion temperature to thermospheric motion. The inclusion of neutral winds, which are themselves not inconsiderable, appears to have only a limited effect on the normalised collision frequencies derived.
Altitude variations in the amplitude and phase of tidal oscillations at high latitude
Abstract Measurements of ion velocity from EISCAT Common Programme Two (CP-2) have been used to determine the profile of neutral winds in the high latitude E-region, following the method proposed by Brekke etal. [(1974) J. geophys. Res. 78, 8235]. CP-2 has a number of advantages over the previously-used Common Programme One (CP-1) : in particular it provided a complete profile of neutral wind velocity whereas CP-1 only determined values at four separate heights. The time variation of neutral wind velocity at each height in turn was analysed into diurnal, semi-diurnal and ter-diurnal components. The height profile of amplitude and phase for each component was interpreted in terms of tidal modes and the results were compared with previous results from EISCAT and the Chatanika incoherent-scatter radar and the theoretical model derived by forbes [(1982) J. geophys. Res. 87, 5222 and 5241].
The Accuracy of Reported Insurance Status in the MEPS
Estimates of the number of insured and uninsured Americans are watched by numerous policymakers and the public, yet studies find respondents do not report their insurance status perfectly. Using four sources of validation data, including surveys of employers and providers, this paper assesses the quality of respondents' reports of private insurance and uninsurance in the Medical Expenditure Panel Survey Household Component (MEPS-HC), a nationally representative household survey. Regression analysis is used to assess the extent to which factors are associated with disagreements in reported insurance status across sources.