Intrinsic time scale for reconnection on the dayside magnetopause

Recently much attention has been focused on the transient behavior of the magnetopause in response to pressure pulses and southward fluctuations of the interplanetary magnetic field. We examine the motion of the magnetopause behind the foreshock and conclude that this motion is affected by foreshock pressure variations but not by fluctuations in the direction of the magnetic field. Neither magnetopause erosion nor flux transfer event occurrence is controlled by the foreshock. On the contrary, flux transfer events occur at times of steady IMF and thier quasi-periodic behavior is controlled by the magnetopause or the magnetosphere and is not driven by the external boundary conditions. Since flux transfer events are clearly due to reconnection, this observation implies that the IMF must be southward some time perhaps as long as 7 minutes before flux transfer begins.     

Forecasting the 23 and 24 solar cycles on the basis of MGM spectrum

A new method of nonlinear spectral analysis (called the method of global minimum: MGM), based on the best presentation (in sense of minimal squares) of a given time data set as a sum of sinusoids whose frequencies, amplitudes and phases are to be determined, has been used to find periodicities in annual Wolf sunspot numbers (W) during the period 1700–1995. The possible future behaviour of the 11-year solar cycle (based on an extrapolation of the calculated model) is also presented. The main characteristics of the 23^rd solar cycle are as follows: the W maximum occurs about 2004, with a peak of nearly 220. An unusually large value of W will occur during the 23^rd cycle, which should be characterised by the longest maximum, specifically, W will be greater than 100 during the 11-year period from 1997 to 2007. The first sharp rise will occur during the period 1996–1998, the second sharp during 2002–2004. The main features of the 24 year cycle are as follows: the next minimum in W, associated with the 24^th solar cycle, should occur in the year 2008 and the maximum in 2014. W is expected to peak at about 180. The minimum value for the 25^th year cycle is expected to occur in the year 2019. It is shown that the accuracy of these predictions depends, first of all, on the extrapolation of the hyperlong harmonic of the calculated polyharmonic model fit of observed annual sunspot numbers during the period 1700–1995. The error bars in the definition of the maximum and minimum epochs can be as large as two years.     

EUV emission from normal galaxies

Using data from the Wide Field Camera EUV all-sky survey, we have established upper limits to the EUV flux from a sample of 30 bright, nearby, non-active spiral galaxies. These galaxies were chosen to be those most likely to be detected in the EUV on the basis of (i) low interstellar absorption within our own galaxy, (ii) brightness in other wavebands, (iii) high star formation activity, and (iv) proximity. The derived EUV upper limits are restrictive, and establish for the first time that the EUV flux escaping from galaxies does not constitute a major component of their bolometric luminosity, and in particular that it cannot be the sink for the energy injected into the interstellar medium by supernova explosions, as had been suggested following the failure to detect this power in the X-ray band.     

Senrad: an advanced wideband air-surveillance radar

The generic characteristics and performance of an experimental long-range air-surveillance radar, known at the Naval Research Laboratory as Senrad, is described. Its distinguishing feature is that it can operate with simultaneous transmissions over a very wide bandwidth-from 850 to 1400 MHz. The technology and type of experimental radar equipment employed are discussed and examples are given of its performance capabilities obtained by means of very wideband operation. The unusually wide bandwidth of this radar allows 1) improved detection and tracking performance because of the absence of the nulls that are common in the antenna elevation radiation-pattern of a single-frequency radar; 2) moving target indication (MTI) without loss of targets due to blind speeds and without the need for multiple PRFs (pulse repetition frequencies); 3) accurate height finding with a fan-beam radar by taking advantage of the multipath time difference as a function of target height; 4) a form of limited target recognition based on high range-resolution; and 5) a reduction of the effectiveness of electronic countermeasures that can seriously degrade more narrowband radars     

Steady-state analysis and design of a switched-capacitor DC-DCconverter

A representative switched-capacitor DC-DC converter topology is presented, circuit operation is explained, and control strategies are identified. State-space averaging is used to analyze steady-state performance and to develop control criteria and design equations. The analytical results are verified by SPICE simulation     

Broadening of Fe X (6374 Å) profiles above the limb in a coronal hole

Profiles of the visible Fe X (6374 Å) coronal emission line as a function of height above the limb were obtained out to 1.16 solar radii in a coronal hole using the NSO/Sacramento Peak Observatory Coronagraph, Universal Spectrograph and a CCD camera. These are the first coronal line profiles obtained as a function of height in a coronal hole from the ground. Analysis of the line widths suggests a large component of nonthermal broadening which increases with height ranging from 40 to 60 km/s, depending upon the assumed temperature or thermal component of the profile.     

The Freja ultraviolet imager

Auroral images acquired by satellite instrumentation have proven to be a crucial component of the scientific equiry into the physical processes of the Earth's magnetosphere. TheFreja mission provided an opportunity to extend these measurements into the temporal and spatial regime commonly associated with ground-based optical imagers. Employing the basic procedure used successfully in theViking program allowed image repetition rates of 6 s to be achieved with simultaneous exposure of all pixels within the field-of-view. Typical exposure times of 0.3 s required development of an improved image intensifier system and operational requirements resulted in image formats covering approximately one-third of a spin. Simultaneously exposing two broad-band UV cameras, the instrument generates in its normal operational mode 264.6 kbytes per image pair. Results from initial operations confirm the design approach and suggest such imagers can be routinely included on challenging low cost missions such asFreja.