Cesar La Hoz

Radar scattering from dusty plasmas

A calculation of the scattering cross section of charged dust particles in a plasma is carried out for an incident electromagnetic wave with frequency much larger than the electron plasma frequency. The present derivation employs the dressed test particle theorem of Hubbard and Rostoker. A critical discussion on the applicability of conventional plasma theory - as employed here - is given. It is shown that there is a range of values of the relevant parameters for which the underlying assumptions implied by the plasma approximation are applicable. The results depend crucially on neglecting the collective interactions of the dust particles among themselves. This is justified when the number of dust particles in a Debye sphere is less than one. The calculation is applied subsequently to the case of charged dust in the earths mesosphere in connection with polar mesospheric summer echoes. Scattering enhancements comparable to observations at 224 MHz are possible provided that the mesospheric dust particles attain charge numbers of several hundred. However, the dependence of the scattering cross section on the radar frequency as calculated here seems too weak to explain the observations.

On the ponderomotive force and the effect of loss reaction on parametric instability

In this paper, the growth rate, ponderomotive force and the exciting condition for parametric instability are derived by considering the loss reaction using a new method. On the basis of the hydrodynamic equations, we take the production and loss reactions in plasma into account to derive the coupling equations for the electron plasma oscillation and ion acoustic oscillation, and obtain the growth rate for the parametric instability, the ponderomotive force and the exciting condition. The result shows that (a) the production reaction has no effect on the parametric instability, and the effect of loss reaction on the parametric instability is a damping one, (b) the more intensive the external field or pump is, the larger the growth rate is, (c) there exist two modes of the ponderomotive force, i.e.the high frequency mode and the low frequency mode, and (d) when ponderomotive force counteracts the damping force, the oscillations become non-damping and non-driving. The ratio of the electron plasma oscillation to ion acoustic oscillation is independent of the loss reaction and the external field.

Fractal dimension of mesospheric radar backscatter at 2.75 MHz

We have identified the fractal dimension of radar returns from the mesopause region at 2.75MHz. The input dataset was a time series of echo amplitude at a discrete height obtained from a partial reflection radar operating at Ramfjordmoen in northern Norway. Two different algorithms both of which yield approximations to the fractal dimension have been employed and give almost identical results. The radar echo dataset in question exhibits a dimension of between 7 and 8.

EISCAT aperture synthesis imaging (EASI 3D) for the EISCAT 3D project

Aperture Synthesis Imaging Radar (ASIR) is the technology, code-named EASI 3D, adopted by the EISCAT 3D project, that will give the new radar system imaging capabilities in 3-dimensions including sub-beam resolution in the plane across the transmitter antenna beam. When complemented by pulse compression techniques, it will provide 3-dimensional images of certain types of incoherent scatter radar targets with resolution of the order of 100 metres at 100 km range in any direction illuminated by the transmitter beam. The cross-beam resolution will vary as the inverse of the range squared. This ability will open new research opportunities to map small structures associated with non-homogeneous, non-steady, unstable processes such as aurora, summer and winter polar radar echoes (PMSE and PMWE), Natural Enhanced Ion Acoustic Lines (NEIALs), structures excited by HF ionospheric heating, meteors, space debris, and possibly others.

The EISCAT 3D project in Norway: E3DN

Summary form only given. EISCAT 3D (E3D) is a project to build the next generation of incoherent scatter radars endowed with 3-dimensional scalar and vector capabilities that will replace the current EISCAT radars in Northern Scandinavia. One active (transmitting) site in Norway and four passive (receiving) sites in the Nordic countries will provide 3-D vector imaging capabilities by rapid scanning and multi-beam forming. The unprecedented flexibility of the solid-state transmitter with high duty-cycle, arbitrary wave-forming and polarisation and its pulsed power of 10 MW will provide unrivalled experimental capabilities to investigate the highly non-stationary and non-homogeneous state of the polar upper atmosphere. Aperture Synthesis Imaging Radar (ASIR) will to endow E3D with imaging capabilities in 3-dimensions that includes sub-beam resolution. Complemented by pulse compression, it will provide 3-dimensional images of certain types of incoherent scatter radar targets resolved to about 100 metres at 100 km range, depending on the signal-to-noise ratio. The Norwegian scientific programme is inspired by the pioneer polar scientist Kristian Birkeland (picture) and includes pressing questions on polar upper atmospheric research, among others: (Q1) How to proceed beyond the present simplistic, static, stationary and homogeneous analysis of upper atmospheric and ionospheric processes? (Q2) How does space weather affect ionospheric processes and how to support modelling and space weather services? (Q3) How to advance fundamental plasma physics by employing the ionosphere as a natural plasma physics laboratory? (Q4) How does the influx of extraterrestrial material interact with the upper atmosphere and where does the material originate from? (Q5) How does solar activity couple from geospace into the lower atmosphere and climate system, and does this energy change the wave forcing of geospace from below?