Michael Sulzer

In this work, we are analyzing incoherent scatter radar (ISR) data for H+, He+, and O+ ion fractions from the Arecibo Observatory for the period of June solstice (May, June, July, and August) for 1998 and 2000 with respect to solar flux and geomagnetic variations. Due to the strait dependence of the response of the ion fractions with the mentioned forcing, we isolated the real contribution of these parameters by local time and altitude as variation rates. Our results demonstrate that within the altitude range of this work (350 to 1250km) a positive (negative) response of the ion O+ (H+) with the variation of solar flux while the dependence of He+ rates presented three different behaviors dependents of time and altitude. Additionally, we found evidence of a small layer formation of He+ soon after the local midnight in altitudes around 875km with increased geomagnetic activity. A strong dependence with the variation of geomagnetic activity was detected for the ions of H+ and O+ post-midnight, which generated two layers. However, these layers were located in different altitudes, far from each other for about 340km.

Profiles of the electron number density in the ionosphere are observed at the Arecibo Radio Observatory in Puerto Rico on a regular basis. Here, we report on recent observations showing anomalous irregularities in the density profiles at altitudes >~300 km. The irregularities occurred during a period of "mid-latitude spread F," a space-weather phenomenon relatively common at middle latitudes in summer months characterized by instability and electron density irregularities in the bottomside of the ionospheric F layer. Remarkably, electron density irregularities extended well above the layer, through the ionization peak and into the topside which is regarded as being stable. Neither the neutral atmosphere nor the ionosphere is thought to be able to support turbulence locally at this altitude. A numerical simulation is used to illustrate how a combination of atmospheric and plasma dynamics driven at lower altitudes could explain the phenomenon.

Gyro line in Incoherent Scatter Spectrum is the underused cousin of the more popular Plasma line. This is because it is very weak during the day and stronger during dawn and dusk hours. When the electron density is such that the electron plasma frequency drops below the electron gyro frequency, the gyro line frequency becomes proportional to the electron density. This is during a time when the plasma line is no longer detected, and we have no other means for getting precise measurements for absolute electron density. In this paper, we will present a linear equation for the gyro line frequency and measurements from the Arecibo radar in Puerto Rico, showing comparison with the plasma line data and derived electron density.

The Arecibo Observatory (18.35 N, 66.75 W) can now measure the ionosphere with two antenna beams simultaneously. In June 2002, this new capability was used for the first time to investigate north/south gradients of elctron temperature and electron density. The experiments yielded some unexpected results. In particular,large horizontal north/south gradients in the electron temperature of the ionospheric F-region were observed during the early morning that persisted for hours. In addition to electron temperatures, we also examined north/south electron density gradients looking for - and finding -- evidence of Travelling Ionospheric Disturbances.

In terrestrial aeronomy, remote sensing and active probing of the upper atmosphere are accomplished using both optical and radio techniques. For passive optical systems-imagers, spectrographs and interferometers-applications to studies of planetary atmospheres often involve the innovative use of standard methods. Here we describe three such passive methods recently applied to studies of the moon's exosphere, Mercury's surface, and the atmospheres of Jupiter's moon Io and comet Hale-Bopp. The active probing of a non-terrestrial atmosphere has not yet been attempted. Here we describe the challenges and potential science yield from light detection and ranging (LIDAR) probing of the lunar atmosphere and incoherent scatter radar (ISR) sounding of Venus' ionosphere.

Abstract The radar controller is a crucial, often over-looked, component of a radar system; allowing the transmitter to operate within a safe range and providing the flexibility to generate a variety of complex pulse schemes. Additionally, the radar controller provides ...

Ion beams with between 2 and 11 eV are produced when the Space Shuttle Orbital Maneuver Engines are fired into the ionosphere at low-earth-orbit. The artificial sources of ion beams mimic effects that are found naturally in the auroral ionosphere during periods of strong plasma convection. Ion-neutral charge exchange causes the ionospheric interactions that occur both naturally and artificially. We have scheduled the use of this technique with incoherent scatter radars located at Jicamarca, Peru; Arecibo, Puerto Rico; and Kwajalein, Marshall Islands. Computer modeling has predicted the type of back-scatter expected from ground radars monitoring the ion-beam injection events during the NRL SIMPLEX experiments. The SIMPLEX ion-beam experiments from the Space Shuttle is scheduled for July 1999 during the STS-93 mission. Radar backscatter will be monitored by the ISR systems. The incoherent backscatter measurements will be compared with computational models to determine the nature of th...

ABSTRACT In this work, we investigate the performance of amplitude modulated coding schemes in incoherent scatter radar (ISR) measurements in terms of statistical estimation error, range resolution, and signal-to-noise ratio. We approach this goal by formulating the inherent trade-off between estimation error and resolution as mathematical measures for model order selection. These trade-offs are examined on numerical experiments with several amplitude modulated waveforms with different duty cycles. We demonstrate that compared with an unmodulated long pulse, reduced statistical estimation error with similar range resolution, or finer range resolution with similar estimation accuracy can be obtained by incorporating coding schemes.

The temporal behavior of backscatter by ionospheric Langmuir waves was observed with the 430-MHz radar at Arecibo while a powerful HF wave was cycled 2 s on, 3 s off. Late at night, in the absence of photoelectrons, using an HF equivalent radiated power of 80 MW at 3.175 MHz, the initial enhancement of about 6 percent above system noise of the backscattered power with Doppler shifts between -3.75 and -3.85 MHz was reached about 0.25 s after switching on the HF transmitter. In the following second the enhancement gradually decreased to about 3 percent and remained there until switching off. During the late afternoon, in the presence of photoelectrons, using the same HF power at 5.1 MHz, an initial enhancement by 25 percent of the backscattered power with Doppler shifts between -5.25 and -5.35 MHz appeared within less than 0.1 s after switching on the HF transmitter. The incoherent backscatter by Langmuir waves enhanced by photoelectrons was already above system noise by a factor greatly in excess of 10 before switching on the HF transmitter; the 25 percent enhancement thus corresponds to an enhancement greatly in excess of 250 percent above system noise. The enhancement drops to less than one tenth of its original value in less than a second.

On 11 March 1998 the Langmuir Turbulence sounding rocket was launched through the Arecibo heater beam during an experiment to measure electric fields and plasma densities in the heater interaction region. In spite of a serious degradation of the Arecibo heater, the rocket data has provided evidence of Z mode waves and field aligned striations above the O mode reflection

Using a combination of airglow images and incoherent scatter radar data, we have explored the electrical structure of the airglow depleted, height layer bands over a mid-latitude site. We find a reproducible electrical signature in both components of the electric field in all events studied. The most pronounced feature is a large northward/upward electric field in the heart of the

ABSTRACT It has been known for quite a while now that the there is a problem with the temperatures deduced from Jicamarca autocorrelation function data. Basically, after performing the least squares fitting with the theory currently in use at all other ISR's, the ion temperature often appears higher than the electron temperature, especially at night, leading to a Te/Ti ratio below one -- obviously a geophysically unrealistic result. The problem becomes more severe the closer the Jicamarca beam points to perpendicular to the magnetic field. In the past most efforts were concentrated with finding a systematic error that would explain the problem, but all such attempts failed in providing an explanation. A different approach was taken by Sulzer and Gonzalez [JGR vol 104 pp 22535-22551, 1999], who realized that the Jicamarca ACF measurements appeared correct, so probably the problem was not caused by a systematic error or instrumental error, but rather by an error in the interpretation of the data through the eyes of the IS theory. Working from that assumption they found that electron Coulomb collisions affect the IS spectrum and as the radar points nearly perpendicular to the magnetic field this effect becomes measurable, and thus must be taken into account in the calculation of the theoretical spectrum. The calculation of this effect, however, is extremely complicated, and so far has only been solved with the help of a very accurate computer simulation. The output of this simulation contains the values of a function (Je) proportional to the electron admittance function (ye). The electron admittance is actually a function of electron temperature, electron density, angle with respect to the magnetic field, and frequency. Thus, in order to use the results from the Coulomb collisions simulations to perform least squares fitting, a library of Je functions must be generated for a reasonable grid in all these parameters. Such a library is now available, and we have incorporated it to an incoherent scattering least squares fitting code. We will give an overview of how these collisions affect the spectrum and will show how the predictions from the theory are necessary in order to obtain realistic ion and electron temperatures over a wide range of geophysical conditions and for various antenna pointing positions.

ABSTRACT The measurement of temperatures in the various atmospheric regions is essential for meeting the goals of the CEDAR program. The ion and electron temperatures in the F region and topside ionosphere over the Jicamarca Radio Observatory, one of the world's most powerful incoherent scatter radars, have been under question for almost forty years because carefully-made statistically significant measurements show that the apparent electron temperatures are often less than than the apparent ion temperatures. This violates the physics of the region: energy flows from the electrons to the ions during the day, and equilibrium exists at night. Although measurements at Jicamarca have certain possible biases, no one has ever shown that the problem was due difficulties with interpreting the data. The problem resulted from the omission of the effects of electron-ion and electron-electron Coulomb collisions in the equation for the incoherent scatter spectrum. A numerical solution gives spectra such that comparisons with data imply equal ion and electron temperatures when expected. The new spectra have interesting and unexpected consequences. The collisonal effect is far greater that simple collisonal models such as Langevin's equation or the BGK approximation imply when observations are made looking vertically, or nearly so, with the Jicamarca radar. It has been necessary to include both types of collisions with high accuracy in a numerical model since the resulting effect is dependent upon the interaction between the two and is unlike either alone. A great simplifying principle of incoherent scatter (IS) theory is that in many situations the spectrum is a simple combination of the spectra of the individual species of the plasma which would apply in the absence of the electrostatic interaction. Assuming this, then we need consider only the collisional effect on electrons freely streaming along the magnetic field. Furthermore the gyration radius is small compared to the radar wavelength, and the field enters only as a trigonometric factor which slows the progress of the electrons along the radar line of sight. Numerical simulations show the following results: The rapid decrease of the collisional coefficients with increasing electron speed plays a very important role in the resulting IS spectral shape. Electron-ion collisions, affecting only the directions and not the speeds of the electrons, would alter only the central part of the IS spectrum because of result 1. Electron-electron collisions, affecting both the speeds and directions of the electrons, significantly modify the spectrum of result 2. even though their collisional coefficients are relatively small.