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Articles 181 - 203 of 203

Full-Text Articles in Physical Sciences and Mathematics

The Absolute Scattering Cross Section At 50 Mhz Ofequatorial Electrojet Irregularities, D. T. Farley, H. M. Ierkic, Bela G. Fejer Sep 1981

The Absolute Scattering Cross Section At 50 Mhz Ofequatorial Electrojet Irregularities, D. T. Farley, H. M. Ierkic, Bela G. Fejer

Bela G. Fejer

We have made carefully calibrated radar scattering measurements by using the large 50-MHz Jicamarca antenna. Typical results from the altitudes of maximum echo power for the vertically directed beam are σradar ∼1–2 × 10−10 m−1 for strong daytime electrojet conditions with type 1 irregularities present, with values a factor of 10 or so smaller during moderate conditions when only type 2 are observed. These cross sections, which are very large in comparison with those for incoherent scatter (σradar ≃5 × 10−18 m−1 for an electron density of 1011 m−3), are not nearly large enough, however, to cause pseudo-absorption events on …

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Interferometer Studies Of Equatorial Fregion Irregularities And Drifts, E. Kudeki, Bela G. Fejer, D. T. Farley, H. M. Ierkic Apr 1981

Interferometer Studies Of Equatorial Fregion Irregularities And Drifts, E. Kudeki, Bela G. Fejer, D. T. Farley, H. M. Ierkic

Bela G. Fejer

A radar interferometer technique developed at Jicamarca, Peru and first used to study electrojet irregularities has now been used successfully to study plasma turbulence in the equatorial F region. Our first results have shown that the most ‘turbulent’ echoes appear to come from a region that extends for tens of kilometers in altitude but for only a kilometer or less in the east-west direction. This slab may very well be the wall of a depleted region, a plasma ‘bubble’. Sometimes the irregularities can be tracked as they move eastward or westward. Velocity profiles for the evening period obtained in this …

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Radar Interferometry: A New Technique For Studyingplasma Turbulence In The Ionosphere, D. T. Farley, H. M. Ierkic, Bela G. Fejer Mar 1981

Radar Interferometry: A New Technique For Studyingplasma Turbulence In The Ionosphere, D. T. Farley, H. M. Ierkic, Bela G. Fejer

Bela G. Fejer

A new radar interferometer technique has been developed and used successfully at the Jicamarca Radio Observatory in Peru to study the strong nighttime plasma turbulence in the equatorial electrojet. The technique represents a major step forward in radar probing of turbulent irregularities such as (but not limited to) those in the electrojet. In many situations it provides far more information than previous Doppler measurements. We form the cross spectrum of the backscattered signals received from approximately overhead on two antennas, separated in this case along an east-west baseline, as well as the individual power spectra. From the phase of the …

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A Quantitative Test Of Unimolecular Rate Theory In The Multi‐Photon Dissociation Of Cf2Cfcl, John C. Stephenson, Stephen E. Bialkowski, David S. King, Everet Thiele, James Stone, Myron F. Goodman Jan 1981

A Quantitative Test Of Unimolecular Rate Theory In The Multi‐Photon Dissociation Of Cf2Cfcl, John C. Stephenson, Stephen E. Bialkowski, David S. King, Everet Thiele, James Stone, Myron F. Goodman

Stephen E. Bialkowski

We have measured the distribution of total energy in reaction products for the CO2 laser‐induced MPD: CF2CFCl→CF2+CFC1. From a separate study of MPD rates as a function of laser intensity and inert buffer gas pressure, reliable estimates of the radiative pumping rates are known for this reaction. These results, when analyzed together, allow us to extract a unimolecular A factor from the MPD data. The determined value A = 3×1016 sec−1 agrees well with estimates based on independent thermal data.

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F-Region East-Westdrifts At Jicamarca, Bela G. Fejer, D. T. Farley, C. A. Gonzales, R. F. Woodman, C. Calderson Jan 1981

F-Region East-Westdrifts At Jicamarca, Bela G. Fejer, D. T. Farley, C. A. Gonzales, R. F. Woodman, C. Calderson

Bela G. Fejer

F region east-west drifts have been measured at Jicamarca for almost 10 years, using incoherent scatter. The drifts are westward during the day and eastward at night. The daytime drift velocities are about 50 m/s and change very little with season or solar cycle. The evening reversal occurs at about 1600 local time throughout the solar cycle. The maximum nighttime eastward drifts are about 105 and 130 m/s during solar minimum and maximum, respectively. The daytime and nighttime drifts show very litle variation with magnetic activity. These Jicamarca incoherent scatter results (especially the reversal times) differ appreciably from results obtained …

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The Dependence On Zenith Angle Of The Strength Of 3-Meter Equatorial Electrojet Irregularities, H. M. Ierkic, Bela G. Fejer, D. T. Farley Dec 1980

The Dependence On Zenith Angle Of The Strength Of 3-Meter Equatorial Electrojet Irregularities, H. M. Ierkic, Bela G. Fejer, D. T. Farley

Bela G. Fejer

Radar measurements in Peru were used to deduce the zenith angle dependence of the scattering cross section of plasma irregularities generated by instabilities in the equatorial electrojet. The irregularities probed by the 50 MHz Jicamarca radar had a wavelength of 3m. The cross section for the type 2 irregularities was isotropic in the plane perpendicular to the magnetic field, while the cross section for the stronger type 1 irregularities varied with zenith angle at a rate of approximately 0.3 dB/degree; the horizontally traveling waves were more than 100 times stronger than those traveling vertically.

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An Empirical Model Of Quiet Dayionospheric Electric Fields Of Middle And Low Latitudes, A. D. Richmond, M. Blanc, B. A. Emery, R. H. Wand, Bela G. Fejer, R. F. Woodland, S. Ganguly, P. Amyenc, R. A. Behnke, C. Calderon, J. V. Evans Sep 1980

An Empirical Model Of Quiet Dayionospheric Electric Fields Of Middle And Low Latitudes, A. D. Richmond, M. Blanc, B. A. Emery, R. H. Wand, Bela G. Fejer, R. F. Woodland, S. Ganguly, P. Amyenc, R. A. Behnke, C. Calderon, J. V. Evans

Bela G. Fejer

Seasonally averaged quiet-day F region ionospheric E × B drift observations from the Millstone Hill, St. Santin, Arecibo, and Jicamarca incoherent scatter radars are used to produce a model of the middle and low-latitude electric field for solar minimum conditions. A function similar to an electrostatic potential is fitted to the data to provide model values continuous in latitude, longitude, time of day, and day of the year. This model is intended to serve as a reference standard for applications requiring global knowledge of the mean electric field or requiring information at some location removed from the observing radars. This …

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Ionospheric Irregularities, Bela G. Fejer, M. C. Kelley Jun 1980

Ionospheric Irregularities, Bela G. Fejer, M. C. Kelley

Bela G. Fejer

Extensive experimental and theoretical research has been performed in the last decade to study ionospheric irregularities. These studies have shown that plasma instabilities play a major role in the generation of the irregularities. In this work we describe in detail the recent experimental studies of the E and F region irregularities and also the extensive work on plasma instability theories developed to explain them. We also describe both radio wave and spacecraft-borne experimental techniques to allow a common ground for the understanding of the data from ground-based and in situ experiments. To date, theoretical work has been mostly concentrated on …

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Simple Parallel Interface Between An Optical Multichannel Analyzer And A Microprocessor, Stephen E. Bialkowski Jan 1980

Simple Parallel Interface Between An Optical Multichannel Analyzer And A Microprocessor, Stephen E. Bialkowski

Stephen E. Bialkowski

A simple circuit is given which will allow data transfer from a LSI‐11 DRV11 parallel interface unit to a PARC 1216 Optical Multichannel Detector Controller. The Circuit for OMA to LSI‐11 data transfer is slightly more complicated. Data buffering is used so that data transfer can occur without time‐out loss due to the dynamic memory refresh cycle of the LSI‐11. The circuit may be constructed and mounted within the PARC 1216 unit with only minor, noncritical, modifications to the controller unit. The unit is able to transmit data from the 1216 controller running at dwell times as short as 40 …

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The Determination Of Mass Transport Coefficients And Vibrational Relaxation Rates Of Speciesformed In Laser Photolysis Experiments, Stephen E. Bialkowski, David S. King, John C. Stephenson Jan 1980

The Determination Of Mass Transport Coefficients And Vibrational Relaxation Rates Of Speciesformed In Laser Photolysis Experiments, Stephen E. Bialkowski, David S. King, John C. Stephenson

Stephen E. Bialkowski

A simple analytical solution of the equations which govern the formation, collisional relaxation, and mass transport rates of species produced in radially symmetric laser‐induced processes is given. These equations are specifically applied to the CO2 laser‐induced dissociations of CF2HCl and C2F3Cl dilute in argon. The concentration of the vibrational ground state of the CF2 radical product was probed as a function of time and pressure both during and after the photolyzing laser pulse by the laser‐excited fluorescence technique. From these measurements, the vibrational relaxation rate of ? CF2 in argon was …

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Energy Partitioning In The Ir Multiphoton Dissociation Of Molecules: Energy Of Xcf2 And Xcfcl Fromcf2Cfcl, John C. Stephenson, Stephen E. Bialkowski, David S. King Jan 1980

Energy Partitioning In The Ir Multiphoton Dissociation Of Molecules: Energy Of Xcf2 And Xcfcl Fromcf2Cfcl, John C. Stephenson, Stephen E. Bialkowski, David S. King

Stephen E. Bialkowski

We have measured the vibrational (v), rotational (J,K), and translational energy, (ET), of the X̃ CF2 and X̃ CFCl fragments formed in the CO2 laser induced multiphoton dissociation of CF2CFCl (chlorotrifluoroethylene): CF2CFCl→CF2(v,J,K)+CFCl(v,J,K)+ET(v,J,K), which was the only detectable reaction path for CF2CFCl. More vibrational energy (Ev) appears in CF2 than in CFCl. Direct spectroscopicmeasurements of populations in levels 0<ν2<7 show that Ev is distributed statistically in the bending mode (ν2) of CF2 according to P(Ev)=exp(−Ev/k Tv), …

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Type I Radar Echoes From Theequatorial Electrojet With Double Peaked Doppler Spectra, Bela G. Fejer, D. T. Farley, P. Johnston, B. B. Balsley Jan 1980

Type I Radar Echoes From Theequatorial Electrojet With Double Peaked Doppler Spectra, Bela G. Fejer, D. T. Farley, P. Johnston, B. B. Balsley

Bela G. Fejer

Normal type 1 radar echoes obtained from relatively large zenith angles have a power spectrum with a single narrow peak whose Doppler shift corresponds approximately to the acoustic velocity in the medium. On some occasions, however, this single maximum splits into two distinct peaks, separated in phase velocity on one occasion by 270 m/s. This bifurcation is most easily observed at large zenith angles during daytime when a narrow antenna beam is used. It has also been seen in a daytime experiment in which radars at Jicamarca and Huancayo simultaneously probed the same region from two different radar zenith angles. …

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Equatorial Electricfields During Magnetically Disturbed Conditions, 1. The Effect Of The Interplanetary Magneticfield, Bela G. Fejer, C. A. Gonzales, D. T. Farley, M. C. Kelley, R. F. Woodman Sep 1979

Equatorial Electricfields During Magnetically Disturbed Conditions, 1. The Effect Of The Interplanetary Magneticfield, Bela G. Fejer, C. A. Gonzales, D. T. Farley, M. C. Kelley, R. F. Woodman

Bela G. Fejer

Radar measurements of E and F region drift velocities have been used to look for correlations between changes in equatorial electric fields and the interplanetary magnetic field (IMF). The east-west component of the IMF appears to be unimportant, but the north-south component has some effect; rapid reversals from south to north are sometimes correlated with reversals of the equatorial east-west electric field during both daytime and nighttime. This is not always true, however, the IMF may reverse without any apparent effect at the equator. Furthermore, large equatorial field perturbations are sometimes observed when the IMF Bz is large and southward …

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Gas Phase Laser Induced Fluorescence Spectroscopy Of Cfcl, Stephen E. Bialkowski, David S. King, John C. Stephenson Jan 1979

Gas Phase Laser Induced Fluorescence Spectroscopy Of Cfcl, Stephen E. Bialkowski, David S. King, John C. Stephenson

Stephen E. Bialkowski

The CFCl radical has been produced in the gas phase by both IR multiphotonphotolysis of C2F3Cl and He metastable reaction with C2F3Cl. Single vibronic level fluorescence and excitation spectra taken of this species have yielded sufficient information to determine certain vibronic constants. The excited state was found to have an origin of T0=25 283±5 cm−1 with vibrational frequencies: ω2′=394±3 cm−1 and ω3′=739±5 cm−1. In the ground state, the vibrational frequencies were found to be: ω3″=118±10 cm−1, ω2″=448±6 cm …

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Equatorialelectric Fields During Magnetically Disturbed Conditions, 2. Implications Of Simultaneousauroral And Equatorial Measurements, C. A. Gonzales, M. C. Kelley, Bela G. Fejer, J. F. Vickrey, R. F. Woodman Jan 1979

Equatorialelectric Fields During Magnetically Disturbed Conditions, 2. Implications Of Simultaneousauroral And Equatorial Measurements, C. A. Gonzales, M. C. Kelley, Bela G. Fejer, J. F. Vickrey, R. F. Woodman

Bela G. Fejer

Simultaneous auroral and equatorial electric field data are used along with magnetic field data to study anomalous electric field patterns during disturbed times. During some substorms, accompanied by ring current activity, the worldwide equatorial zonal electric field component reverses from the normal pattern. This is interpreted as a partial closure of high latitude field aligned currents in the dayside, low latitude ionosphere. These currents flow westward across the dayside. In several cases the zonal equatorial electric field component was nearly identical in form to the zonal auroral component, indicating the close electrical coupling between these regions. Less certain, but equally …

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Collisionless Formation And Rovibronic Relaxation Of Ch And Oh From The Ir Multiphoton Photolysisof Ch3Oh, Stephen E. Bialkowski, William A. Guillory Jan 1978

Collisionless Formation And Rovibronic Relaxation Of Ch And Oh From The Ir Multiphoton Photolysisof Ch3Oh, Stephen E. Bialkowski, William A. Guillory

Stephen E. Bialkowski

A CO2 TEA laser has been used to initiate the collisionless multiphotondissociation of CH3OH between 1000 and 10 mtorr. The appearance of OH(X2Πi) 50±20 nsec after the laser pulse, independent of initial CH3OH pressure (50–200 mtorr), suggests the primary dissociative channel CH3OH+n hν→CH3 +OH(X2Πi); although CH3 could not be correspondingly confirmed. The appearance of CH(X2Πr) 70±20 nsec after the OH(X) appearance, independent of initial CH3OH pressure (70–400 mtorr), suggests secondary collisionless dissociation. Initial rovibronic distributions of OH(X) …

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Radar Observations Of Two Dimensional Turbulencein The Equatorial Electrojet, 3. Nighttime Observations Of Type I Waves, D. T. Farley, Bela G. Fejer, B. B. Balsley Jan 1978

Radar Observations Of Two Dimensional Turbulencein The Equatorial Electrojet, 3. Nighttime Observations Of Type I Waves, D. T. Farley, Bela G. Fejer, B. B. Balsley

Bela G. Fejer

The large vertically directed 50-MHz radar at Jicamarca has sufficient sensitivity to study nighttime echoes from the equatorial electrojet in detail with good resolution. Here we concentrate on type 1 (‘two-stream’) echoes. We find that (1) these echoes sometimes dominate the spectrum (which is never the case in daytime for a vertically directed radar), (2) they are observed over a much wider range of altitudes than they are during daytime, (3) they show an asymmetry which reverses from day to night (downgoing waves are more common at night), (4) the magnitude of the mean Doppler shift appears to increase somewhat …

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Radar Observations Of Two Dimensional Turbulence In The Equatorial Electrojet, 2, Bela G. Fejer, D. T. Farley, B. B. Balsley, R. F. Woodman Jan 1976

Radar Observations Of Two Dimensional Turbulence In The Equatorial Electrojet, 2, Bela G. Fejer, D. T. Farley, B. B. Balsley, R. F. Woodman

Bela G. Fejer

Observations with an altitude resolution of about 1 km were made with the large, vertically directed 50-MHz radar system at the Jicamarca Radar Observatory during the day, when the electrojet was strong. Type 1 (‘two stream’) echoes were seen in a limited range of altitudes, with Doppler shifts corresponding to upward and downward motion at the acoustic velocity. Most of the radar returns were due to type 2 echoes, however. The direction of motion of the type 1 waves sometimes reversed in as little as 1 s, supporting a turbulent model of the electrojet region. During the day the upgoing …

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Radar Measurements Of Neutral Winds And Temperatures In The Equatorial E Region, B. B. Balsley, Bela G. Fejer, D. T. Farley, R. F. Woodman Jan 1976

Radar Measurements Of Neutral Winds And Temperatures In The Equatorial E Region, B. B. Balsley, Bela G. Fejer, D. T. Farley, R. F. Woodman

Bela G. Fejer

The phase velocity of type 1 irregularities in the equatorial electrojet, which can be easily measured by radar, depends upon both the ion acoustic velocity (and hence the temperature) in the medium and the neutral wind velocity. By measuring the phase velocity at several zenith angles both of these quantities in principle can be determined. This note describes the technique and its limitations and presents a few preliminary results obtained at 50 MHz at the Jicamarca Radar Observatory in Peru. These results show E region east-west wind velocities as large as 100 m/s, temperature variations of greater than 100°K, and …

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Radar Studies Of Anomalousvelocity Reversals In The Equatorial Ionosphere, Bela G. Fejer, D. T. Farley, B. B. Balsley, R. F. Woodman Jan 1976

Radar Studies Of Anomalousvelocity Reversals In The Equatorial Ionosphere, Bela G. Fejer, D. T. Farley, B. B. Balsley, R. F. Woodman

Bela G. Fejer

Radar observations made at Jicamarca show that the equatorial electrojet current and the E and F region electric fields can reverse from their normal direction during the day or night and during magnetically quiet or disturbed conditions. The nighttime reversals can only be detected by such radar measurements. The observations support most of the current hypotheses concerning the electrojet plasma instabilities. The rapid reversals sometimes seen during disturbed conditions indicate that high-latitude currents and electric fields associated with substorm activity strongly perturb the dynamo current system at all latitudes.

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The Effect Of The Gradient-Drift Term On Type I Electrojet Irregularities, D. T. Farley, Bela G. Fejer Jan 1975

The Effect Of The Gradient-Drift Term On Type I Electrojet Irregularities, D. T. Farley, Bela G. Fejer

Bela G. Fejer

We hypothesize that type 1 VHF radar echoes can only be observed when the electrojet plasma is linearly unstable at half the radar wavelength and that further, for reasons not yet understood, the phase velocity of the unstable waves always corresponds to the threshold conditions for instability, even when the destabilizing forces (electron drift and plasma density gradient) exceed the threshold. This phase velocity, which produces the Doppler shift of the radar echoes, is usually close to the ion acoustic velocity of the medium but can differ from it to some extent because of the effect of the density gradient. …

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Vertical Structure Of The Vhf Backscattering Region In The Equatorial Electrojet And The Gradient Drift Instability, Bela G. Fejer, D. T. Farley, B. B. Balsley, R. F. Woodman Jan 1975

Vertical Structure Of The Vhf Backscattering Region In The Equatorial Electrojet And The Gradient Drift Instability, Bela G. Fejer, D. T. Farley, B. B. Balsley, R. F. Woodman

Bela G. Fejer

Radar measurements made with high spatial resolution and large dynamic range at the Jicamarca Radar Observatory near the time of reversal of the electrojet current provide further proof that the gradient drift instability is in fact responsible for the type 2 irregularities. Echoes are received over a much wider range of altitudes at night than during the day partly because of the change in character of the background electron density profile and partly because of recombination effects, which can be important during the day. It is also shown that one must be cautious, particularly at night, in associating the mean …

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Oblique Vhf Spectral Studies Ofthe Equatorial Electrojet, Bela G. Fejer, D. T. Farley, B. B. Balsley, R. F. Woodman Jan 1975

Oblique Vhf Spectral Studies Ofthe Equatorial Electrojet, Bela G. Fejer, D. T. Farley, B. B. Balsley, R. F. Woodman

Bela G. Fejer

A new narrow-beam antenna at the Jicamarca Observatory permits oblique (zenith angle, 25°) radar spectral studies of the electrojet with an altitude resolution down to 1.1 km. Only daytime observations are possible presently, however. The general altitude variations in spectral shape observed are consistent with linear instability theory, if the effect of recombination is included. The height at which the mean Doppler shift of the echo maximizes, however, is about 4 km higher than one would expect on the basis of electrojet models. An increase in the assumed collision frequency would remove the discrepancy. Other data presented strongly suggest that …

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