Engineering Papers⌕ Search

Engineering topics

Lee, L. C.

Publications and source records attributed to Lee, L. C..

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Structure of the magnetopause rotational discontinuity

A model is developed for the rotational discontinuities associated with the reconnection configuration on the dayside magnetopause and the energy transfer process in the tail magnetopause. The model, in which the ion dynamics is described by the fluid equations and electrons are assumed to move adiabatically along the magnetic field lines, is valid for a rotational discontinuity with a thickness greater than a few ion gyroradii. It is shown, by the inclusion of self-consistency for trapped electrons, that (1) the trapped electron density profile is uniquely related to the rate of angular rotation of the magnetic field, and (2) the sense of magnetic field rotation is determined by the ratio of the normal and tangential components of the magnetic field. It is found that the electron polarization of magnetopause rotational discontinuities should be in agreement with satellite observations.

Lee, L. C.↗
NASA NTRS1981

Quantitative absorption and fluorescence studies of NO between 1060 and 2000 A

Synchrotron radiation in the 1060 to 2000 A region was used to measure the average absorption and fluorescence cross sections of NO and to determine approximate photodissociation quantum yields. Several vibrational levels of the D(2) sigma(+), E(2) sigma(+), and B(2) delta states have high fluorescence quantum yields. The C(2) and B(2) states do not fluoresce when the excitation energies are above the first dissociation limit, in accord with previous experiments. In general, the fluorescence yields decrease with increasing photon energy. The quantitative measurements are compared with spectroscopic observations and are found to be reasonably consistent.

Guest, J. A.↗
NASA NTRS1981

Kelvin-Helmholtz instability in the magnetopause-boundary layer region

The Kelvin-Helmholtz instability in the magnetopause-boundary layer region is studied on the basis of an idealized model which consists of three uniform plasma regions: the magnetosheath, the boundary layer, and the magnetosphere. There are two unstable modes in the magnetopause-boundary layer region: one is excited at the magnetopause (the magnetopause mode) and the other is excited at the inner surface of the boundary layer (the inner mode). The inner mode is found to be unstable most of the time, while the excitation of the magnetopause mode depends on the magnetic field in the magnetosheath. The observed variation of the boundary layer thickness can be attributed to the unstable inner mode. Possible relationships between the Pc 3-5 geomagnetic pulsations and the surface waves excited on the magnetospheric boundary are also discussed.

Lee, L. C.↗
NASA NTRS1980

Kelvin-Helmholtz instability and the variation of geomagnetic pulsation activity

It is shown that the observed local time variation of dayside geomagnetic micropulsations is consistent with the Kelvin-Helmholtz generation mechanism operating at the magnetopause. The variation of the angle between the interplanetary magnetic field and the magnetopause around the magnetosphere causes variations in the magnetosheath magnetic field, which in turn lead to local time variations in micropulsation amplitudes. Morning sector pulsations are expected to be larger than afternoon sector pulsations. Furthermore, large-amplitude pulsations are expected to be more frequently observed when the angle between the interplanetary magnetic field and the solar wind velocity in front of the bow shock is small.

Lee, L. C.↗
NASA NTRS1980

The energy coupling function and the power generated by the solar wind-magnetosphere dynamo

A solar wind parameter epsilon, known as the energy coupling function, has been shown to correlate with the power consumption in the magnetosphere. It is shown in the present paper that the parameter epsilon can be identified semi-quantitatively as the dynamo power delivered from the solar wind to an open magnetosphere. This identification not only provides a theoretical basis for the energy coupling function, but also constitutes an observational verification of the solar wind-magnetosphere dynamo along the magnetotail. Moreover, one can now conclude that a substorm results when the dynamo power exceeds 10 to the 18th erg/s.

Kan, J. R.↗
NASA NTRS1980

O/1S/ yield from O3 photodissociation at 1700-2400 A

The paper discusses the O(1S) yield from O3 photodissociation measured in the 1700-2400 A region using synchrotron radiation as a light source. An upper limit for the yield set at 0.1% for the entire photon energy range indicates that the contribution of O(1S) to atmospheric OH production is not significant. The spin restriction for going into the O(1S) + O2/X3Sigma(-)(g)/ channel appears to be the determining factor in the low yield. There are three spin-allowed channels to produce excited O2 molecules with thresholds between 2300 and 2650 A; it is recommended to investigate these dissociative pathways.

Lee, L. C.↗
NASA NTRS1980

Amplification of radiation near cyclotron frequency due to electron population inversion

Amplification of electromagnetic waves via the cyclotron maser mechanism by a population of weakly relativistic electrons is studied. The effect of a tenuous population of low energy background plasma is included. It is found that both the ordinary and extraordinary modes can be excited by the weakly relativistic electrons with a loss-cone distribution. The growth rate for the extraordinary mode is much higher than that for the ordinary mode. Velocity spread in the energetic electron distribution function may reduce the growth rate by a factor of approximately 10 from that in the monoenergetic case. The maximum growth rate for the fast extraordinary mode (X mode) occurs near the upper hybrid cutoff frequency. Numerical results are obtained and discussed.

Lee, L. C.↗
NASA NTRS1980

Generation of auroral kilometric radiation and the structure of auroral acceleration region

Generation of auroral kilometric radiation (AKR) in the auroral acceleration region is studied. It is shown that auroral kilometric radiation can be generated by backscattered electrons trapped in the acceleration region via a cyclotron maser process. The parallel electric field in the acceleration region is required to be distributed over 1-2 earth radii. The observed AKR frequency spectrum can be used to estimate the altitude range of the auroral acceleration region. The altitudes of the lower and upper boundaries of the acceleration region determined from the AKR data are respectively approximately 2000 and 9000 km.

Lee, L. C.↗
NASA NTRS1980

Quantitative absorption and fluorescence study of CO from 1060 to 1550 A

Measurement of the photoabsorption cross section of CO in the 1060-1550 A region using synchrotron radiation is described. The oscillator strengths for the transitions from CO (Chi1Sigma+ to various excited states are obtained from these data. Fluorescence from excited CO was observed in the 1150 to 3000 A and 3000 to 8000 A regions. The quantum yields for the production of fluroescence from the Alpha(1)P and B(1)Sigma(+) states are unity because their excitation energies are below the dissociation limit. The C(1)Sigma(+) , v = O level has significant fluorescence quantum yields both in the UV and visible region, but the yields for the E(1)Pi, v = O and C(1)Sigma(+), v = 1 levels are very small. The C(1)Sigma(+), v = 1 level is presumably predissociated. The cross sections for the production of fluroescence from the a'(3)Sigma(+), d(3)Delta sub 1, e(3)Sigma(-) yields a(3)Pi, and B(1)Sigma(+), C(1)Sigma(+) yields A(1)Pi transitions upon excitation from the X(1)Sigma(+) were measured.

Lee, L. C.↗
NASA NTRS1980

A model of the heliospheric magnetic field configuration

A three-dimensional model of the magnetic field configuration in the heliosphere is constructed by assuming that the interplanetary magnetic field consists of four components, (1) the solar dipole, (2) a large number of small spherical dipoles located along an equatorial circle just inside the sun (representing the magnetic field line arcade), (3) the field of the poloidal current system generated by the solar unipolar induction, and (4) the field of an extensive current disc around the sun lying in the ecliptic plane. The magnetic field intensity at a distance of 1 AU (about 20 solar radii above the ecliptic plane) is normalized to fit the observed spiral configuration.

Akasofu, S.-I.↗
NASA NTRS1980

OH/A 2 Sigma + - X 2 Pi sub i/ yield from H2O photodissociation in 1050-1370 A

The cross section and quantum yield for the production of the OH(A 2 Sigma + - X 2 Pi sub i) emission from H2O photodissociation by synchrotron radiation in the region 1050-1370 A are determined. Measurements of the photoemission and photoabsorption cross sections obtained for incident radiation bandwidths of 2 A reveal different vibrational structures in the range 1250-1370 A, and the photoemission is attributed to the 3a1-4a1 valence and 3a1-3sa1 Rydberg transitions. Photoemission quantum yields determined from the ratio of photoemission to photoabsorption cross sections are found to increase sharply at a threshold of 1362-5 A to a peak of 11% at 1300 A, then to decrease slowly with decreasing wavelength. Implications of the results for the dissociation processes of H2O are considered.

Lee, L. C.↗
NASA NTRS1980

Field-aligned currents in the magnetospheric boundary layer

A self-consistent magnetopause-boundary layer model is constructed which contains two current layers, one for the magnetopause and one for the magnetosphere-boundary layer transition region. Field-aligned sheet currents in the boundary layer are generated by the plasma flow along the boundary layer. The magnitude of these boundary layer field-aligned currents is about 10 to the -8th A/sq m, which can be scaled along field lines to about 5 x 10 to the -6th A/sq m near the ionosphere and therefore can be identified as a possible source for the auroral sheet currents. The cross-field current density in the model is also about 10 to the -8th A/sq m, which is sufficient to excite the lower-hybrid-drift waves to produce the observed electromagnetic fluctuations in the magnetopause-boundary layer region.

Lee, L. C.↗
NASA NTRS1979

Photoabsorption cross sections of CH3F, CHF3, CH3Cl, and CF2Cl2 from 175 to 760 A

The study of fluorinated and chlorinated hydrocarbons is of great interest because of their suspected effect on the ozone layer in the atmosphere. Using synchrotron radiation as a continuum background, the present study measures photoelectrically the photoabsorption cross sections of CH3F, CHF3, CH3Cl, and CF2Cl2 in the 175-760 A (70.8-16.3 eV) region, using a double ionization chamber. The absolute absorption cross sections and a tentative interpretation of the observed discrete structures are presented.

Wu, C. Y. R.↗
NASA NTRS1979

A unified kinetic model of the tangential magnetopause structure

In the self-consistent model of the tangential magnetopause, formulated in the present paper on the basis of the Vlasov-Maxwell equations, the plasmas on both sides are magnetized and the magnetic field is everywhere parallel to the magnetopause (i.e., the normal field component is zero) and rotates through an arbitrary angle across the magnetopause. It is shown that the thickness of the magnetopause is greater than the gyroradius of the plasma ions. The presence of a trapped particle population within the magnetopause is shown to be required to allow the magnetic field to rotate more than a certain critical angle (-90 degrees). The model proposed can reproduce the observed features of the tangential magnetopause structure by specifying boundary conditions on both sides of the magnetopause.

Lee, L. C.↗