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Mcgee, T. J.

Publications and source records attributed to Mcgee, T. J..

12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Multi-wavelength profiles of aerosol backscatter over Lauder, New Zealand, 24 November 1992

Simultaneous profiles of aerosol backscatter ratio were measured over Lauder, New Zealand (45 deg S, 170 deg E) on the night of November 24, 1992. Instrumentation comprised two complementary lidar systems and a backscattersonde, to give measurements at wavelengths 351, 490, 532, and 940 nm. The data from the lidars and the backscattersonde were self-consistent, enabling the wavelength dependence of aerosol backscatter to be determined as a function of altitude. This wavelength-dependence is a useful parameter in radiative transfer calculations. In the stratosphere, the average wavelength exponent between 351 and 940 nm was -1.23 +/- 0.1, which was in good agreement with values derived from measured physical properties of aerosols.

Mckenzie, R. L.↗
NASA NTRS1986

Rotationally resolved collisional transfer rates in OH

Fluorescence lidar measurements of the hydroxyl radical require detailed information concerning collision induced processes in order to deduce the radical number density from a lidar return. The Goddard SFC OH lidar currently utilizes a broadband detector which precludes the necessity of fully understanding collisional redistribution of rotational energy within the excited state. Numerous advantages result however from the inclusion of a detector with a bandpass only slightly larger that the Doppler width of a rotational line. This however places more stringent requirements on the spectroscopy. Measurements were accordingly made of rotationally resolved quenching rates for collisions with O2, N2, and H2O. Rotational transfer rates were also measured for the same colliders. Quenching rates were measured using a Nd-YAG pumped Rh6G dye laser doubled into the UV. The OH lifetimes were measured as a function of pressure of quenching gas at total pressures of between 50 and 250 microns. Rotational transfer rates were measured by recording the emission spectrum on an intensified diode array and integrating over 10.000 laser shots.

Mcgee, T. J.↗
NASA NTRS1986

The GSFC gound-based lidar for the measurement of stratospheric ozone

Concern has risen over the last decade concerning the release of gases into the atmosphere which when photolyzed in the stratosphere can catalyze the destruction of ozone. Although the expected change is only on the order of 5%, significant changes in the vertical profile are anticipated. Predictions at 40 km run as high as a 60% change in the next 50 to 100 years. Because of the importance of ozone in the thermal budget of the atmosphere, such a change will have a direct impact on the earth's climate. Long term monitoring of stratospheric ozone is required to validate the predictions and Differential Absorption Lidar is particularly well suited to this measurement. GSFC is currently constructing a mobile lidar system based on a high powered XeCl excimer laser. The system is expected to be operating by fall 1986 and a campaign to compare the lidar results with a series of ROCOZ flights is planned.

Mcgee, T. J.↗
NASA NTRS1985

Progress in stratospheric hydroxyl measurement by balloon-borne lidar

Knowledge of the concentration of hydroxyl radical is crucial to understanding the chemistry of the stratosphere. Hydroxyl participates in several catalytic cycles which destroy ozone and strongly influences the cycles of chlorine and nitrogen oxides by its reactions which form or destroy reservoirs for chlorine and odd-nitrogen compounds. Measurements have been conducted of the concentration of hydroxyl radical between the altitudes of 32.5 and 38.5 km using the technique of laser-induced fluorescence. The results ranging from 4 to 9 x 10 to the 6th per cu cm (with an accuracy of + or - 50 percent) are about 2-3 times lower than predicted by current one-dimensional models, although the uncertainties in the determination and in the models are sufficiently large to explain the differences. A number of potential improvements to the instrument are discussed.

Heaps, W. S.↗
NASA NTRS1985

Fluorescence branching ratios in nitric oxide - Emission from the A2 Sigma(+) (v prime = 1)

The most complete set of branching ratios from the v-prime = 1 level of the A-state in NO measured to data is reported. The assumption that virtually all of the emitted radiation has been sampled is used to extract Franck-Condon factors from the v-prime = 1 manifold. A comparison with previously published results indicates that, except for the (1,0) band, there is reasonably good agreement.

Mcgee, T. J.↗
NASA NTRS1985

Time-resolved laser-induced fluorescence of selected even-parity 7p states of Xe I

Lifetimes and self-quenching rates have been measured for excited states of Xe I that were populated using simultaneous two-photon absorption. Lifetimes measured in this study are somewhat shorter than those measured using the broadband-excitation technique. Lifetimes reported here are all faster than 100 nsec. Deactivation rates are approximately 2 x 10 to the -10th cu cm/sec per mol.

Mcgee, T. J.↗
NASA NTRS1984

Absolute OH absorption cross sections (for lidar measurements)

Experimental data are employed to calculate absorption cross sections for several rotational lines in the OH A-X system. The cross sections are computed as functions of the spectral and line widths and temperature of a laser beam, and account for lifetimes and branching ratios. Detection limits for the P1(2) transition of the (1,0) band were examined. The oscillator strengths and cross-sections obtained are important for quantifying OH concentrations in the stratosphere from lidar return signals.

Mcgee, T. J.↗
NASA NTRS1983

Balloon borne LIDAR measurements of stratospheric hydroxyl radical

A balloon-borne laser radar (LIDAR) system for determining the stratospheric hydroxyl radical concentration constructed and flown by the Goddard Space Flight Center is discussed. The system measured hydroxyl in the altitude range of 34-37 km during an afternoon and early evening, producing the first post-sunset hydroxyl determination ever obtained. Daytime values (approximately 5 x 10 to the 6th/cu cm) are somewhat lower than previous measurements using in situ resonance fluorescence. Nighttime values (approximately 7 x 10 to the 5th/cu cm at 2100 CDT) are found to be higher than predicted by current one-dimensional models. Possible sources of these discrepancies, together with improvements possible in future systems, are outlined.

Heaps, W. S.↗
NASA NTRS1983

Fluorescence branching ratios from the A2Sigma + (v-prime = 0) state of NO

The emission spectrum of NO from several rotational levels in the first excited state has been recorded. Branching ratios have been measured and Franck-Condon Factors calculated from the experimental data. Lifetimes of the lines used have been measured and Einstein A-values calculated.

Mcgee, T. J.↗
NASA NTRS1982

Stratospheric ozone and hydroxyl radical measurements by balloon-borne lidar

An experiment is reported in which a balloon-borne lidar system was used to measure ozone and the hydroxyl radical in the stratosphere by two lidar techniques. Ozone was measured in the 20-37 km altitude range using differential absorption lidar, and the hydroxyl radical was measured in the 34-37 km range using remote laser-induced fluorescence. Ozone concentrations were determined with a vertical resolution of 0.5 km, and in addition, horizontally resolved ozone measurements with 0.15-km resolution were obtained over a 2-km range. The temporal variation of the hydroxyl radical concentration ranged from 40 parts/trillion shortly after noon to about 5 parts/trillion two hours after sunset. Possible modifications to the system are discussed which can yield an improvement in the sensitivity of between one and two orders of magnitude, thus permitting measurements of the hydroxyl radical in the 20-30-km altitude range.

Heaps, W. S.↗