Engineering topics

London, Julius

Publications and source records attributed to London, Julius.

14 records

NASA NTRS2003

Solar/Stellar Irradiance Comparison Experiment (SOLSTICE) on the Upper Atmosphere Research Satellite (UARS)

A final report on the operational activities related to the UARS Solar Stellar irradiance Comparison Experiment (SOLSTICE) is presented. Scientific activities of SOLSTICE has also been supported. The UARS SOLSTICE originated at the University of Colorado in 1981. One year after the UARS launch in 1991, the operations and research support activities for SOLSTICE were moved to the High Altitude Observatory (HAO) of the National Center for Atmospheric Research (NCAR). The SOLSTICE program continued at HAO with the National Science Foundation, and after four years, it was moved once again back to the University of Colorado. At the University after 1997 this subject grant was issued to further extend the operations activities from July 2001 through September 2002. Although this is a final report for one particular activity, in fact the SOLSTICE operations activity -first at the University, then at HAO, and now again at the University -has continued in a seamless fashion.

Rottman, Gary J.↗

NASA NTRS1995

The effect of moonlight on observation of cloud cover at night, and application to cloud climatology

Ten years of nighttime weather observations from the Northern Hemisphere in December were classified according to the illuminance of moonlight or twilight on the cloud tops, and a threshold level of illuminance was determined, above which the clouds are apparently detected adequately. This threshold corresponds to light from a full moon at an elevation angle of 6 deg, light from a partial moon at higher elevation, or twilight from the sun less than 9 deg bvelow the horizon. It permits the use of about 38% of the observations made with the sun below the horizon. The computed diurnal cycles of total cloud cover are altered considerably when this moonlight criterion is imposed. Maximum cloud cover over much of the ocean is now found to be at night or in the morning, whereas computations obtained without benefit of the moonlight criterion, as in our published atlases, showed the time of maximum to be noon or early afternoon in many regions. The diurnal cycles of total cloud cover we obtain are compared with those of the International Satellite Cloud Climatology Project (ISCCP) for a few regions; they are generally in better agreement if the moonlight criterion is imposed on the surface observations. Using the moonlight criterion, we have analyzed 10 years (1982-91) of surface weather observations over land and ocean, worldwide, for total cloud cover and for the frequency of occurrence of clear sky, fog, and precipitation. The global average cloud cover (average of day and night) is about 2% higher if the moonlight criterion is imposed than if all observations are used. The difference is greater in winter than in summer, because of the fewer hours of darkness in summer. The amplitude of the annual cycle of total cloud cover over the Arctic Ocean and at the South Pole is diminished by a few percent when the moonlight criterion is imposed. The average cloud cover for 1982-91 is found to be 55% for Northern Hemisphere land, 53% for Southern Hemisphere land, 66% for Northern Hemisphere ocean, and 70% for Southern Hemisphere ocean, giving a global average of 64%. The global average for daytime is 64.6%; for nighttime 63.3%.

Hahn, Carole J.↗

NASA NTRS1994

Observed solar UV irradiance variations of importance to middle atmosphere energetics and photochemistry

Absorption of solar UV irradiance in the spectral interval 120-420 nm is chiefly responsible for radiative heating and photodissociation of important atmospheric constituents (e.g., O2, O3, H2O, NO2, etc.) in the stratosphere, mesosphere, and lower thermosphere. Thus, the absolute value and time perturbations of the UV irradiance could significantly affect the energetics, photochemistry, and subsequent dynamics of these regions. Analysis of preliminary data from the SOLSTICE (UARS) observations for a period of 244 days (3 Oct 1991-2 Jun 1992) is discussed in this paper. The data provide mean daily values of the spectral distribution of the observed irradiances at 1-nm resolution and their solar rotation and semirotation variations. The average amplitudes of the 27-day irradiance oscillations for the 244-day data period were 5.7% at Lyman-alpha (121 nm), 1% at 200 nm, 0.5% at 210 nm, and generally less than 0.2% at wavelengths longer than 280 nm. The average amplitudes of 13.5-day oscillations were, by and large, about half of these values. Solar irradiance variations at 10.7 cm are highly correlated with those at Ly-alpha and other chromospheric emission lines (r = 0.7 to 0.8) and only moderately correlated with irradiances at wavelengths of 180-208 nm (r = 0.5). The correlation decreases as the source region of the irradiance gets closer to the base of the photosphere. At the 2-nm interval 279-281 nm, however, which contains the cores of the Mg II h and k lines, the correlation is again approximately 0.8.

London, Julius↗

NASA NTRS1994

Long-term observed ozone trends in the free troposphere and lower stratosphere

The vertical distributions of ozone trends in the free troposphere and lower stratosphere were derived from ozonesonde observations taken over an average period of approximately 20 years. The results for the annual trends show a consistent pattern of increased ozone of approximately 1 percent/yr to 2 percent/yr up to approximately 300 mb and decreased ozone of approximately -0.6 percent/yr from approximately 100 to 50 mb. Statistically significant positive trends found in midtroposphere (approximately 500 mb) at a set of representative stations in the Northern Hemisphere have little apparent seasonal variation. Negative trends are generally strongest at 50-70 mb with a tendency to be larger during spring. A highly significant negative trend of approximately -5 percent/yr is found near 100 mb over Syowa (69 deg S) during spring.

London, Julius↗

NASA NTRS1994

The response of middle atmospheric ozone to solar UV irradiance variations with a period of 27 days

A one-dimensional photochemical-dynamical-radiative time-dependent model was used to study the response of middle atmospheric temperature and ozone to solar UV irradiance variations with the period of 27 days. The model solar UV O(x), HO(x), NO(x), and CIO(x)families and modeled solar UV variations. The amplitude of the primary temperature response to the solar UV variation is plus 0.4 K at 85-90 km with a phase lag of about 6 days. A secondary maximum response of plus 0.3 K at 45-50 km appears with a phase lag of 1 day. There is a maximum positive ozone response to the 27-day solar UV oscillation of 2.5 percent at 80-90 km with a phase lag of about 10 days after the solar irradiance maximum. At 70 km the ozone response is about 1.2 percent and is out of phase with the solar variation. In the upper stratosphere (40-50 km) the relative ozone variation is small, about 0.2 percent to 0.3 percent, and there is a negative phase of about 4 days between the ozone and solar oscillations. These oscillations are in phase in the middle stratosphere (35-40 km) where there is again a maximum relative response of about 0.6 percent. The reasons for these ozone amplitude and phase variations are discussed.

Chen, LI↗

NASA NTRS1993

Time variations of solar UV irradiance as measured by the SOLSTICE (UARS) instrument

An analysis is presented of solar ultraviolet irradiance measurements made by the SOLSTICE spectrometers on the Upper Atmosphere Research Satellite (UARS). Reported observations cover the wavelength interval 119-420 nm, and the analysis discussed here is for the time period 26 Nov 1991 to 31 Dec 1992, during which time solar activity decreased in intensity. At the time of peak activity, the average 27-day variation had a relative amplitude of about 8 percent at Ly-alpha, tailing off to about 0.6 percent at 260 nm. It is shown that over the spectral interval 119-260 nm, the relative 27-day harmonic was about a factor of two larger during the strongly disturbed as compared with the moderately disturbed period.

London, Julius↗

NASA NTRS1990

Wavelength Dependence of Solar Rotation and Solar Cycle UV Irradiance Variations

It is shown that for the 5-year period 1982 to 1987 the solar irradiance decrease is estimated to be about 5 to 7 percent over the spectral interval 195 to 225 nm. This change becomes progressively smaller with increasing wavelength. For the 2-1/3 year period, January 1987 to April 1989, the irradiance increases about 6 percent at 195 to 205 nm and about 2 percent between 215 to 250 nm. Both 27-day and 13.5-day relative amplitudes peak at the time near solar maximum (1982) but remain comparatively small between 1983 and the onset of solar cycle 22. An average 280 day oscillation is noted for wavelengths up to 230 nm. No physical mechanism is offered for this variation.

London, Julius↗

NASA NTRS1990

Cloud information for FIRE from surface weather reports

Surface weather observations of clouds were analyzed to obtain a global cloud climatology (Warren et al, 1986; 1988). The form of the synoptic weather code limits the types of cloud information which are available from these reports. Comparison of surface weather reports with instrumental observations during the FIRE field experiments can help to clarify the operational definitions which were made in the climatology because of the nature of the synoptic code. The long-term climatology from surface weather observations is also useful background for planning the location and timing of intensive field experiments.

Hahn, Carole J.↗

NASA NTRS1990

Studies of the observed and theoretical variations of atmospheric ozone

The four related topics covered include: (1) distributions of total and upper atmospheric ozone and their time and space variations; (2) observed and theoretical models of the quasi-biennial oscillation (QBO) ozone variation; (3) radiative processes in the upper atmosphere; and (4) relations between ozone and solar variations. The results of these studies are presented. They come from twenty-three published papers.

London, Julius↗

NASA NTRS1989

Satellite observed long-term averaged seasonal and spatial ozone variations in the stratosphere

Nine years of Nimbus-7 SBUV ozone mixing ratio data (October 1978-September 1987) have been used to analyze the distributions of the long-term average annual and semiannual ozone oscillations in the lower, middle, and upper stratosphere over the region 65 deg S to 65 deg N. It is shown that the derived harmonics are consistent with the result of earlier investigations based on limited sets of data. Year-to-year changes of amplitudes of the annual and semiannual variations are generally small except in the tropical midstratosphere (due to the effect of El Chichon) and the southern subpolar upper stratosphere. Analyses are also presented to show the vertical and seasonal distribution of the zonal ozone variations. It is shown that, for the long-term averaged data, wave 1 is larger during winter than summer and in winter larger in the Northern than Southern Hemisphere. The importance of photochemical and thermal/dynamic processes in modifying the time and zonal variations is discussed.

Perliski, Lori M.↗

NASA NTRS1989

On the interpretation of seasonal variations of stratospheric ozone

The causes of the annual and semiannual ozone oscillations were investigated. Using the middle-atmosphere model of Garcia and Solomon (1983), the monthly variations of the ozone mixing ratio were computed and Fourier-analyzed, with excellent agreement found between the computed values and those measured with the SBUV instrument. It was found that, at high latitudes and low altitudes, the modeled ozone abundances increased in the winter due to transport and decreased in the summer due to chemical destruction. In the middle stratosphere, the calculated annual ozone variation was found to be largely due to the annual variation in the odd-oxygen production rate, while in the upper stratosphere, the annual ozone variation was found to be caused by the large annual oscillation in temperature.

Perliski, Lori M.↗

NASA NTRS1989

Observed solar near UV variability: A contribution to variations of the solar constant

Continuous Measurements of the Solar UV have been made by an instrument on the Solar Mesosphere Explorer (SME) since October 1981. The results for the wavelength interval 200 to 300 nm show an irradiance decrease to a minimum in early 1987 and a subsequent increase to mid-April 1989. The observed UV changes during part of solar cycles 21 to 22 represent approx. 35 percent (during the decreasing phase) and 25 percent (during the increasing phase) of the observed variations of the solar constant for the same time period as the SME measurements.

London, Julius↗

NASA NTRS1989

The global distribution of observed cloudiness - A contribution to the ISCCP

Satellite-inferred overall global cloud patterns generally corroborate those derived from ground-based observations. Both show significant differences of cloudiness between the two hemispheres and over extended land as compared with ocean areas. However, the averaged latitudinal values of surface-based observed cloud amounts are about 10 percent higher than those derived from Nimbus-7 observations. The largest difference (10-20 percent) is in the subtropics of each hemisphere and at subpolar and polar latitudes during the summer. The difference in reported average global total cloud amounts is about 10 percent.

London, Julius↗

NASA NTRS1986

The quasi-biennial oscillation of ozone in the tropical middle stratosphere - A one-dimensional model

A one-dimensional model of the quasi-biennial oscillation (QBO) of ozone in the tropical middle stratosphere is derived based on assumed (observed) zonal wind QBO in a coupled dynamic, radiative/photochemical system. It is found that the derived vertical variation of the ozone QBO amplitude has two maxima, one at 32 km and the other at 22 km, and a minimum at 28 km. These are in qualitative agreement with observations. In the height interval 30-35 km, the ozone QBO is closely related to temperature dependent photochemistry, and the ozone and temperature variations are out of phase. Below 28 km, where vertical ozone and thermal transports are important, ozone and temperature oscillations are in phase, but both are approximately 270 deg out of phase with the vertical wind variation.

Ling, Xiu-De↗