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Pfister, L.

Publications and source records attributed to Pfister, L..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Troposphere-to-Stratosphere Transport in the Lowermost Stratosphere from Measurements of H2O, CO2, N2O and O3

The origin of air in the lowermost stratosphere is investigated with measurements from the NASA ER-2 aircraft. Air with high water vapor mixing ratios was observed in the stratosphere at theta = 330-380 K near 40 N in May 1995, indicating the influence of intrusions of tropospheric air. Assuming that observed tracer-tracer relationships reflect mixing lines between tropospheric and stratospheric air masses, we calculate mixing ratios of H2O (12-24 ppmv) and CO2 for the admixed tropospheric air at theta = 352-364 K. Temperatures on the 355 K surface at 20-40 N were low enough to dehydrate air to these values. While most ER-2 CO2 data in both hemispheres are consistent with tropical or subtropical air entering the lowermost stratosphere, measurements from May 1995 for theta < 362 K suggest that entry of air from the midlatitude upper troposphere can occur in conjunction with mixing processes near the tropopause.

Hintsa, E. J.↗
NASA NTRS1997

The Relationship of Subvisible Cirrus Clouds Observed During NASA's Tropical Ozone

Thin, subvisible cirrus (SVC) clouds at the tropical tropopause have been observed by a number of methods in a variety of observational programs, including in situ sampling and aircraft and space-based lidar. Modeling studies suggest that these clouds play an important role in dehydrating tropospheric air as it enters the stratosphere. This is because particles large enough to have significant fall speeds can form under the conditions of slow cooling that are implied by the large horizontal extent of the SVC sheets. The IRA radiation that these clouds absorb, and the upward vertical motion this implies, also make them candidates for a tropical troposphere-to-stratosphere mass transfer mechanism. These sheets were observed on five flights during the Tropical Ozone Transport Experiment (TOTE) by the NASA Langley DIAL lidar aboard NASA's DC-8 research aircraft, operating during December 1995 and February 1996 south of Hawaii (12 S to 21 N). This experiment provided a unique look at these clouds since temperature profiles were available for all the SVC observations. Thus, the observed distributions of SVC's can be compared with the position of the tropopause to establish whether the SVC's are tropospheric or stratospheric. It also allows comparison of TOTE observations with in situ experiments, where water and cloud particle data is available as a function of temperature and potential temperature.

Pfister, L.↗
NASA NTRS1994

The Diurnal Variation of Hydrogen, Nitrogen, and Chlorine Radicals: Implications for the Heterogeneous Production of HNO2

In situ measurements of hydrogen, nitrogen, and chlorine radicals obtained through sunrise and sunset in the lower stratosphere during SPADE are compared to results from a photochemical model constrained by observed concentrations of radical precursors and environmental conditions. Models allowing for heterogeneous hydrolysis of N205 on sulfate aerosols agree with measured concentrations of NO, NO2, and ClO throughout the day, but fail to account for high concentrations of OH and H02 observed near sunrise and sunset. The morning burst of [OH] and [HO2] coincides with the rise of [NO] from photolysis of N02, suggesting a new source of HO, that photolyzes in the near UV (350 to 400 nm) spectral region. A model that allows for the heterogeneous production of HN02 results in an excellent simulation of the diurnal variations of [OH] and [HO2].

Salawitch, R. J.↗
NASA NTRS1994

The Distribution of Hydrogen, Nitrogen, and Chlorine Radicals in the Lower Stratosphere: Implications for Changes in O3 due to Emission of NO(y) from Supersonic Aircraft

In situ measurements of hydrogen, nitrogen, and chlorine radicals obtained in the lower stratosphere during the Stratospheric Photochemistry, Aerosols and Dynamics Expedition (SPADE) are compared to results from a photochemical model that assimilates measurements of radical precursors and environmental conditions. Models allowing for heterogeneous hydrolysis of N2O5 agree well with measured concentrations of NO and ClO, but concentrations of HO2 and OH are underestimated by 10 to 25%, concentrations of NO2 are overestimated by 10 to 30%, and concentrations of HCl are overestimated by a factor of 2. Discrepancies for [OH] and [HO2] are reduced if we allow for higher yields of O(sup 1)D) from 03 photolysis and for heterogeneous production of HNO2. The data suggest more efficient catalytic removal of O3 by hydrogen and halogen radicals relative to nitrogen oxide radicals than predicted by models using recommended rates and cross sections. Increases in [O3] in the lower stratosphere may be larger in response to inputs of NO(sub y) from supersonic aircraft than estimated by current assessment models.

Salawitch, R. J.↗
NASA NTRS1993

A case study of the mountain lee wave event of January 6, 1992

A mountain wave event, observed at the southern tip of Greenland on January 6, 1992, was corroborated by three experiments: the Meteorological Measurement System (MMS), the Microwave Temperature Profiler (MTP), and the Reactive Nitrogen Instrument (NO/NO(y)). Gravity wave signatures with classical phase relationship between wind and temperature were observed on both the outbound and inbound legs at different altitudes. The waves showed both vertically propagating and evanescent properties. Characteristics of the dominant wave mode are: wavelength about = 35 km; vertical displacement about = 0.8 km, and peak-to-peak vertical wind about = 6/ms. With the prevailing wind at about = 37/ms, the stratospheric temperature was reduced by 6K to 195.5 K within 8 minutes. The implication and potential impact of mountain lee waves on the formation of polar stratospheric clouds (PSC's) are discussed.

Chan, K. R.↗
NASA NTRS1993

Post-Pinatubo optical depth spectra vs. latitude and vortex structure: Airborne tracking sunphotometer measurements in AASE 2

In January and March 1992, DC-8-measured stratospheric particle optical depth spectra, tau(sub P)(lambda), peaked broadly at midvisible or longer wavelenghts. At mid-to-high northern latitudes outside the vortex, tau(sub p)(526 nm) above about 11 km was as large as 0.22 in both January and March, reflecting continued Pinatubo volcanic influence. In both months, in-vortex tau(sub p)(lambda) above 11 km was smaller than outside-vortex values by a factor of two or more, and in January a strong anticorrelation was observed between tau(sub p)(lambda) and HF column content (an indicator of vortex penetration). In late January at 18-20S, near the edge of the southern subtropical jet, tau(sub p)(526 nm) above 12 km was only about 0.07-0.09, with a flatter spectral shape than northern mid- to high-latitude measurements in both January and March. Occasional high-latitude vertical profiles indicate 6-11-km slab optical depths, Delta tau(sub p)(526 nm), of 0.05 to 0.1, which should be added to the above-11-km values to yield values above 6 km.

Russell, P. B.↗
NASA NTRS1993

Post-Pinatubo Optical Depth Spectra VS. Latitude and Vortex Structure: Airborne Tracking Sunphotometer Measurements in AASE 2

In January and March 1992, DC-8-measured stratospheric particle optical depth spectra, (tau)(sub p)(lambda), peaked broadly at midvisible or longer wavelengths. At mid-to-high northern latitudes outside the vortex, tau(sub p)(526 microns) above about 11 km was as large as 0.22 in both January and March, reflecting continued Pinatubo volcanic influence. In both months, in-vortex tau(sub p) above 11 km was smaller than outside-vortex values by a factor of two or more, and in January a strong anticorrelation was observed between tau(sub p)(lambda) and HF column content (an indicator of vortex penetration). In late January at 18-20S, near the edge of the southern subtropical jet, tau(sub p)(526 microns) above 12 km was only about 0.07- 0.09, with a flatter spectral shape than northern mid-to high-latitude measurements in both January and March. Occasional high-latitude vertical profiles indicate 6-1 km slab optical depths, delta(tau)(sub p)(526 micron), of 0.05 to 0.1, which should be added to the above-11-km values to yield values above 6 km.

Russell, P. B.↗
NASA NTRS1993

A Case Study of the Mountain Lee Wave Event of January 6, 1992

A mountain wave event, observed at the southern tip of Greenland on January 6, 1992, was corroborated by three experiments: the Meteorological Measurement System (MMS), the Microwave Temperature Profiler (MTP), and the Reactive Nitrogen Instrument (NO/NO(y)). Gravity wave signatures with classical phase relationship between wind and temperature were observed on both the outbound and inbound legs at different altitudes. The waves showed both vertically propagating and evanescent properties. Characteristics of the dominant wave mode are: wavelength approximately equals 35 km, vertical displacement approximately equals 0.8 km, and peak-to-peak vertical wind approximately equals 6 ms-1. With the prevailing wind at approximately equals 37 m/s, the stratospheric temperature was reduced by 6 K to 195.5 K within 8 minutes. The implication and potential impact of mountain lee waves on the formation of polar stratospheric clouds (PSC's) are discussed.

Chan, K. R.↗
NASA NTRS1993

Post-Pinatubo Optical Depth Spectra vs Latitude and Vortex Structure: Airborne Tracking Sunphotometer Measurements in AASE 2

In January and March 1992, DC-8-measured stratospheric particle optical depth spectra, tau(sub p)(lambda), peaked broadly at midvisible or longer wavelengths. At mid-to-high northern latitudes outside the vortex, tau(sub p)(526 nm) nm) above about 11 km was as large as 0.22 in both January and March, reflecting continued Pinatubo volcanic influence. In both months, in-vortex tau(sub p)(lambda) above 11 km was smaller than outside-vortex values by a factor of two or more, and in January a strong anticorrelation was observed between tau(sub p)(lambda) and HF column content (an indicator of vortex penetration). In late January at 18-20S, near the edge of the southern subtropical jet, tau(sub p)(526 nm) above 12 km was only about 0.07-0.09, with a flatter spectral shape than northern mid- to high-latitude measurements in both January and March. Occasional high-latitude vertical profiles indicate 6-11-km slab optical depths, Delta tau(sub p)(526 nm), of 0.05 to 0.1, which should be added to the above-11-km values to yield values above 6 km.

Russell, P. B.↗
NASA NTRS1993

The tropical experiment of the Stratosphere-Troposphere Exchange Project (STEP) - Science objectives, operations, and summary findings

An overview is presented of the tropical component of STEP. The STEP cooperative experiments are described and summaries are presented of the STEP tropical ER-2 aircraft flights. STEP tropical results on dehydration and transfer and the mechanisms of upward transfer are summarized. Illustrations show flight paths for each sortie on satellite images and on 100 hPa synoptic flow charts, as well as the timing of flights with respect to overall cloudiness in the Australian region.

Russell, P. B.↗
NASA NTRS1993

Gravity waves generated by a tropical cyclone during the STEP tropical field program - A case study

Overflights of a tropical cyclone during the Australian winter monsoon field experiment of the Stratosphere-Troposphere Exchange Project (STEP) show the presence of two mesoscale phenomena: a vertically propagating gravity wave with a horizontal wavelength of about 110 km and a feature with a horizontal scale comparable to that of the cyclone's entire cloud shield. The larger feature is fairly steady, though its physical interpretation is ambiguous. The 110-km gravity wave is transient, having maximum amplitude early in the flight and decreasing in amplitude thereafter. Its scale is comparable to that of 100-to 150-km-diameter cells of low satellite brightness temperatures within the overall cyclone cloud shield; these cells have lifetimes of 4.5 to 6 hrs. These cells correspond to regions of enhanced convection, higher cloud altitude, and upwardly displaced potential temperature surfaces. The temporal and spatial distribution of meteorological variables associated with the 110-km gravity wave can be simulated by a slowly moving transient forcing at the anvil top having an amplitude of 400-600 m, a lifetime of 4.5-6 hrs, and a size comparable to the cells of low brightness temperature.

Pfister, L.↗
NASA NTRS1991

Horizontal wind fluctuations in the stratosphere during large-scale cyclogenesis

The meteorological measurement system (MMS) on the U-2 aircraft measured pressure, temperature, and the horizontal wind during a cyclogenesis event over western United States on April 20, 1984. The mean horizontal wind in the stratosphere decreases monotonically with altitude. Superimposed on the mean stratospheric wind is a perturbation wind vector, which is an elliptically polarized wave with an amplitude of 4 to 10 m/s and a vertical wavelength of 2 to 3 km. The perturbation wind vector rotates anticyclonically (clockwise) with altitude and produces alternating advection in the plane of the aircraft flight path. This differential advection folds surfaces of constant tracer mixing ratio and contributes to the observed tracer laminar structures and inferred cross-jet transport.

Chan, K. R.↗
NASA NTRS1989

The radiative budget of tropical clouds - A case study

Data collected during flight 9 of the Stratosphere-Troposphere Exchange Project (STEP), in Australia (1987), are used in an attempt to define the nature of one particular cirrus outflow region and its radiative impact. To explore the mechanisms by which air is exchanged between the stratosphere and troposphere, a series of instruments was flown on the NASA ER-2 high-altitude research aircraft to make measurements relevant to the radiative budget of tropical clouds. The data acquired included upwelling infrared radiance at 10.5 and 6.5 microns (spectral bandwidth of 1 micron); net infrared flux (spectral bandwidth of 3 to 40 microns); cloud particle size distribution; water-vapor and total water (vapor plus condensed phase); aerosol particle size distribution; and ambient temperature.

Ackerman, T. P.↗
NASA NTRS1985

Baroclinic instability of easterly jets with applications to the summer mesosphere

A two-dimensional numerical analysis of baroclinic instability waves in zonally and seasonally averaged wind fields in the summer mesosphere is presented. The analysis is based on the linearized quasi-geostrophic potential vorticity equation of Simmons and Moskins (1973). Solutions are obtained for the wave structure, wave growth rates, and wave periods on the basis of idealized and realistic data, and the results are compared with one-dimensional analyses. It is shown that the wavenumbers of peak growth with periods of 1.4-3 days were consistently lower for the two-dimensional analysis than for previous one-dimensional analyses. The possibility of detecting baroclinic instability in summer winds at 80-100 km by means of nadir-sounding satellite observations is discussed.

Pfister, L.↗
NASA NTRS1984

Baroclinic instability in the Venus atmosphere

A three-dimensional, spherical, primitive equation eigenvalue model is used to investigate the baroclinic stability properties of the wind and temperature fields in the Venus atmosphere as measured by Pioneer Venus. It is found that baroclinic instability occurs in the region of the middle cloud deck. The most unstable modes have growth times less than eight days and are vertically confined to the region near the middle cloud layer. The most unstable baroclinic mode at zonal wavenumber 2 has characteristics similar to those observed for the high latitude rotating dipole thermal feature. Certain planetary scale baroclinic modes can penetrate to relatively high altitudes under the right circumstances, and may therefore explain some of the wave features observed between 60 and 90 km. For example, thermal oscillations with periods between four and seven days occurring at middle latitudes have characteristics which appear to be consistent with computed properties of planetary scale baroclinic modes.

Young, R. E.↗
NASA NTRS1982

The satellite power system - Assessment of the environmental impact on middle atmosphere composition and on climate

Numerical models were developed to calculate the total deposition of watervapor, hydrogen, CO2, CO, SO2, and NO in the middle atmosphere from operation of heavy lift launch vehicles (HLLV) used to build a satellite solar power system (SPS). The effects of the contaminants were examined for their effects on the upper atmosphere. One- and two-dimensional models were formulated for the photochemistry of the upper atmosphere and for rocket plumes and reentry. An SPS scenario of 400 launches per year for 10 yr was considered. The build-up of the contaminants in the atmosphere was projected to have no significant effects, even at the launch latitude. Neither would there by any dangerous ozone depletion. It was found that H, OH, and HO2 species would double in the thermosphere. No measurable changes in climate were foreseen.

Whitten, R. C.↗
NASA NTRS1980

Stratospheric pollutant transports by planetary waves and tropical circulations

Radiosonde and U-2 aircraft data from the Intertropical Convergence Zone experiment of July, 1977 were analyzed. The radiosonde data above 15 km was plotted in the form of time-height sections so that wave motions in the meteorological variables (temperature, zonal wind, and meridional wind) could be easily delineated. The results showed the presence of a planetary 16 day Kelvin wave. More significantly, large amplitude gravity waves with vertical wavelengths on the order of 3-6 km were found. Spectral analysis of frequencies showed peaks in meridional wind variance at 2-3 days and 5 days, with the shorter periods stronger at higher altitudes. In the time domain, two instances of organized wave groups propagating upward into the stratosphere were isolated. Associated with one of these wave groups was a region of very large vertical shear in which either turbulence or small scale (10 km wavelength or less) gravity wave activity had been found by the U-2 aircraft.

Riegel, C. A.↗