Engineering topics

Lait, Leslie R.

Publications and source records attributed to Lait, Leslie R..

36 records · Page 2

NASA NTRS1990

Radiative heating rates during the Airborne Arctic Stratospheric Experiment

A radiative transfer model and observed temperature and ozone profiles are used to compute three-dimensional fields of heating rates for the Northern Hemisphere during 1989 Airborne Arctic Stratospheric Experiment. For a clear atmosphere, an average cooling of 0.2 to 0.4 K/day is computed in the regions of the ER-2 aircraft during flight days. Tropospheric clouds will increase the cooling by 0.1 to 0.2 K/day. These cooling rates are in good agreement with the diabatic cooling estimated from N2O data, Net heating rather than cooling is computed in the area of the ozone 'minihole' which had its maximum on 1/31/89 and 2/1/89 in the vicinity of the mission. On 1/31/89 the 50 and 30 mb net heating rates are 0.1 to 0.2 K/day for clear skies, and 0.05 to 0.1 K/day for cloudy skies.

Rosenfield, Joan E.↗

NASA NTRS1990

Small-scale waves encountered during AASE

Variability on scales of 200 km or less in the lower stratosphere is examined using potential temperature data collected during the AASE campaign. Enhanced variability is found over regions containing topography presumably due to gravity waves. The effect of gravity wave critical levels on topographically induced variability is examined. A significant reduction in variability is found when a critical level is present.

Bacmeister, Julio T.↗

NASA NTRS1990

Stratospheric constituent trends from ER-2 profile data

Trend analysis of the Airborne Arctic Stratospheric Expedition's ER-2 profile data reveals an average decrease in N2O on potential temperature isentropes which can be attributed to diabatic cooling of inner vortex air. This conclusion is independently supported by radiative transfer computations. Trends in ozone and water vapor over the same period are not consistent with the magnitude of the diabatic descent. After accounting for the diabatic motion (estimated from N2O), an additional 0.44 + or - 0.3 percent/day average anomalous O3 decrease above 440 K (about 20 km) is needed to balance the continuity equation. This ozone decrease suggests additional photochemical destruction of ozone in the presence of the high amounts of ClO observed during the mission. A 0.4 + or - 0.3 percent/day average anomalous increase in H2O is also observed near 420 K (about 18 km) which may be due to the evaporation of ice crystals falling from higher, colder stratospheric layers.

Schoeberl, Mark R.↗

NASA NTRS1990

Airborne measurements of stratospheric constituents over the Arctic in the winter of 1989

A Fourier transform spectrometer aboard the NASA DC-8 aircraft was used during the Airborne Arctic Stratospheric Expedition (AASE) to record infrared absorption spectra of the polar stratosphere. From these high resolution spectra, vertical column amounts above flight altitude were derived of O3, CH4, N2O, H2O, HCl, HF, NO, NO2, ClONO2, and HNO3 for eleven flights poleward of 60 deg N. In this paper, measurements on the flight of January 26, 1989 were derived when the flight path during the observations crossed from outside the polar vortex to inside. This allowed a clear comparison of the conditions of the air within the vortex with that outside. Observations of passive tracers such as CH4 and HF indicate that air of a certain composition within the polar vortex occurs at lower altitude than air outside. Within the vortex, markedly reduced columns of HCl and NO2. The ratio of HCl to HF column dropped from its typical midlatitude value of 4.5 to as low as 1.7 within the vortex, implying that the HCl had been chemically or physically removed from the air in the vortex. In contrast to the Antarctic observations, HNO3 values were elevated within the vortex.

Mankin, William G.↗

NASA NTRS1990

Reconstruction of O3 and N2O fields from ER-2, DC-8, and balloon observations

Measurements of N2O and O3 during the Airborne Arctic Stratospheric Expedition have been composited using the potential vorticity and potential temperature of each measurement as coordinates. For ozone, data sources included the ER-2 and balloon ozonesonde in situ measurements, DC-8 DIAL lidar, and Stratospheric Aerosol and Gas Experiment satellite profiles. For N2O, only ER-2 data were used. These chemical composites have been reconstructed onto average meteorological fields for the mission in a latitude-altitude cross section, yielding a picture of the chemical composition of the polar vortex during this period. Tracers inside the vortex show an apparent descent of about 2 km relative to those outside, resulting in an apparent chemical edge on isentropic and isobaric surfaces.

Schoeberl, Mark R.↗

NASA NTRS1990

Effects of atmospheric transport on column abundances of nitrogen and chlorine compounds in the arctic stratosphere

In the absence of heterogeneous processes, distributions of NO(y), HNO3, Cl(x) and HCl in the polar winter stratosphere should be determined by transport. A model simulating distributions of these species in the arctic for January and February 1989 is developed using observed fields of potential vorticity and potential temperature. Comparison of model results with column measurements from the DC-8 indicates conversion of NO(x) to HNO3, condensation of HNO3, conversion of HCl to CINO3, and conversion of HCl plus CINO3 to an unmeasured species. Heterogeneous processes strongly affect abundances of NO(y) and Cl(x) species in the winter arctic stratosphere.

Yatteau, John H.↗

NASA NTRS1990

Loss of ozone in the Arctic vortex for the winter of 1989

Measurements of ClO (Brune et al., 1990) acquired during the Airborne Arctic Stratospheric Expedition are used to infer concentrations of reactive chlorine (ClO + 2 x Cl2O2). Observed fields of potential temperature and potential vorticity are used to extrapolate in situ data to larger regions of the vortex. Calculated values of the loss rate of O3, based on estimates of reactive chlorine and measurements of BrO (Toohey et al., 1990), suggest that the loss of O3 was abut 12 pct for levels of the atmosphere with potential temperatures between 440 and 470 K over the 39 day duration of the ER-2 flights into the polar vortex. Calculated loss rates agree with observed rates of removal of O3, although significant uncertainties exist for each.

Salawitch, Ross J.↗

NASA NTRS1990

ER-2 mountain wave encounter over Antarctica - Evidence for blocking

Orographically forced large-amplitude gravity waves (mountain waves) encountered during the AAOE experiment by ER-2 on September 22, 1987 over Alexander Island (73-70 deg W, 69-72 deg S) were analyzed using a three-dimensional steady-state model of stratified flow over realistic topography, similar to the model used by Smith (1980). Taking into account the effects of low-level flow blocking, reasonable agreement was obtained between the model and observations, indicating that blocking may be an important feature of real flow over topography.

Bacmeister, Julio T.↗

NASA NTRS1989

Reconstruction of the constituent distribution and trends in the Antarctic polar vortex from ER-2 flight observations

The measurements of ozone, ClO, and N2O concentrations in the south polar region taken aboard the ER-2 aircraft during the Airborne Antarctic Ozone Experiment are analyzed using conservative coordinate transformations to potential temperature-N2O and potential temperature-potential vorticity space. The latter transformation is equivalent to interpreting trace species observations within the modified Lagrangian mean (MLM) coordinate system. The results show that the MLM transformed ozone concentration decreases at about 0.06 ppmv per day between 20- and 16-km altitude inside the polar vortex during the mid-August to mid-September period. These ozone changes are collocated with the region of high ClO concentration. Outside the chemically perturbed region, at the highest aircraft altitudes, ozone concentration systematically increases, suggesting a diabatic cooling of the order 0.3-0.6 K/day.

Schoeberl, Mark R.↗

NASA NTRS1989

Meteorological atlas of the Northern Hemisphere lower stratosphere for January and February 1989 during the Airborne Arctic Stratospheric Expedition

Northern Hemisphere meteorological data for the months of January and February 1989 in the lower stratosphere are shown. National Meteorological Center (NMC) data, and Total Ozone Mapping Spectrometer (TOMS) data are used to display polar stereographic projections of 100-mb temperatures, 50-mb temperatures, 50-mb geopotential heights, total ozone, and Ertel's potential vorticity (Epv) on both 400 K and 460 K isentropic surfaces. In addition, latitude/height cross sections at 10 E of balanced wind isotachs, wind vectors, potential temperature, and temperature are also shown. Horizontal traces of NASA ER-2 and DC-8 flight tracks are also included. Vertical profiles of NMC temperatures following flight paths of both aircraft are shown. In addition, vertical profiles of wind speed are contoured following the ER-2 for estimating the lateral penetration into the polar vortex, while vertical profiles of Ertel's potential vorticity are included for estimating the vertical penetration of the DC-8 into the stratosphere.

Newman, Paul A.↗

NASA NTRS1989

Quasi-biennial modulation of the Antarctic ozone depletion

The quasi-biennial oscillation (QBO) in total ozone and temperature has been extracted from 9 years of Total Ozone Mapping Spectrometer (TOMS) observations and National Meteorological Center (NMC) analyses. Years in which QBO-related variations in the total ozone and temperature are positive are found to correspond to years with smaller September Antarctic total ozone hole decline rates and vice versa. The QBO appears to be responsible for September decline rate deviations up to 0.4 Dobson units (DU) per day. Also, the QBO at mid-latitudes appears to be better correlated with the 30-mbar tropical QBO winds than with those at 50 mbar. Possible mechanisms that would explain these phenomena are discussed.

Lait, Leslie R.↗

NASA NTRS1988

Applications of asynoptic space - Time Fourier transform methods to scanning satellite measurements

A method proposed by Salby (1982) for computing the zonal space-time Fourier transform of asynoptically acquired satellite data is discussed. The method and its relationship to other techniques are briefly described, and possible problems in applying it to real data are outlined. Examples of results obtained using this technique are given which demonstrate its sensitivity to small-amplitude signals. A number of waves are found which have previously been observed as well as two not heretofore reported. A possible extension of the method which could increase temporal and longitudinal resolution is described.

Lait, Leslie R.↗

NASA NTRS1988

Fast, long-lived features in the polar stratosphere

The analysis method of Salby (1982) is applied to Stratospheric Sounding Unit brightness temperatures from the TIROS-N and NOAA-6 satellites. The resulting spectra are used to present further evidence for the wave two and three oscillations found by Prata (1984) and to demonstrate the existence of a wave four feature. Maps of synoptic reconstructions of the brightness temperature fields from the spectra are then used to further characterize the warm pools.

Lait, Leslie R.↗

NASA NTRS1988

The morphology and meteorology of Southern Hemisphere spring total ozone mini-holes

Two case studies of miniholes, rapid ozone decreases, noted in 1987 near the base of the Antarctic peninsula are studied using a digital filter. The results show a strong correlation of the total ozone minihole with a temperature minihole (a negative temperature perturbation), and a westward tilt with altitude of the temperature minihole. The ozone minihole is phase shifted both slightly to the east of a high in the geopotential height field and slightly to the west of a local low in the Ertel potential vorticity field.

Newman, Paul A.↗

NASA NTRS1988

The morphology and meteorology of Southern Hemisphere spring total ozone mini-holes

The purpose of this paper is to describe the properties of mini-hole events. Both Total Ozone Mapping Spectrometer (TOMS) data and National Meteorological Center (NMC) meteorological analyses will be used to determine the horizontal, vertical and temporal characteristics of the mini-holes. Mini-holes are rapidly developing (1 to 5 days), small horizontal scale (1000 to 3000 km) features which appear in the polar total ozone field during September and October of each year. Typically, a total of 1 to 6 mini-holes appear each year in either the Palmer penninsula region or over the East Antarctica ice sheet. The mini-holes do not develop over these two regions, but they intensify most dramatically there (possibly associated with the local orography). The mini-holes are associated with cold pools of air in the lower stratosphere, anti-cyclonic (geopotential height highs) disturbances to their west, high potential vorticity slightly to the east, and strong northward flow. These meteorological features are baroclinic, having a distinct westward tilt with increasing altitude.

Newman, Paul A.↗

NASA NTRS1988

The evolution of AAOE observed constituents with the polar vortex

One of the difficulties in determining constituent trends from the ER-2 flight data is the large amount of day to day variability generated by the motion of the polar vortex. To reduce this variability, the observations have been transformed into the conservative (Lagrangian) reference frames consisting of the coordinate pairs, potential temperature (PT) and potential vorticity (PV), or PT and N2O. The requirement of only two independent coordinates rests on the assumption that constituent distributions and their chemical processes are nearly zonal in that coordinate system. Flight data is used everywhere for these transformation except for potential vorticity. Potential vorticity is determined from level flight segments, and NMC PV values during flight dives and takeoffs are combined with flight data in a smooth fashion.

Schoeberl, Mark R.↗

NASA NTRS1988

The QBO and interannual variation in total ozone

Garcia and Soloman (1987) have noted that the October monthly mean minimum total ozone amounts south of 30 S were modulated by a quasibiennial oscillation (QBO) signal. The precise mechanism behind this effect, however, is unclear. Is the modulation brought about by the circulation-produced QBO signal in the ozone concentration itself, or does the temperature QBO modulate the formation of polar stratospheric clouds (PSCs), leading to changes in the chemically induced Antarctic spring ozone decline rate. Or is some other phenomenon involved. To investigate the means through which the QBO effect occurs, a series of correlation studies has been made between polar ozone and QBO signal in ozone and temperature.

Lait, Leslie R.↗

NASA NTRS1987

A search for fast planetary-scale instabilities in the equatorial stratosphere

A method proposed by Salby for computing space-time Fourier transforms of asynoptic satellite data has been applied to stratospheric brightness temperature measurements from January and February 1979 in a search for two fast-moving low-wavenumber instabilities predicted in a numerical study by Lynch. The method is capable of producing spectra down to periods of approximately one day with no distortion due to the asynopticity of the data. No spectral peaks corresponding to the predicted modes were found; taking the noise level as the upper limit for their amplitudes at the altitudes observed, an upper limit of approximately 0.6 to 1.2 degrees Kelvin may be set for their peak amplitudes near the mesopause.

Lait, Leslie R.↗