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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Arctic polar stratospheric cloud measurements by means of a four wavelength depolarization lidar

A four wavelength depolarization backscattering lidar has been operated during the European Arctic Stratospheric Ozone Experiment (EASOE) in Sodankyl, in the Finnish Arctic. The lidar performed measurements during the months of December 1991, January, February and March 1992. The Finnish Meteorological Institute during the same period launched regularly three Radiosondes per day, and three Ozone sondes per week. Both Mt. Pinatubo aerosols and Polar Stratospheric Clouds were measured. The use of four wavelengths, respectively at 355 nm, 532 nm , 750 nm, and 850 nm permits an inversion of the lidar data to determine aerosol particle size. The depolarization technique permits the identification of Polar Stratospheric Clouds. Frequent correlation between Ozone minima and peaks in the Mt. Pinatubo aerosol maxima were detected. Measurements were carried out both within and outside the Polar Vortex.

Stefanutti, L.↗
NASA NTRS1994

Compendium of NASA data base for the Global Tropospheric Experiment's Arctic Boundary Layer Experiments ABLE-3A and ABLE-3B

The report provides a compendium of NASA aircraft data that are available from NASA's Global Tropospheric Experiment's (GTE) Arctic Boundary Layer Experiments (ABLE) conducted in July and August of 1988 (ABLE-3A) and 1990 (ABLE-3B). ABLE-3A flight experiments were based at Barrow and Bethel, Alaska, and included survey/transit flights to Thule, Greenland. ABLE-3B flight experiments were based at North Bay (Ontario) and Goose Bay, Canada, and included flights northward to Frobisher Bay, Canada. The primary purposes of the experiments were (1) the measurement of the flux of various trace gases from high-arctic ecosystems, (2) the elucidation of factors important to the production and destruction of ozone, and (3) the documentation of source and chemical signature of air common to and transported into the regions. The report provides a representation, in the form of selected data plots, of aircraft data that are available in archived format via NASA Langley's Distributed Active Archive Center. The archived data bases include data for other species measured on the aircraft as well as numerous supporting data, including meteorological observations/products, results from surface studies, satellite observations, and sondes releases.

Gregory, Gerald L.↗
NASA NTRS1994

Intrusions into the lower stratospheric Arctic vortex during the winter of 1991-1992

Investigations of the kinematics of the lower stratospheric Arctic vortex during the winter of 1991-1992 using the contour advection with surgery technique reveal three distinct events in which there was substantial intrusion of midlatitude air into the vortex, in apparent contradiction of the view that the polar vortex constitutes an isolated air mass. Two of these events, in late January and mid-February, were well documented. They were predicted in high-resolution forecasts by the European Centre for Medium-Range Weather Forecasts, most clearly in experimental forecasts with reduced diffusion. Direct confirmation of the presence of the intrusions and of their calculated locations was provided by aerosol observations from the airborne differential absorption laser lidar aboard the NASA DC-8, taken as part of the second Airborne Arctic Stratospheric Expedition campaign; aerosol-rich air of midlatitude origin was seen in the expected position of the intrusions. The reality of the February event was also confirmed by in situ measurements from the NASA ER-2. Such events may be significant for the chemical processes taking place within the winter vortex. The intrusions were evidently related to the meteorology of the northern stratosphere during this winter and in particular to persistent tropospheric blocking over the northeastern Atlantic Ocean and western Europe and concomitant ridging into the lower stratospheric vortex in this region. Nevertheless, preliminary investigations have indicated that such events are not uncommon in other northern hemisphere winters, although no such events were found in the southern hemisphere during the Antarctic winter of 1987.

Plumb, R. A.↗
NASA NTRS1994

Arctic ocean radiative fluxes and cloud forcing estimated from the ISCCP C2 cloud dataset, 1983-1990

Radiative fluxes and cloud forcings for the ocean areas of the Arctic are computed from the monthly cloud product of the International Satellite Cloud Climatology Project (ISCCP) for 1983-90. Spatially averaged short-wave fluxes are compared well with climatological values, while downwelling longwave fluxes are significantly lower. This is probably due to the fact that the ISCCP cloud amounts are underestimates. Top-of-the-atmosphere radiative fluxes are in excellent agreement with measurements from the Earth Radiation Budget Experiment (ERBE). Computed cloud forcings indicate that clouds have a warming effect at the surface and at the top of the atmosphere during winter and a cooling effect during summer. The net radiative effect of clouds is larger at the surface during winter but greater at the top of the atmosphere during summer. Overall the net radiative effect of clouds at the top of the atmosphere is one of cooling. This is in contrast to a previous result from ERBE data showing arctic cloud forcings have a net warming effect. Sensitivities to errors in input parameters are generally greater during winter with cloud amount being the most important paarameter. During summer the surface radiation balance is most sensitive to errors in the measurements of surface reflectance. The results are encouraging, but the estimated error of 20 W/sq m in surface net radiative fluxes is too large, given that estimates of the net radiative warming effect due to a doubling of CO2 are on the order of 4 W/sq m. Because it is difficult to determine the accuracy of results with existing in situ observations, it is recommended that the development of improved algorithms for the retrieval of surface radiative properties be accompanied by the simultaneous assembly of validation datasets.

Schweiger, Axel J.↗
NASA NTRS1994

Evolution of the 1991-1992 Arctic vortex and comparison with the Geophysical Fluid Dynamics Laboratory SKYHI general circulation model

Nitrous oxide (N2O) measured on board the ER-2 aircraft during the Airborne Arctic Stratospheric Expedition 2 (AASE 2) has been used to monitor descent of air inside the Arctic vortex between October 1991 and March 1992. Monthly mean N2O fields are calculated from the flight data and then compared with mean fields calculated from the high-resolution Geophysical Fluid Dynamics Laboratory general circulation model SKYHI in order to evaluate the model's simulation of the polar vortex. From late fall through winter the model vortex evolves in much the same way as the 1991-1992 vortex, with N2O gradients at the edge becoming progressively steeper. The October to March trends in N2O profiles inside the vortex are used to verify daily net heating rates in the vortex that were computed from clear sky radiative heating rates and National Meteorological Center temperature observations. The computed heating rates successfully estimate the descent of vortex air from December through February but suggest that before December, air at high latitudes may not be isolated from the midlatitudes. SKYHI heating rates are in good agreement with the computed rates but tend to be slightly higher (i.e., less cooling) due to meteorological differences between SKYHI and the 1991-1992 winter. Three ER-2 flights measured N2O just north of the subtropical jet. These low-midlatitude profiles show only slight differences from the high-midlatitude profiles (45 deg - 60 deg N), indicating strong meridional mixing in the midlatitude 'surf zone.' Mean midwinter N2O profiles inside and outside the vortex calculated from AASE 2 data are shown to be nearly identical to 1989 AASE profiles, pointing to the N2O/potential temperature relationship as an excellent marker for vortex air.

Strahan, S. E.↗
NASA NTRS1994

In situ measurements of nitric oxide, ozone, and aerosols in the Scandinavian Arctic stratosphere in January 1992

During the European Arctic Stratospheric Ozone Experiment (EASOE) the Arctic stratosphere was investigated with a set of instruments flown on a CNES high altitude balloon from ESRANGE, northern Sweden (67 deg 52 minutes N, 21 deg 4 minutes E) on January 22, 1992. The vertical profiles to an altitude of 30 km are presented for ozone, nitric oxide, aerosols, and the temperature. The ozone mixing ratio was less than 0.1 ppmv below 13 km, and increased significantly only above the 18.5 km level. The aerosol concentration profile shows a large peak between 13 km and 21 km, centered at 18.5 km, reaching as high as about 10 particles/cu cm. Above 24 km the aerosols were absent. Below 22 km, the NO mixing ratio was lower than 50 pptv; however it increased rapidly from 23 km with a sharp peak at 27 km. The rapid increase in NO occurs just at the altitude where the aerosol concentration falls below the detection limit: on this day, NO was present only in the absence of aerosols.

Aimedieu, P.↗
NASA NTRS1995

Isentropic mixing in the Arctic stratosphere during the 1992-1993 and 1993-1994 winters

Dynamic isolation of the winter Arctic circumpolar vortex during 1992-1993 and 1993-1994 (the second and third northern hemisphere winters of the UARS mission) is studied using quasi-horizontal isentropic trajectories. Ejection of vortex air and entrainment of mid-latitude air into the vortex are quantified and compared with climatological values obtained from the analysis of 16 Arctic winters. A number of unusual features of both winters are discussed. The most notable features are the anomalous isolation experienced by the vortex during December 1992 and the unusual degree of isolation and persistence of the vortex during February and March of both years. the 1992-1993 winter season is the most consistently isolated vortex on record. Only during January 1993, when entrainment is large, is this pattern of extreme isolation broken.

Dahlberg, Steven P.↗
NASA NTRS1993

Chemical Loss of Ozone in the Arctic Polar Vortex in the Winter of 1991-1992

In situ measurements of chlorine monoxide, bromine monoxide, and ozone are extrapolated globally, with the use of meteorological tracers, to infer the loss rates for ozone in the Arctic lower stratosphere during the Airborne Arctic Stratospheric Expedition II (AASE II) in the winter of 1991-1992. The analysis indicates removal of 15 to 20 percent of ambient ozone because of elevated concentrations of chlorine monoxide and bromine monoxide. Observations during AASE II define rates of removal of chlorine monoxide attributable to reaction with nitrogen dioxide (produced by photolysis of nitric acid) and to production of hydrochloric acid. Ozone loss ceased in March as concentrations of chlorine monoxide declined. Ozone losses could approach 50 percent if regeneration of nitrogen dioxide were inhibited by irreversible removal of nitrogen oxides (denitrification), as presently observed in the Antarctic, or without denitrification if inorganic chlorine concentrations were to double.

Salawitch, R. J.↗
NASA NTRS1998

Dehydration and Denitrification in the Arctic Polar Vortex During the 1995-1996 Winter

Dehydration of more than 0.5 ppmv water was observed between 18 and 19 km (theta about 450-465 K) at the edge of the Arctic polar vortex on February 1, 1996. More than half the reactive nitrogen (NO(sub y)) had also been removed, with layers of enhanced (sub y) at lower altitudes. Back trajectory calculations show that air parcels sampled inside the vortex had experienced temperatures as low as 188 K within the previous 12 days, consistent with a small amount of dehydration. The depth of the dehydrated layer (about 1 km) and the fact that trajectories passed through the region of ice saturation in one day imply selective growth of a small fraction of particles to sizes large enough (>10 micron) to be irreversibly removed on this timescale. Over 25% of the Arctic vortex in a 20-30 K range of theta is estimated to have been dehydrated in this event.

Hintsa, E. J.↗
NASA NTRS1998

Dehydration and Denitrification in the Arctic Polar Vortex During the 1995-1996 Winter

Dehydration of more than 0.5 ppmv water was observed between 18 and 19 km (0-450-465 K) at the edge of the Arctic polar vortex on February 1, 1996. More than half the reactive nitrogen (NO(y)) had also been removed, with layers of enhanced NO(y) at lower altitudes. Back trajectory calculations show that air parcels sampled inside the vortex had experienced temperatures as low as 188 K within the previous 12 days, consistent with a small amount of dehydration. The depth of the dehydrated layer (approximately 1 km) and the fact that trajectories passed through the region of ice saturation in one day imply selective growth of a small fraction of particles to sizes large enough (>10 microns) to be irreversibly removed on this timescale. Over 25% of the Arctic vortex in a 20-30 K range of 0 is estimated to have been dehydrated in this event.

Hintsa, E. J.↗
NASA NTRS1998

Dehydration and Denitrification in the Arctic Polar Vortex During the 1995-1996 Winter

Dehydration of more than 0.5 ppmv water was observed between 18 and 19 km (theta approximately 450-465 K) at the edge of the Arctic polar vortex on February 1, 1996. More than half the reactive nitrogen (NO(y)) had also been removed, with layers of enhanced NO(y) at lower altitudes. Back trajectory calculations show that air parcels sampled inside the vortex had experienced temperatures as low as 188 K within the previous 12 days, consistent with a small amount of dehydration. The depth of the dehydrated layer (approximately 1 km) and the fact that trajectories passed through the region of ice saturation in one day imply selective growth of a small fraction of particles to sizes large enough (>10 micrometers) to be irreversibly removed on this timescale. Over 25% of the Arctic vortex in a 20-30 K range Transport of theta is estimated to have been dehydrated in this event.

Hintsa, E. J.↗
NASA NTRS1996

Arctic Ozone Depletion Observed by UARS MLS During the 1994-95 Winter

During the unusually cold 1994-95 Arctic winter, the Microwave Limb Sounder observed enhanced chlorine monoxide (ClO) in late Dec and throughout Feb and early Mar. Late Dec ClO was higher than during any of the previous 3 years, consistent with the colder early winter. Between late Dec 1994 and early Feb 1995, 465 K (about 50 hPa) vortex-averaged ozone (03) decreased by about 15%, with local decreases of about 30%; additional local decreases of about 5% were seen between early Feb and early Mar. Transport calculations indicate that vortex-averaged chemical loss between late Dec and early Feb was about 20% at 465 K, with about 1/4 of that masked by downward transport of O3. This Arctic chemical O3 loss is not readily detectable in MLS column O3 data.

Manney, G. L.↗
NASA NTRS1999

Airborne Spectral Measurements of Surface-Atmosphere Anisotropy for Arctic Sea Ice and Tundra

Angular distributions of spectral reflectance for four common arctic surfaces: snow-covered sea ice, melt-season sea ice, snow-covered tundra, and tundra shortly after snowmelt were measured using an aircraft based, high angular resolution (1-degree) multispectral radiometer. Results indicate bidirectional reflectance is higher for snow-covered sea ice than melt-season sea ice at all wavelengths between 0.47 and 2.3 pm, with the difference increasing with wavelength. Bidirectional reflectance of snow-covered tundra is higher than for snow-free tundra for measurements less than 1.64 pm, with the difference decreasing with wavelength. Bidirectional reflectance patterns of all measured surfaces show maximum reflectance in the forward scattering direction of the principal plane, with identifiable specular reflection for the melt-season sea ice and snow-free tundra cases. The snow-free tundra had the most significant backscatter, and the melt-season sea ice the least. For sea ice, bidirectional reflectance changes due to snowmelt were more significant than differences among the different types of melt-season sea ice. Also the spectral-hemispherical (plane) albedo of each measured arctic surface was computed. Comparing measured nadir reflectance to albedo for sea ice and snow-covered tundra shows albedo underestimated 5-40%, with the largest bias at wavelengths beyond 1 pm. For snow-free tundra, nadir reflectance underestimates plane albedo by about 30-50%.

Arnold, G. Thomas↗
NASA NTRS2000

Arctic chemical Ozone Loss Observed by the AROTEL Instrument during the SOLVE Campaign, December 1999 - March 2000

During the winter of 1999-2000, the AROTEL instrument was deployed on the NASA DC-8 at Kiruna, Sweden for the SAGE III Ozone Loss Validation Experiment (SOLVE). Measurements of ozone, temperature and aerosols were made on 18 local science flights from December to March. Extremely low temperatures were observed throughout most of the Arctic vortex and polar stratospheric clouds were observed throughout the Arctic area during January. Significant ozone loss was measured after the sun began to rise on the vortex area in February. Ozone mixing ratios as low as 800 ppbv were observed during flights in March.

McGee, Thomas J.↗
NASA NTRS2000

Processes Controlling Water Vapor in the Winter Arctic Stratospheric Middleworld

Abstract: Water vapor in the winter arctic stratospheric middleworld (that part of the stratosphere with potential temperatures lower than the tropical tropopause) is important for two reasons: (1) the arctic middleworld is a source of air for the upper troposphere because of the generally downward motion, and thus its water vapor content helps determine upper tropospheric water, a critical part of the earth's radiation budget; and (2) under appropriate conditions, relative humidities will be large even to the point of stratospheric cirrus cloud formation, leading to the production of active chlorine species that could destroy ozone. On a number of occasions during SOLVE, clouds were observed in the stratospheric middleworld by the DC-8 aircraft. The relationship between ozone and CO from aircraft measurements taken during the early, middle and late part of the winter of 1999-2000 show that recent mixing with tropospheric air extends up to ozone values of about 350-450 ppbv. Above that level, the relationship suggests stratospheric air with minimal tropospheric influence. The transition is quite abrupt, particularly in early spring. Trajectory analyses are consistent with these relationships, with a significant drop-off in the percentage of trajectories with tropospheric PV values in their 10-day history as in-situ ozone increases above 400 ppbv. The water distribution is affected by these mixing characteristics, and by cloud formation. Significant cloud formation along trajectories occurs up to ozone values of about 400 ppbv during the early spring, with small, but nonzero probabilities extending to 550 ppbv. Cloud formation in the stratospheric middleworld is minimal during early and midwinter. Also important is the fact that, during early spring 30% of the trajectories near the tropopause (ozone values less than 200 ppbv) have minimum saturation mixing ratios less than 5 ppmv. Such parcels can mix out into the troposphere and could lead to very dry conditions in the upper troposphere at high latitudes during spring,

Pfister, Leonhard↗
NASA NTRS2000

Arctic Ocean

The Arctic Ocean is the smallest of the Earth's four major oceans, covering 14x10(exp 6) sq km located entirely within the Arctic Circle (66 deg 33 min N). It is a major player in the climate of the north polar region and has a variable sea ice cover that tends to increase its sensitivity to climate change. Its temperature, salinity, and ice cover have all undergone changes in the past several decades, although it is uncertain whether these predominantly reflect long-term trends, oscillations within the system, or natural variability. Major changes include a warming and expansion of the Atlantic layer, at depths of 200-900 m, a warming of the upper ocean in the Beaufort Sea, a considerable thinning (perhaps as high as 40%) of the sea ice cover, a lesser and uneven retreat of the ice cover (averaging approximately 3% per decade), and a mixed pattern of salinity increases and decreases.

Parkinson, Claire L.↗
NASA NTRS2000

Scaling Issues Between Plot and Satellite Radiobrightness Observations of Arctic Tundra

Data from generation of satellite microwave radiometer will allow the detection of seasonal to decadal changes in the arctic hydrology cycle as expressed in temporal and spatial patterns of moisture stored in soil and snow This nw capability will require calibrated Land Surface Process/Radiobrightness (LSP/R) model for the principal terrains found in the circumpolar Arctic. These LSP/R models can than be used in weak constraint. Dimensional Data Assimilation (DDA)of the daily satellite observation to estimate temperature and moisture profiles within the permafrost in active layer.

Kim, Edward J.↗
NASA NTRS1998

Dehydration and Denitrification in the Arctic Polar Vortex During the 1995-1996 Winter

Dehydration of more than 0.5 ppmv water was observed between 18 and 19 km (theta = 450-465 K) at the edge of the Arctic polar vortex on February 1, 1996. More than half the reactive nitrogen (NOy) had also been removed, with layers of enhanced NOy at lower altitudes. Back trajectory calculations show that air parcels sampled inside the vortex had experienced temperatures as low as 188 K within the previous 12 days, consistent with a small amount of dehydration. The depth of the dehydrated layer (approx. 1 km) and the fact that trajectories passed through the region of ice saturation in one day imply selective growth of a small fraction of particles to sizes large enough (>10 micrometers) to be irreversibly removed on this timescale. Over 25% of the Arctic vortex in a 20-30 K range of theta is estimated to have been dehydrated in this event.

Hintsa, E. J.↗