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NASA NTRS2012

Modeling Solar Zenith Angle Effects on the Polar Wind

We use the Polar Wind Outflow Model (PWOM) to study the geomagnetically quiet conditions in the polar cap during solar maximum. The PWOM solves the gyrotropic transport equations for O+, H+, and He+ along several magnetic field lines in the polar region in order to reconstruct the full 3D solution. We directly compare our simulation results to the data based empirical model of Kitamura et al. (2011) of electron density which is based on 63 months of Akebono satellite observations. The modeled ion and electron temperatures are also compared with a statistical compilation of quiet time data obtained by the EISCAT Svalbard Radar (ESR) and Intercosmos Satellites. The data and model agree reasonably well, albeit with some differences. This study shows that photoelectrons play an important role in explaining the differences between sunlit and dark results of electron density, ion composition, as well as ion and electron temperatures of the quiet time polar wind solution. Moreover, these results provide an initial validation of the PWOM s ability to model the quiet time "background" solution.

Glocer, A↗

NASA NTRS1996

Polar Vortex Conditions During the 1995-96 Artic Winter: Meteorology and MLS Ozone

The 1995-96 northern hemisphere (NH) winter was colder than any of the previous 17 NH winters, with temperatures continuously below the type 1 polar stratospheric cloud (PSC) threshold for over 2 1/2 months; upper tropospheric ridges in late Feb and early Mar 1996 led to the lowest observed NH winter lower stratospheric temperatures, and the latest observation of HN temperatures below the type 2 PSC threshold.

arctic↗

NASA NTRS1986

Simultaneous polar cap and magnetotail observations of intense polar rain

The significance of acceleration processes in accounting for the energies and temperatures of the electrons seen during periods of intense polar rain is investigated along with the role of the IMF and solar wind in controlling the polar rain. Evidence for an acceleration region is sought by comparing DMSP observations of the precipitating electrons over the polar cap with simultaneous ISEE 1 electron measurements in the conjugate tail lobe at distances between 10 and 22.6 earth radii. The second question is explored by examining the solar wind and IMF conditions during which the intense polar rain events occur. It is found that intense polar rain can pass through the tail lobes without undergoing acceleration between 22.6 earth radii and 800 km altitude.

Greenspan, M. E.↗

NASA NTRS1994

Preparation and characterization of poly (arylene ether isoxazole)s by fluoride ion-mediated aromatic nucleophilic displacement reactions

As part of a continuing effort to prepare novel thermally stable high-performance polymers, poly(arylene ether isoxazole)s have been prepared by fluoride ion-catalyzed aromatic nucleophilic substitution reactions with bis(trimethylsiloxyphenyl) isoxazoles and activated bisarylhalides in diphenyl sulfone. Initial investigation involving the preparation of these materials with isoxazole bisphenols and activated bisarylhalides in the presence of potassium carbonate indicated that, under reaction conditions necessary to prepare high-molecular-weight materials, the isoxazole monomer was converted to an enamino ketone. This side reaction was avoided by using fluoride as a base. However, trimethylsilyl ether derivatives of the isoxazole bisphenols were required in these polymerizations for the preparation of high-molecular-weight materials. Moderate to high inherent viscosity eta(sub inh): 0.43-0.87 dl/g) materials with good thermal stability (air: 409-477 C, helium: 435-512 C) can be prepared by the silyl ether method. Glass transition temperatures ranged from 182 to 225 C for polymers with phenyl pendants and from 170 to 214 C for those without. Molecular weight control by 2% endcapping and the incorporation of a phenyl pendant at the 4 position of the isoxazole is necessary to yield polymers soluble in polar aprotic solvents at room temperature. There is evidence, however, indicating the existence of crosslinks between the polymer chains when the silyl ether approach is utilized.

Herbert, C. G.↗

NASA NTRS1973

Microwave properties of n-type InSb in a magnetic field between 4 and 300 K.

A two-band conduction model is used to determine the properties of shallow-type impurity semiconductors in the presence of microwave and dc magnetic fields as a function of temperature. Measurements using cavity perturbation techniques are employed to determine the properties of n-type InSb and theoretical and experimental results between 4 and 300 K are compared. The hot-electron effect was found to be insignificant between 77 and 300 K, and the scattering mechanisms are dominated by acoustic and polar modes over the same temperature range.-

Eldumiati, I. I.↗

NASA NTRS1987

Reaction of chlorine nitrate with hydrogen chloride and water at Antarctic stratospheric temperatures

Laboratory studies of heterogeneous reactions important for ozone depletion over Antarctica are reported. The reaction of chlorine nitrate (ClONO2) with H2O and HCl on surfacers that simulate polar stratospheric clouds are studied at temperatures relevant to the Antarctic stratosphere. The gaseous products of the resulting reactions, HOCl, Cl2O, and Cl2, could readily photolyze in the Antarctic spring to produce active chlorine for ozone depletion. Furthermore, the additional formation of condensed-phase HNO3 could serve as a sink for odd nitrogen species that would otherwise scavenge the active chlorine.

Tolbert, Margaret A.↗

NASA NTRSDate not supplied

Polarization Difference - The Scientific Story Behind One Variable and Its Practical Applications

Cloud ice and snow microphysical characteristics play an important role in determining cloud radiative effect. They are also closely connected to the details of surface precipitation characteristics. Ice orientation is one microphysical property that is traditionally believed to have trivial impact on the weather systems/climate, and it is hard to measure from space. In this presentation, I will show how many scientific stories can be told from one variable – the brightness temperature difference between vertically-polarized and horizontally-polarized 166 GHz measurements from the Global Precipitation Measurement Microwave Imager (GPM-GMI). Through scrutinizing collocated CloudSat, GMI and GPM radar observations together with the aid of radiative transfer model simulations, we can not only tell apart the particle size, shape and orientation, but also understand the precipitation regime as well as the life stage of a a precipitation system. In the second half of my talk, I will showcase how this variable can be used for predicting precipitation flags and separating mixed-phase cloud from liquid and ice with the powerful machine learning/artificial intelligence (ML/AI) technique.

cloud ice and snow microphysical characteristics↗

NASA NTRS1985

Studies on Physical Properties of Snow Based on Multi Channel Microwave Radiometer

The analysis of the data observed over a snow field with a breadboard model of MSR (microwave scanning radiometer) to be installed in MOS-1 (Marine Observation Satellite-1) indicates that: (1) the influence of incident angle on brightness temperature is larger in horizontal polarization component than in vertical polarization component. The effect of incident angle depends upon the property of snow with larger value for dry snow; (2) the difference of snow surface configuration consisting of artifically made parallel ditches of 5 cm depth and 5 cm width with spacing of 10 and 30 cm respectively which are oriented normal to electrical axis do not affect brightness temperature significantly; and (3) there is high negative correlation between brightness temperature and snow depth up to the depth of 70 cm which suggests that the snow depth can be measured with a two channel microwave radiometer up to this depth.

Tsuchiya, K.↗

NASA NTRS1991

Titan's atmosphere from Voyager infrared observations. III - Vertical contributions of hydrocarbons and nitriles near Titan's north pole

Voyager 1 IR spectra have been used to infer the Titan north polar region minor stratospheric constituents' temperature structure and vertical distribution. The mixing ratios of the species C4H2, C2H6, C3H4, HCN, HC3N, and C2N2 increase with altitude, implying upper stratosphere (and higher) formation regions. When compared with abundances obtained near the equator, it is found that the HC3N and C2N2 nitriles, together with such hydrocarbons as C2H4, C3H4, and C4H2, are substantially enhanced over the north polar region. A factor-of-2 (minimum) depletion of CO2 relative to the equator is noted; it is judged that current photochemical models are inadequate bases for interpretation of these observations.

Coustenis, A.↗

NASA NTRS1995

UARS MLS observations of lower stratospheric ClO in the 1992-93 and 1993-94 Arctic winter vortices

Upper Atmosphere Research Satellite (UARS) Microwave Limb Sounder (MLS) measurements of lower stratospheric ClO during 1992-93 and 1993-94 Arctic winters are presented. Enhanced ClO in the 1992-93 winter was first observed in early December, and extensively during February when temperatures were continually low enough for polar stratospheric cloud (PSCs). Sporadic episodes of enhanced ClO were observed for most of the 1993-94 winter as minimum temperatures hovered near the PSC threshold, with largest ClO amounts occurring in early March after a sudden deep cooling in late February.

Waters, J. W.↗

NASA NTRS2010

The Peculiar Solar Minimum 23/24 Revealed by the Microwave Butterfly Diagram

The diminished polar magnetic field strength during the minimum between cycles 23 and 24 is also reflected in the thermal radio emission originating from the polar chromosphere. During solar minima, the polar corona has extended coronal holes containing intense unipolar flux. In microwave images, the coronal holes appear bright, with a brightness enhancement of 500 to 2000 K with respect to the quiet Sun. The brightness enhancement corresponds to the upper chromosphere, where the plasma temperature is approx.10000 K. We constructed a microwave butterfly diagram using the synoptic images obtained by the Nobeyama radioheliograph (NoRH) showing the evolution of the polar and low latitude brightness temperature. While the polar brightness reveals the chromospheric conditions, the low latitude brightness is attributed to active regions in the corona. When we compared the microwave butterfly diagram with the magnetic butterfly diagram, we found a good correlation between the microwave brightness enhancement and the polar field strength. The microwave butterfly diagram covers part of solar cycle 22, whole of cycle 23, and part of cycle 24, thus enabling comparison between the cycle 23/24 and cycle 22/23 minima. The microwave brightness during the cycle 23/24 minimum was found to be lower than that during the cycle 22/23 minimum by approx.250 K. The reduced brightness temperature is consistent with the reduced polar field strength during the cycle 23/24 minimum seen in the magnetic butterfly diagram. We suggest that the microwave brightness at the solar poles is a good indicator of the speed of the solar wind sampled by Ulysses at high latitudes..

Gopalswamy, Natchimuthuk↗

NASA NTRS2002

Spatial Patterns of Variability in Antarctic Surface Temperature: Connections to the Southern Hemisphere Annular Mode and the Southern Oscillation

The 17-year (1982-1998) trend in surface temperature shows a general cooling over the Antarctic continent, warming of the sea ice zone, with moderate changes over the oceans. Warming of the peripheral seas is associated with negative trends in the regional sea ice extent. Effects of the Southern Hemisphere Annular Mode (SAM) and the extrapolar Southern Oscillation (SO) on surface temperature are quantified through regression analysis. Positive polarities of the SAM are associated with cold anomalies over most of Antarctica, with the most notable exception of the Antarctic Peninsula. Positive temperature anomalies and ice edge retreat in the Pacific sector are associated with El Nino episodes. Over the past two decades, the drift towards high polarity in the SAM and negative polarity in the SO indices couple to produce a spatial pattern with warmer temperatures in the Antarctic Peninsula and peripheral seas, and cooler temperatures over much of East Antarctica.

Kwok, Ron↗

NASA NTRS2006

AIRS Observations of DomeC in Antarctica and Comparison with Automated Weather Stations (AWS)

We compare the surface temperatures at Dome Concordia (DomeC) deduced from AIRS data and two Automatic Weather Stations at Concordia Station: AWS8989 , which has been in operation since December 1996, and AWS.it, for which data are available between January and November 2005. The AWS8989 readings are on average 3 K warmer than the AWS.it readings, with a warmer bias in the Antarctic summer than in the winter season. Although AIRS measures the skin brightness temperature, while the AWS reports the temperature of the air at 3 meter above the surface, the AIRS measurements agree well with the AWS.it readings for all data and separately for the summer and winter seasons, if data taken in the presence of strong surface inversions are filtered out. This can be done by deducing the vertical temperature gradient above the surface directly from the AIRS temperature sounding channels or indirectly by noting that extreme vertical gradients near the surface are unlikely if the wind speed is more than a few meters per second. Since the AIRS measurements are very well calibrated, the agreement with AWS.it is very encouraging. The warmer readings of AWS8989 are likely due to thermal contamination of the AWS8989 site by the increasing activity at Concordia Station. Data from an AWS.it quality station could be used for the evaluation of radiometric accuracy and stability of polar orbiting sounders at low temperatures. Unfortunately, data from AWS.it was available only for a limited time. The thermal contamination of the AWS8989 data makes long-term trends deduced from AWS8989 and possibly results about the rapid Antarctic warming deduced from other research stations on Antarctica suspect. AIRS is the first hyperspectral infrared sounder designed in support of weather forecasting and climate research. It was launched in May 2002 on the EOS Aqua spacecraft into a 704 km altitude polar sun-synchronous orbit. The lifetime of AIRS, estimated before launch to be at least 5 years is, based on the latest evaluation, limited by the amount of attitude control gas on the EOS Aqua spacecraft, which is expected to last through 2015.

atmospheric↗

NASA NTRS1988

Photochemical trajectory modelling studies of the 1987 Antarctic spring vortex

Simulations of Antarctic ozone photochemistry performed using a photochemical model integrated along air parcel trajectories are described. This type of model has a major advantage at high latitudes of being able to simulate correctly the complex interaction between photolysis and temperature fields, which, because of the polar night cannot be represented accurately in a zonally averaged framework. Isentropic air parcel trajectories were computed using Meteorological Office global model analyses and forecast fields from positions along the ER-2 flight paths during the Airborne Antarctic Ozone Experiment in Austral Spring 1987. A photochemical model is integrated along these trajectories using the aircraft observations to initialize constituent concentrations. The model includes additional reactions of the ClO dimer and also bromine reactions, which are thought to play a significant role in Antarctica. The model also includes heterogeneous reactions which are invoked when the air parcel passes through a polar stratospheric cloud (PSC). The existence of a PSC is determined throughout the course of the model integration from the parcel temperature and the saturated vapour pressure of water over an assumed H2O/HNO3 mixture. The air parcel temperature is used to determine the saturated vapor pressure of HNO3 over the same mixture. Mixing ratios which exceed saturation result in condensation of the excess in the model and hence lead to a reduction of the amount of gas phase NO2 available for chemical reaction.

Austin, J.↗

NASA NTRS2000

AROTEL - An Airborne Ozone, Aerosol and Temperature Lidar

The AROTEL instrument is a collaboration between scientists at NASA, Goddard Space Flight Center and NASA Langley Research Center. The instrument was designed and constructed to be flown on the NASA DC-8, and to measure vertical profiles of ozone, temperature and aerosol. The instrument transmits radiation at 308, 355, 532, and 1064 nm. Depolarization is measured at 532 nm. In addition to the transmitted wavelengths, Raman scattered signals at 332 nm and 387 nm are also collected. The instrument was installed aboard the DC-8 for the SAGE III Ozone Loss and Validation Experiment (SOLVE) which deployed from Kiruna, Sweden, during the winter of 1999-2000 to study the polar stratosphere. During this time, profile measurements of polar stratospheric clouds, ozone and temperature were made. This paper provides an instrumental overview as an introduction to several data papers to be presented in the poster sessions. In addition to samples of the measurements, examples will be given to establish the quality of the various data products.

McGee, Thomas J.↗

NASA NTRS2003

South Polar Cryptic Region Revisited: THEMIS Observations

The early part of the Mars Global Surveyor mission provided good TES coverage of the Mars south polar region. These data allow mapping of the polar cap recession, surface and atmospheric temperatures, and albedo features found within the seasonal cap itself over Ls = 180 - 270 deg. During this period, the seasonal south polar cap retreated continuously and asymmetrically around the geographic pole, similar to the observations of Viking in 1976- 1977 [3]. A prominent albedo feature on the seasonal cap is a region that appears almost as dark as bare ground, yet remains cold. We refer to this region, generally located between latitudes 85 deg. S and 75 deg. S and longitudes 150 deg. W and 310 deg. W, as the Cryptic region.

Titus, T. N.↗

NASA NTRS2004

Detecting the Recovery of the Antarctic Ozone Hole

The Antarctic ozone hole develops each year and culminates by early Spring. Antarctic ozone values have been monitored since 1979 using satellite observations from the TOMS instrument. The severity of the hole has been assessed from TOMS using the minimum total ozone value from the October monthly mean (depth of the hole) and by calculating the average size during the September-October period. Ozone is mainly destroyed by halogen catalytic cycles, and these losses are modulated by temperature variations in the collar of the polar lower stratospheric vortex. In this presentation, we show the relationships of halogens and temperature to both the size and depth of the hole. Because atmospheric halogen levels are responding to international agreements that limit or phase out production, the amount of halogens in the stratosphere should decrease over the next few decades. Using projections of halogen levels combined with age-of-air estimates, we find that the ozone hole is recovering at an extremely slow rate and that large ozone holes will regularly recur over the next 2 decades. We will show estimates of both when the ozone hole will begin to show first signs of recovery, and when the hole will fully recover to pre-1980 levels.

Newman, Paul A.↗

NASA NTRS2005

When Will the Antarctic Ozone Hole Recover?

Newman, Paul A.↗