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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

The quasi-biennial oscillation in atmospheric ozone

It is noted that the region of strongest relationship between tropical stratospheric zonal winds and total ozone (that is, maximum ozone associated with strong west winds) is in the tropics, in the midlatitudes of the Southern Hemisphere, and, it is thought, at high latitudes of the Northern Hemisphere. The observed period of the ozone quasi-biennial oscillation (QBO) decreases from 27 months at the equator to approximately 24 months in midlatitudes, possibly due to local modification of the QBO, as it propagates poleward. In the tropics the ozone variation is seen to be nearly in phase with the tropical wind QBO while at middle and high latitudes of the Northern Hemisphere and midlatitudes of the Southern Hemisphere and ozone oscillation seems to lag the wind oscillation by about 12-14 months. The out-of-phase relationship at middle and high latitudes indicates a possible interaction between the tropical stratosphere QBO in zonal winds and the annual variation in the poleward transport of ozone by quasi-horizontal eddies.

Oltmans, S. J.↗
NASA NTRS1987

Distribution of flares on the sun - Superactive regions and active zones of 1980-1985

The author analyzed coordinates of energetic solar flares observed with the hard X-ray burst spectrometer during the period from February 1980 through August 1985. A small number of 'superactive regions' produced the majority of the major flares during this period. There exist active zones, in which the flare occurrence rate is much higher. Two active zones are in the northern hemisphere, and two are in the southern hemisphere. The longitudinal separation of the two active zones in the same hemisphere is about 180 deg, but tha active zones of the southern hemisphere are misaligned from those of the northern hemisphere by about 80 deg. The rotation period of the active zones is 26.75 d. Active zones last several years or longer. There is a hint of active centers rotating at a period of 23.7 d.

Bai, Taeil↗
NASA NTRS2005

A Model Assessment of Satellite Observed Trends in Polar Sea Ice Extents

For more than three decades now, satellite passive microwave observations have been used to monitor polar sea ice. Here we utilize sea ice extent trends determined from primarily satellite data for both the Northern and Southern Hemispheres for the period 1972(73)-2004 and compare them with results from simulations by eleven climate models. In the Northern Hemisphere, observations show a statistically significant decrease of sea ice extent and an acceleration of sea ice retreat during the past three decades. However, from the modeled natural variability of sea ice extents in control simulations, we conclude that the acceleration is not statistically significant and should not be extrapolated into the future. Observations and model simulations show that the time scale of climate variability in sea ice extent in the Southern Hemisphere is much larger than in the Northern Hemisphere and that the Southern Hemisphere sea ice extent trends are not statistically significant.

Vinnikov, Konstantin Y.↗
DOE OSTI2026

A Mountain Glacier Perspective on the Bipolar Seesaw

A global record of mountain glacier terminations during the last deglaciation (∼19–11 ka) dated by a large, uncurated data set of cosmogenic-nuclide exposure ages highlights a statistically significant asynchrony in termination ages between the Northern and Southern Hemispheres. This interhemispheric offset in the timing of glacier terminations is consistent with previously correlated ice core records that show a systematic interhemispheric lag in the timing of abrupt climate events, with the Southern Hemisphere leading the Northern Hemisphere by ∼300–3,500 years. Our analysis (a) aggregates cosmogenic-nuclide exposure ages from a global data set of moraines to discern climatically driven peaks in moraine emplacement events, and (b) utilizes a Monte Carlo simulation based on a null hypothesis that moraine emplacement is interhemispherically synchronous to estimate the statistical significance of the observed offset. The observed lag of Northern Hemisphere emplacement events compared to the Southern Hemisphere is statistically significant and is consistent with the “bipolar seesaw” pattern observed in ice core records.

58 GEOSCIENCES↗
NASA NTRS1977

Soft diffuse X-rays in the southern galactic hemisphere

A map is presented of the soft X-ray diffuse background flux in the C band (approximately 0.13-0.28 keV) covering almost all of the southern galactic hemisphere. A comparison at constant galactic latitude of both C band and B band (about 0.1-0.18 keV) soft X-ray data with neutral-hydrogen maps shows that the intensity does decrease with increasing neutral-hydrogen column density but in a manner that is inconsistent with photoelectric absorption. It is suggested that the inverse correlation is a displacement effect. X-ray emission regions appear to be where the cool gas is not. Further, the evidence against photoelectric absorption implies that the bulk of the cool gas is beyond the X-ray emitting regions. Fewer than 10 to the 20th power H atoms per sq cm can be between the sun and the X-ray emitting regions. The sun appears to be surrounded by a soft X-ray emission region consisting of gas at a temperature of about 1 million K.

Sanders, W. T.↗
NASA NTRS2020

The Warm Gas in the MW: A Kinematical Model

We develop a kinematical model for the Milky Way Si IV-bearing gas to determine its density distribution and kinematics. This model is constrained by a column density line-shape sample extracted from the Hubble Space Telescope/Cosmic Origins Spectrograph archival data, which contains 186 active galactic nucleus sight lines. We find that the Si IV ion density distribution is dominated by an extended disk along the z-direction (above or below the midplane), i.e., n(z) = n0 exp(-(z z/0 ) 0.82 , where z0 is the scale height of - 6.3+1.5 -1.6 kpc (northern hemisphere) and 3.6+0.9 -1.0 kpc (southern hemisphere). The density distribution of the disk in the radial direction shows a sharp edge at 15–20 kpc given by, n(rXY) = n0 exp(-(rXY/r0) 3.36 , where r0≈12.5±0.6 kpc. The difference of density distributions over rXY and z directions indicates that the warm gas traced by Si IV is mainly associated with disk processes (e.g., feedback or cycling gas) rather than accretion. We estimate the mass of the warm gas (within 50 kpc) is log(M(50kpc) M(sun)) ≈ 8.1 (assuming Z≈0.5 Z(sun)), and a 3σ upper limit of log(M(250kpc) M(sun)) ≈ 9.1 (excluding the Magellanic system). Kinematically, the warm gas disk is nearly co-rotating with the stellar disk at vrot = 215 ± 3 km s-1, which lags the midplane rotation by about 8 km s-1 kpc-1 (within 5 kpc). Meanwhile, we note that the warm gas in the northern hemisphere has significant accretion with vacc of 69±7 km s-1 at 10 kpc (an accretion rate of -0.60+0.13- 0.11 M(sun) yr-1), while in the southern hemisphere, there is no measurable accretion, with an upper limit of 0.4M(sun) yr−1.

Zhijie Qu↗
DOE OSTI2024

Near-global summer circulation response to the spring surface temperature anomaly in Tibetan Plateau –– the GEWEX/LS4P first phase experiment

Subseasonal to seasonal (S2S) prediction of droughts and floods is one of the major challenges of weather and climate prediction. Recent studies suggest that the springtime land surface temperature/subsurface temperature (LST/SUBT) over the Tibetan Plateau (TP) can be a new source of S2S predictability. The project “Impact of Initialized Land Surface Temperature and Snowpack on Subseasonal to Seasonal Prediction (LS4P)” was initiated to study the impact of springtime LST/SUBT anomalies over high mountain areas on summertime precipitation predictions. The present work explores the simulated global scale response of the atmospheric circulation to the springtime TP land surface cooling by 16 current state-of-the-art Earth System Models (ESMs) participating in the LS4P Phase I (LS4P-I) experiment. The LS4P-I results show, for the first time, that springtime TP surface anomalies can modulate a persistent quasi-barotropic Tibetan Plateau-Rocky Mountain Circumglobal (TRC) wave train from the TP via the northeast Asia and Bering Strait to the western part of the North America, along with the springtime westerly jet from TP across the whole North Pacific basin. The TRC wave train modulated by the TP thermal anomaly play a critical role on the early summer surface air temperature and precipitation anomalies in the regions along the wave train, especially over the northwest North America and the southern Great Plains. The participant models that fail in capturing the TRC wave train greatly under-predict climate anomalies in reference to observations and the successful models. These results suggest that the TP LST/SUBT anomaly via the TRC wave train is the first order source of the S2S variability in the regions mentioned. Furthermore, the TP surface temperature anomaly can influence the Southern Hemispheric circulation by generating cross-equator wave trains. However, the simulated propagation pathways from the TP into the Southern Hemisphere show large inter-model differences. More dynamical understanding of the TRC wave train as well as its cross-equator propagation into the Southern Hemisphere will be explored in the newly launched LS4P phase II experiment.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2004

Depths and Geologic Setting of Northern Hemisphere Gullies (and Comparison to Their Southern Counterparts)

Gullies are recognized as having an incised (often sinuous) channel, alcove, and apron morphology as defined. Previous detailed work has focused on the characteristics of southern hemisphere gullies; here we examine the distribution, morphology and depth of northern hemisphere gullies. Gully locations (both hemispheres) were compiled from the literature, not a global search, and thus the gullies studied here are the subset of the whole for which corresponding MOLA tracks are available. We find that the heads of the majority of N. hemisphere gullies commence in a specific cliff-forming layer, and average 250 m below the local surface. This observation suggests that the rock layer has a genetic relationship to gullies and is difficult at present to reconcile with gully formation from snowmelt, which predicts no correlation to rock layers. Gully locations and depths correspond to specific geologic units. We propose that in addition to ground ice and a melting mechanism, gully formation requires groundwater flow along or within specific rock units.

Gilmore, Martha S.↗
NASA NTRS2001

The Annual Cycle of Water Vapor on Mars as Observed by the Thermal Emission Spectrometer

Spectra taken by the Mars Global Surveyor Thermal Emission Spectrometer (TES) have been used to monitor the latitude, longitude, and seasonal dependence of water vapor for over one full Martian year (March 1999-March 2001). A maximum in water vapor abundance is observed at high latitudes during mid-summer in both hemispheres, reaching a maximum value of approximately 100 pr-micrometer in the north and approximately 50 pr-micrometer in the south. Low water vapor abundance (<5 pr-micrometer) is observed at middle and high latitudes in the fall and winter of both hemispheres. There are large differences in the hemispheric (north versus south) and seasonal (perihelion versus aphelion) behavior of water vapor. The latitudinal and seasonal dependence of the decay of the northern summer water vapor maximum implies cross-equatorial transport of water to the southern hemisphere, while there is little or no corresponding transport during the decay of the southern hemisphere summer maximum. The latitude-longitude dependence of annually-averaged water vapor (corrected for topography) has a significant positive correlation with albedo and significant negative correlations with thermal inertia and surface pressure. Comparison of TES results with those retrieved from the Viking Orbiter Mars Atmospheric Water Detectors (MAWD) experiments shows some similar features, but also many significant differences. The southern hemisphere maximum observed by TES was not observed by MAWD and the large latitudinal gradient in annually-averaged water vapor observed by MAWD does not appear in the TES results.

Smith, Michael D.↗
NASA NTRS2014

Understanding the Formation and Evolution of Water Ice Clouds in the Hellas Basin During NH Summer on Mars

Water in the atmosphere of Mars moves between the northern and southern hemispheres seasonally, with north-to-south transport during northern hemisphere (NH) summer and south-to-north transport during southern hemisphere (SH) summer. Understanding the processes that control this seasonal transport of water is critical for understanding the current climate of Mars. Because water ice clouds both track and influence atmospheric circulations on a range of spatial scales, investigations about when and why clouds form enhance our knowledge of the water cycle as a whole. We focus here on a population of clouds that has recently been observed by the MARs Color Imager (MARCI) instrument on the Mars Reconnaissance Orbiter (MRO) to persist in the Hellas Basin throughout the majority of NH summer. Centered at 321 nm, Band 7 of the MARCI instrument is ideally suited for mapping water ice clouds on Mars because water ice is bright in the UV. It is notable that the clouds observed by MARCI in Hellas during NH summer are not as easily observed by the Thermal Emission Spectrometer (TES) on Mars Global Surveyor (MGS), which observes in the IR. We use a Global Climate Model (GCM) to investigate the dynamical mechanisms that control the formation and evolution of Hellas water ice clouds.

water ice clouds↗
NASA NTRS2007

Diurnal Lightning Distributions as Observed by the Optical Transient Detector (OTD) and the Lightning Imaging Sensor (LIS)

Data obtained from the OTD (April 1995 to March 2000) and LIS (December 1997 to December 2005) satellites (70 and 35 degree inclination low earth orbits, respectively) are used to statistically determine the number of flashes in the diurnal cycle both as a function of local and universal time. Also included are global flash density maps. The data are further subdivided by season, continental versus oceanic, night time versus day time, northern versus southern hemisphere, and other regions of interest. The data include corrections for detection efficiency and instrument view time. The data are compared with both the "Carnegie Curve" and the diurnal global thunderstorm contributions from thunderday statistics from different continents, and are found to agree closely in phase and amplitude with the global thunderday statistics. The analysis also indicates that the southern hemisphere spring (September to November) has larger amplitude than the southern hemisphere fall (March to May). This may be due to differences in the contribution from the Brazilian rain forest during these periods. In general, as highlighted by a difference analysis, more lightning is observed in local springtime than the fall for continental locations, while oceanic regions display an opposite effect. For some areas of the world, the peak of diurnal curve appears to be shifted to later in the evening.

Bailey, Jeff C.↗
NASA NTRS2000

Aerosol Radiative Forcing Derived From SeaWIFS - Retrieved Aerosol Optical Properties

To understand climatic implications of aerosols over global oceans, the aerosol optical properties retrieved from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) are analyzed, and the effects of the aerosols on the Earth's radiation budgets (aerosol radiative forcing, ARF) are computed using a radiative transfer model. It is found that the distribution of the SeaWiFS-retrieved aerosol optical thickness is distinctively zonal. The maximum in the equatorial region coincides with the Intertropical Convergence Zone, and the maximum in the Southern Hemispheric high latitudes coincides with the region of prevailing westerlies. The minimum aerosol optical thickness is found in the subtropical high pressure regions, especially in the Southern Hemisphere. These zonal patterns clearly demonstrate the influence of atmospheric circulation on the oceanic aerosol distribution. Over global oceans, aerosols reduce the annual mean net downward solar flux by 5.4 W m-2 at the top of the atmosphere and by 6.1 W m-2 at the surface. The largest ARF is found in the tropical Atlantic, Arabian Sea, Bay of Bengal, the coastal regions of Southeast and East Asia, and the Southern Hemispheric high latitudes. During the period of the Indonesian big fires (September-December 1997), the cooling due to aerosols is greater than 15 W m-2 at the top of the atmosphere and greater than 30 W m(exp -1) at the surface in the vicinity of the maritime continents. The atmosphere receives extra solar radiation by greater than 15 W m(exp -1) over a large area. These large changes in radiative fluxes are expected to have enhanced the atmospheric stability, weakened the atmospheric circulation, and augmented the drought condition during that period. It would be very instructive to simulate the regional climatic. The model-calculated clear sky solar flux at the top of the atmosphere is compared with that derived from the Clouds and the Earth's Radiant Energy System (CERES). The net downward solar flux of CERES is systematically larger than the model calculations by -3 W M-2. In the equatorial region, the CERES-derived net downward solar flux is even larger than the model calculations without including aerosols. It is possible that the CERES incorrectly identified regions of high humidity and high aerosol concentration as being cloud contaminated and, hence, overestimated the clear sky net downward solar flux.

Chou, Mong-Dah↗
NASA NTRS2009

Hydrogen Cyanide in the Upper Troposphere: GEM-AQ Simulation and Comparison with ACE-FTS Observations

We investigate the spatial and temporal distribution of hydrogen cyanide (HCN) in the upper troposphere through numerical simulations and comparison with observations from a space-based instrument. To perform the simulations, we used the Global Environmental Multiscale Air Quality model (GEM-AQ), which is based on the threedimensional Gobal multiscale model developed by the Meteorological Service of Canada for operational weather forecasting. The model was run for the period 2004-2006 on a 1.5deg x 1.5deg global grid with 28 hybrid vertical levels from the surface up to 10 hPa. Objective analysis data from the Canadian Meteorological Centre were used to update the meteorological fields every 24 h. Fire emission fluxes of gas species were generated by using year-specific inventories of carbon emissions with 8-day temporal resolution from the Global Fire Emission Database (GFED) version 2. The model output is compared with HCN profiles measured by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) instrument onboard the Canadian SCISAT-1 satellite. High values of up to a few ppbv are observed in the tropics in the Southern Hemisphere; the enhancement in HCN volume mixing ratios in the upper troposphere is most prominent in October. Low upper-tropospheric mixing ratios of less than 100 pptv are mostly recorded at middle and high latitudes in the Southern Hemisphere in May-July. Mixing ratios in Northern Hemisphere peak in the boreal summer. The amplitude of the seasonal variation is less pronounced than in the Southern Hemisphere. The comparison with the satellite data shows that in the upper troposphere GEM-AQ perform7s well globally for all seasons, except at northern hi gh and middle latitudes in surnmer, where the model has a large negative bias, and in the tropics in winter and spring, where it exhibits large positive bias. This may reflect inaccurate emissions or possible inaccuracies in the emission profile. The model is able to explain most of the observed variability in the upper troposphere HCN field, includin g the interannual variations in the observed mixing ratio. A complementary comparison with daily total columns of HCN from two middle latitude ground-based stations in Northern Japan for the same simulation period shows that the model captures the observed seasonal variation and also points to an underestimation of model emissions in the Northern Hemisphere in the summer. The estimated average global emission equals 1.3 Tg N/yr. The average atmospheric burden is 0.53 Tg N, and the corresponding lifetime is 4.9 months.

Lupu, A.↗
NASA NTRS1996

Chlorine Deactivation in the Lower Stratospheric Polar Regions during late Winter: Results from UARS

Recovery from enhanced chlorine conditions in the lower stratospheric polar regions of both hemispheres is investigated using data from the Upper Atmosphere Research Satellite (UARS). Microwave Limb Sounder (MLS) measurements of ClO within the polar vortices are used to infer ClO(sub x) (ClO + 2Cl202) abundances that are then correlated with simultaneous Cryogenic Limb Array Etalon Spectrometer (CLAES) measurements of ClON02 and Halogen Occultation Experiment (HALOE) measurements of HCl obtained starting within 5 days of the end of the MLS and CLAES high-latitude observing periods in each hemisphere. Time series of vortex-averaged mixing ratios are calculated on two potential temperature surfaces (585 K and 465 K) in the lower stratosphere for approximately month-long intervals during late winter: August 17 - September 17, 1992, in the southern hemisphere and February 12 - March 16, 1993, in the northern hemisphere. The observed mixing ratios are adjusted for the effects of vertical transport using diabatic vertical velocities estimated from CLAES tracer data. In the northern hemisphere, the decrease in ClO, is balanced on both surfaces by an increase in ClON02- In the southern hemisphere, continuing polar stratospheric cloud activity prevents ClO from undergoing sustained decline until about September 3. In contrast to the northern hemisphere, there is no significant chemical change in vortex-averaged ClON02 at 465 K, and there is an apparent decrease in ClON02 at 585 K, even after the enhanced ClO abundances have started to recede. Results from the SLIMCAT chemical transport model initialized with UARS data and run with OH + ClO yields HCl + 02 as an 8% channel suggest that the primary recovery product in the south during this time period is not ClON02, but HCl. HALOE HCl mixing ratios are extrapolated back to the time of the MLS and CLAES data. At 585 K, the chlorine budget can be made to balance by extrapolating HCl back to a value of 0.6 parts per billion by volume (ppbv) at the beginning of the study period; at 465 K, the contribution from extrapolated HCl is not sufficient to offset the loss in ClOx, and there is a slight imbalance between the decrease in reactive chlorine and the change in chlorine reservoirs. The difficulty in closing the chlorine budget in the southern hemisphere may arise from complications caused by ongoing activation, incomplete photochemical assumptions, and/or inadequate data quality.

Santee, M. L.↗
NASA NTRS1985

Satellite observations of the nitric oxide dayglow Implications for the behavior of mesospheric and lower-thermospheric odd nitrogen

The solar backscattered ultraviolet spectral radiometer on the Nimbus 7 satellite routinely measures fluorescence emissions from the nitric oxide (1, 4) gamma band that are imposed on the large Rayleigh-scattered signal in the wavelength range 255-256 nm. The gamma band feature, when isolated from the background radiance, provide information on the seasonal and latitudinal variations in the nitric oxide column abundance over the altitude region from 40 to 45 km upward through the thermosphere. At latitudes from 30 deg to 45 deg in the Northern Hemisphere the measurements show an annual cycle with maximum nitric oxide abundance in summer. The Southern Hemisphere pattern is qualitatively similar to this, although the amplitude of the seasonal variation is substantially smaller. The most prominent feature of the data base is a large maximum in nitric oxide emission that develops poleward of 45 deg latitude in both Hemispheres during late autumn and early winter. These maxima dissipate rapidly as spring approaches and are no longer evident in the data for Northern Hemisphere March and Southern Hemisphere September.

Frederick, J. E.↗
NASA NTRS2014

Mercury's Surface Magnetic Field Determined from Proton-Reflection Magnetometry

Solar wind protons observed by the MESSENGER spacecraft in orbit about Mercury exhibit signatures of precipitation loss to Mercury's surface. We apply proton-reflection magnetometry to sense Mercury's surface magnetic field intensity in the planet's northern and southern hemispheres. The results are consistent with a dipole field offset to the north and show that the technique may be used to resolve regional-scale fields at the surface. The proton loss cones indicate persistent ion precipitation to the surface in the northern magnetospheric cusp region and in the southern hemisphere at low nightside latitudes. The latter observation implies that most of the surface in Mercury's southern hemisphere is continuously bombarded by plasma, in contrast with the premise that the global magnetic field largely protects the planetary surface from the solar wind.

loss cone↗
NASA NTRS1997

The Role of Sea Ice in 2 x CO2 Climate Model Sensitivity: Hemispheric Dependencies - Part 2

How sensitive are doubled CO2 simulations to GCM control-run sea ice thickness and extent? This issue is examined in a series of 10 control-run simulations with different sea ice and corresponding doubled CO2 simulations. Results show that with increased control-run sea ice coverage in the Southern Hemisphere, temperature sensitivity with climate change is enhanced, while there is little effect on temperature sensitivity of (reasonable) variations in control-run sea ice thickness. In the Northern Hemisphere the situation is reversed: sea ice thickness is the key parameter, while (reasonable) variations in control-run sea ice coverage are of less importance. In both cases, the quantity of sea ice that can be removed in the warmer climate is the determining factor. Overall, the Southern Hemisphere sea ice coverage change had a larger impact on global temperature, because Northern Hemisphere sea ice was sufficiently thick to limit its response to doubled CO2, and sea ice changes generally occurred at higher latitudes, reducing the sea ice-albedo feedback. In both these experiments and earlier ones in which sea ice was not allowed to change, the model displayed a sensitivity of -0.02 C global warming per percent change in Southern Hemisphere sea ice coverage.

Rind, D.↗
NASA NTRS1995

Seasonal variations in the atmospheric distribution of a reactive chlorine compound, tetrachloroethene (CCl2 = CCl2)

Tropospheric mixing ratios of CCl2 = CCl2 were measured at remote surface locations in the Pacific between 71 deg N and 47 deg S during September and December of 1989, and March and June of 1990. The observed gradient of decreasing concentrations from the northern to the southern hemisphere, and very low concentrations in the southern hemisphere throughout the year, indicates a predominant input from the northern hemisphere. Seasonal measurements in the northern hemisphere showed maximum CCl2 = CCl2 concentrations occurring in the late summer. This distinct seasonal variation is strongly coupled to the atmompheric abundance of hydroxyl radical, the only important species responsible for CCl2 = CCl2 removal. With the estimated global CCl2 =CCl2 emissions, the lifetime is calculated to be about 5.4 months which is in good agreement with the 4.0 month estimate obtained from the inverse ratio of its measured hydroxyl reaction rate constant compared with that of methyl-chloroform CH3CCl3.

Wang, Charles J.-L.↗