Search NASA⌕ Search

SEARCH · Search NASA

Results for “interhemispheric”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Chemistry of the global troposphere - Fluorocarbons as tracers of air motion

Winds and convective mixing from a general circulation model of the atmosphere have been applied in a chemical tracer model (CTM) to simulate the global distribution and temporal variability of chlorofluorocarbons (CFCs). The seasonal cycle in moist convection, with maximum activity over continents in summer, leads to an annual cycle in the surface concentration of CFCs. Emissions are retained in the lowest levels of the atmosphere during winter, and surface concentrations peak near sources. In this season, CFCs from European sources are carried by low-level winds into the Arctic. During summer, vertical exchange is more efficient, and pollutants are transported more rapidly to the middle atmosphere. Consequently, concentrations of CFCs during summer are relatively low near the surface and elevated in the middle troposphere. Time series analysis of data from Adrigole, Ireland, indicates that the model accurately simulates long-range transport of air pollution. The model reproduces global distributions and trends for CFC-11 and CFC-12 observed by the ALE experiment; however, subgrid diffusion must be introduced into the model in order to reproduce the observed interhemispheric gradient. Interhemispheric exchange occurs mainly in the upper tropical troposphere, producing a profile which increases with altitude in the Southern Hemisphere, in agreement with observations. The distribution of CFCs is such that it is necessary to apply important corrections to observations at surface stations in order to derive global distributions.

Prather, Michael↗
NASA NTRS1990

Mid- and low-latitude model of thermospheric emissions. I - O(+) (2P) 7320 A and N2 (2P) 3371 A

This paper presents an interhemispherically coupled model of airglow emissions of the O(+) (2P) metastable state (7320 A) and the 0-0 band of the N2 second positive system (3371 A), covering mid- and low-latitudes. The model produces volume emission rates as a function of altitude, latitude, longitude, and local time for any selected data and solar and magnetic conditions, and, thus, can be used to provide three-dimensional maps of the selected emission for comparison with data obtained from orbiting vehicles. The semiglobal graphical maps of the 7320 A and 3371 A emissions illustrate the seasonal, diurnal, and solar cyclic variations on a scale that covers mid- and low-latitudes, as well as the effects of interhemispheric coupling (conjugate photoelectrons). It is shown that, in both cases, conjugate photoelectrons result in excitation at mid- to high- nighttime-latitudes in the winter hemisphere.

Torr, Marsha R.↗
NASA NTRS1992

Three-dimensional simulations of atmospheric methyl chloroform - Effect of an ocean sink

A global three-dimensional chemical tracer model of the distribution and seasonal cycles of the surface concentration of CH3CCl3 is compared with surface observations from the Atmospheric Lifetime Experiment (ALE) for the years 1980-1985. Two-dimensional OH distributions calculated by a photochemical model are empirically adjusted from observed trends in the global average and the interhemispheric ratio of methyl chloroform. The effects of the recently discovered ocean sink for methyl chloroform were investigated. The model simulates the 5-year record of observations made at the five ALE sampling sites to generally within +/- 5 percent of the observed mean. The calculated average global lifetime of methyl chloroform is 5.7 +/- 0.3 years. The estimated global mean OH concentration is 6.5 +/- 0.4 x 10 exp 5/cu cm. However, the inclusion of the ocean sink does not significantly improve the simulation of the observed interhemispheric gradient of methyl chloroform. Atmospheric transport dominates the simulated CH3CCl3 seasonal cycle throughout the Northern Hemisphere but is less important in the Southern Hemisphere.

Tie, X.↗
NASA NTRS1995

Studies on Equatorial Shock Formation During Plasmaspheric Refilling

During the grant period from August 1, 1994 to October 31, 1995 we have continued to investigate the effects of plasma wave instabilities on the early stage plasmaspheric refilling. Since ion beams are the primary feature of the interhemispheric plasma flows during the early stage refilling, ion-beam driven instabilities and associated waves are of primary interest. The major findings of this research are briefly summarized here. After a systematic examination of the relevant plasma instabilities, we realized that when the interhemispheric plasma flows begin to interpenetrate at the equator, the most relevant plasma instability is the electrostatic ion cyclotron wave instability. Only at later stages the ion-acoustic instability may be affecting the plasma flow. An interesting property of the electrostatic ion cyclotron wave is that it heats ions perpendicular to the magnetic field. When the ions in the field-aligned flows are transversely heated, they are trapped in the magnetic flux tube, thus affecting the refilling process. The eic wave instability is a microprocess with scale length of the order of ion Larmor radius and the corresponding time scale is the ion cyclotron period. We have attempted to tackle the problem for the plasmaspheric refilling by incorporating the effects of eic wave instability on the mesoscale plasma flow when the properties of the latter exceeds the critical conditions for the former. We have compared the results on refilling from the model with and without the eic instability effects.

Singh, Nagendra↗
NASA NTRS1998

Prediction of Dynamical Impact of Changes in Stratospheric Ozone

Under this grant one paper by Lou et al and a second paper by Kindler et al is in journal. These papers both describe N2O simulations using UKMO and Goddard assimilated wind fields and comparisons of the results against CLAES N2O observations. The results of these studies indicate some of the difficulties of using the assimilated wind fields, and the vertical motions in particular, in simulating long term variations in trace gases in the stratosphere. On the other hand, qualitatively the results possess a number of features of the observations even on time scales longer than a month or two. More recently we have started to examine results obtained using NCAR models a 3D version of which also uses the UKMO assimilated wind fields. Calculations have already been made with their 2D model with emphasis on the seasonal cycle in ozone at high latitudes in the upper stratosphere. Simultaneously trends in stratospheric ozone have been studied in detail from SAGE and UARS observations. Moreover, observations of the trends since 1984 do not show a significant interhemispheric asymmetry in upper stratospheric ozone. Therefore any asymmetry in the trends must have occurred prior to the mid-eighties and would most likely have been related to interhemispheric differences in upper stratospheric temperature trends. Another activity has been to compile an ozone climatology from UARS and SAGE observations. This effort has been performed as part of a UARS team activity to assemble a climatology of all the UARS long-lived trace gases for 1992-1993.

Cunnold, Derek M.↗
NASA NTRS2003

Conjugate Auroral Imagery

Conjugate studies of high-latitude geomagnetic activity are central to understanding the (truly) global magnetospheric response to external perturbations, i.e. the solar wind, and the role of the ionosphere in modulating and coupling with the magnetosphere. Interhemispheric asymmetries as manifested in auroral emissions have been observed for over 40 years. Unfortunately, the nature of the problem has limited the type and extent of studies that can be performed to either conjugate ground based observations or comparison of space based images with all-sky cameras. Recently Frank and Sigwarth (2002) published results using unique simultaneous images from Polar of the northern and southern aurora, but these are necessarily limited to the nighttime and at oblique angles. However, conjunctive images made with the cameras from the Polar and IMAGE missions contain simultaneous conjugate images of the large-scale aurora under many and varying conditions. This rich data set provides an opportunity to study interhemispheric auroral asymmetries and investigate their occurrence as a function of solar wind conditions and ionospheric parameters such as conductivity. In order to use images of different scenes from each of these cameras, knowledge of their relative response is required. To that end, this paper will present preliminary results of comparing the images with emphasis on data from the Polar UVI LBH filters and the IMAGE FUV WIC.

Spann, Jim↗
NASA NTRS2005

Interannual Rainfall Variability in the Tropical Atlantic Region

Rainfall variability on seasonal and interannual-to-interdecadal time scales in the tropical Atlantic is quantified using a 25-year (1979-2003) monthly rainfall dataset from the Global Precipitation Climatology Project (GPCP). The ITCZ measured by monthly rainfall between 15-37.5 deg W attains its peak as moving to the northernmost latitude (4-10 deg N) during July-September in which the most total rainfall is observed in the tropical Atlantic basin (17.5 deg S-22.5 deg N, 15 deg-37.5 deg W); the ITCZ becomes weakest during January-February with the least total rainfall as it moves to the south. In contrast, rainfall variability on interannual to interdecadal time scales shows a quite different seasonal preference. The most intense interannual variability occurs during March-May when the ITCZ tends to be near the equator and becomes weaker. Significant, negative correlations between the ITCZ strength and latitude anomalies are observed during boreal spring and early summer. The ITCZ strength and total rainfall amount in the tropical Atlantic basin are significantly modulated by the Pacific El Nino and the Atlantic equatorial mode (or Atlantic Nino) particularly during boreal spring and summer; whereas the impact of the Atlantic interhemispheric mode is considerably weaker. Regarding the anomalous latitudes of the ITCZ, the influence can come from both local, i.e., the Atlantic interhemispheric and equatorial modes, and remote forcings, i. e., El Nino; however, a direct impact of El Nino on the latitudes of the ITCZ can only be found during April-July, not in winter and early spring in which the warmest SST anomalies are usually observed in the equatorial Pacific.

Gu, Guojun↗
NASA NTRS2007

Interannual Variability of Boreal Summer Rainfall in the Equatorial Atlantic

Tropical Atlantic rainfall patterns and variation during boreal summer [June-July-August (JJA)] are quantified by means of a 28-year (1979-2006) monthly precipitation dataset from the Global Precipitation Climatology Project (GPCP). Rainfall variability during boreal spring [March-April-May (MAM)] is also examined for comparison in that the most intense interannual variability is usually observed during this season. Comparable variabilities in the Intertropical Convergence Zone (ITCZ) strength and the basin-mean rainfall are found during both seasons. Interannual variations in the ITCZ's latitudinal location during JJA however are generally negligible, in contrasting to intense year-to-year fluctuations during MAM. Sea surface temperature (SST) oscillations along the equatorial region (usually called the Atlantic Nino events) and in the tropical north Atlantic (TNA) are shown to be the two major local factors modulating the tropical Atlantic climate during both seasons. During MAM, both SST modes tend to contribute to the formation of an evident interhemispheric SST gradient, thus inducing anomalous shifting of the ITCZ and then forcing a dipolar structure of rainfall anomalies across the equator primarily in the western basin. During JJA the impacts however are primarily on the ITCZ strength likely due to negligible changes in the ITCZ latitudinal location. The Atlantic Nino reaches its peak in JJA, while much weaker SST anomalies appear north of the equator in JJA than in MAM, showing decaying of the interhemispheric SST mode. SST anomalies in the tropical central-eastern Pacific (the El Nino events) have a strong impact on tropical Atlantic including both the tropical north Atlantic and the equatorial-southern Atlantic. However, anomalous warming in the tropical north Atlantic following positive SST anomalies in the tropical Pacific disappears during JJA because of seasonal changes in the large-scale circulation cutting off the ENSO influence passing through the mid-latitudes. Hence the anomalies associated with the tropical Pacific during JJA are forced through an anomalous Walker circulation primarily working on the western basin, and likely a lagged oceanic response in the equatorial region.

Gu, Guojun↗
NASA NTRS2009

Water Vapor, Temperature, and Ice Particles in Polar Mesosphere as Measured by SABER/TIMED and OSIRIS/Odin Instruments

Although many new details on the properties of mesospheric ice particles that farm Polar Mesospheric Clouds (PMCs) and also cause polar mesospheric summer echoes have been recently revealed, certain aspects of mesospheric ice microphysics and dynamics still remain open. The detailed relation between PMC parameters and properties of their environment, as well as interseasonal and interhemispheric differences and trends in PMC properties that are possibly related to global change, are among those open questions. In this work, mesospheric temperature and water vapor concentration measured by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite are used to study the properties of PMCs with respect to the surrounding atmosphere. The cloud parameters, namely location, brightness, and altitude, are obtained from the observations made by the Optical Spectrograph and Infrared Imager System (OSIRIS) on the Odin satellite. About a thousand of simultaneous common volume measurements made by SABER and OSIRIS in both hemispheres from 2002 until 2008 are used. The correlation between PMC brightness (and occurrence rate) and temperatures at PMC altitudes and at the mesopause is analysed. The relation between PMC parameters, frost point temperature, and gaseous water vapor content in and below the cloud is also discussed. Interseasonal and interhemispheric differences and trends in the above parameters, as well as in PMC peak altitudes and mesopause altitudes are evaluated.

Feofilov, A. G.↗
NASA NTRS2016

QBO Modulation of the Mesopause Gravity Wave Momentum Flux over Tierra del Fuego

The interannual variability of the mesosphere and lower thermosphere (MLT) gravity wave momentum flux over southern mid latitudes (53.7degS) has been studied using more than 7 years of meteor radar observations at Ro Grande, Argentina. A modulation, with periods similar to that of the equatorial stratospheric quasi-biennial oscillation (QBO), is observed in the vertical flux of zonal as well as meridional momentum. The QBO signal is largest in the zonal component during summer and is in phase with the stratospheric QBO at 50 hPa (approx. 21 km). The relation between the stratospheric QBO and the QBO modulation in the MLT gravity wave forcing (derived from the divergence of the momentum flux) was found to be consistent with that expected from the Holton-Tan effect coupled to the interhemispheric coupling mechanism. These results provide the first observational support for the existence of the midlatitude gravity wave forcing anomalies as hypothesized in the interhemispheric coupling mechanism.

De Wit, R. J.↗
NASA NTRS2014

The Carbon Tetrachloride (CCl4) Budget: Mystery or Not

Carbon tetrachloride (CCl4) is a major anthropogenic ozone-depleting substance and greenhouse gas and has been regulated under the Montreal Protocol. However, atmospheric observations show a very slow decline in CCl4 concentrations, inconsistent with the nearly zero emissions estimate based on the UNEP reported production and feedstock usage in recent years. It is now apparent that there are either unidentified industrial leakages, an unknown production source of CCl4, or large legacy emissions from CCl4 contaminated sites. In this paper we use a global chemistry climate model to assess the budget mystery of atmospheric CCl4. We explore various factors that affect the global trend and the gradient between the Northern and Southern hemispheres or interhemispheric gradient (IHG): emissions, emission hemispheric partitioning, and lifetime variations. We find a present-day emission of 30-50 Gg per yr and a total lifetime 25 - 36 years are necessary to reconcile both the observed CCl4 global trend and IHG.

CC14↗
NASA NTRS2021

Evaluating the Large-Scale Hydrological Cycle Response within the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) Ensemble

The mid-Pliocene (∼3 Ma) is one of the most recent warm periods with high CO2 concentrations in the atmosphere and resulting high temperatures, and it is often cited as an analog for near-term future climate change. Here, we apply a moisture budget analysis to investigate the response of the large-scale hydrological cycle at low latitudes within a 13-model ensemble from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). The results show that increased atmospheric moisture content within the mid-Pliocene ensemble (due to the thermodynamic effect) results in wetter conditions over the deep tropics, i.e., the Pacific intertropical convergence zone (ITCZ) and the Maritime Continent, and drier conditions over the subtropics. Note that the dynamic effect plays a more important role than the thermodynamic effect in regional precipitation minus evaporation (PmE) changes (i.e., northward ITCZ shift and wetter northern Indian Ocean). The thermodynamic effect is offset to some extent by a dynamic effect involving a northward shift of the Hadley circulation that dries the deep tropics and moistens the subtropics in the Northern Hemisphere (i.e., the subtropical Pacific). From the perspective of Earth's energy budget, the enhanced southward cross-equatorial atmospheric transport (0.22 PW), induced by the hemispheric asymmetries of the atmospheric energy, favors an approximately 1∘ northward shift of the ITCZ. The shift of the ITCZ reorganizes atmospheric circulation, favoring a northward shift of the Hadley circulation. In addition, the Walker circulation consistently shifts westward within PlioMIP2 models, leading to wetter conditions over the northern Indian Ocean. The PlioMIP2 ensemble highlights that an imbalance of interhemispheric atmospheric energy during the mid-Pliocene could have led to changes in the dynamic effect, offsetting the thermodynamic effect and, hence, altering mid-Pliocene hydroclimate.

mid-Pliocene↗
NASA NTRSDate not supplied

Observations of the Age of Air from the Northern Hemisphere Midlatitude Surface

Understanding and modeling the interhemispheric transport (IHT) of trace gases and aerosols is important for interpreting past (and projecting future) changes in atmospheric composition. One IHT measure -- the mean age since air was last at the Northern Hemisphere (NH) midlatitude surface – represents a fundamental property of tropospheric transport that can be estimated from measurements of sulfur hexafluoride (SF6). Here we use SF6 measurements obtained from the recent NASA Atmospheric Tomography Mission (ATom) to construct observational estimates of the mean age throughout the troposphere. We compare the ATom based ages, which span all four seasons during the period 2016-2018 over both the Pacific and Atlantic Oceans, with previous in situ-based estimates obtained from the HIAPER Pole‐to‐Pole Observations (HIPPO) project, which are available only for the Pacific. In order to interpret the observed variations in mean age and their relationship with the large-scale flow we use simulations of the Goddard Earth Observing System (GEOS) general circulation model, constrained with meteorological fields derived from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), performed over the entire MERRA-2 period (including ATom). We confirm results from previous studies showing that the model ages are biased old compared to the observational estimates. However, we also show that this model bias is reduced in more recent years, which we interpret in terms of changes in the latitudinal distribution of SF6 emissions over the 2000s.

interhemispheric transport (IHT)↗
NASA NTRS1972

Effects of surface anomalies on certain model generated meteorological histories

The Mintz-Arakawa 2-level general circulation model has been used in a series of experiments to compute the response of the model atmosphere to: (1) a positive sea surface temperature anomaly in the North Pacific Ocean in summer and in winter, (2) an identical anomaly in the South Pacific Ocean in the Southern Hemisphere winter, and (3) anomalous northward and southward displacements of the Northern Hemisphere snow line over the continents. In each case computations were carried out for 90 forecast days. Results are shown in terms of the differences between anomaly and control histories. Time series of certain regional response indices, including area-average sea level pressure and 600 mb circulation indices, as well as 30-day mean sea level pressure maps are used in the analysis. Of particular interest is the evidence of significant interhemisphere influence.

Spar, J.↗
NASA NTRS1973

Ogo 6 measurements of supercooled plasma in the equatorial exosphere.

Plasma measurements performed on Ogo 6 reveal electron and ion temperature values that on occasion appear to be well below the expected neutral gas temperature. The phenomenon is observed only at night above 500 km near the magnetic equator. It is suggested that the expansion cooling of the plasma is accomplished by downward motions of the F region plasma induced by winds or diffusion, by outward E x B drift, or more probably by the upward flow of plasma during interhemisphere transport along magnetic field lines. It is also suggested that preferential cooling of electrons because of their greater thermal conductivity should tend to give ion temperatures greater than electron temperatures during the postsunset cooling of the plasmasphere when photoelectrons are absent.

Hanson, W. B.↗
NASA NTRS1973

Some effects of surface anomalies in a global general circulation model.

The Mintz-Arakawa two-level general circulation model has been used in a series of experiments to compute the response of the atmosphere to certain persistent sea-surface temperature anomalies and to changes in the position of the continental Northern Hemisphere snow line over periods up to 90 days. Results are shown in terms of differences between anomaly and control histories are revealed by global, 30-day mean sea-level pressure maps, and time series of three regional indices of synoptic activity. The experiments show significant interhemispheric effects after about 1 month, phase shifts of 1 to 2 weeks in major cyclone developments, stronger reactions to sea-temperature anomalies in winter than in summer, and marked influence of the snow line on the winter monsoonal pressure difference between the continents and the North Atlantic Ocean.

Spar, J.↗
NASA NTRS1974

Behavior of atmospheric ozone determined from Nimbus satellite backscatter ultraviolet data

A substantial global data base on the spatial and temporal variations of high level atmospheric ozone distribution and total ozone amount for the time period 1970 through 1973 was obtained by the Backscatter Ultraviolet (BUV) instrument onboard the Nimbus 4 satellite. BUV total ozone data from all available orbits on each day of the period were processed to obtain zonal mean ozone amounts. Northern Hemisphere ozone and Southern Hemisphere ozone values are given, and the interhemispheric relationships identified. Vertical ozone profile information is interpreted to furnish data on seasonal total ozone changes. Selected ozone mixing ratio cross sections were analyzed, and the resulting zonally-symmetric patterns are presented.

Krueger, A. J.↗