Multi-Output Approximate Control Variate Estimation for Enhanced Variance Reduction
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Thomas Dixon↗
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Sources of mesoscale variability of gravity waves. I - Topographic excitation. II - Frontal, convective, and jet stream excitation
The effect of topography as a source of mesoscale variability was investigated using aircraft measurements of winds and temperature collected during the Global Atmospheric Sampling Program, with results showing marked increases in the variance of zonal and meridional wind speeds and of potential temperature over rough terrain. In addition, four cases of mesoscale variance enhancements of horizontal velocity and temperature due to frontal activity, nonfrontal convection, and wind shear were studied. The implications of these episodic enhancements of variances for the vertical transports of energy and momentum are considered in the framework of the gravity wave theory.
Nastrom, Gregory D.↗
Analysis of Small-Scale Atmospheric Gravity Waves Using UARS MLS Radiance Measurements
Gravity waves play an important role in determining atmospheric circulation and small-scale mixing. Upper Atmosphere Research Satellite (UARS) Microwave Limb Sounder (MLS) 63-GHz radiances can be used to calculate small-scale wave variances at 30-80 km altitudes. The major results from this new data set are summarized in the following: (1) MLS radiance fluctuations are contributed mostly by gravity waves of small (about 100 km) horizontal and large (>10 km) vertical scales. (2) MLS observations show that variance enhancements are strongly correlated with the stratospheric polar vortices, tropospheric deep convection zones, and surface topography. (3) As expected for gravity wave propagation, the normalized wave variances grow exponentially with height in the stratosphere but saturate in the mesosphere. (4) The long-term variations of the wave variance are dominated by an annual cycle in the stratosphere and a semiannual cycle in the mesosphere. (5) Separate analyses of the ascending and descending measurements show that the variances are sensitive to wave propagation directions. The subtropical variances, which are associated with deep convection, are likely caused by the gravity waves that propagate upward and eastward in the westward background wind. Additional information contained in the original.
Wu, Dong L.↗
Stochastic dynamics of baroclinic waves
The maintenance of variance and attendant heat flux in linear, forced dissipative baroclinic shear flows subject to stochastic excitation is examined. The baroclinic problem, is intrinsically nonnormal and its stochastic dynamics is found to differ significantly from the more familiar stochastic dynamics of normal systems. When the shear is sufficiently great in comparison to dissipative effects, stochastic excitation supports highly enhanced variance levels in these nonnormal systems compared to variance levels supproted by the same forcing and dissipation in related normal systems. The eddy variance and associated heat flux are found to arise in response to transient amplification of a subset of forcing functions that obtain energy from the mean flow and project this energy on a distinct subset of response functions (EOFs) that are in turn distinct from the set of normal modes of the system. A method for obtaining the dominant forcing and response functions as well as the distribution of heat flux for a given flow is described.
Farrell, Brian F.↗
Nonlinear equilibration of localized instabilities on a baroclinic jet
Dynamical mechanisms underlying the equilibration of absolute instability are examined in a nonlinear, quasigeostrophic, two-layer model. The key to understanding the nonlinear equilibration is in recognizing that linear absolute instabilities can be stabilized both by a reduction of the vertical shear and by enhancement of the mean barotropic velocity. In a localized domain, the equilibration process proceeds with the creation of locally convectively unstable regions downstream, which encroach onto the locally absolutely unstable region until the local instability is suppressed. That local instabilities exist only if absolutely unstable regions span a minimum size is verified by eigenvalue calculations of three-dimensional flows. Numerical examples suggest that this critical size is at least 9000 km for a wide range of parameter values chosen to investigate the midlatitude storm tracks. Fluctuations arising from local absolute instability obtain maximum amplitude in the downstream convectively unstable regions rather than in the absolutely unstable regions themselves. Together, these results suggest that if an equilibrated absolute instability were to occur in midlatitudes, a zonal band of surface easterlies exceeding 900 km would be required and the associated enhanced variances would not be found coincident with the regions of absolute instability.
Delsole, Timothy M.↗
Variance and bias computation for enhanced system identification
A study is made of the use of a series of variance and bias confidence criteria recently developed for the eigensystem realization algorithm (ERA) identification technique. The criteria are shown to be very effective, not only for indicating the accuracy of the identification results (especially in terms of confidence intervals), but also for helping the ERA user to obtain better results. They help determine the best sample interval, the true system order, how much data to use and whether to introduce gaps in the data used, what dimension Hankel matrix to use, and how to limit the bias or correct for bias in the estimates.
Bergmann, Martin↗
Gravity Wave Variances and Propagation Derived from AIRS Radiances
As the first gravity wave (GW) climatology study using nadir-viewing infrared sounders, 50 Atmospheric Infrared Sounder (AIRS) radiance channels are selected to estimate GW variances at pressure levels between 2-100 hPa. The GW variance for each scan in the cross-track direction is derived from radiance perturbations in the scan, independently of adjacent scans along the orbit. Since the scanning swaths are perpendicular to the satellite orbits, which are inclined meridionally at most latitudes, the zonal component of GW propagation can be inferred by differencing the variances derived between the westmost and the eastmost viewing angles. Consistent with previous GW studies using various satellite instruments, monthly mean AIRS variance shows large enhancements over meridionally oriented mountain ranges as well as some islands at winter hemisphere high latitudes. Enhanced wave activities are also found above tropical deep convective regions. GWs prefer to propagate westward above mountain ranges, and eastward above deep convection. AIRS 90 field-of-views (FOVs), ranging from +48 deg. to −48 deg. off nadir, can detect large-amplitude GWs with a phase velocity propagating preferentially at steep angles (e.g., those from orographic and convective sources). The annual cycle dominates the GW variances and the preferred propagation directions for all latitudes. Indication of a weak two-year variation in the tropics is found, which is presumably related to the Quasi-biennial oscillation (QBO). AIRS geometry makes its out-tracks capable of detecting GWs with vertical wavelengths substantially shorter than the thickness of instrument weighting functions. The novel discovery of AIRS capability of observing shallow inertia GWs will expand the potential of satellite GW remote sensing and provide further constraints on the GW drag parameterization schemes in the general circulation models (GCMs).
AIRS↗
Signatures of shock drivers in the solar wind and their dependence on the solar source location
Solar wind and energetic ion observations following 40 interplanetary shocks with well-established solar source locations have been examined in order to determine whether signatures characteristic of the coronal material forming the shock driver are present. The signatures considered include magnetic-field-aligned bidirectional ion flows observed by the ISEE 3 and IMP 8 spacecraft; bidirectional solar wind electron heat fluxes; solar wind plasma proton and electron temperature depressions; low-beta plasma; enhanced, low-variance magnetic fields; and energetic ion depressions. Several shock driver signatures are commonly observed following shocks originating from within about 50 deg of central meridian, and are generally absent for other events. We conclude that shock drivers generally extend up to about 100 deg in longitude, centered on the solar source longitude. Since shocks from central meridian events are not usually associated with all the shock driver signatures examined, the absence of a driver cannot be confirmed from consideration of one of these signatures alone. We also find evidence that a few bidirectional energetic ion and solar wind electron heat flux events following shocks (in particular from far eastern sources) may occur on open field lines outside of shock drivers.
Richardson, I. G.↗
Global Gravity Wave Variances from Aura MLS: Characteristics and Interpretation
The gravity wave (GW)-resolving capabilities of 118-GHz saturated thermal radiances acquired throughout the stratosphere by the Microwave Limb Sounder (MLS) on the Aura satellite are investigated and initial results presented. Because the saturated (optically thick) radiances resolve GW perturbations from a given altitude at different horizontal locations, variances are evaluated at 12 pressure altitudes between 21 and 51 km using the 40 saturated radiances found at the bottom of each limb scan. Forward modeling simulations show that these variances are controlled mostly by GWs with vertical wavelengths z 5 km and horizontal along-track wavelengths of y 100-200 km. The tilted cigar-shaped three-dimensional weighting functions yield highly selective responses to GWs of high intrinsic frequency that propagate toward the instrument. The latter property is used to infer the net meridional component of GW propagation by differencing the variances acquired from ascending (A) and descending (D) orbits. Because of improved vertical resolution and sensitivity, Aura MLS GW variances are 5?8 times larger than those from the Upper Atmosphere Research Satellite (UARS) MLS. Like UARS MLS variances, monthly-mean Aura MLS variances in January and July 2005 are enhanced when local background wind speeds are large, due largely to GW visibility effects. Zonal asymmetries in variance maps reveal enhanced GW activity at high latitudes due to forcing by flow over major mountain ranges and at tropical and subtropical latitudes due to enhanced deep convective generation as inferred from contemporaneous MLS cloud-ice data. At 21-28-km altitude (heights not measured by the UARS MLS), GW variance in the tropics is systematically enhanced and shows clear variations with the phase of the quasi-biennial oscillation, in general agreement with GW temperature variances derived from radiosonde, rocketsonde, and limb-scan vertical profiles.
MLS (MICROWAVE LIMB SOUNDER)↗
Color enhancement of landsat agricultural imagery: JPL LACIE image processing support task
Color enhancement techniques were applied to LACIE LANDSAT segments to determine if such enhancement can assist analysis in crop identification. The procedure involved increasing the color range by removing correlation between components. First, a principal component transformation was performed, followed by contrast enhancement to equalize component variances, followed by an inverse transformation to restore familiar color relationships. Filtering was applied to lower order components to reduce color speckle in the enhanced products. Use of single acquisition and multiple acquisition statistics to control the enhancement were compared, and the effects of normalization investigated. Evaluation is left to LACIE personnel.
Madura, D. P.↗
A survey of bidirectional greater than or equal to MeV ion flows during the Helios 1 and Helios 2 mission: Observations from the Goddard Space Flight Center instruments
A survey is made of 1.1-2.1 MeV and 3-21 MeV bidirectional ion flows (BIFs) in the solar wind at 0.3-1.0 AU observed by the Goddard Space Flight Center instruments on the Helios 1 and Helios 2 spacecraft during the spacecraft mission in 1974-1984 and 1979-1980, respectively. Some 774 events have been identified Helios 1, and 223 at Helios 2, with mean durations of approximately 2.5 hr at each spacecraft. BIFs were observed for approximately 1%-3% of the observation time during solar minimum conditions in 1975-1977 and for approximately 10%-14% in 1980-1981 around solar maximum. These occurrence rates are similar to those of approximately 1 MeV BIFs observed at the Interplanetary Monitoring Platform 8 and International Sun Earth Explorers (ISEE) 3 spacecraft, and of bidirectional electron heat fluxes at ISEE 3. Solar wind plasma parameters during BIFs were similar to those found generally during the Helios missions, though BIFs have a greater tendency to be associated with cool, low-beta plasma, moderately enhanced and low-variance magnetic fields, both less than 300 km/s and greater than 750 km/s solar wind. Solar wind features associated with the greater than 4 hr duration BIFs include clear plasma shock-driver signatures: approximately 36% of the events; postshock plasma, not associated with shock-driver signatures: approximately 13%; noncompressive density enhancements: approximately 22% (half associated with plasma proton temperature depression); high-speed streams not associated with shocks: approximately 10%; corotating interaction regions: approximately 5%; immediately upstream of shocks: approximately 5%. Around 8% were associated with other solar wind structures, while approximately 4% showed no associated structure. BIFs were present in several of the shock drivers associated with coronal mass ejections (CMEs) observed by the Solwind coronagraph during intervals when Helios 1 was off the limbs of the Sun, showing directly the association of some BIFs with CMEs. some BIFs with CMEs.
Richardson, I. G.↗
Satellite Detection of Orographic Gravity-wave Activity in the Winter Subtropical Stratosphere over Australia and Africa
Orographic gravity-wave (OGW) parameterizations in models produce waves over subtropical mountain ranges in Australia and Africa that propagate into the stratosphere during austral winter and deposit momentum, affecting weather and climate. Satellite sensors have measured stratospheric GWs for over a decade, yet find no evidence of these waves. So are parameterizations failing here? Here we argue that the short wavelengths of subtropical OGWs place them near or below the detection limits of satellite sensors. To test this hypothesis, we reanalyze nine years of stratospheric radiances from the Atmospheric Infrared Sounder (AIRS) on NASA's Aqua satellite during austral winter, applying new averaging techniques to maximize signal-to-noise and improve thresholds for OGW detection. Deep climatological enhancements in stratospheric OGW variance over specific mountain ranges in Australia and southern Africa are revealed for the first time, which exhibit temporal and vertical variations consistent with predicted OGW responses to varying background winds.
Australia and Africa↗
Seven Years of ACTS Technology Verification Experiments Reviewed
The Advanced Communications Technology Satellite (ACTS) was designed to achieve a 99.5-percent system availability rate and signals with less than one error in 10(exp 7) bits throughout the continental United States. To accomplish such a high rate of system availability, ACTS uses multiple narrow hopping beams and very small aperture terminal (VSAT) technology. In addition, ACTS uses an adaptive rain fade compensation protocol to reduce the negative effects of propagation on the system. To enhance knowledge on how propagation and system variances affect system availability, researchers at the NASA Glenn Research Center at Lewis Field performed technology verification experiments over a 7-yr period (from September 1993 to the present). These experiments include T1VSAT System Availability, Statistical Rain Fade Compensation Characterization, Statistical Characterization of Ka-Band Propagation Effects on Communication Link Performance, and Multibeam Antenna Performance.
Acosta, Roberto J.↗
Angiogenesis and osteogenesis in an orthopedically expanded suture
The purpose of this study was to examine the angiogenic and the subsequent osteogenic responses during a 96-hour time-course after sutural expansion. Fifty rats were divided into: (1) a control group that received only angiogenic induction through injection of 5 ng/gm recombinant human endothelial cell growth factor (rhECGF); (2) an experimental group that received orthopedic expansion and rhECGF; (3) a sham group that received expansion and sodium chloride (NaCl) injection; and (4) a baseline group that received no expansion or injection. All rats were injected with 3H-thymidine (1.0 microCi/gm) 1 hour before death to label the DNA of S-phase cells. Demineralized sections (4 microm thick) were stained with hematoxylin and eosin. Angiogenesis and cell migration were analyzed with a previously established cell kinetics model. Analysis of variance was used to test the hypothesis that enhancement of angiogenesis stimulates reestablishment of osteogenic capability. Blood vessel number, area, and endothelial cell-labeled index significantly increased in experimental groups, but no difference was found between control and baseline groups. Labeled-pericyte index and activated pericyte numbers in the experimental group were also higher than in the sham groups. These results show that supplemental rhECGF enhances angiogenesis in expanded sutures but not in nonexpanded sutures. Data also suggest that pericytes are the source of osteoblasts in an orthopedically expanded suture.
NASA Discipline Musculoskeletal↗
Introducing and Evaluating the Climate Hazards Center IMERG with Stations (CHIMES) Timely Station-Enhanced Integrated Multisatellite Retrievals for Global Precipitation Measurement
As human exposure to hydroclimatic extremes increase and the number of in situ precipitation observations declines, precipitation estimates, such as those provided by the Integrated Multisatellite Retrievals for Global Precipitation Measurement (GPM) (IMERG) mission, provide a critical source of information. Here, we present a new gauge-enhanced dataset [the Climate Hazards Center IMERG with Stations (CHIMES)] designed to support global crop and hydrologic modeling and monitoring. CHIMES enhances the IMERG Late Run product using an updated Climate Hazards Center (CHC) high-resolution climatology (CHPclim) and low-latency rain gauge observations. CHPclim differs from other products because it incorporates long-term averages of satellite precipitation, which increases CHPclim ’s fidelity in data-sparse areas with complex terrain. This fidelity translates into performance increases in unbiased IMERGlate data, which we refer to as CHIME. This is augmented with gauge observations to produce CHIMES. The CHC’s curated rain gauge archive contains valuable contributions from many countries. There are two versions of CHIMES: preliminary and final. The final product has more copious and better-curated station data. Every pentad and month, bias-adjusted IMERGlate fields are combined with gauge observations to create pentadal and monthly CHIMESprelim and CHIMESfinal. Comparisons with pentadal, high-quality gridded station data show that IMERG late performs well (r = 0.75), but has some systematic biases which can be reduced. Monthly cross-validation results indicate that unbiasing increases the variance explained from 50% to 63% and decreases the mean absolute error from 48 to 39 mm month −1. Gauge enhancement then increases the variance explained to 75%, reducing the mean absolute error to 27 mm month −1.
Chris C funk↗
Multispectral histogram normalization contrast enhancement
A multispectral histogram normalization or decorrelation enhancement which achieves effective color composites by removing interband correlation is described. The enhancement procedure employs either linear or nonlinear transformations to equalize principal component variances. An additional rotation to any set of orthogonal coordinates is thus possible, while full histogram utilization is maintained by avoiding the reintroduction of correlation. For the three-dimensional case, the enhancement procedure may be implemented with a lookup table. An application of the enhancement to Landsat multispectral scanning imagery is presented.
Soha, J. M.↗
Measurements of ultraheavy cosmic rays with HEAO-3
The HEAO-3 Heavy Nuclei Experiment has measured abundances of elements from Ar-18 to U-92 in the cosmic rays. The results on the ultraheavy elements, those with atomic numbers greater than 30, indicate that the source of the cosmic rays contain a mixture of r-process and s-process material similar to that found in the solar system. This result is at variance with previous indications that the sources are greatly enhanced with freshly synthesized r-process material. Apparent discrepancies between the results and the accepted solar-system abundance have led to a reexamination of data on photospheric abundances of Ge and Pb, resulting in suggested reductions in their values.
Binns, W. R.↗
Department of Geology/NASA-GSFC geobotanical investigation
Geobotanical mapping in the southern Appalachians and soil metal associated changes in vegatation spectral responses in the reflective and emissive portions of the electromagnetic spectrum (EMS) is studied. It is determined whether deciduous forest vegetation reflection and emission characteristics show detectable changes that can be related to residual soil characteristics. Analyses of such related characteristics enhances the ability to discriminate underlying lithologies as well as variances within lithologies associated with natural heavy metal occurences. An understanding is developed of the factors which contribute to the differing spectral signatures of various lithology/soil types. A combination of field data and remote spectral analysis is studied.
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