Deeply Penetrating Banded Zonal Flows in the Solar Convection Zone     

Howe R  Christensen-Dalsgaard J  Hill F  Komm RW  Larsen RM  Schou J  Thompson MJ  Toomre J 《The Astrophysical journal》2000,534(2):L163-L166

We discuss the spectrum arising from synchrotron emission by fast cooling (FC) electrons, when fresh electrons are continually accelerated by a strong blast wave, into a power-law distribution of energies. The FC spectrum has so far been described by four power-law segments divided by three break frequencies nusaHowever, hot electrons are located right after the shock, while most electrons are farther downstream and have cooled. This spatial distribution changes the optically thick part of the spectrum, introducing a new break frequency, nuac相似文献   

Surface evolution and carbon sequestration in disturbed and undisturbed wetland soils of the Hunter estuary,southeast Australia   总被引：2，自引：0，他引：2  

A.J. Howe  J.F. Rodríguez  P.M. Saco 《Estuarine, Coastal and Shelf Science》2009

The aim of this work was to quantify the soil carbon storage and sequestration rates of undisturbed natural wetlands and disturbed wetlands subject to restriction of tidal flow and subsequent rehabilitation in an Australian estuary. Disturbed and undisturbed estuarine wetlands of the Hunter estuary, New South Wales, Australia were selected as the study sites for this research. Vertical accretion rates of estuarine substrates were combined with soil carbon concentrations and bulk densities to determine the carbon store and carbon sequestration rates of the substrates tested. Relationships between estuary water level, soil evolution and vertical accretion were also examined. The carbon sequestration rate of undisturbed wetlands was lower (15% for mangrove and 55% for saltmarsh) than disturbed wetlands, but the carbon store was higher (65% for mangrove and 60% for saltmarsh). The increased carbon sequestration rate of the disturbed wetlands was driven by substantially higher rates of vertical accretion (95% for mangrove and 345% for saltmarsh). Estuarine wetland carbon stores were estimated at 700–1000 Gg C for the Hunter estuary and 3900–5600 Gg C for New South Wales. Vertical accretion and carbon sequestration rates of estuarine wetlands in the Hunter are at the lower end of the range reported in the literature. The comparatively high carbon sequestration rates reported for the disturbed wetlands in this study indicate that wetland rehabilitation has positive benefits for regulation of atmospheric carbon concentrations, in addition to more broadly accepted ecosystem services.  相似文献   

In situ experimental formation and growth of Fe nanoparticles and vesicles in lunar soil          下载免费PDF全文

Michelle S. Thompson  Thomas J. Zega  Jane Y. Howe 《Meteoritics & planetary science》2017,52(3):413-427

We report the results of the first dynamic, in situ heating of lunar soils to simulate micrometeorite impacts on the lunar surface. We performed slow‐ and rapid‐heating experiments inside the transmission electron microscope to understand the chemical and microstructural changes in surface soils resulting from space‐weathering processes. Our slow‐heating experiments show that the formation of Fe nanoparticles begins at ~575 °C. These nanoparticles also form as a result of rapid‐heating experiments, and electron energy‐loss spectroscopy measurements indicate the Fe nanoparticles are composed entirely of Fe⁰, suggesting this simulation accurately mimics micrometeorite space‐weathering processes occurring on airless body surfaces. In addition to Fe nanoparticles, rapid‐heating experiments also formed vesiculated textures in the samples. Several grains were subjected to repeated thermal shocks, and the measured size distribution and number of Fe nanoparticles evolved with each subsequent heating event. These results provide insight into the formation and growth mechanisms for Fe nanoparticles in space‐weathered soils and could provide a new methodology for relative age dating of individual soil grains from within a sample population.  相似文献   

Planetary X-ray fluorescence analogue laboratory experiments and an elemental abundance algorithm for C1XS     

Shoshana Z. Weider  Bruce M. Swinyard  Barry J. Kellett  Chris J. Howe  Katherine H. Joy  Ian A. Crawford  Jason Gow  David R. Smith 《Planetary and Space Science》2011,59(13):1393-1407

We have conducted laboratory experiments as an analogue to planetary XRF (X-ray fluorescence) missions in order to investigate the role of changing incidence (and phase) angle geometry and sample grain-size on the intensity of XRF from regolith-like samples. Our data provide evidence of a grain-size effect, where XRF line intensity decreases with increasing sample grain-size, as well as an almost ubiquitous increase in XRF line intensity above incidence angles of ∼60°. Data from a lunar regolith simulant are also used to test the accuracy of an XRF abundance algorithm developed at the Rutherford Appleton Laboratory (RAL), which is used to estimate the major element abundance of the lunar surface from Chandrayaan-1 X-ray Spectrometer (C1XS) XRF data. In ideal situations (i.e., when the input spectrum is well defined and the XRF spectrum has a sufficient signal to noise ratio) the algorithm can recover a known rock composition to within 1.0 elemental wt% (1σ).  相似文献   

History and climate: a road map to humanistic scholarship on climate change   总被引：1，自引：1，他引：0  

Joshua P. Howe 《Climatic change》2011,105(1-2):357-363

  相似文献   

Multimegameter-range acoustic data obtained by bottom-mountedhydrophone arrays for measurement of ocean temperature     

Dushaw  B.D. Howe  B.M. Mercer  J.A. Spindel  R.C. Baggeroer  A.B. Menemenlis  D. Wunsch  C. Birdsall  T.G. Metzger  K. Clark  C. Colosi  J.A. Comuelle  B.D. Dzieciuch  M. Munk  W. Worcester  P.F. Costa  D. Forbes  A.M.G. 《Oceanic Engineering, IEEE Journal of》1999,24(2):202-214

Acoustic signals transmitted from the ATOC source on Pioneer Seamount off the coast of California have been received at various sites around the Pacific Basin since January 1996. We describe data obtained using bottom-mounted receivers, including US Navy Sound Surveillance System arrays, at ranges up to 5 Mm from the Pioneer Seamount source. Stable identifiable ray arrivals are observed in several cases, but some receiving arrays are not well suited to detecting the direct ray arrivals. At 5-Mm range, travel-time variations at tidal frequencies (about 50 ms peak to peak) agree well with predicted values, providing verification of the acoustic measurements as well as the tidal model. On the longest and northernmost acoustic paths, the time series of resolved ray travel times show an annual cycle peak-to-peak variation of about 1 s and other fluctuations caused by natural oceanic variability. An annual cycle is not evident in travel times from shorter acoustic paths in the eastern Pacific, though only one realization of the annual cycle is available. The low-pass-filtered travel times are estimated to an accuracy of about 10 ms. This travel-time uncertainty corresponds to errors in range- and depth-averaged temperature of only a few millidegrees, while the annual peak-to-peak variation in temperature averaged horizontally over the acoustic path and vertically over the upper 1 km of ocean is up to 0.5°C  相似文献   

Vorticity of Subsurface Flows of Emerging and Decaying Active Regions     

R. Komm  R. Howe  F. Hill 《Solar physics》2012,277(2):205-226

We study the temporal variation of the vorticity of subsurface flows of 828 active regions and 977 quiet regions. The vorticity of these flows is derived from measured subsurface velocities. The horizontal flows are determined by analyzing high-resolution Global Oscillation Network Group Doppler data with ring-diagram analysis covering a range of depths from the surface to about 16 Mm. The vertical velocity component is derived from the divergence of the measured horizontal flows using mass conservation. We determine the change in unsigned magnetic flux density during the disk passage of each active region using Michelson Doppler Imager (MDI) magnetograms binned to the ring-diagram grid with centers spaced by 7.5° ranging ± 52.5° in latitude and central meridian distance with an effective diameter of 15° after apodization. We then sort the data by their flux change from decaying to emerging flux and divide the data into five subsets of equal size. We find that the vorticity of subsurface flows increases during flux emergence and decreases when active regions decay. For flux emergence, the absolute values of the zonal and meridional vorticity components show the most coherent variation with activity, while for flux decrease the strongest signature is in the absolute values of the meridional and vertical vorticity components. The temporal variation of the enstrophy (residual vorticity squared) is thus a good indicator for either flux increase or decrease. There are some indications that the increase in vorticity during flux emergence happens about a day later at depths below about 8 Mm compared to layers shallower than about 4 Mm. This timing difference might imply that the vorticity signal analyzed here is caused by the interaction between magnetic flux and turbulent flows near the solar surface. There are also hints that the vorticity decrease during flux decay begins about a day earlier at layers deeper than about 8 Mm compared to shallower ones. However, the timing difference between the change at different depths is comparable to the time step of the analysis.  相似文献   

Subsurface Zonal Flows     

R. Komm  R. Howe  F. Hill  I. González Hernández 《Solar physics》2009,254(1):1-15

We study the zonal flow in solar subsurface layers, analyzing about six years of GONG++ high-resolution Doppler data with ring-diagram analysis. We focus on the variation of zonal flow with magnetic activity over a range of depths from the surface to about 16 Mm. There is a positive correlation between unsigned magnetic flux and zonal flow at most depths. We calculate the average zonal flow for a quiet- and an active-region subset defined as dense-pack locations with an unsigned magnetic flux less than 3.4 G and locations with greater than 65.0 G, respectively. The average zonal flow of active regions is about 4 m s⁻¹ larger than the average flow of quiet regions. This difference increases slightly with increasing depth, which might be explained by a nonradial inclination of the flux tubes or a different extent in depth of different magnetic features. The difference shows no apparent pattern in time and latitude, which makes it unlikely that it is simply a manifestation of the torsional-oscillation pattern. As a byproduct, we find that the size of the North – South asymmetry of the rotation rate decreases during the same epoch.  相似文献   

Reciprocal acoustic transmissions: Instrumentation for Mesoscale monitoring of ocean currents     

Worcester  P. Spindel  R. Howe  B. 《Oceanic Engineering, IEEE Journal of》1985,10(2):123-137

By simultaneously transmitting acoustic pulses in opposite directions between two points in midocean, one can separate the effects of ocean currents on acoustic propagation from the effects of sound-speed structure. Reciprocal acoustic transmissions can therefore be used to measure ocean currents. Acoustic transceivers have been designed and built to measure the mean currents between two points separated by 300 km. The equipment functioned satisfactorily during a sbort test conducted during 1983. Preliminary analysis of that experiment has yielded differential travel times that appear reasonable, but more work is required to relate the differential travel times to meaningful ocean-current estimates.  相似文献   

Modeling Geographic Variation in Household Disaster Preparedness across U.S. States and Metropolitan Areas     

Peter D. Howe 《The Professional geographer》2018,70(3):491-503

Emerging statistical techniques, combined with the increasing accessibility of primary social survey data, can provide policy-relevant tools for understanding how perceptions and behaviors vary geographically. Planning for natural disasters requires local data, yet data on topics such as household preparedness behaviors are often unavailable at the appropriate spatial resolution. This article presents new nationwide estimates of one element of household preparedness—having supplies in the home to use in case of a disaster—across all states and metropolitan areas in the United States. Estimates are based on a 2015 national survey combined with multilevel regression and poststratification (MRP), a statistical technique to develop subnational estimates from national data sets. The model uses sociodemographic and geographic predictors informed by prior research. Estimates were externally validated against independent surveys, including data from the 2013 American Housing Survey. Comparing the estimates against historical disaster losses demonstrates broad variation in preparedness even among places with historically high rates of death and injury from natural disasters and allows identification of high-risk places with high disaster losses and low preparedness according to this survey item. Leveraging large survey data sets in combination with MRP can be an effective tool for researchers and decision makers to understand geographic variation in perceptions and behaviors at subnational scales.  相似文献