bluuebunny/crossref_metadata_2025 huggingface dataset:
NASA team algorithm for sea ice concentration retrieval from Defense Meteorological Satellite Program special sensor microwave imager: Comparison with Landsat satellite imagery
Authors: Steffen Konrad , Schweiger Axel
Published: February 2008

Validation of the NASA team algorithm for the determination of sea ice concentrations from the Defense Meteorological Satellite Program special sensor microwave imager (SSM/I) is described. A total of 28 cloud‐free Landsat scenes were selected in order to permit validation of the passive microwave ice concentration algorithm for a range of ice concentrations and ice types. The sensitivity of the NASA team algorithm to the selection of locally and seasonally adjusted algorithm parameters is discussed in detail. Mean absolute differences between SSM/I and Landsat ice concentrations are within 1% during fall using local and global tie points. Standard deviations of the difference are ±3.1% and ±6.2% respectively. The overall accuracy of the NASA team algorithm is lower in spring than in fall. In areas with greater amounts of nilas and young ice, we found that the NASA team algorithm underestimates ice concentrations by as much as 9%. The Landsat and SSM/I ice concentrations have a correlation of 0.968 for all spring and fall case studies with a standard deviation of ±6.6% using global tie points and a correlation of 0.982 with a standard deviation of ±4.5% using local tie points. The NASA team algorithm tends to underestimate ice concentration in areas of close pack ice and to overestimate ice concentrations in areas of open pack ice. In summer, mean differences between SSM/I and Landsat ice concentrations are 3.8% for local tie points and 11.0% for global tie points for Arctic areas and 7.2% for local tie points and 11.7% for global tie points for Antarctic areas. These large differences are attributable to surface melt during summer and comparison problems arising from a time lag of up to 8 hours between the DMSP and Landsat satellites. It appears that seasonally and regionally adjusted tie points (local tie points) will improve the overall performance of the NASA team algorithm. Our work suggests that the standard deviation between SSM/I and Landsat ice concentrations decreases from ±7% to ±5% with local tie points compared to global ones for spring and fall.
Kinetic energy analysis of an eddy resolving, primitive equation model of the North Atlantic
Authors: Treguier A. M.
Published: February 2008

As part of the World Ocean Circulation Experiment community modelling effort, a realistic primitive equation model of the North Atlantic Ocean has been implemented with a resolution high enough to allow the generation of eddies. In the present paper, the kinetic energy of the model ocean circulation is analyzed. The eddy kinetic energy distribution in the model shows a good agreement with data in the western Atlantic but a deficit in the eastern Atlantic, especially at periods of about 100 days. Kinetic energy balances are computed to allow comparison between the primitive equation model and previous quasi‐geostrophic eddy resolving models. Essential instability mechanisms are present in both cases, but they are not efficient enough in the primitive equation model, which is too viscous and lacks the inertial character of quasi‐geostrophic solutions. Our study therefore emphasizes the need for even higher resolution models.
Retention of Greenland runoff by refreezing: Implications for projected future sea level change
Authors: Pfeffer W. Tad , Meier Mark F. , Illangasekare Tissa H.
Published: February 2008

Melting produced at the surface of subfreezing permeable firn does not freely percolate but instead refreezes near its point of origin, raising the firn temperature and decreasing the pore space. If sufficient meltwater is introduced, the firn will warm to 0°C, and subsequent water will fill the remaining pore space without freezing. Only after the residual water content of the firn is exceeded will water flow through the firn and possibly escape as runoff. This process prevents summer melt on high Arctic glaciers and ice caps from escaping in its entirety, and it must be accounted for in modeling glacier runoff on the basis of surface energy balance. A model is presented here which describes in a simple way the transient process of infiltration, refreezing, and runoff in a future warming climate. The model is applied to Greenland, for which predictions of runoff‐induced sea level rise that do not consider the refreezing process could be as much as 5.0 cm too high over 150 years.
Convective flow patterns in an eight‐box cube driven by combined wind stress, thermal, and saline forcing
Authors: Huang Rui Xin , Stommel Henry M.
Published: February 2008

An eight‐box cube model ocean, simulating the subpolar gyre in the North Atlantic, is formulated in order to understand how the wind‐induced horizontal gyre affects the thermohaline circulation and its catastrophe. The model is forced from above by thermal conduction and fresh‐water flux. The structure of the thermohaline circulation and its catastrophe during the process of gradually increasing or reducing the evaporation/precipitation are examined. The results indicate that, although adding the third dimension and a wind‐driven horizontal gyre of medium strength splits the catastrophe into several separate ones, only some of these catastrophes remain of significant amplitude. With choice of parameters appropriate for the North Atlantic, the model predicts a single stable state, circulating in the thermal sense (sinking at the pole). This can be driven smoothly to a reversed saline sense (sinking at the equator), without catastrophe, by increasing the precipitation/evaporation rate beyond 3 times the present‐day value.
Surface chlorophyll concentration in the tropical Pacific Ocean: An analysis of data collected by merchant ships from 1978 to 1989
Authors: Dandonneau Y.
Published: February 2008

The time and space variations of the chlorophyll concentration at the surface of the Tropical Pacific are examined from 1978 to 1989, on the basis of an extensive sampling carried out in cooperation with the crews of merchant ships. The data are distributed into three sets, which correspond to shipping tracks from New Caledonia to Panama (east, 203 transects interpolated at each degree between 7°N and 23°S), to North America (center, 182 transects between 15°N and 15°S), or to Japan (west, 119 transects between 15°N and 15°S). The data are log‐transformed, in order to stabilize the variance, and an empirical orthogonal function (EOF) analysis is applied. For each of the three data sets, the first EOF has a uniform eigenvector (spatial pattern) and extracts about 50% of the total variance; it mostly results from biases which affect the transects. In the central and western Pacific, the second, third and fourth EOFs correspond respectively to the equatorial upwelling, to a north‐south balance centered at the equator, and to phenomena which produce maxima at 5°N or 5°S, probably related to the equatorial countercurrents. In the eastern Pacific the second EOF opposes the northern to the southern waters and seems to account for the meridional displacements of the thermal front located near the Galapagos Islands. The multiyear variations caused by the El Niño ‐ Southern Oscillation dominate most EOF time functions (eastern and central Pacific, EOFs 1, 2 and 3; western Pacific, EOFs 2 and 4). Weak seasonal variations are sometimes suggested by these time functions. The results from the EOF analysis are used to reconstruct a tentative, unbiased chlorophyll field from 1979 to 1989.
Evolution and kinematics of a loop current eddy in the Gulf of Mexico during 1985
Authors: Forristall George Z. , Schaudt Kenneth J. , Cooper Cortis K.
Published: February 2008

The large eddy that broke off from the Loop Current in July 1985 was the most extensively studied eddy ever to appear in the Gulf of Mexico. Other investigators have described its early evolution based on Lagrangian drifters and its later evolution using moored current meters in the western gulf. This paper provides additional insight on the early evolution of the eddy using results from air dropped expendable bathythermographs and air dropped expendable current profilers in early May, a hydrographic ship survey in mid July, and a detailed ship survey in August using expendable bathythermographs and a current profiler. The May survey established a center of circulation at about 26°N but showed that the eddy had not separated from the Loop Current. A maximum velocity of 171 cm/s was observed near the northern edge of the feature. The evidence suggests that a large elongated eddy then separated from the Loop Current and later split into two smaller eddies. The July hydrographic cruise showed a clear separation of the large eddy from the Loop Current to the southeast. Two weeks later, the August survey showed an asymmetric eddy, with the maximum surface current 178 cm/s south of the center of circulation and 132 cm/s to the north. A western eddy named Ghost Eddy then separated from an eastern eddy named Fast Eddy. Using the current profiles and data from the drifters, we constructed a simple kinematic feature model for eddies in the Gulf of Mexico.
Short‐term variations of the bio‐optical properties of the ocean in response to cloud‐induced irradiance fluctuations
Authors: Stramska Malgorzata , Dickey Tommy D.
Published: February 2008

Variations in natural irradiance caused by changing cloud cover were examined as a potential source for the variability of the bio‐optical properties in the open ocean. Time series of the scalar irradiance (PAR), beam attenuation coefficient (at 660 nm), stimulated chlorophyll fluorescence, concentration of dissolved oxygen, and water temperature were subject to spectral analysis. These data were acquired in the Sargasso Sea at a depth of 23 m during the Biowatt mooring experiment in 1987. Three cloudy days, on which power spectra of PAR exhibited distinct maxima at periods of about 40 to 100 min, were selected for the analysis. Similar variations occurred in beam attenuation, fluorescence and dissolved oxygen as evidenced by relatively high coherence (> 0.5) between PAR and these variables. This is suggested to be related to rapid photoadaptive responses in the phytoplankton community on time scales of minutes. Possible explanations for these responses include changes in fluorescence yield, photosynthetic rate, cellular absorption, cell size and refractive index. No relationship between PAR and the bio‐optical parameters was observed when hydrodynamical factors prevailed over time scales similar to those for cloud‐induced irradiance fluctuations. The hydrodynamical effects were successfully traced by water temperature variations which, in further studies, may prove useful for separation of phenomena controlling within‐day bio‐optical variability in the ocean.
Classification of snow cover and precipitation using the special sensor microwave imager
Authors: Grody Norman C.
Published: February 2008

The special sensor microwave imager (SSMI) is a seven‐channel microwave radiometer which has dual polarized channels at 19, 37, and 85 GHz and a vertically polarized channel at 22 GHz. A detailed evaluation of all SSMI channels is made in arriving at the optimum channel selection for the global identification of precipitation and snow cover without the use of any ancillary information. The resulting algorithm takes the form of a decision tree which uses the dual polarized channels at 19 GHz and the vertically polarized channels at 22 and 85 GHz. These four channels enable the identification of precipitation from all other atmospheric and surface features, including snow cover.
Spaceborne observation of columnar water vapor: SSMI observations and algorithm
Authors: Tjemkes Stephen A. , Stephens Graeme L. , Jackson Darren L.
Published: February 2008

An analysis of the transfer of microwave radiation with a frequency between 10 and 40 GHz through a cloud‐free atmosphere is given, and the limitations of employing observations at 22.235 GHz for sensing the columnar water vapor (CWV) in the moist atmosphere (CWV > 40 kg m−2) are shown. It is because of this limitation that a new method for the retrieval of columnar water vapor is described. This method uses both the horizontally and vertically polarized brightness temperatures measured at 19.35 GHz by the special sensor microwave imager (SSMI) which was launched as part of the Defense Military Satellite Program. The water vapor derived from the SSMI observations is validated against radiosonde observations that are near coincident in time and space with an rms error of 6 kg m−2. This large rms is in part due to sensitivity of the retrieval method to the surface emission. Distributions of CWV over the oceans were obtained for a 3‐month period starting September 1987. These results are compared to other water vapor retrievals for the same period using the same microwave radiance data; they show close agreement except over the warmest water in the equatorial tropics.
Experimental and theoretical study of isotope effects on ozone decomposition
Authors: Wen J. , Thiemens Mark H.
Published: February 2008

Experimental and theoretical studies of O3 decomposition are reported which resolve kinetic mechanisms for isotopic fractionations in O‐O2‐O3 chemistry. The thermal gas phase decomposition of O3 at high temperatures (90°C, 110°C) produces isotopically heavy O2 with respect to precursor O3 with a non‐mass‐dependent fractionation pattern (δ17O ≠ 0.5δ18O). At 90°C, a noticeable component of heterogeneous decomposition is present, but is insignificant at 110°C. The product O2 from O3 photolysis by visible (532 nm) and UV light is depleted in the heavy isotopes, opposite from thermal decomposition. These well controlled experiments permit a quantitative kinetic analysis. A one‐box, time‐dependent model was used to simulate the evolution of the isotopic composition of the O2 and O3. The comparison of thermal and photolysis experiments indicates that the initial decomposition step is most likely responsible for the observed isotopic fractionations. Based upon detailed kinetic model calculations, the roles of isotope exchange reactions, initial O3 isotopic distribution, and various branching ratios of isotopic reactions involved in the isotopic fractionation have been examined. The possible importance of these conclusions for understanding stratospheric isotopically heavy O3, and possible implications for non‐mass‐dependent isotopic fractionations and chemical kinetic theory are discussed.
Effects of surface temperature and clouds on the CO2 forcing
Authors: Schmitt Christina , Randall David A.
Published: February 2008

CO2 forcing is defined as the initial change in heating rate, with no feedbacks included, that is the direct response to an increase in the CO2 concentration in the atmosphere. We have conducted a study of the effects of surface temperature and clouds on the CO2 forcing, based on use of the Colorado State University general circulation model. We report results from a pair of perpetual July simulations in which the sea surface temperatures differ by 4 K. The precipitable water is about 1.5 times larger in the warm run. The increased water vapor concentration amplifies the radiative effects of CO2, leading to greater CO2 forcing in the warm run. In the colder run the globally averaged reduction in upward longwave radiation due to a doubling of CO2 is 4.3 W m−2 at the level of maximum forcing, or the “CO2 tropopause.” Above and below this level the CO2 forcing decreases, resulting in a net tropospheric warming of 3.3×10−2 K day−1, and a net stratospheric cooling. In the warm run the CO2 forcing at the CO2 tropopause is 4.6 W m−2, and is associated with a tropospheric warming of 4.×10−2 K day−1. The clear‐sky CO2 forcing at the CO2 tropopause is 5.0 W m−2 in the cold run, and 5.2 W m−2 in the warm run. By blocking infrared radiation that would otherwise be blocked by CO2, the clouds reduce the CO2 forcing of the surface‐troposphere system by 0.66 W m−2 in the cold run, and by 0.59 W m−2 in the warm run. Our results for the CO2 forcing are model‐dependent, of course. Every GCM‐based study of CO2‐induced climate change produces a CO2 forcing, however, and the warming scenarios generated depend very directly on this forcing. A thorough investigation of the CO2 forcings produced by GCMs is thus a rather basic prerequisite for understanding the climate change predictions produced by the models.
Determination of absolute strengths of N2 quadrupole lines from high‐resolution ground‐based IR solar observations
Authors: Demoulin P. , Farmer C. B. , Rinsland C. P. , Zander R.
Published: February 2008

High‐resolution, high signal‐to‐noise ratio, solar absorption spectra recorded with a Fourier transform spectrometer at the International Scientific Station of the Jungfraujoch, Switzerland, have been analyzed to determine the strengths of several lines belonging to the S branch of the N2 (1–0) electric quadrupole vibration‐rotation band centered at 2329.9168 cm−1. The method which was applied here was based on equivalent width measurements of lines observed over a broad range of air masses; extrapolation of these measurements to zero air mass gave the line strengths for the transitions S7 to, S10, independent of half widths, an ambiguity unavoidable with the use of curve‐fitting techniques. The resulting absolute accuracies of the line strengths derived here, estimated to be better than ±2.5% for S8, ±2.6% for S10, ±3.4% for S9, and ±5.1% for S7, are due largely to the high quality and quantity of the spectra retained in this analysis and the accuracy with which the observation conditions are known. An important application of the improved values for these N2 transitions, which have low initial ground state energies, is the direct determination of the line‐of‐sight atmospheric air masses associated with remotely sensed infrared spectroscopic observations. Positions of the N2 transitions studied here have further been redetermined with an absolute accuracy better than 0.0002 cm−1.
Ozone climatology at Natal, Brazil, from in situ ozonesonde data
Authors: Kirchhoff V. W. J. H. , Barnes R. A. , Torres A. L.
Published: February 2008

Results are presented from analysis of a large ozone profile data set obtained from balloon ozonesonde soundings made at Natal, Brazil (6°S, 35°W) during the last 10 years (1978–1988). The measurements have been made through an Instituto Nacional de Pesquisas Espaciais (INPE)/NASA long‐term collaboration program. The balloons were released by the Brazilian Air Force at the Natal rocket range. The data set is sufficiently large to provide useful climatology on the average ozone concentration behavior and its seasonal variation. The day‐to‐day ozone concentration variability in the troposphere is rather large, giving standard deviations of about 30–40% for seasonal averages. Maximum ozone concentrations occur during local spring, September–October, and minimum concentrations during late autumn, April‐May. The seasonal variation in the troposphere is much larger than in the stratosphere. If there were no seasonal variation at all in the stratosphere, the seasonal variation observed in the troposphere alone would be strong enough to drive a total ozone column variation of about 5%, which is about one half the size of the variation observed in the Natal Dobson spectrophotometer data. The ozone concentration at Natal increases with height between the surface and about 500 mbar, almost linearly, from about 15 parts per billion by volume (ppbv) to about 38 ppbv, in autumn. For the spring average the ozone concentration increases from about 25 ppbv at the surface to about 66 ppbv at 500 mbar. The sonde data suggest that limitations in aneroid pressure sensors used until 1986 caused the Natal sondes to indicate too much ozone above 6 mbar. Because of the relative sparsity and uneven distribution in time of the ozone soundings, the data are not adequate to study ozone trends. The Dobson data time series shows no definitive ozone trend but displays a pronounced quasi‐biennial oscillation in ozone.
Snow on sea ice: Competing effects in shaping climate
Authors: Ledley Tamara Shapiro
Published: February 2008

The impact of the addition of snow and its thermal properties on sea ice and leads and the subsequent effect on climate are examined in this study. The results show that the thermal properties of snow introduce competing effects on climate. The first effect is that the snow acts as an insulator, keeping the ice warm and thus thin. The second effect is that snow has a lower volumetric specific heat and volumetric heat of fusion than ice, causing it to cool, warm, and melt more easily than ice. This produces longer periods of ice free conditions during the summer and thus a warmer climate. The third effect is that snow has a higher albedo than ice. This causes a reduction in the absorbed solar energy by the entire Earth‐atmosphere system and results in a cooling of the climate. The results described here indicate that the albedo effect is dominant, so that the addition of snow cools the climate. These results show that snow on sea ice is a very important factor in shaping polar climate and that significant changes in the thickness and/or extent of the snow cover could have important implications for understanding changes in our climate.
Spontaneous breakup of charged and uncharged water drops freely suspended in a wind tunnel
Authors: Kamra A. K. , Bhalwankar Rohini V. , Sathe A. B.
Published: February 2008

Time for which charged or uncharged water drops of different sizes can be suspended over a vertical wind tunnel before their spontaneous breakup and the size distribution of droplets resulting from their breakup have been determined. Probability of spontaneous breakup of a drop has been found to increase with the size and charge of the drop. It has been observed that water drops carrying a charge of 5×10−10 C breakup immediately after their suspension if their diameter > 8 mm. Total number of droplets produced on spontaneous breakup of a drop increases with the size of the drop, and if the drop size is > 6.6 mm, the total number of droplets is more when the drop is uncharged than that when it is charged. However, the number of droplets larger than a critical size is more if the parent drop is charged and the number of droplets smaller than that critical size is more if the parent drop is uncharged. It has been attempted to qualitatively explain the experimental results as the result of enhanced surface charge density around the waist of the drop during its oscillation. Charge on the drop has been suggested to cause an increase in width of the base of suspended drop.
The relative impact of stratospheric photochemical production on tropospheric NOy levels: A model study
Authors: Kasibhatla P. S. , Levy H. , Moxim W. J. , Chameides W. L.
Published: February 2008

The 11‐level Geophysical Fluid Dynamics Laboratory (GFDL) global chemical transport model has been used to assess the impact of stratospheric NOx production on tropospheric reactive nitrogen (NOy) concentrations. A temporally varying source function was constructed using specified two‐dimensional, monthly average O3, N2O, temperature, and surface pressure data generated by the GFDL “SKYHI” model. The calculated yearly NOy, production rate is 0.64 Tg N (0.64×1012 g N). A wet removal scheme, which distinguishes between stable and convective rain based on the bulk Richardson number, is introduced. Simulations have been performed with a simplified chemical mechanism which fractionates NOy, into soluble and insoluble species. The role of peroxyacetyl nitrate (PAN) in determining the impact of stratospheric injection on the tropospheric NOy, budget is studied by comparing results of simulations with and without PAN chemistry. We conclude that (1) the stratospheric source is too small to account for background surface NOy, concentrations observed in the remote (i.e., regions a few thousand kilometers from continental source regions) troposphere. Surface NOy, mixing ratios seldom exceed 10 parts per trillion by volume (pptv) in the model northern hemisphere and are always below 20 pptv. Together, fossil fuel combustion emissions and stratospheric injection account for less than 10% of observed surface nitrate concentrations in the remote tropical Pacific. (2) The impact of the stratospheric source is comparable to that of the fossil fuel combustion source in terms of NOy, mixing ratios in the northern hemisphere at the 500 mbar model level and is more important in the middle and high latitudes of the southern hemisphere. At the 315 mbar model level the stratospheric source contribution to NOy, levels is more important than that of the fossil fuel source at all latitudes, except in the tropics. However, substantial contributions from other NOy sources are needed to explain observations in the remote middle and upper troposphere. (3) Inclusion of PAN chemistry has the effect of increasing model‐calculated surface NOy, mixing ratios in the northern hemisphere middle and high latitudes by factors of 1.5–3 during winter/spring and by factors of 2–4 during summer/fall. Surface NOy, mixing ratios in the southern hemisphere show a smaller increase due to slower rates of PAN formation. This is a direct result of lower hydrocarbon concentrations in the southern hemisphere.
Precipitation composition and its variability in the southern Indian Ocean: Amsterdam Island, 1980–1987
Authors: Moody J. L. , Pszenny A. A. P. , Gaudry A. , Keene W. C. , Galloway J. N. , Polian G.
Published: February 2008

Event precipitation samples have been collected on Amsterdam Island (37° 47′ S, 77° 31′ E) from May 1980 through January 1987 and analyzed for SO4=, NO3−, Cl−, Na+, Mg++, K+, Ca++, H+, HCOOt, and CH3COOt. The objective of this paper is to assess the processes which influence variability in the chemical composition of precipitation at this remote marine site. Back trajectories and gas phase 222Rn measurements were used to identify source regions and their relative contributions to precipitation composition. The technique of cluster analysis was applied to trajectory data as a method for determining to what degree different atmospheric flow patterns influence variability in the observed composition. The dominant source regions for chemical deposition were found to be Madagascar and/or S.E. Africa and the ocean region north and east of Amsterdam Island. A strong seasonal signal in the precipitation composition is illustrated. Processes which influence variability in the chemical composition include the following: seasonality in the source strength of biogenic precursors for non‐sea‐salt (nss) SO4=, NH4+ and carboxylic acids; seasonality in biomass‐burning continental sources for the concentration of NO3− and a portion of nss Cl−; and variations in source region driven by daily changes in meteorology, as well as seasonal and annual differences in transport and removal patterns. In addition, interannual differences in nss SO4= concentration appear to be related to fluctuations in large‐scale circulation patterns as defined by the Southern Oscillation.
Simulations of microphysical, radiative, and dynamical processes in a continental‐scale forest fire smoke plume
Authors: Westphal Douglas L. , Toon Owen B.
Published: February 2008

A numerical model of meteorology, aerosols, and radiative transfer is used to study the impact of a large forest fire smoke plume on atmospheric processes. The simulated smoke optical depths at 0.63 μm. wavelength are in agreement with analyses of satellite data and show values as high as 1.8. The smoke has an albedo of 35%, or more than double the clear‐sky value, and cools the surface by as much as 5 K. The best agreement with the analyses of optical depth and surface cooling is obtained when a fuel loading more than 10 times that which has been previously suggested is used to calculate the initial smoke mass load. An imaginary refractive index, nim, of 0.01 yields results which closely match the observed cooling, single scattering albedo, and the Ångström wavelength exponent. An nim of 0.1, typical of smoke from urban fires, produces 9 K cooling. Coagulation causes the geometric mean radius by number to increase from the initial value of 0.08 μm to a final value of 0.15 μm while the specific extinction and absorption increase by 40% and 25%, respectively. After 42 hours, these changes in the smoke optical properties lead to a 32% increase in optical depth and an 11% increase in surface cooling over that found in a simulation where coagulation is not allowed. In the model, 47% of the smoke is removed by scavenging as it is incorporated into the frontal zone over the Great Lakes. Self‐lofting of the smoke in a direct, smoke‐induced circulation is observed in the baseline simulation and is much stronger in the urban smoke simulation.
Outgoing longwave radiation and its diurnal variations from combined Earth Radiation Budget Experiment and Meteosat observations :2. Using Meteosat data to determine the longwave diurnal cycle
Authors: Cheruy F. , Kandel R. S. , Duvel J. P.
Published: February 2008

For April and July 1985, applying the narrow to broadband conversion of part 1 to Meteosat observations obtained at 3‐hour intervals (ISCCP B2 data), we determine the monthly mean radiant exitance as well as the mean diurnal variation, over 2.5°×2.5° latitude‐longitude regions of tropical Africa and the neighboring Atlantic Ocean. We compare these determinations with those obtained directly from the ERBS and NOAA 9 Earth Radiation Budget Experiment (ERBE) data for this month, for which the time sampling is sparser and not so uniform. Excellent agreement is obtained in most cases, in particular for the overall monthly means. However, for the monthly mean diurnal variation there are situations in which the ERBE time sampling, the nature of the ERBE diurnal modeling scheme and the convolution of weather system changes with the diurnal cycle, combine to produce significant differences between the ERBE determination and the Meteosat result. These differences would mostly have been much smaller had the third ERBE instrument package been in operation (at 0730/1930 LT) as originally planned. We consider possible improvements in diurnal interpolation procedures, but note that there is no general way to remove bias resulting from inadequate time sampling.
New measurements of the 6190‐Å band of methane
Authors: Mickelson M. E. , Larson L. E. , Schubert A.
Published: February 2008

New laboratory measurements have been made of the absorption coefficient of the visible methane band at 6190 Å. Data were obtained using a tunable dye laser system operating with a line width of 0.067 cm−1 (0.025 Å). Spectra were recorded at approximately 1‐Å intervals with the beam coupled to a 22‐m base length White‐type absorption cell adjusted for an optical path of 1.584 km and filled to a density of 0.884 amagats. These room temperature results are compared with previous low‐resolution measurements in the spectral region from 6000 to 6400 Å.
Laboratory investigations of impact‐generated plasma
Authors: Crawford David A. , Schultz Peter H.
Published: February 2008

The production of magnetic fields by hypervelocity meteoroid impact has been proposed to explain the presence of paleomagnetic fields in some lunar samples as well as on the lunar surface. Impact‐generated magnetic fields also may be significant for the paleomagnetic record on a variety of cratered surfaces in the solar system, such as the Moon, Mercury, Phobos, and asteroids. Previous experiments with the two‐stage hydrogen light gas gun at the NASA Ames Vertical Gun Range demonstrated that hypervelocity impacts can produce impact‐generated magnetic fields by the expansion of an impact‐derived ionized vapor cloud (impact‐generated plasma).Here we further characterize impact‐generated magnetic fields and plasma with hypervelocity impact experiments at the NASA Ames Vertical Gun. Spherical projectiles (0.32 cm Fe, Cu; 0.64 cm Al, nylon) with velocities from 5.2 to 6.0 km/s were impacted at impact angles of 15°, 30°, 60°, and 90° (measured from horizontal) into powdered dolomite, silica sand, and aluminum plate. Three sets of experiments using search coils as magnetic detectors characterized impact‐generated magnetic fields as functions of ambient field strength and orientation, projectile/target composition, and impact angle. Experiments using Langmuir probes indicated a charged particle density (between 109 and 1011 ions/el cm−3) and an electron temperature (∼4500 K) of the impact‐generated plasma, the inferred source of impact‐induced magnetic fields. These new results demonstrate that impact‐generated magnetic fields at the laboratory scale exhibit spatial and temporal complexity dependent on impact angle, velocity, and projectile/target composition thereby suggesting that crater‐related paleomagnetism associated with this mechanism should exhibit similar complexity with spatial wavelengths on the order of a fraction of the crater radius.
Thermally driven diffusion of SO2 within the surface of Io
Authors: Meade Paul E. , Jakosky Bruce M.
Published: February 2008

The presence of sulfur dioxide (SO2) on Io, together with the fact that the surface layer of Io has extremely high porosity, suggests the possibility of diffusion of this volatile within the surface, as well as exchange between the surface and an atmosphere. We investigate the former possibility through the development of a surface layer thermal model and subsequent calculations of the thermally driven diffusion flux of SO2 within the layer. The major factors affecting the diffusion process are the temperature and temperature gradient in the surface layer throughout the day (which are results of the thermal model), and the porosity and grain size in the surface layer. Our results indicate that the net transport of SO2 in the near‐surface region is downward into the subsurface, causing near‐surface depletion of SO2‐Near‐surface depletion would result in a layer of reduced thermal inertia overlying the bulk of the surface, consistent with thermal eclipse observations of Io. For our nominal model with 10‐μm grains and a porosity of 85%, the peak net diurnal downward flux reaches nearly 8×10−3 g cm−2 period−1.
Glacial pCO2 Reduction by the World Ocean: Experiments With the Hamburg Carbon Cycle Model
Authors: Heinze C. , Maier‐Reimer E. , Winn K.
Published: February 2008

Possible mechanisms for the 80 ppm reduction of atmospheric CO2 partial pressure during the last glaciation were investigated using the Hamburg Ocean Carbon Cycle Model. The three‐dimensional carbon cycle model is based on the velocity field of the Hamburg Large‐Scale Geostrophic Ocean General Circulation Model and uses the same grid as that model. The horizontal resolution (3.5° × 3.5°) is lower than the length scale of narrow upwelling belts which could not be represented adequately in this study, but the large‐scale features of the ocean carbon cycle are reproduced rather well. Sensitivity experiments were carried out to investigate the role of chemical and biological parameters (nutrient cycling, composition of biogenic particulate matter, CO2 solubility) and different circulation regimes for the atmospheric CO2 content. The model responses were compared to deep‐sea sediment core records and ice core data from the last glaciation. Each experiment was compared with observed average tracer patterns during 18–65 kyr B.P. It was found that none of the sensitivity experiments alone could explain all observed tracer changes (atmospheric pCO2, Δδ13Cplanktonic‐benthic, δ13Cbenthic differences, CaCO3 corrosivity indices) simultaneously, even in a qualitative sense. Thus according to the model none of the scenarios tested proves to be completely acceptable. The residual discrepancies between the observed and modeled tracer records can probably be attributed to the as yet inadequate reconstruction of the glacial ocean circulation. It is therefore suggested that more effort should be devoted to realistically reproducing the ice age ocean circulation field making use of the forthcoming glacial radiocarbon data base. The residuals between the realistically modeled and observed carbon cycle tracers (δ13C, CaCO3 saturation) should then reveal more clearly the real cause for the observed pCO2 decrease in the glacial atmosphere.
Modeling continental and submarine hydrothermal systems
Authors: Lowell Robert P.
Published: February 2008

Continental and submarine hydrothermal systems are an integral part of the Earth's thermal regime. Continental systems account for less than 1% of the global heat loss, whereas submarine systems account for nearly 25%. Naturally heated waters of continental hydrothermal systems have been utilized for centuries, yet mathematical models of these systems have been developed only during the past 40 years. By contrast, direct observation of seafloor hydrothermal venting occurred just slightly more than a decade ago. However, mathematical models of submarine hydrothermal heat transfer were developed to explain conductive heat flow anomalies at ocean ridge crests even before the vents were found. Both cellular convection in fluid‐saturated porous media and single‐pass, pipe model flow provide a conceptual framework for the construction of mathematical models hydrothermal systems. Recent numerical simulations of low‐ and high‐temperature hydrothermal systems in continental and submarine settings highlight the role of permeability in controlling the style of hydrothermal circulation. Future modeling will likely focus on the complexities of heat transfer between magma and the hydrothermal system as well as on the tectonic, thermal, and chemical processes that affect rock permeability in space and time. Future work must also address the three‐dimensional nature of hydrothermal systems and two‐phase flow in submarine hydrothermal systems. Whether hydrothermal systems might record climatic changes has yet to be investigated.
Recent developments in dating ancient crustal fluid flow
Authors: Halliday Alex N. , Ohr Matthias , Mezger Klaus , Chesley John T. , Nakai Shun'ichi , DeWolf Charles P.
Published: February 2008

Several isotopic techniques have recently been developed or substantially improved, allowing the accurate determination of the timing of fluid‐related processes. These include K‐Ar, Rb‐Sr, and Sm‐Nd dating of diagenetic minerals in clastic rocks, U‐Pb dating of carbonates, Sm‐Nd dating of fluorite and uraninite, Re‐Os and Rb‐Sr dating of sulfides, 40Ar‐39Ar and Rb‐Sr dating of fluid inclusions, and U‐Pb dating of ilmenite/magnetite, sphene, and rutile. While many of these techniques require further evaluation, some have already resulted in new constraints on a variety of crustal fluid flow models.
Slip line model for southern California crustal kinematics
Authors: Chen Yongshun , Minster J. Bernard
Published: February 2008

We propose a simple slip line model to explain the faulting and seismicity patterns of southern California. We assume the Sierra Nevada–Great Valley (SNGV) block to be rigid, in view of its low seismicity, and other regions to undergo plastic deformation. From this point of view, the complex deformation patterns observed in southern California, including the Borderland region, result from the “plowing” of the eastern margin of the Pacific plate by the nondeforming SNGV block. A simple analogy can then be made between regional tectonics in southern California and two‐dimensional flow solutions obtained in metallurgy for the extrusion of rigid‐plastic metals. We use a simplified geometry based on the geology and seismicity of southern California to calculate a two‐dimensional slip line field which predicts the shape of the San Andreas fault near the “big bend” surprisingly well. The largely aseismic, high‐topography western Mojave can then be interpreted as an analogue to the nondeforming “dead metal” zone which arises for certain metal extrusion geometries. The slip field agrees quite well with the strikes and slip orientation of major dextral faults in southern California, including the San Jacinto, Elsinore, and Newport‐Inglewood faults. It also predicts correctly the strikes and slip orientation of sinistral “cross faults” found in some areas of the region. In the Transverse Ranges, where thrust faulting dominates, the slip lines are no longer potential fault planes, but a simple argument predicts that they should lie at 45° on the strikes of thrust faults, in fair agreement with the observations.
Tectonic evolution of the Corsica‐Apennines‐Alps region studied by the method of successive approximations
Authors: Alvarez Walter
Published: February 2008

Paleotectonic and paleogeographic maps are often very complex. Users find it difficult to evaluate the extent to which the features shown are based on reliable geologic data, and it is not generally possible to estimate uncertainties in shapes and positions. In the scientific tradition of designing simple models to represent complex reality, this study uses systematically simplified palinspastic models to study the tectonic evolution of the central Mediterranean. The prime constraint is northwestward motion of the African continent toward Europe at 7.5 km/m.y. In the “first‐approximation” model, only unidirectional plate motion is allowed, and the model is unable to generate both the Alpine and Apennine orogenic belts, at right angles to each other. The “second approximation” allows rotations. It is surprising how well this very simple model, with its rigidly restrictive rules, reproduces the known evolution of the central Mediterranean. This agreement allows some optimism that the second approximation is correctly modeling the primary features of the tectonic evolution of the central Mediterranean. Revising the shapes of the tectonic entities in a “third approximation” would allow the final pattern to mimic even more closely the present tectonic situation in the Mediterranean, but here the advantages of rigid simplification would start to diminish. The first conclusion of the paper is thus that strongly simplified models are useful in tectonic studies and are justified in light of the uncertainties. Simplified models are used to explore the recently proposed “Ancient‐Apennine” hypothesis, in which Apennine deformation begins with a reversal of subduction polarity at about 100–90 Ma. This view contrasts with the standard “Young‐Apennine” hypothesis, in which subduction reversal and the onset of Apennine orogensis do not occur until 35–30 Ma. Study of the simplified tectonic models leads to the second conclusion of the paper, that the Ancient‐Apennine hypothesis honors regional constraints as well as the standard view does. The simplified modeling suggests specific tests in Alpine Corsica for choosing between the Young‐Apennine and Ancient‐Apennine hypotheses.
Collapse of the Luzon Volcanic Arc during onset of arc‐continent collision: Evidence from a Miocene‐Pliocene unconformity, eastern Taiwan
Authors: Dorsey Rebecca J.
Published: February 2008

A regional Miocene‐Pliocene unconformity in the Coastal Range of eastern Taiwan provides information about vertical motions that affected the colliding volcanic arc during initiation of arc‐continent collision. The unconformity separates precollisional volcanic and volcaniclastic rocks of the Miocene Luzon arc and forearc basin from an overlying thick sequence of syncollisional, Pliocene‐Pleistocene sedimentary rocks derived from the metasedimentary accretionary wedge of Taiwan. The duration of time represented by the unconformity averages 1–2 m.y. and locally ranges up to 4 m.y. The basal unit of the younger syncollisional sequence consists of bathyal, mega‐slump‐folded mudstone, pebbly mudstone, and thin‐bedded turbidites. Sharp stratigraphic juxtaposition of these deep‐marine deposits directly above shallow‐marine limestone and epiclastic rocks (upper part of the older arc sequence) requires extremely rapid subsidence during initiation of the collisional basin. The Coastal Range unconformity is interpreted to represent a period of latest Miocene nondeposition and/or erosion in the Luzon arc that was related to initial subduction of the Eurasian continental margin along the Manila Trench. This period was followed in Pliocene time by very rapid subsidence, or collapse, of the arc platform to 1–2 km water depth. There are two dissimilar mechanisms of basin subsidence that may have controlled initiation of the collisional basin: (1) extension, rifting, and crustal thinning in the Luzon arc massif to form a series of small rift or pull‐apart subbasins or (2) flexural subsidence of oceanic lithosphere in a foreland‐style basin due to crustal loading in the expanding accretionary wedge of proto‐Taiwan. Although data are insufficient to provide a unique solution, the flexural subsidence model is supported by systematic younging of the initial subsidence event from west to east, which may record eastward migration of an outer flexural bulge. Notable differences between the unconformity and paleogeography of the early collisional basin and analogous present‐day basins in the offshore region to the south suggest that arc‐continent collision and basin development in eastern Taiwan have experienced secular change since late Pliocene time.
Earthquake focal mechanisms, moment tensors, and the consistency of seismic activity near plate boundaries
Authors: Frohlich Cliff , Apperson K. Denise
Published: February 2008

Catalogs of moment tensors for more than 8000 earthquakes provide a more objective and complete description of the earthquake source than do focal mechanisms derived from first motions, and therefore moment‐tensors provide a valuable resource for tectonic analysis. We here present background information about the properties of moment tensors and examples of moment tensor analysis. We also introduce a new statistic, the seismic consistency Cs, which measures the similarity of earthquakes within a group. Cs is 1.0 if earthquakes are all alike and 0.0 if they cancel one another. Triangle diagrams provide a practical method for defining the fraction of normal, strike‐slip, and thrust fault components for an earthquake and are a new graphical method for displaying source properties of groups of earthquakes. We apply these methods to the Harvard centroid moment tensor catalog to study the characteristics of shallow earthquakes (<50 km depth) within 200 km of typical ridge‐transform and subduction zone plate boundaries. In this way, we have reached four major conclusions. First, even along relatively simple plate boundaries, there is considerable variation in the type and orientation of earthquake mechanisms. Second, along individual plate boundaries, groups of thrust, normal, or strike‐slip earthquakes generally have Cs equal to 0.8 or higher. Thus for many types of tectonic analyses it is unnecessary to add moment tensors to study seismic deformation; rather, it is sufficient to add scalar earthquake moments of the individual events. Third, moment tensors for some individual earthquakes are quite different from those produced by slip along a planar fault. However, summing up moment tensors shows that the deformation pattern produced by groups of earthquakes is generally more like fault slip than the pattern of typical earthquakes within the group. Fourth, by dividing the sum of moments by the velocity of plate motion and the length of the boundary, we calculate Rmom, the efficiency of seismic moment produced along individual plate boundaries. For the 12.75 years of data available, normal fault earthquakes along spreading ridges produce moment less efficiently than strike‐slip earthquakes along transforms. These in turn produce moment less efficiently than thrust earthquakes along subduction zones. For ridge‐transform earthquakes, boundaries with fast plate velocities produce seismic moment less efficiently than do boundaries with slow velocities.