bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of land use in Southwest Australia: 1. Observations of cumulus cloudiness and energy fluxes
Authors: Ray Deepak K. , Nair Udaysankar S. , Welch Ronald M. , Han Qingyuan , Zeng Jian , Su Wenying , Kikuchi Tokio , Lyons Tom J.
Published: July 2003

The Southwest Australian region has large homogeneous tracts of differing vegetation types separated by a sharp transition called the vermin or bunny fence which runs for almost 750 km. Seasonal winter agriculture is found to the west of the fence, whereas to the east native perennial vegetation grows. Geostationary Meteorological Satellite‐5 imagery are used to construct monthly cumulus cloud frequency of occurrence maps for the region 0800 to 1500 LT in hourly increments for 1999 and 2000. Moderate Resolution Imaging Spectroradiometer (MODIS) imagery are used to retrieve regional values of surface temperature, albedo, Normalized Difference Vegetation Index, fractional soil moisture availability, sensible and latent heat fluxes. High spatial resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery are used to retrieve detailed values along the fence. MODIS imagery also is utilized to retrieve cloud optical thickness, droplet sizes, and liquid water paths. This study shows that higher soil moisture availability is found over agricultural areas during winter (September) and over native vegetation areas during summer (December). Latent heat fluxes are higher over native vegetation than over agricultural areas during summer, while sensible heat fluxes are lower. Cumulus clouds occur with higher frequency and have higher optical thicknesses, cloud liquid water contents, and effective radii over agricultural areas during the winter and over native perennial vegetation during the dry summer. This is due to higher latent heat fluxes and available energy over agriculture during winter and over native vegetation during summer. We conclude that land use differences result in differences in available soil moisture and surface energy fluxes, which in turn lead to the observed preferential enhancement of cumulus cloudiness and cumulus cloud properties.
Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century
Authors: Rayner N. A. , Parker D. E. , Horton E. B. , Folland C. K. , Alexander L. V. , Rowell D. P. , Kent E. C. , Kaplan A.
Published: July 2003

We present the Met Office Hadley Centre's sea ice and sea surface temperature (SST) data set, HadISST1, and the nighttime marine air temperature (NMAT) data set, HadMAT1. HadISST1 replaces the global sea ice and sea surface temperature (GISST) data sets and is a unique combination of monthly globally complete fields of SST and sea ice concentration on a 1° latitude‐longitude grid from 1871. The companion HadMAT1 runs monthly from 1856 on a 5° latitude‐longitude grid and incorporates new corrections for the effect on NMAT of increasing deck (and hence measurement) heights. HadISST1 and HadMAT1 temperatures are reconstructed using a two‐stage reduced‐space optimal interpolation procedure, followed by superposition of quality‐improved gridded observations onto the reconstructions to restore local detail. The sea ice fields are made more homogeneous by compensating satellite microwave‐based sea ice concentrations for the impact of surface melt effects on retrievals in the Arctic and for algorithm deficiencies in the Antarctic and by making the historical in situ concentrations consistent with the satellite data. SSTs near sea ice are estimated using statistical relationships between SST and sea ice concentration. HadISST1 compares well with other published analyses, capturing trends in global, hemispheric, and regional SST well, containing SST fields with more uniform variance through time and better month‐to‐month persistence than those in GISST. HadMAT1 is more consistent with SST and with collocated land surface air temperatures than previous NMAT data sets.
Radiative properties and direct radiative effect of Saharan dust measured by the C‐130 aircraft during SHADE: 1. Solar spectrum
Authors: Haywood Jim , Francis Pete , Osborne Simon , Glew Martin , Loeb Norman , Highwood Eleanor , Tanré Didier , Myhre Gunnar , Formenti Paola , Hirst Edwin
Published: July 2003

The physical and optical properties of Saharan dust aerosol measured by the Met Office C‐130 during the Saharan Dust Experiment (SHADE) are presented. Additional radiation measurements enable the determination of the aerosol optical depth, τaerλ, and the direct radiative effect (DRE) of the mineral dust. The results suggest that the absorption by Saharan dust is significantly overestimated in the solar spectrum if standard refractive indices are used. Our measurements suggest an imaginary part of the refractive index of 0.0015i is appropriate at a wavelength λ of 0.55 μm. Different methods for determining τaerλ=0.55 are presented, and the accuracy of each retrieval method is assessed. The value τaerλ=0.55 is estimated as 1.48 ± 0.05 during the period of heaviest dust loading, which is derived from an instantaneous DRE of approximately −129 ± 5 Wm−2 or an enhancement of the local planetary albedo over ocean of a factor of 2.7 ± 0.1. A comparison of the DRE derived from the C‐130 instrumentation and from the Clouds and the Earth's Radiant Energy System (CERES) instrument on the Tropical Rainfall Measuring Mission (TRMM) satellite is presented; the results generally showing agreement to within a factor of 1.2. The results suggest that Saharan dust aerosol exerts the largest local and global DRE of all aerosol species and should be considered explicitly in global radiation budget studies.
Estimation of diurnal shortwave dust aerosol radiative forcing during PRIDE
Authors: Christopher Sundar A. , Wang Jun , Ji Qiang , Tsay Si‐Chee
Published: July 2003

Using measured and derived aerosol properties from the Puerto Rico Dust Experiment (PRIDE), a four‐stream broadband radiative transfer model is used to calculate the downward shortwave irradiance (DSWI) at the surface and the shortwave irradiance at the top of atmosphere (TOA). The results of the calculated DSWI are compared against pyranometer measurements from the Surface Measurements For Atmospheric Radiative Transfer (SMART) instrument suite at Roosevelt Road (18.20°N, 65.60°W). Using aerosol optical thickness retrievals from half‐hourly geostationary satellite data (GOES 8 imager), the diurnal short wave aerosol forcing (SWARF) of dust aerosols both at the surface and TOA are calculated for the entire study area (14°N ∼ 26°N, 61°W ∼ 73°W). For selected days, the Clouds and the Earth Radiant Energy System (CERES) TOA shortwave irradiance values from Terra are compared with radiative transfer calculations. Wang et al. [2003] show that the satellite derived aerosol optical thickness is in excellent agreement with Aerosol Robotic Network (AERONET) values. Results of this study show that the calculated direct, diffuse and total DSWI are in excellent agreement with the corresponding SMART values with biases of 1.8%, −3.3% and 0.5% respectively, indicating that dust aerosols are well characterized in the radiative transfer model. This is well within the measured uncertainties (1.3%) and the model uncertainties (5%). The monthly mean value and standard deviation of aerosol optical thickness at 670 nm (AOT670) during PRIDE are 0.26 ± 0.13, and the corresponding monthly mean daytime SWARF values are −12.34 ± 9.62 W m−2 at TOA and −18.13 ± 15.81 W m−2 at the surface, respectively. Our results also show that if diurnal changes in aerosol optical thickness are not considered, it leads to uncertainties in SWARF of 4 W m−2 at the surface and 2 W m−2 at the TOA. The CERES TOA short wave irradiance underestimates calculated values by about 10 W m−2 mainly due problems in misclassification of aerosols and lack of aerosol angular dependence models (ADMs) in the current CERES algorithms. This study is among the first to demonstrate the potential of the GOES 8 imagers in retrieving aerosol optical thickness and estimating the daytime diurnal SWARF of dust, both at the TOA and surface, in low to moderate dust loading regions over the oceans.
Absorption of shortwave radiation in a cloudy atmosphere: Observed and theoretical estimates during the second Atmospheric Radiation Measurement Enhanced Shortwave Experiment (ARESE)
Authors: O'Hirok William , Gautier Catherine
Published: July 2003

The ARM Enhanced Shortwave Experiment (ARESE) II was conducted in spring 2000 to address unresolved issues about the absorption of solar radiation in the atmosphere in the presence of clouds. In this study, apparent atmospheric absorption derived from surface and aircraft measurements are compared to 3‐D radiative transfer model computations. Three cloud fields are examined with the heaviest overcast condition of 29 March being the most reliable from the standpoint of cloud structure and sampling. For this cloud field the model underestimates absorption by 18 W m−2 (9%) when compared to the Kipp and Zonen CM‐22s and by 35 W m−2 (18%) compared to the Scripps Institution for Oceanography Radiation Measurement System. By including aerosols with modest absorbing properties into the model computations, the discrepancy is isolated to the near‐infrared spectral region (0.68–3.9 μm). A comprehensive sensitivity analysis demonstrates that to match simultaneously the observed absorptance, transmittance, and cloud albedo with theory, cloud droplets must have optical properties similar to droplets with sizes three to four times as large as inferred in this study's cloud retrievals.
International Photolysis Frequency Measurement and Model Intercomparison (IPMMI): Spectral actinic solar flux measurements and modeling
Authors: Bais A. F. , Madronich S. , Crawford J. , Hall S. R. , Mayer B. , van Weele M. , Lenoble J. , Calvert J. G. , Cantrell C. A. , Shetter R. E. , Hofzumahaus A. , Koepke P. , Monks P. S. , Frost G. , McKenzie R. , Krotkov N. , Kylling A. , Swartz W. H. , Lloyd S. , Pfister G. , Martin T. J. , Roeth E.‐P. , Griffioen E. , Ruggaber A. , Krol M. , Kraus A. , Edwards G. D. , Mueller M. , Lefer B. L. , Johnston P. , Schwander H. , Flittner D. , Gardiner B. G. , Barrick J. , Schmitt R.
Published: July 2003

The International Photolysis Frequency Measurement and Model Intercomparison (IPMMI) took place in Boulder, Colorado, from 15 to 19 June 1998, aiming to investigate the level of accuracy of photolysis frequency and spectral downwelling actinic flux measurements and to explore the ability of radiative transfer models to reproduce the measurements. During this period, 2 days were selected to compare model calculations with measurements, one cloud‐free and one cloudy. A series of ancillary measurements were also performed and provided parameters required as input to the models. Both measurements and modeling were blind, in the sense that no exchanges of data or calculations were allowed among the participants, and the results were objectively analyzed and compared by two independent referees. The objective of this paper is, first, to present the results of comparisons made between measured and modeled downwelling actinic flux and irradiance spectra and, second, to investigate the reasons for which some of the models or measurements deviate from the others. For clear skies the relative agreement between the 16 models depends strongly on solar zenith angle (SZA) and wavelength as well as on the input parameters used, like the extraterrestrial (ET) solar flux and the absorption cross sections. The majority of the models (11) agreed to within about ±6% for solar zenith angles smaller than ∼60°. The agreement among the measured spectra depends on the optical characteristics of the instruments (e.g., slit function, stray light rejection, and sensitivity). After transforming the measurements to a common spectral resolution, two of the three participating spectroradiometers agree to within ∼10% for wavelengths longer than 310 nm and at all solar zenith angles, while their differences increase when moving to shorter wavelengths. Most models agree well with the measurements (both downwelling actinic flux and global irradiance), especially at local noon, where the agreement is within a few percent. A few models exhibit significant deviations with respect either to wavelength or to solar zenith angle. Models that use the Atmospheric Laboratory for Applications and Science 3 (ATLAS‐3) solar flux agree better with the measured spectra, suggesting that ATLAS‐3 is probably more appropriate for radiative transfer modeling in the ultraviolet.
A summer simulation of biogenic contributions to ground‐level ozone over the continental United States
Authors: Tao Zhining , Larson Susan M. , Wuebbles Donald J. , Williams Allen , Caughey Michael
Published: July 2003

The role of biogenic emissions in the production of ground‐level ozone has been the subject of considerable scientific investigation. However, because existing studies generally draw their conclusions from simulations of episodes lasting days to a week, there is a need to evaluate the biogenic impact over a relatively long timescale. Moreover, the magnitude of synergistic interaction between anthropogenic and biogenic emissions should be carefully quantified, and this issue is not accounted for in most previous investigations. In this study, we performed a summer seasonal (June to August 1995) model evaluation of surface ozone across the continental United States. A three‐dimensional regional climate, emissions, and air quality modeling system was used to do the simulations. The factor separation (FS) technique was applied to quantify the contributions from biogenic emissions alone and those from the synergy between anthropogenic and biogenic emissions. In the first step of this study, U.S. Environmental Protection Agency's National Emission Trends (NET) 1996 and 2020 “control case” raw anthropogenic emissions inventories were processed through Sparse Matrix Operator Kernel Emissions (SMOKE), an emissions model, to generate the speciated, gridded, and hourly emissions data needed for the air quality model. Next, six air quality simulations were carried out assuming zero emissions, biogenic only emissions, 1995 anthropogenic only emissions, biogenic plus 1995 anthropogenic emissions, 2020 anthropogenic only emissions, and biogenic plus 2020 anthropogenic emissions. The model results show that ground‐level ozone concentrations decrease moderately under the EPA's 2020 emissions scenario for many areas within the continental United States, with large reductions in vast areas of the eastern United States. They also show that the 1995 summer average “total biogenic contribution” to daily maximum surface ozone concentrations can reach 34 ppb. Biogenic emissions are associated with at least 20% of surface ozone concentrations for the most areas of the continental United States, with the peaks reaching more than 40% in California coastal areas, the southeastern states, and northeastern areas. A sizable portion of this “total biogenic contribution,” however, (up to 80% in some areas) is due to the synergy between anthropogenic and biogenic emissions and would thus be influenced by controls on anthropogenic source emissions.
Modulation of the Great Plains low‐level jet and moisture transports by orography and large‐scale circulations
Authors: Byerle Lee A. , Paegle Jan
Published: July 2003

This paper describes orographic processes that modulate the Great Plains low‐level jet (LLJ) and related hydrology of the Mississippi River basin. Mechanical flow deflection by the Rocky Mountains is diagnosed in 50 years of monthly averaged National Centers for Environmental Prediction‐National Center for Atmospheric Research (NCEP‐NCAR) Reanalysis fields and in a series of integrations using a primitive equation version of the Utah Global Model (UGM). Although the mountain profiles are fixed over periods of short‐to medium‐range climate changes, their influence on the LLJ is not stationary because evolving ambient flows produce changing LLJ responses. Ensembles of medium‐range forecasts are made for the 1993 U.S. floods and for the 1988 U.S. drought. The forecasts distinguish some of the observed precipitation differences between these years, but the magnitude of the differences is underestimated. Seasonal and longer‐term changes of the ambient flow occur on large scales, while the response of the LLJ occurs on smaller scales that may promote cloud generation and precipitation. Month‐long simulations with monthly averaged conditions suggest that the Great Plains LLJ is a component of the large‐scale circulation associated with the topography of the western United States. Orography thus provides a scale transfer mechanism that focuses global‐scale features into the regional‐scale responses. These are relevant to precipitation distribution and to moisture budgets of the larger individual river basins comprising the GCIP domain. A theoretical interpretation of the large‐scale, mechanical influence of orography on surrounding low‐level circulations is proposed.
Determining the striking distance of lightning through its relationship to leader potential
Authors: Mazur Vladislav , Ruhnke Lothar H.
Published: July 2003

A new method for estimating lightning leader potential in negative stepped leaders from electric field changes during the first return stroke process in cloud‐to‐ground flashes is applied for determining the striking distance to a ground structure. This method may serve as an alternative to calculating the striking distance from formulas that relate it to the peak return stroke current. Presented are the characteristics of downward leaders (potential, vertical extent, and the length of the final step) and the charges transferred during return strokes; these were obtained from electric field measurements during a thunderstorm in Florida using the line charge model. The final step lengths of the leaders are compared with striking distances calculated using the peak current values of return strokes taken from National Lightning Detection Network data for the same flashes.
Chemical characterization of ambient aerosol collected during the northeast monsoon season over the Arabian Sea: Labile‐Fe(II) and other trace metals
Authors: Johansen Anne M. , Hoffmann Michael R.
Published: July 2003

Ambient aerosol samples were collected over the Arabian Sea during the month of March of 1997, aboard the German R/V Sonne, as part of the German Joint Global Ocean Flux Study (JGOFS) project. This is the third study in a series of analogous measurements taken over the Arabian Sea during different seasons of the monsoon. Dichotomous high‐volume collector samples were analyzed for ferrous iron immediately after collection, while trace metals, anions, and cations were determined upon return to the laboratory. The main crustal component was geochemically well represented by the average crustal composition and amounted to 5.94 ± 3.08 μg m−3. An additional crustal constituent of clay‐like character, rich in water‐soluble Ca and Mg, was seen in the fine fraction in air masses of Arabian origin. Total ferrous iron concentrations varied from 3.9 to 17.2 ng m−3 and averaged 9.8 ± 3.4 ng m−3, with 87.2% of Fe(II) present in the fine aerosol fraction. Fe(II) concentrations accounted for on average 1.3 ± 0.5% of the total Fe. While ferrous iron in the coarse fraction appeared to be correlated with the main crustal component, the fine Fe(II) fraction exhibited a more complex behavior. The anthropogenic contribution to the aerosol, as traced by Pb, Zn, and some anions and cations, was found to be considerably larger, especially during the first 10 days of this cruise, than in previously collected samples from the inter‐monsoon and southwest monsoon of 1995.
Development of a passive microwave global snow depth retrieval algorithm for Special Sensor Microwave Imager (SSM/I) and Advanced Microwave Scanning Radiometer‐EOS (AMSR‐E) data
Authors: Kelly Richard E. J. , Chang Alfred T. C.
Published: July 2003

This paper describes research conducted to develop an integrated snow monitoring algorithm at global and regional scales for the Special Sensor Microwave Imager (SSM/I) and the planned Advanced Microwave Scanning Radiometer‐EOS. Methods to detect global snow cover are well advanced and have been applied routinely at local, regional, and global scales. Current snow cover retrieval methods tend to underestimate snow volume because important fractional forest cover and snowpack physical properties are not well parameterized in simple snow parameter retrieval schemes. Building on a static approach to snow depth retrieval, a spatially dynamic algorithm is described that incorporates information about fractional forest cover and snowpack physical development. SSM/I brightness temperatures of land surfaces are calibrated with ground measurements of snow depth through empirical statistical and geostatistical models to produce globally distributed snow depth estimates. The calibration is based on a 4‐year and a one winter season record of daily snow depth and SSM/I observations. The biasing effect of forest cover on microwave estimates is quantified and short‐term fluctuations of microwave‐estimated snow depth (caused by physical changes in the pack) are reduced by time smoothing daily estimated snow depth values. For the data sets used the estimated snow depth from the new algorithm gives global seasonal errors of 13.7 and 22.1 cm for the two data sets. Further major improvements in snow depth retrieval methods will only be achieved through enhancements to forest and snow metamorphism parameterizations.
On the lithosphere‐atmosphere coupling of seismo‐electromagnetic signals
Authors: Singh Raj Pal , Singh Birbal , Mishra P. K. , Hayakawa M.
Published: July 2003

Employing borehole and terrestrial antennas, vertical electric field components of the naturally occurring very low frequency electromagnetic emissions at the frequency of 3 kHz have been monitored simultaneously at Agra (geographic latitude 27.8°N, longitude 78°E), India, from 15 March 1999 to 30 September 1999. This period of observation included a major seismic swarm activity in the months of March and April which occurred in the Chamoli hills of north India, the next two months of May and June being quiet with respect to local lightning and spheric activities, and the rest of the three months from July to September being highly disturbed due to local lightning and thunderstorm activities. The abnormal electric field changes occurred in the form of noise bursts of varying amplitude and duration and included three kinds of data: (1) noise bursts observed by borehole antenna only, (2) noise bursts observed by terrestrial antenna only, and (3) noise bursts observed by both the antennas. We find that the occurrence of the first kind of data is positively correlated with major seismic activities in the region over the period of observations. The third kind of data indicates coupling between the two antennas dominated overall by atmospheric emissions. The long distance propagation of the seismo‐electromagnetic emissions through the middle layer crust working as waveguide or through seismic faults is found to be associated with large attenuation ≈13 dB/km. Hence, the observation of the emissions at Agra, about 400 km from Chamoli, is interpreted in terms of leakage to the atmosphere through “windows” of low conductivity in the skin layer near the epicenter, possibly produced by some geophysical formations as discussed by other workers and then propagation in the Earth‐ionosphere waveguide.
Simulation‐based analysis of rainrate estimation errors in dual‐wavelength precipitation radar from space
Authors: Adhikari Nanda Bikram , Nakamura Kenji
Published: July 2003

A variety of major sources of rainrate retrieval errors in a conventional dual‐wavelength radar technique (DWRT) as well asZe‐Rmethod are analyzed based on simulations upon utilizing a disdrometer‐measured raindrop size distribution (DSD) as well as vertical rain field structure (VRS) data collected by Tropical Rainfall Measuring Mission’s (TRMM) precipitation radar (PR). A spaceborne dual‐wavelength radar geometry comprising 13.6 and 35 GHz operating frequencies are considered in the simulations. Through first fold of the simulation, we statistically examined the significance of the VRS effect in the DWRT, which is found to be negligible. Next, we attempted to gauge relative sensitivities of the DWRT andZe14(at 13.6 GHz)‐Rmethod to the natural fluctuation of DSD. Statistical error analyses suggest some distinct lower bounds of rainrate retrieval accuracies of the two estimates. For instance, if the minimum sensitivity of 35‐GHz radar is equivalent to about 10 dBZand the rainrate is about 10 mm h−1, DWRT shows ∼51% of improvement in the accuracy for 3‐km range resolution, while it has ∼44% improvement for 1‐km range resolution compared to theZe14‐Rmethod. Finally, the effects of nonuniform rain field (NUR) and mismatching in the observed field‐of‐views (FOV) of the radars are analyzed. It is noticed that the NUR effect introduces small amount of enhancement in the errors comparing to that due to the effect of the DSD variation and/or the coupling of the Mie scattering effect, while mismatching in the FOV significantly enhances errors as well as biases in the DWRT estimates.
Enhancement of the outer approximation method for the solution of concentration‐constrained optimal‐design groundwater‐remediation problems
Authors: Papadopoulou Maria P. , Pinder George F. , Karatzas G. P.
Published: July 2003

Nonlinearity and nonconvexity are two major characteristics of groundwater quality management models. The classical solutions of such problems require enormous computational effort without ensuring a global optimum. To circumvent this problem, the outer approximation method, a global optimization technique, was introduced to solve groundwater quality management problems characterized by a nonconvex objective function with minima at the boundary of the feasible region and constraints that have convex or nonconvex behavior. In this paper, a more sophisticated and computationally efficient approach for the case of the nonconvex constraints is presented. To illustrate the efficacy and efficiency of this new approach, a hypothetical and a field‐scale problem are considered.
Modeling unsaturated flow and transport in the saprolite of fractured sedimentary rocks: Effects of periodic wetting and drying
Authors: Van der Hoven Stephen J. , Solomon D. Kip , Moline Gerilynn R.
Published: July 2003

Whereas a number of unsaturated zone modeling studies have been conducted on dual‐porosity systems where the matrix has low permeability, few have been conducted on systems where the matrix has relatively high permeability. In humid climates, in situ weathering of bedrock can form saprolite. Saprolite usually has high matrix porosity (and variable permeability) that is a reservoir for solute storage and can have relict fractures that transport solute rapidly. On the basis of a field investigation where natural chemical tracers were monitored at high resolution during storm events, a numerical model was created that simulated variably saturated transport in the saprolite. A series of simulations were performed to explore solute transport during cycles of wetting and drying. Modeling results indicated that the advective flux of solutes from the fractures into the matrix during wetting was greater than from the matrix back into the fractures during drying, resulting in a net storage of solutes in the matrix. We hypothesize that the amount of net solute storage in the matrix may increase as the frequency of wetting/drying cycles increases, up to an optimum frequency. At frequencies higher than the optimum, the amount of solute storage in the matrix may decrease because the system behaves more like a fully saturated system where diffusion is the dominant transport process between fractures and matrix. These conclusions have significant implications for such processes as remedial strategies for contaminants in the unsaturated zone, the application of fertilizers, and quantification of mineral weathering and dissolution rates.
Multiple jets and zonal flow on Jupiter
Authors: Jones C. A. , Rotvig J. , Abdulrahman A.
Published: July 2003

We investigate the occurrence of multiple jet zonal flows in the 2D rotating annulus model, extended to include the possibility of boundary friction. We consider Rayleigh numbers up to 10 times critical. Without boundary friction the majority of our solutions are single‐jet zonal flows, but when boundary friction is present, persistent multiple jet solutions are found much more easily. Compared to the stress‐free case, the number of jets increases, though the strength of the zonal flow decreases. The dependence of these features on Ekman and Rayleigh number is discussed, suggesting that at values well beyond the reach of present 3D simulations, solutions resembling the observed jovian zonal flow may exist. The boundary condition at the metallic/insulating hydrogen interface will be an important part of any explanation of the occurrence of multiple jets on the planet Jupiter.
A linear relationship between ENSO intensity and tropical instability wave activity in the eastern Pacific Ocean
Authors: Yu Jin‐Yi , Liu W. Timothy
Published: July 2003

The interannual variations of tropical instability waves (TIWs) in the eastern Pacific Ocean and their relationships with ENSO intensity are studied using a 28‐year long coupled atmosphere‐ocean general circulation model (CGCM) simulation. The activity of TIWs is measured by the root‐mean‐square value of the 50‐day high‐pass filtered sea surface temperature (SST) perturbations produced in the simulation. The CGCM realistically produces two branches of large TIW activity near the equator: one at 2°N and the other at 2°S. It is found that along both branches there are linear relationships between the year‐to‐year variations of TIW activity and those of ENSO intensity. TIW activity is enhanced or reduced in proportion to the NINO3 SST anomalies, with larger activity in La Niña years and smaller activity in El Niño years. It is found that ENSO modulates TIW activity in both branches primarily by changing the latitudinal SST gradient associated with the SST front immediately north of the equator. Weaker correlations are found between the year‐to‐year variations of TIW activity and those of the ocean current shears between the south equatorial current and the equatorial undercurrent or the north equatorial countercurrent. This CGCM study suggests that the baroclinic instability associated with the northern SST front is a major generation mechanism for both the northern and southern TIW branches in the eastern Pacific Ocean.
Recent frequent dust events and their relation to surface wind in East Asia
Authors: Kurosaki Yasunori , Mikami Masao
Published: July 2003

A remarkable increase in dust outbreaks has occurred in the eastern part of the Asian Continent over the last three years (2000–2002) compared with the previous seven years (1993–1999). This finding corresponds well with the annual change of Kosa (i.e., yellow sand) events for the same period in Japan. Dust outbreaks occurred in limited regions around southern Mongolia, the Badain Jaran Desert, and the western Loess Plateau from 1993–1999. However, the area of frequent dust outbreaks expanded extensively to the east, and dust outbreaks also frequently occurred in regions around the North China Plain, northeastern China, and the Korean Peninsula in 2000–2002. Good correspondence was found between the surface wind and dust outbreaks in year‐to‐year variations and in spatial distributions. This indicates that frequent strong winds are the primary cause of the recurrent dust outbreaks in the last three years.
Large scale atmosphere‐ocean anomalies in the northeast Pacific during 2002
Authors: Murphree Tom , Bograd Steven J. , Schwing Franklin B. , Ford Bruce
Published: July 2003

In summer‐fall 2002, the coastal northeast Pacific (NEP) was characterized by anomalously cool, fresh waters extending from Vancouver Island to southern California, increased equatorward transport in the California Current System (CCS), and higher surface productivity in the northern CCS. The evolution of large scale atmosphere‐ocean anomalies in the NEP from winter 2001–02 through fall 2002 contributed to these coastal anomalies by setting up wind stress anomalies that led to: 1) anomalous transport of subarctic waters into the North Pacific Current (NPC); 2) enhanced eastward flow in the NPC; 3) anomalously strong upwelling in the CCS; and 4) enhanced equatorward transport in the CCS.
Tropical/Extratropical forcing of the AO/NAO: A corrigendum
Authors: Greatbatch Richard J. , Lin Hai , Lu Jian , Peterson K. Andrew , Derome J.
Published: July 2003

In two of our previous papers, we described the separate influence of tropical and extratropical forcing on the North Atlantic (NAO) and the Arctic (AO) Oscillations. Here, we point out a problem with the way the split between tropical and extratropical forcing was carried out. In the corrected model results, we find that extratropical forcing dominates tropical forcing in accounting for interannual variance in both the observed NAO and AO indices. We find that the recent upward trend in the NAO index is driven from the tropics, whereas for the AO index, we now find that extratropical forcing also contributes to the upward trend in the model. It follows that our corrected model results do not support a strong link between tropical forcing and the interannual variability of the wintertime AO, as claimed previously.
Anomalous satellite‐measured chlorophyll concentrations in the northern California Current in 2001–2002
Authors: Thomas Andrew C. , Strub P. Ted , Brickley Peter
Published: July 2003

Five years (1997–2002) of northern California Current SeaWiFS ocean color data place cold, low salinity hydrographic anomalies observed in summer 2002 into a larger spatial/temporal context and present their biological ramifications. Monthly mean chlorophyll concentrations were >1.0 mg m−3 larger than the previous 3 year average over the entire shelf from British Columbia (BC) to northern California (CA) in 2001–2002, spatially most extensive over the BC and Washington (WA) shelves but strongest (>2.0 mg m−3) on the southern Oregon shelf. Positive anomalies develop in August 2001 off BC and October 2001 off WA. By October 2002, shelf anomalies are reduced. Offshore, spatially extensive anomalies develop off CA (36°–42°N) in fall 2002, disappearing by December. Concurrent altimeter data show over 1000km of equatorward displacement. The positive chlorophyll anomalies, their spatial patterns and displacement are consistent with advection of subarctic, nutrient‐enriched water into the California Current.
African dust aerosols as atmospheric ice nuclei
Authors: DeMott Paul J. , Sassen Kenneth , Poellot Michael R. , Baumgardner Darrel , Rogers David C. , Brooks Sarah D. , Prenni Anthony J. , Kreidenweis Sonia M.
Published: July 2003

Measurements of the ice nucleating ability of aerosol particles in air masses over Florida having sources from North Africa support the potential importance of dust aerosols for indirectly affecting cloud properties and climate. The concentrations of ice nuclei within dust layers at particle sizes below 1 μm exceeded 1 cm−3; the highest ever reported with our device at temperatures warmer than homogeneous freezing conditions. These measurements add to previous direct and indirect evidence of the ice nucleation efficiency of desert dust aerosols, but also confirm their contribution to ice nuclei populations at great distances from source regions.
A 2,326‐year tree‐ring record of climate variability on the northeastern Qinghai‐Tibetan Plateau
Authors: Zhang Qi‐Bin , Cheng Guodong , Yao Tandong , Kang Xingcheng , Huang Jianguo
Published: July 2003

High‐resolution climate proxy records covering the last two millennia on the Qinghai‐Tibetan Plateau are scarce yet essential to evaluation of the patterns, synchroneity and spatial extent of past climatic changes including those in the Medieval Warm Period (MWP) and the Little Ice Age (LIA). Here we present a 2326‐year tree‐ring chronology of Sabina przewalskii Kom. for Dulan area of northeastern Qinghai‐Tibetan Plateau. We find that the annual growth rings mainly reflect variations in regional spring precipitation. The greatest change in spring precipitation during the last two millennia seems to occur in the second half of the 4th century. The North Atlantic MWP was accompanied by notable wet springs in the study region during A.D. 929–1031 with the peak occurring around A.D. 974. Three intervals of dry springs occurred in the period of LIA. Our tree‐ring data will facilitate intercontinental comparisons of large‐scale synoptic climate variability for the last two millennia.
Enhanced southward flow over the Oregon shelf in 2002: A conduit for subarctic water
Authors: Kosro P. Michael
Published: July 2003

Moored current measurements from the Oregon shelf during 1998–2003 are used to estimate time series of anomalous alongshore currents and pseudo‐displacements, after accounting for the mean and seasonal cycle. From early January through mid‐June, 2002, currents at 10 m were anomalously strong toward the south by an average 12 cm/s, producing an anomalous displacement of more than 1500 km over about 5 months. This may be compared with the finding by Freeland et al. [2003] that waters at the same latitude off Oregon, and off Vancouver Island, were anomalously cool and fresh at depths between 30 and 150 m, suggesting displacement from a more northern source. Anomalous displacements of several hundred kilometers were also found during at least three other periods in the record. Moored temperature measurements at the same location confirm that local waters were persistently cooler during March to October of 2002 than during the previous two years, with the strongest anomaly near 20 m. Coastal sea levels were lower than usual along the northwest coast during spring and early summer 2003, consistent with a southward current anomaly of large scale. Local winds near Newport did not show strong mean anomalies during this period.
Anomalous subarctic influence in the southern California Current during 2002
Authors: Bograd Steven J. , Lynn Ronald J.
Published: July 2003

A highly anomalous water mass of apparent subarctic origin, characterized by negative temperature and salinity anomalies, high concentrations of dissolved oxygen and inorganic nutrients, and unusually high chlorophyll fluorescence, was observed off southern California during summer 2002. This water mass was confined spatially to a narrow ribbon in the upper pycnocline: at a density of σt = 25.0 kg m−3 and ∼150–350 km offshore, within and seaward of the main California Current core. These observations are very similar to those made off the Oregon and Vancouver Island coasts at about the same time, implying a displacement of subarctic waters more than 1200 km equatorward within the California Current. The maintenance of strong water property anomalies over this distance demonstrates the efficacy of the California Current as a conduit of water masses and plankton. The magnitude of the anomalies observed in July 2002 suggest the occurrence of the largest subarctic intrusion into the California Current System in the 50+ year historical record and may reflect low‐frequency climate variability.
Seismic anisotropy in gas‐hydrate‐ and gas‐bearing sediments on the Blake Ridge, from a walkaway vertical seismic profile
Authors: Pecher Ingo A. , Holbrook W. Steven , Sen Mrinal K. , Lizarralde Daniel , Wood Warren T. , Hutchinson Deborah R. , Dillon William P. , Hoskins Hartley , Stephen Ralph A.
Published: July 2003

We present results from an analysis of anisotropy in marine sediments using walkaway vertical seismic profiles from the Blake Ridge, offshore South Carolina. We encountered transverse isotropy (TI) with a vertical symmetry axis in a gas‐hydrate‐bearing unit of clay and claystone with Thomsen parameters ε = 0.05 ± 0.02 and δ = 0.04 ± 0.06. TI increased to ε = 0.16 ± 0.04 and δ = 0.19 ± 0.12 in the underlying gas zone. Rock physics modeling suggests that the observed TI is caused by a partial alignment of clay particles rather than high‐velocity gas‐hydrate veins. Similarly, the increase of TI in the gas zone is not caused by thin low‐velocity gas layers but rather, we speculate, by the sharp contrast between seismic properties of an anisotropic sediment frame and elongated gas‐bearing pore voids. Our results underscore the significance of anisotropy for integrating near‐vertical and wide‐angle seismic data.
Altimeter estimates of anomalous transports into the northern California Current during 2000–2002
Authors: Strub P. Ted , James Corinne
Published: July 2003

Surface transports into the California Current are calculated from TOPEX/POSEIDON altimeter surface height slopes during the 9.5 year period from October 1992–May 2002. These quantify the anomalous onshore and southward displacements of the water column during the 2000–2002 period, which had been hypothesized by others based on anomalous water properties observed in mid‐2002 off Oregon. Anomalous eastward transport into the boundary between 52°–54°N occurred first (mid‐2000 to mid‐2001) followed by eastward transport into the boundary between 50°–52°N in 2001. Equatorward transports during 2001 and 2002 resulted in approximately 800 km of anomalous southward displacements during the 1.5 years prior to the anomalous observations off Oregon. This sequence suggests that both onshore and southward displacement anomalies off British Columbia and the Pacific Northwest contributed to the subarctic characteristics of the water observed off Oregon.
Large‐scale global surface mass variations inferred from GPS measurements of load‐induced deformation
Authors: Wu Xiaoping , Heflin Michael B. , Ivins Erik R. , Argus Donald F. , Webb Frank H.
Published: July 2003

Detrended crustal deformation measurements from a global network of up to 200 continuous Global Positioning System (GPS) tracking sites are inverted for low degree and order (n, m ≤ 6) spherical harmonic series of surface mass variations. An independent geophysical model of the atmosphere, oceans, and water and snow on land is also used to guide the spherical harmonic truncation and to evaluate aliasing errors in the results. Inversion uncertainties decrease significantly as spatial coverage and data quality improve with time, especially in the last few years. Consequently, GPS inverted seasonal geocenter and low degree zonal harmonics converge to those determined by measurements from satellite laser ranging (SLR). Significant n > 1 and non‐zonal variations have also been found.
Finite element analysis and approximate estimation of the cross coupling effect in fractured reservoirs
Authors: Lewis Roland W. , Pao William K. S. , Yang Xin‐She
Published: July 2003

The influence of cross coupling terms in double porosity models for fractured reservoirs has been studied in this paper using numerical and perturbation methods. Attention is focused on the influence of the cross coupling coefficients on the transient solutions for the matrix and fissure pressures. Numerical simulations show that the addition of the cross coupling terms is equivalent to reducing the compressibility of the matrix block. A simple approximate solution is proposed for a quick estimation of the significance of the cross coupling effect in reservoir simulation, based on the solution of an uncoupled model.
Validating the microwave sounding unit stratospheric record using GPS occultation
Authors: Schrøder Thomas , Leroy Stephen , Stendel Martin , Kaas Eigil
Published: July 2003

We validate the temperature climatology recorded by the Microwave Sounding Unit with GPS occultation data collected by the GPS/MET experiment. We choose to validate only the lower stratospheric MSU climatology in order to circumvent the wet‐dry ambiguity associated with GPS occultation in the mid‐ to lower troposphere. We simulate the lower stratospheric channel's brightness temperature by convolving each GPS/MET temperature profile with a vertical weighting function and then map the irregularly gridded data using a Bayesian interpolation scheme. In northern polar night, the MSU Tls deviates from GPS occultation by as much as 10 K while occultation is consistent with the NCEP Reanalysis used for diagnostic purposes. NCEP and GPS occultation deviate by 1 K in the tropics, consistent with a warm bias in NCEP Reanalysis. GPS occultation renders the problems MSU encounters with inter‐satellite calibration obsolete, because calibration by atomic clocks is free of systematic error and can completely cover the diurnal cycle.
Ground‐based observation of high‐altitude, high‐temperature emission in the O2 atmospheric band nightglow
Authors: Slanger T. G. , Cosby P. C. , Huestis D. L.
Published: July 2003

O2(b1Σg+ − X3Σg−) atmospheric band emission, when viewed from the ground outside the auroral zone, is considered to originate in the 90–100 km altitude region, from O‐atom recombination. However, the v = 0,1 levels of the b1Σg+ state can also be generated through an energy transfer process, when O(1D) collides with O2. In the absence of specific altitude information, as in ground‐based measurements, the two sources can still be distinguished because of different characteristic temperatures. We have analyzed sky spectra from the Keck I and II telescopes on Mauna Kea, contrasting solar minimum and maximum conditions and variations with time of night. Utilizing the O2(b‐X) 1‐1 band, we find that in averaged solar minimum conditions, ∼75% of the emission comes from an altitude corresponding to 200 K, while ∼25% has a temperature near 700 K and therefore originates at high altitude. The fraction of high‐temperature emission is often considerably greater early in the evening. At solar maximum, the high altitude component can be dramatically enhanced in the early evening; emission in the 1‐1 band reaches intensitities of 100–150 R, with a rotational temperature near 1000 K. We also observe high‐J b‐X 0‐0 band lines penetrating the Fraunhofer A‐band region, the normal absorption becoming emission. Emission intensites deduced from such observations indicate that the ionospheric 0‐0 band is at least as intense as the 1‐1 band, as expected.
Nonlinear dynamics of inertial Alfvén waves in the upper ionosphere: Parametric generation of electrostatic convective cells
Authors: Pokhotelov Oleg A. , Onishchenko Oleg G. , Sagdeev Roald Z. , Treumann Rudolf A.
Published: July 2003

We consider the excitation of convective cells in the parametric decay of finite amplitude (inertial) Alfvén waves. We formulate a set of coupled equations describing the nonlinear interaction of Alfvén waves and the electrostatic convective mode and obtain the nonlinear dispersion relation for electrostatic convection cells. Generation of convection cells takes place only when dispersive effects due to the electron skin depth come into play. The generation of such cells is due to the Reynolds stresses of short‐scale Alfvén waves. These are nonzero when the perpendicular Alfvén wavelengths are of the order of the collisionless electron skin depth. The convective cells are nonoscillatory two‐dimensional modes with wave vector perpendicular to that of the pump Alfvén wave. The nonlinear growth rate of these cells is a sensitive function (proportional to k5) of the wave number k of the Alfvénic pump wave. This implies that the instability transfers wave energy from the short wavelength regime of the inertial Alfvén wave to the long wavelength regime of the convective cells which is typical for an inverse turbulent cascade. We also discuss the relation of the new parametric regime to the parametric wave‐wave interaction of two counterstreaming inertial Alfvén waves. Application to satellite observations of inertial Alfvén waves in the auroral ionosphere shows agreement of the scales and explains the observed large amplitudes of the waves. It is shown that convective cells produced by the parametric instability could cause the fine structure of the turbulent Alfvén boundary layer and can play an important role in the ionospheric plasma turbulence as well as the energy source for auroral structures.