bluuebunny/crossref_metadata_2025 huggingface dataset:
Possible effects of iron fertilization in the Southern Ocean on atmospheric CO2 concentration
Authors: Joos Fortunat , Siegenthaler Ulrich , Sarmiento Jorge L.
Published: April 2008

Recently, it was proposed (Baum, 1990 and Martin et al, 1990a, 1990b) that the southern ocean should be fertilized with iron to stimulate biological productivity, thus enhancing the flux of organic carbon from surface to depth, thereby lowering the concentration of inorganic carbon in surface water and in turn the atmospheric CO2 concentration. We explore the possible impact of a hypothetical iron fertilization on atmospheric CO2 levels during the next century using a high‐latitude exchange/interior diffusion advection model. Assuming as an upper‐limit scenario that it is possible to stimulate the uptake of the abundant nutrients in the southern ocean, the maximum atmospheric CO2 depletion is 58 ppm after 50 years and 107 ppm after 100 years. This scenario requires completely effective Fe fertilization to be carried out over 16% of the world ocean area. Sensitivity studies and comparison with other models suggest that the errors in these limits due to uncertainties in the transport parameters, which are determined by calibrating the model with radiocarbon and validated with CFC‐11 measurements, range from −29% to +17%. If iron‐stimulated biological productivity is halted during the six winter months, the additional oceanic CO2 uptake is reduced by 18%. Possible changes in surface water alkalinity alter the result of iron fertilization by less than +9% to −28%. Burial of the iron‐induced particle flux as opposed to remineralization in the deep ocean has virtually no influence on the atmospheric response for the considered time scale of 100 years. If iron fertilization were terminated, CO2 would escape from the ocean and soon cancel the effect of the fertilization. The factors which determine the atmospheric CO2 reduction most strongly are the area of fertilization, the extent to which biology utilizes the abundant nutrients, and the magnitude of future CO2 emissions. The possible effect of fertilizing the ocean with iron is small compared to the expected atmospheric CO2 increase over the next century, unless the increase is kept small by means of stringent measures to control CO2 emissions.
Atmospheric iron inputs and primary productivity: Phytoplankton responses in the North Pacific
Authors: Young R. W. , Carder K. L. , Betzer P. R. , Costello D. K. , Duce R. A. , DiTullio G. R. , Tindale N. W. , Laws E. A. , Uematsu M. , Merrill J. T. , Feely R. A.
Published: April 2008

As part of the Asian Dust Inputs to the Ocean System (ADIOS) project, atmospheric dust fluxes and primary productivity were monitored during the dusty season (spring) of 1986 at 26°N, 155°W, in the North Pacific Ocean. The arrival of major pulses of dust from Asia was followed by major increases in primary production. Extensive chemical analyses of the atmospheric particles showed that they were iron‐rich (10‐15%) and, further, that if only a small proportion (e.g. 10%) of this iron dissolved in the euphotic zone, it would be sufficient to support the increases in carbon production at this location. The systematic increases in production noted with increasing depth and time may result from a continual release of iron from the settling particles in the euphotic zone. At all depths, systematic decreases in production followed the initial surge in production, indicating that the phytoplankton may have evolved from being iron‐limited to being nitrogen‐limited. Comparison of particle concentrations calculated by a particle settling model with primary productivity profiles indicated that mineral particles with settling velocities equivalent to those of 14 to 18‐μm‐diameter spherical quartz particles were the most likely source for the iron stimulating the increases in primary production.
Mitigation of methane emissions from rice fields: Possible adverse effects of incorporated rice straw
Authors: Sass R. L. , Fisher F. M. , Harcombe P. A. , Turner F. T.
Published: April 2008

Increased world demand for rice production may lead to an increase in methane emission to the atmosphere and future global warming. One suggested way to reduce methane emission is to discourage the practice of incorporating previous crop residue prior to planting rice, since the residue may enhance methane emission from flooded rice fields. This concept is supported by data from a 2‐year study of flooded rice fields on two different soil types in Texas. In 1990, rice stubble from 1989 was incorporated into both soils. Seasonal methane emission from a Lake Charles clay field increased from 15.9 g m−2 in 1989 to 31.0 g m−2 in 1990. In the Beaumont clay field, seasonal methane emission increased from 4.5 to 11.4 g m−2. While methane emission increased between 1989 and 1990, grain yield dropped by 2100 and 840 kg ha−1 in the Lake Charles and Beaumont fields, respectively. Visual inspection at harvest indicated that the 1990 rice yield decrease resulted from grain abortion, presumably caused by the rice cultivar's sensitivity to soil anaerobiosis. The calculated amount of organic carbon not translocated to grain was comparable to the estimated amount of organic carbon required for the increased methane emission. We hypothesize that labile carbon in straighthead susceptible rice cultivars can "leak" from roots damaged by excessively anaerobic soil and be metabolized to its equivalent in methane. These data suggest that minimizing incorporation of crop residue prior to planting can decrease methane emission from flooded rice and reduce the potential for yield loss, particularly with some cultivars and in soils with low rates of seepage and percolation.
The effect of vertical nutrient redistribution on surface ocean δ13C
Authors: Keir Robin S.
Published: April 2008

Processes that shift nutrients from mid to lower ocean depths may or may not increase the ocean's vertical carbon pump. Redistribution of δ13C produced by these processes is compared in two box models: a vertical three‐box ocean and a thirteen‐box ocean. In the former there is no δ13C fractionation laterally between surface waters, and the ocean nutrient and δ13C distributions are linearly correlated. This correlation is not changed when these tracers become redistributed, and if the model surface ocean is nutrient limited, the surface δ13C cannot change. In the 13‐box ocean there is a transfer of negative δ13C from the cold surface water through the atmosphere into the warm ocean. Its δ13C is therefore lower than it would be as a result of the carbon pump by itself. If a middepth nutrient depletion occurs because of lower nutrients in Antarctic waters, the warm surface δ13C increases. If the vertical nutrient shift occurs because of ocean circulation or biological recycling changes, the warm surface water δ13C change depends on the ratio of its vertical CO2 fluxes, i.e., exchange of atmospheric CO2 versus upwelling total CO2 and net biological production. If this ratio remains about the same, then little change occurs in surface δ13C, and the δ13C of Pacific deep water decreases about 0.3%. In this case, no change in the average ocean δ13C is required to explain observations from sediment data. This would imply that the ice age land biota carbon mass was about the same as that of today. The vertical CO2 flux ratio could be an important consideration if greater wind‐driven upwelling is a factor in the nutrient redistribution.
False advertising in the greenhouse?
Authors: Banse K.
Published: April 2008

Most scientists are convinced of the importance of their own research subjects. Broecker [1991] has deplored the temptation, if not the tendency, to go overboard and exaggerate this importance once funding enters the mind. In particular, he alleges inflated or even false claims by biological (and other) oceanographers regarding the relevance of their research to the “greenhouse effect,” caused by the anthropogenic enhancement of the atmospheric CO2 content. He writes [Broecker, 1991, p. 191]: “In my estimation, on any list of subjects requiring intense study with regard to the prediction of the consequences of CO2 buildup in the atmosphere, I would place marine biological cycles near the bottom.”
VHF radar interferometry measurements of vertical velocity and the effect of tilted refractivity surfaces on standard Doppler measurements
Authors: Palmer Robert D. , Larsen Miguel F. , Woodman Ronald F. , Fukao Shoichiro , Yamamoto Mamoru , Tsuda Toshitaka , Kato Susumu
Published: April 2008

At VHF wavelengths, aspect sensitivity may result in an apparent beam direction that is off vertical even for a nominally vertically pointing beam direction if the refractivity surfaces responsible for the scatter are tilted with respect to the horizontal plane. Middle and upper atmosphere radar measurements obtained by using the system in a standard multireceiver configuration typical for radar interferometry (RI) and spaced antenna measurements have been analyzed for evidence of such effects. The analysis is based on the linear variation of the cross‐spectral phase as a function of the radial velocity in the frequency domain for the RI cross spectra. True‐vertical velocity estimates are obtained by using the fact that the phase difference between two antennas should be equal to zero when the echoes are being received from the vertical direction. The tilt angles of the refractivity surfaces were obtained from the phase of the cross‐correlation function at zero lag, and the radial velocity in that direction was determined from the cross spectra. The results indicate that the vertical velocity derived from standard Doppler analyses is actually the velocity perpendicular to the refractivity surfaces and thus can be biased by the projection of the horizontal wind along the effective pointing direction.
Frequency and transient analysis of a thin conductive slab in lossy Earth due to a uniform magnetic line source
Authors: Nabulsi K. A. , Iskanderani A. I. , Banah A. H.
Published: April 2008

In this paper we present frequency and transient analysis of a thin tabular conductive slab in lossy Earth due to a uniform magnetic line source excitation. The line source is parallel to the slab, and thus the problem is two dimensional. Under these conditions the frequency domain solution can be expressed in the form of a series which has an exact time domain representation. Our results are checked against two well‐known limiting cases. This problem can model ore slabs and fluid‐filled cracks in geophysical applications. The analytical and numerical results give a diagnosis of the thickness and conductivity of the slab and provide physical insight in the interpretation of actual field data.
Observations of quasi‐periodic scintillations and their possible relation to the dynamics of Es plasma blobs
Authors: Maruyama Takashi
Published: April 2008

Quasi‐periodic scintillations at a mid‐latitude station, Wakkanai, Japan, are examined using 136‐MHz geostationary satellite transmissions. Observations are compared with the ionospheric parameter obtained at the same station and random scintillation records. The results indicate that the quasi‐periodic scintillations are most likely produced by plasma blobs within the sporadic E layers. Discussion focuses on characteristics of the ringing pattern which precedes and follows the primary deep fade‐out, in field strength. In the majority of events the ringing pattern tends to develop after the distinct deep fade‐out, i.e., the pattern is asymmetric. Quasi‐periodic scintillation patterns are produced by the movement of plasma blobs in the case of geostationary satellite experiments. Thus the shape of the blob must be deformed so that a steep density gradient is attained on the backside. When the blob is highly deformed by the plasma instability which grows at the steep density gradient, burstlike random scintillations may be produced by the blob.
Evaluation of six ionospheric models as predictors of total electron content
Authors: Brown Lincoln D. , Daniell Robert E. , Fox Matthew W. , Klobuchar John A. , Doherty Patricia H.
Published: April 2008

We have gathered total electron content (TEC) data from a range of mid‐latitudes and low latitudes and longitudes for a wide range of solar activity. This data was used to evaluate the performance of six publicly available ionospheric models as predictors of total electron content. TEC is important for correcting modern DoD space systems, which propagate radio waves from the earth to satellites, for time delay effects of the ionosphere. The TEC data were obtained from polarimeter receivers located in North America, the Pacific, and the East coast of Asia. The ionospheric models evaluated are (1) the International Reference Ionosphere, (2) the Bent model, (3) the Ionospheric Conductivity and Electron Density model, (4) the Penn State model, (5) the Fully Analytic Ionospheric Model, and (6) a hybrid model consisting of the Union Radio Scientifique Internationale 88 (URSI‐88) coefficients coupled with the Damen‐Hartranft profile model. We will present extensive comparisons between monthly median TEC and model TEC obtained by integrating electron density profiles produced by the six models. These comparisons demonstrate that although most of the models do very well at representing ƒ0F2, none of them do very well with TEC, probably because of inaccurate representation of the topside profile. We suggest that one approach to obtaining better representations of TEC is the use of ƒ0F2 from the CCIR or URSI‐88 coefficients coupled with a good climatological slab thickness model.
HF channel occupancy and band congestion: The other‐user interference problem
Authors: Stehle Roy H. , Hagn George H.
Published: April 2008

Information on other‐user interference is important in predicting the performance of high frequency (HF) systems. For many systems, especially frequency‐hopping systems, other‐user interference frequently is more important than man‐made noise from incidental radiators (for example, power lines) or atmospheric noise from lightning. Occupancy of individual channels and congestion of allocated HF bands (for example, fixed and mobile, amateur) vary with type of service, frequency, time of day, season, angle of arrival, type of receiving antenna, bandwidth, threshold, geographic location, and sunspot number. This paper summarizes channel occupancy and band congestion observations made in the continental United States and Europe in 1987 with SRI International's Mobile Spectrum Monitoring Unit. The data on band congestion are compared with the empirical model developed by researchers at the University of Manchester Institute for Science and Technology (UMIST), Manchester, United Kingdom. A concept for extending the UMIST model for congestion at a point to a model for congestion within a region is described.
Effects of absorption on high‐latitude meteor scatter communication systems
Authors: Ostergaard J. C. , Weitzen J. A. , Kossey P. A. , Bailey A. D. , Bench P. M. , Li S. W. , Katan J. R. , Coriaty A. J. , Rasmussen J. E.
Published: April 2008

Data acquired with the Geophysics Laboratory's high‐latitude meteor scatter test‐bed between Sondrestrom Air Base (AB) and Thule AB, Greenland, during the solar disturbances of March and August 1989 are presented. These disturbances provided a unique opportunity to observe a number of naturally occurring disturbance effects on meteor scatter links operated in the frequency range (35 to 147 MHz) covered by the test‐bed. The disturbances range from signal absorption to system noise variations. The properties of ionospheric absorption in general are discussed and illustrated with computations using electron density profiles from the September 1978 solar proton event (SPE). It has been found that accurate measurements of high levels of ionospheric absorption with riometers pose special problems. These problems are identified and discussed. The data acquired during the March and August 1989 solar disturbances are then related to the zenith absorption measured at Thule, and the influence of absorption as well as system noise variations are discussed. The two events presented are very different. The August event was dominated by ionospheric absorption which affected meteor arrival rates and duty cycles primarily at the lower frequencies (35 and 45 MHz), although some effects could also be seen at the higher frequencies (65 to 147 MHz). The March event combined weak ionospheric absorption with large solar noise bursts. The effects of this event on the test‐bed were dominated by increased solar noise at all frequencies. The relative influence of solar noise and ionospheric absorption during SPE events is discussed along with speculation as to the validity of frequency dependence conclusions based on testing of the JANET system.
HF noise environment models
Authors: Keller Catherine M.
Published: April 2008

An L‐shaped antenna array with a large aperture is used for characterizing the spatial distribution and temporal variability of the noise environment for several frequencies in the high‐frequency (HF) band. The process of whitening is used to compare spatial covariance matrices constructed from data collected on the array. The eigenvalue spread and the maximum likelihood method (MLM) spectrum are measures applied to these spatial covariance matrices to characterize the spatial distribution of the sources of HF noise. MLM spectra of the HF noise environment show a fairly flat distribution, but there is higher noise power in the directions of the continental U.S. In the temporal variability analysis it is determined that the HF noise environment at lower HF frequencies (8 and 10 MHz) has an underlying structure that is fairly stationary; the noise environment at 16 MHz does not show this stationarity. Models for HF noise fields are compared to the data. The model including both a symmetrical sky noise field and receiver thermal noise fits the data the best of the models examined.
The investigations of the atmospheric precipitations by using Chung‐Li VHF radar
Authors: Chu Yen‐Hsyang , Chian Lee‐Po , Liu Chao‐Han
Published: April 2008

In this paper the results of precipitation observed by Chung‐Li VHF radar during the passage of typhoon Susan through the Taiwan area on June 2, 1988, are presented. We find that VHF radar can not only observe the falling speed of the rain drops but can also detect that of the ice particles. The observational results show that the former is about 6–8 m/s, while the latter is about 1 m/s, consistent with those observed by the conventional Doppler meteorological radar. The echo power due to precipitation is generally far smaller than that due to atmospheric refractivity fluctuations. However, it is enhanced strikingly at the height of melting layer (about 5 km in Taiwan area), and its value can be greater than that due to refractivity fluctuations by about 5 dB. Moreover, it also shows that the feature of bright band only occurs in the echo power profile of precipitation, and it cannot be observed in that of atmospheric refractivity. The echo power profiles of the vertical and oblique beams (with zenith angle 17°) are also examined. They indicate that there is no aspect sensitivity for the echoes scattered from the atmospheric refractivity fluctuations during the precipitating environment. However, for the echo power of precipitation the feature of aspect sensitivity does exist above the melting layer and disappears below this altitude. The correlation between the horizontal wind speed and the Doppler spectral width of precipitation is found to be fairly high, with a correlation coefficient of 0.86. This suggests that the beam‐broadening effect due to the advection of horizontal wind may be one of the important factors contributed to the precipitation spectral width and has to be taken into consideration when the precipitation spectra are analyzed.
A sensitivity study of weather data inaccuracies on evaporation duct height algorithms
Authors: Cook John
Published: April 2008

The sensitivity of five evaporation duct height algorithms to errors in shipboard meteorological data is examined, and the algorithms are intercompared. The data set used was generated parametrically so a large variation of environmental conditions could be considered. The errors in the meteorological data consisted of two types: uncorrelated random errors associated with sensor inaccuracies and both random and systematic errors due to the influence of ship‐induced distortions. Before considering any errors, however, algorithm‐to‐algorithm differences of 10%–70% in the computed duct height are demonstrated and related to the assumptions and simplifications used during algorithm development. The sensitivity study shows that although the evaporation duct height algorithms have different genealogies, they have similar sensitivities. The sensitivities to errors caused by sensor inaccuracies range from 10% to 50% relative uncertainty in the calculated duct height, except for extremely low duct heights where the uncertainties are greater. During the daytime the relative uncertainties due to errors caused by ship‐induced distortions are approximately 10%–20% higher than those due to the sensor errors, and they are about 50%–75% smaller at night because of a lack of solar heating of the ship. These conclusions represent a best‐case scenario for Navy operational applications because of the omission of some sources of error, the optimistic ship error characteristics used, and the assumption of horizontal homogeneity in the near‐surface refractivity field.
Wind and reflectivity fields around fronts observed with a VHF radar
Authors: May Peter T. , Yamamoto Mamoru , Fukao Shoichiro , Sato Toru , Kato Susumu , Tsuda Toshitaka
Published: April 2008

The wind and VHF radar reflectivity fields around frontal zones are examined. While even weak upper level baroclinic zones can be seen in both the reflectivity and wind fields, the reflectivity signature of low level fronts may be obscured. Humidity terms dominate the refractive index gradient in the lower troposphere and can mask the enhancement of the gradient as a result of the stable frontal layers.
Prospects for the measurement of ice cloud particle shape and orientation with elliptically polarized radar signals
Authors: Matrosov S. Y.
Published: April 2008

A method to estimate cloud particle orientation and shape parameters using a polarization diversity radar is presented. The method is demonstrated for low‐reflectivity ice clouds containing crystals that are modeled as prolate and oblate spheroids. The parameters to be estimated are the particle mean canting angle and the axis ratio in the incident wave polarization plane. The scattering matrix concept is used to obtain a relationship between two orthogonally polarized received powers and the parameters of interest. It is shown that the use of an elliptically polarized radar signal diminishes the expected difference between received powers in the two receiving polarization channels. This makes polarization studies of ice clouds with relatively low reflectivities possible; these clouds often are “invisible” in one of the receiving channels when conventional linear or circular polarization is used. An estimation of errors in the retrieved mean canting angle value caused by the spread in particle orientation is also given.
Determination of field correlations from spectral measurements with application to synthetic aperture imaging
Authors: James Daniel F. V. , Wolf Emil
Published: April 2008

By making use of some new results in optical coherence theory we show that spectral analysis, rather than fringe visibility measurements, can be used to determine correlation properties of the field. A principle is also formulated, according to which, in many interferometric measurements a trade‐off can be made between the length of the baseline and the frequency at which measurements are made. This principle is a rigorous generalization of the so‐called space‐frequency equivalence theorem for two antenna detection systems, and it applies to radiation from a broader class of sources than previously considered.
Simultaneous measurements of the polarization, angles of arrival, Doppler frequency, and amplitude of the VHF radio signal from ETS 2
Authors: Afraimovich E. L. , Min'ko N. P. , Shapovalov A. N. , Zvezdin V. N.
Published: April 2008

This paper gives a description of the transionospheric radiosonde (TIR) designed for simultaneous measurements of the main parameters of the ETS 2 radio signal at 136 MHz (polarization, angles of arrival, frequency Doppler shift, and amplitude, with a time resolution of 3O s; amplitude scintillations using spaced antennas with a resolution of 0.2 s). These data, referenced to exact time, are stored on magnetic tape and diskettes for the purpose of making a subsequent digital processing on a PDP‐11 computer and personal computers. Data from the TIR radio interferometer can be useful when studying the dynamics of a geostationary satellite in orbit; when making a complex study of the transionospheric propagation of radio waves; and when studying the structure, dynamics, interaction, and transformation of ionospheric irregularities simultaneously in a wide range of scales (from 100 m to 1000 km). The objective of this paper is also to attract the researcher's attention to the data obtained by these authors, for possible cooperation on the level of problem formulation or joint secondary treatment and interpretation of data.
Meteor wind observations with the MU radar
Authors: Nakamura T. , Tsuda T. , Tsutsumi M. , Kita K. , Uehara T. , Kato S. , Fukao S.
Published: April 2008

We conducted meteor wind observations with the middle and upper atmosphere (MU) radar at Shigaraki, Japan (35°N, 136°E), utilizing an interferometer to determine the arrival angle of a meteor echo. We found that meteor echoes are widely distributed in zenith angles as large as 50° and that the narrow main lobe of a transmitting antenna cannot effectively detect meteor trails but that the sidelobes of the antenna illuminate most of meteor trails. Wind velocity profiles determined using meteor echoes are consistent with MU radar observations determined using turbulence echoes. The amplitudes and phases of both diurnal and semidiurnal tides were analyzed for a 96‐hour continuous run in September 1989, which agreed reasonably well with the characteristics of tides determined from Kyoto meteor radar observations.
Radar interferometry technique: Three‐dimensional wind measurement theory
Authors: Van Baelen J. S. , Richmond A. D.
Published: April 2008

Generalizing radar interferometry to three‐dimensional space, we present a model which predicts the variation with respect to frequency of the phase of the cross‐spectrum obtained between two separate antennas. The slope of this variation is proportional to the cosine of the angle between the horizontal wind and the interferometer baseline, and inversely proportional to the horizontal wind amplitude. The zero‐frequency phase depends on the horizontal wind speed and direction, on the vertical wind velocity, and on the anisotropy of the backscattered power with respect to the zenith. The model also allows us to predict qualitatively the effects of specularity, beam shape, and random turbulence on the phase versus frequency variation. Assuming a spaced receiver setup with three baselines rotated by 120°, we present an implementation scheme of the radar interferometry technique which yields a three‐dimensional wind estimate and a parameter characterizing the anisotropy of the echo power distribution. Finally, we argue that the radar interferometry horizontal wind measurements will suffer from limitations similar to those of the so‐called apparent velocity as both techniques are related by Fourier transform, and that the vertical wind component will be unbiaised by anisotropy in the backscattered power.
Radar interferometry technique and anisotropy of the echo power distribution: First results
Authors: Van Baelen J. S. , Richmond A. D. , Tsuda T. , Avery S. K. , Kato S. , Fukao S. , Yamamoto M.
Published: April 2008

The theory of radar interferometry developed in the companion paper [ Van Baelen and Richmond, this issue] is applied to a set of measurements obtained with the middle and upper atmosphere (MU) radar in order to demonstrate the technique and to test the theory. The variations with respect to Doppler frequency of the coherencies and phases of the signals cross‐correlated between receiver pairs depend on the amplitude and direction of the wind in the manner predicted by the theory. The horizontal wind derived by the interferometric technique agrees quite well with the so‐called apparent velocity obtained by cross‐correlating signals in the time domain from different receiver pairs, and under our experimental conditions the latter estimate has been determined to be a good representation of the true wind, in spite of slight tendencies to overestimate the wind amplitude. The vertical wind derived by the interferometric technique shows significant differences with the Doppler wind obtained from a vertically pointing antenna, but these differences disappear when the Doppler wind is corrected for the off‐zenith distribution of the received power. An examination of the mean angle‐of‐arrival of the received signal reveals that there is a tendency for the angle to approach, though not attain, perpendicularity with the three‐dimensional wind vector, and perhaps also to tend to be perpendicular to isentropes in the crosswind direction. A postset beam steering analysis of several examples of data illustrates the behavior of the angular distribution of received power in time and space. When the signal‐to‐noise ratio is large, there is a tendency for the power to be fairly isotropic with respect to zenith angle, but highly distorted patterns can be encountered when the signal is weaker. There appears to be a tendency for the patterns to vary relatively slowly over time, but strong variations in altitude are observed in passing from one 300‐m range gate to the next. The direction of most intense received power does not necessarily correspond to the direction of mean angle‐of‐arrival of the signal as determined by interferometry.
Two‐dimensional chirp mapping of delay and Doppler spread targets
Authors: Hagfors T. , Tereshchenko E.
Published: April 2008

A procedure for the mapping of radar targets which are spread both in delay and frequency offset is described. The procedure is based on transmitted pulses with linearly chirped frequency variation. The reconstruction of the properties of the target scattering function is achieved by combining observations made with a large number of different chirp rates. The procedure is closely related to tomography methods employed in other observational contexts. The relationship between tomographic reconstruction and multiple chirp reconstruction is discussed. Possible applications of this reconstruction method exist in HF ionospheric modification experiments, in mesosphere‐stratosphere‐troposphere radar applications as well as in the radar astronomy of planetary bodies.
Viscosity waves and thermal‐conduction waves as a cause of “specular” reflectors in radar studies of the atmosphere
Authors: Hocking W. K. , Fukao S. , Yamamoto M. , Tsuda T. , Kato S.
Published: April 2008

We present a new theory to explain the cause of the atmospheric structures which are responsible for specular reflection of radar signals from the atmosphere. Evidence recorded with the middle and upper atmosphere (MU) VHF radar at Shigaraki in Japan, as well as previous reports of specular reflections from other radars and at other frequencies, is used to support our assertions. The theory postulates that the reflectors are produced by a form of highly damped wave which arises in a fluid as a result of the effects of viscosity and thermal conduction. They occur at altitudes where gravity waves are partially reflected and in the vicinity of gravity wave critical levels but are particularly prevalent when such reflections and critical level interactions occurs in a laminar region of the atmosphere. The typical scales of the waves, their reflection efficiency, and their likely location are all considered and found to be consistent with what is currently known about specular reflectors in the atmosphere. Some predictions which will allow further tests of the model are also presented.
An evaluation of water vapor radiometer data for calibration of the wet path delay in very long baseline interferometry experiments
Authors: Kuehn C. E. , Himwich W. E. , Clark T. A. , Ma C.
Published: April 2008

The internal consistency of the baseline length measurements derived from analysis of several independent very long baseline interferometry (VLBI) experiments is an estimate of the measurement precision. In this paper we investigate whether the inclusion of water vapor radiometer (WVR) data as an absolute calibration of the propagation delay due to water vapor improves the precision of VLBI baseline length measurements. We analyzed 28 International Radio Interferometric Surveying runs between June 1988 and January 1989; WVR measurements were made at the G. R. Agassiz Station of the Harvard College Observatory in Ft. Davis, Texas, during each session. We found that the addition of WVR data decreased the scatter of the length measurements of Ft. Davis baselines by 5–10%. The observed reduction in the scatter of the baseline lengths is less than what we would expect from the behavior of the formal errors, which suggest that the baseline length measurement precision should improve 10–20% if WVR data at Ft. Davis are included in the analysis. The discrepancy between the formal errors and the baseline length results could be explained as the consequence of systematic errors in the dry‐mapping function parameters, instrumental biases in the WVR and Ft. Davis barometer, or both.
Cross‐tail magnetic flux ropes as observed by the GEOTAIL spacecraft
Authors: Lepping R. P. , Fairfield D. H. , Jones J. , Frank L. A. , Paterson W. R. , Kokubun S. , Yamamoto T.
Published: April 2008

Ten transient magnetic structures in Earth's magnetotail, as observed in GEOTAIL measurements, selected for early 1993 [at (−) XGSM = 90 ‐ 130 RE], are shown to have helical magnetic field configurations similar to those of interplanetary magnetic clouds at 1 AU but smaller in size by a factor of ≈ 700. Such structures are shown to be well approximated by a comprehensive magnetic force‐free flux‐rope model. For this limited set of 10 events the rope axes are seen to be typically aligned with the YGSM axis and the average diameter of these structures is ≈ 15 RE.
UARS MLS observations of lower stratospheric ClO in the 1992–93 and 1993–94 Arctic winter vortices
Authors: Waters J. W. , Manney G. L. , Read W. G. , Froidevaux L. , Flower D. A. , Jarnot R. F.
Published: April 2008

UARS MLS measurements of lower stratospheric ClO during the 1992–93 and 1993–94 Arctic winters are presented. Enhanced ClO in the 1992–93 winter was first observed in early December, and extensively during February when temperatures were continually low enough for PSCs. Sporadic episodes of enhanced ClO were observed for most of the 1993–94 winter as minimum temperatures hovered near the PSC threshold, with largest ClO amounts occurring in early March after a sudden deep cooling in late February.
Response of vegetation to rising carbon dioxide: Photosynthesis, biomass, and seed yield of soybean
Authors: Allen L. H. , Boote K. J. , Jones J. W. , Jones P. H. , Valle R. R. , Acock B. , Rogers H. H. , Dahlman R. C.
Published: April 2008

Elevated carbon dioxide throughout the lifespan of soybean causes an increase in photosynthesis, biomass, and seed yield. A rectangular hyperbola model predicts a 32% increase in soybean seed yield with a doubling of carbon dioxide from 315 to 630 ppm and shows that yields may have increased by 13% from about 1800 A.D. to the present due to global carbon dioxide increases. Several other sets of data indicate that photosynthetic and growth response to rising carbon dioxide of many species, including woody plants, is similar to that of soybean. Calculations suggest that enough carbon could be sequestered annually from increased photosynthesis and biomass production due to the rise in atmospheric carbon dioxide from 315 ppm in 1958 to about 345 ppm in 1986 to reduce the impact of deforestation in the tropics on the putative current flux of carbon from the biosphere to the atmosphere.
The role of CaCO3 compensation in the glacial to interglacial atmospheric CO2 change
Authors: Broecker Wallace S. , Peng Tsung‐Hung
Published: April 2008

The only viable explanations put forth to date for the glacial to interglacial change in atmospheric CO2 content suggested from measurements of the CO2 content of gas extracted from ice cores involve changes in the ocean's nutrient cycles. Any nutrient change capable of creating the 80 µatm changes in atmosphere CO2 pressure suggested by the ice core results also creates significant change in the deep ocean's CO3= content. Evidence from deep sea sediments suggests that these CO3= changes are compensated on the time scale of a few thousand years by reductions or increases in amount of CaCO3 accumulating in deep sea sediments. This compensation process has two important consequences. First, it significantly increases the magnitude of the CO2 change per unit of nutrient forcing. Second, it causes a delay in the response of the atmospheric CO2 change. While the first of these consequences is a boon to those seeking to explain the CO2 change, the second may prove to be a curse. The ice core CO2 record shows no evidence of a significant lag between the CO2 response and the polar warming. In any case it is important that we improve our knowledge of the magnitude and timing of the CaCO3 preservation events which mark the close of episodes of glaciation and of the dissolution events which mark the onset of these episodes.
Chromium behavior in the ocean: Global versus regional processes
Authors: Jeandel C. , Minster J. F.
Published: April 2008

Total chromium (TCr) has been analyzed by atomic absorption spectrophotometry in seven vertical profiles from the North Atlantic Ocean, three from the Mediterranean Sea, and four from the South and North Pacific Ocean. Chromium (III) data were also obtained for a few of these by isotope dilution mass spectrometry. On the large scale, TCr increases from 3 nmol/kg to 5 nmol/kg between the North Atlantic and the South Pacific deep waters. This distribution, and a slight depletion in surface waters (∼0.5 nmol/kg), suggests a biogeochemical control of Cr. While it is not possible to assess which phase dominates the Cr control, if it is assumed that this is silica, the Cr/Si ratio would be of the order of 0.023 × 10−3 mol/mol. In addition, a decrease of TCr content of 1 to 2 nmol/kg occurs from 21°S to 13°N in the deep Pacific waters, along the East Pacific Rise. This feature, as well as the shape of vertical profiles, suggests that scavenging of Cr also occurs in deep waters. A subtraction flux in the deep Pacific Ocean is estimated as 16 to 20 × 103 nmol/cm/y. It can be partially explained by scavenging Mn and Fe from undersea hydrothermal activity. In the Atlantic subsurface waters, a small minimum of TCr (with concentrations of about 2.5 nmol/kg) is observed in the eastern basin, at depths ranging between 100 and 500 m. This minimum seems to be shallower than a Cr(III) maximum (about 1 nmol/kg) observed at the level of maximum apparent oxygen utilization. It is suggested that the TCr minimum results from advection along isopycnal horizons of slightly depleted surface waters from the relatively productive isopycnal outcrop areas near 40°‐50°N. In the Mediterranean sea, variations of the TCr content are weak (25%): The slightly Cr‐depleted input water from the Atlantic seems to get mixed as the water moves eastward at the surface.
Cross‐system comparisons of soil nitrogen transformations and nitrous oxide flux in tropical forest ecosystems
Authors: Matson Pamela A. , Vitousek Peter M.
Published: April 2008

Soil nitrogen transformations and nitrous oxide flux across the soil‐air interface were measured in a range of tropical forest sites in Costa Rica, Brazil, and Hawaii. Nitrogen mineralization and nitrification potentials were high in the relatively fertile Costa Rica sites and the Amazonian oxisol/ultisols (>1.5 μg g−1 d−1 of N mineralized), intermediate in Amazonian white sand soils (0.5‐0.8 μg g−1 d−1) and low in the Hawaiian montane sites (<0.5 μg g−1 d−1). Nitrous oxide fluxes ranged from 0 to 6.2 ng cm−2 h−1 of N; mean flux per site was highly correlated with mean nitrogen mineralization across 26 sites. These correlated patterns of nitrogen cycling and trace gas production could be useful in the development of regional‐ and global‐scale estimates of nitrous oxide fluxes from tropical forests.
Dynamics of sulfur exchange at the air/forest canopy interface: A review of throughfall inferred deposition rates
Authors: Sievering Herman
Published: April 2008

A review of the literature on the throughfall/incident precipitation approach is presented as it relates to the measurement of sulfur uptake by forest canopies during non‐precipitation dry periods. This measurement approach has produced valuable data on other‐than‐wet deposition of total sulfur. The larger sulfur deposition values obtained when using annual‐budget calculations versus event‐based calculations may be attributed to enhanced deposition during wettened canopy periods or to cloud/fog interception. Substantially greater other‐than‐wet sulfur deposition values for coniferous versus deciduous forest canopies have been observed. However, there are currently too many assumptions regarding throughfall/incident measurements that have not been tested. Canopy exchange may be from about 15% to as much as 70% of the difference between throughfall and incident sulfur. The contribution of gas and particulate phases to other‐than‐wet deposition needs to be quantified. Leaching and retention need to be characterized for various types of forest canopies. Thus, it is concluded that the dry or other‐than‐wet deposition values presented in the throughfall/incident literature are generally of low accuracy.
The oceanic salt pump: Does it contribute to the glacial‐interglacial difference in atmospheric CO2 content?
Authors: Broecker W. S. , Peng T.‐H.
Published: April 2008

Sea ice formation drives salt from the surface to the deep sea. In so doing it lowers the salinity of polar surface waters. We show here that this reduction in turn lowers the CO2 partial pressure of polar surface waters and hence also of the atmosphere. We propose that during glacial time when more sea ice existed, this pumping action may have been stronger. If so, part of the glacial to interglacial atmospheric CO2 content change observed in ice cores may have been driven by the ocean's salt pump.
The National Oceanic and Atmospheric Administration Wp‐3d Meteorolgical, Aerosol, and Gas Systems, and flight operations, on Watox‐86
Authors: Schnell Russell C. , Bridgman Howard A. , Naegele P. Stuart , Waston Thomas B.
Published: April 2008

A National Oceanic and Atmospheric Administration WP‐3D meteorological research aircraft was instrumented with a wide range of gas and aerosol sampling equipment to conduct a component of the Western Atlantic Ocean Experiment (WATOX‐86) intensive study. The added instrumentation provided for measurements of condensation nuclei, aerosol scattering extinction, ozone, soot carbon, NOx, SO2, H2O2, NO2, peroxyacetyl nitrate, CO, HNO3, and aerosol particle size/number. Discrete air samples were collected in both glass and metal flasks for analyses of a wide range of gaseous species. Aerosol collections included bulk samples on high‐volume filters, single‐particle collections with impactors, continuous size segregated aerosol impactors (with up to nine size cuts), and a range of specialty filters designed to collect gases and gases adsorbed on aerosols. Operational aspects of the four WP‐3D WATOX flights are described along with pertinent observer notes and comments.
Aircraft measurements of sulfur, nitrogen, and carbon species during WATOX‐86
Authors: Whelpdale D. M. , Keene W. C. , Hansen A. D. A. , Boatman J.
Published: April 2008

Filter pack and aethalometer systems were successfully used aboard the National Oceanic and Atmospheric Administration WP‐3D and King Air aircraft during the January 1986 intensive field investigation of the Western Atlantic Ocean Experiment (WATOX) to measure concentrations of sulfur and nitrogen species and black carbon aerosol. The mean boundary layer concentrations of SO4=−e, NO3−, NH4+ and black carbon measured on the WP‐3D were 16, 6.6, 23 and 16 nmol m−3 (STP), respectively, and those of SO2 and HNO3 were 0.9 and 0.1 parts per billion by volume (ppbv), respectively. Mean boundary layer concentrations of SO4=−e, NH4+ and HNO3 measured on the King Air were 20 nmol m−3 (STP), 41.4 nmol m−3 (STP) and 0.13 ppbv, respectively. Concentrations in the free troposphere were consistently lower by factors of 1.5 to 4.5 than those in the boundary layer. In the boundary layer SO4=−e accounted for approximately 30% of the total non‐sea‐salt sulfur, and particulate NO3‐ accounted for 40% of the total nitrate. NH4+ and SO4=−e were significantly correlated and present in a molar ratio of approximately 2:1, suggesting that the species existed in the aerosol primarily as (NH4)2SO4.