bluuebunny/crossref_metadata_2025 huggingface dataset:
Calibration and data retrieval algorithms for the NASA Langley/Ames Diode Laser Hygrometer for the NASA Transport and Chemical Evolution Over the Pacific (TRACE‐P) mission
Authors: Podolske James R. , Sachse Glen W. , Diskin Glenn S.
Published: October 2003

This paper describes the procedures and algorithms for the laboratory calibration and field data retrieval of the NASA Langley/Ames Diode Laser Hygrometer as implemented during the NASA Transport and Chemical Evolution Over the Pacific (TRACE‐P) mission during February–April 2000. The calibration is based on a National Institute of Standards and Technology traceable dew point hygrometer using relatively high humidity and short optical path length. Two near‐infrared water vapor absorption lines of widely different strengths are used to increase the dynamic range of the instrument in the course of a flight. The laboratory results are incorporated into a numerical model of the second harmonic spectrum for each of the two spectral window regions using spectroscopic parameters from the HITRAN database and other sources, allowing water vapor retrieval at upper tropospheric and lower stratospheric temperatures and humidity levels. The data retrieval algorithm is simple, numerically stable, and accurate. A comparison with other water vapor instruments on board the NASA DC‐8 and ER‐2 aircraft is presented.
Permeability reduction of a natural fracture under net dissolution by hydrothermal fluids
Authors: Polak A. , Elsworth D. , Yasuhara H. , Grader A. S. , Halleck P. M.
Published: October 2003

Flow‐through tests are completed on a natural fracture in novaculite at temperatures of 20°C, 80°C, 120°C, and 150°C. Measurements of fluid and dissolved mass fluxes, and concurrent X‐ray CT imaging, are used to constrain the progress of mineral dissolution and its effect on transport properties. Under constant effective stress, fracture permeability decreases monotonically with an increase in temperature. Increases in temperature cause closure of the fracture, although each increment in temperature causes a successively smaller effect. The initial differential fluid pressure‐drop across the fracture increases by two orders of magnitude through the 900 h duration of the test, consistent with a reduction of an equivalent hydraulic aperture by a factor of five. Both the magnitude and rate of aperture reduction is consistent with the dissolution of stressed asperities in contact, as confirmed by the hydraulic and mass efflux data. These observations are confirmed by CT imaging, resolved to 35 microns, and define the potentially substantial influence that benign changes in environmental conditions of stress, temperature, and chemistry may exert on transport properties.
Airborne measurements of cirrus‐activated C2Cl4 depletion in the upper troposphere with evidence against Cl reactions
Authors: Simpson Isobel J. , Wingenter Oliver W. , Westberg David J. , Fuelberg Henry E. , Kiley Christopher M. , Crawford James H. , Meinardi Simone , Blake Donald R. , Rowland F. Sherwood
Published: October 2003

Airborne whole air samples collected over the western Pacific in spring, 2001 showed depletion of tetrachloroethene (C2Cl4) in every upper tropospheric (UT) air parcel that had interacted with large areas of cirrus less than three days upwind. The amount of C2Cl4 depletion showed a negative correlation with time since the interaction, consistent with the C2Cl4‐depleted air parcels mixing with the ambient air as they moved downwind of the cirrus. Ethane and C2Cl4 both react relatively quickly with atomic chlorine (Cl) but ethane was not significantly depleted in these same air parcels, indicating that the C2Cl4 depletion cannot be attributed to Cl chemistry alone. Based on the minimum ethane depletion that can be detected by our measurements, a daytime upper limit of roughly 3 × 104 atom Cl cm−3 is indirectly estimated for heterogeneous chlorine activation by cirrus clouds in the UT in tropical‐ and mid‐latitudes during spring.
Small‐scale, field‐aligned currents at the top‐side ionosphere
Authors: Neubert Torsten , Christiansen Freddy
Published: October 2003

High‐precision vector magnetic field observations from the Ørsted satellite are used to investigate small‐scale, field‐aligned currents on spatial scales down to 600 m. Placed in a low‐Earth, polar orbit, the slowly drifting orbit plane has covered all local times since launch in 1999 with more than 25000 polar passes. Small‐scale currents are primarily found in the cusp with densities of 10–100 μAm−2, reaching more than 1000 μAm−2 during disturbed conditions. These values are 1–2 orders of magnitude larger than large‐scale region 1 and 2 currents. Current densities are 2–4 times larger when the ionosphere is illuminated than when in darkness. While the location of currents follows the changes in cusp location with changing IMF, the intensity of the currents seems to depend on the level of solar wind turbulence. The data suggest that small‐scale currents may be associated with significant local heating of the ionosphere and thermosphere.
Analytic method for observation of the gravity waves using radio occultation data
Authors: Liou Y. A. , Pavelyev A. G. , Huang C. Y. , Igarashi K. , Hocke K. , Yan S. K.
Published: October 2003

We present an analytical method for observation of the gravity waves (GWs) in the atmosphere from the amplitude of the radio occultation (RO) signal. We found the height dependence of the GW phase and amplitude (the GW “portrait”) using for example the amplitude data corresponding to one of the GPS/Meteorology (GPS/MET) RO events. We estimated the horizontal wind speed perturbations, which are in fairly good agreement with radiosonde data. The horizontal wind speed perturbations v(h) are changing in the range v ∼ ± 1–±9 m/s with vertical gradients dv/dh ∼ ± 0.5–±15 m/(s km) in the height interval 10–40 km. The height dependence of the GW vertical wavelength has been inferred through the differentiation of the GW phase. Analysis of this dependence gives the estimation of the GW intrinsic phase speed, which varies for the considered event in the interval 1.5–5 m/s. Thus the analytical method has the capability to extract important information from the amplitude of the RO signals helpful for studying the GW activity in the atmosphere.
Rectification and precession signals in the climate system
Authors: Huybers P. , Wunsch C.
Published: October 2003

Precession of the equinoxes has no effect on the mean annual insolation, but does modulate the amplitude of the seasonal cycle. In a linear climate system, there would be no energy near the 21,000 year precession period. It is only when a non‐linear mechanism rectifies the seasonal modulation that precession‐period variability appears. Such rectification can arise from physical processes within the climate system, for example a dependence of ice cover only on summer maximum insolation. The possibility exists, however, that the seasonality inherent in many climate proxies will produce precession‐period variability in the records independent of any precession‐period variability in the climate. One must distinguish this instrumental effect from true climate responses. Careful examination of regions without seasonal cycles, for example the abyssal ocean, and the use of proxies with different seasonal responses, might permit separation of physical from instrumental effects.
A new intermediate coupled model for El Niño simulation and prediction
Authors: Zhang Rong‐Hua , Zebiak Stephen E. , Kleeman Richard , Keenlyside Noel
Published: October 2003

A new intermediate coupled model (ICM) is developed and used to simulate and predict sea surface temperature (SST) variability in the tropical Pacific. The ocean component is based on an intermediate complexity model developed by Keenlyside and Kleeman [2002] that is an extension of the McCreary [1981] baroclinic modal model to include varying stratification and partial nonlinearity effects, allowing realistic simulation of the mean equatorial circulation and its variability. An empirical procedure is developed to parameterize subsurface entrainment temperature (Te) in terms of sea surface pressure (SSP) anomalies. The ocean model is then coupled to a statistical atmospheric model. The coupled system realistically produces interannual variability associated with El Niño. Hindcasts are made during the period 1980–1997 for lead times out to 12 months. Observed SST anomalies are the only field to be incorporated into the coupled system to initialize predictions. Predicted SST anomalies from this model do not show obvious systematic biases. Another striking feature is that the model skill beats persistence at all lead times over the central equatorial Pacific.
Infrasonic tremor observed at Kīlauea Volcano, Hawai'i
Authors: Garcés M. , Harris A. , Hetzer C. , Johnson J. , Rowland S. , Marchetti E. , Okubo P.
Published: October 2003

Infrasonic array data collected at Kīlauea Volcano, Hawai'i, during November 12–21, 2002 indicate that the active vents and lava tube system near the Pu'u 'Ō'ō vent complex emit almost continuous infrasound in the 0.3–10 Hz frequency band. The spectral content of these infrasonic signals matches well that of synchronous seismic tremor. In sites protected from wind noise, significant signal to noise ratios were recorded as far as ∼13 km from the crater of Pu'u 'Ō'ō. The infrasonic recordings suggest that one or more tremor sources may be close to the surface. In addition, these results demonstrate that adequate site and instrument selections for infrasonic arrays are essential in order to obtain consistent and reliable infrasonic detections.
Large‐scale mass redistribution in the oceans, 1993–2001
Authors: Chen J. L. , Wilson C. R. , Hu X. G. , Tapley B. D.
Published: October 2003

A recent study of satellite laser ranging measurements by Cox and Chao [2002] indicates that large‐scale mass redistribution has caused a rapid change in Earth's dynamic oblateness (J2) since 1998. Using satellite altimeter observations and two runs of an ocean general circulation models (OGCM), we examine mass variations in the oceans and their estimated effect on J2. Combined altimeter and OGCM results indicate variations similar to the J2 changes in 1998, and predict considerably larger oceanic effects on the J2 anomaly than purely OGCM estimates, suggesting that the oceans should not be ruled out by any means as a significant source of this interesting geodetic anomaly, until they have been studied further.
Relations between albedos and emissivities from MODIS and ASTER data over North African Desert
Authors: Zhou L. , Dickinson R. E. , Ogawa K. , Tian Y. , Jin M. , Schmugge T. , Tsvetsinskaya E.
Published: October 2003

This paper analyzes relations among MODIS surface albedos, ASTER broadband (3–14 μm) emissivities, and a soil taxonomy map over the arid areas of Algeria, Libya, and Tunisia in North Africa at 30 second (about 1 km) and 2 minute (about 4 km) spatial resolutions. The MODIS albedo data are from 7 spectral bands and 3 broadbands during dust‐free seasons and the emissivity data are derived from a linear combination of the waveband emissivities of the ASTER five thermal infrared channels. Both albedo and emissivity data in the study region show similar considerable spatial variability, larger than assumed by most climate models, and such variability is related to the surface types (sands, rock, and soil orders). Emissivity over bare soils exhibits statistically significant correlations with albedos at both broadbands and most of spectral bands and decreases linearly with albedos. Albedo and emissivity are more strongly correlated with each other than either is to the surface types, apparently because of their higher resolution either spatially or in surface mineralogy. This paper provides guidance for the possible inclusion of such correlation to specify albedo and emissivity in climate models.
New 234U‐230Th coral dates from the western Gulf of Corinth: Implications for extensional tectonics
Authors: Houghton Sarah L. , Roberts Gerald P. , Papanikolaou Ioannis D. , McArthur John M. , Gilmour Mabs A.
Published: October 2003

We derive rates of uplift of ∼0.7–0.8 mm/yr for the western end of the Gulf of Corinth, Greece, using geomorphic paleaoshoreline modeling. We calibrate the modeling with new 234U‐230Th dates on the coral Cladocora caespitosa collected from raised marine terraces uplifted in the footwall of the active Psathopyrgos fault, the only major active normal fault, reported on published maps controlling the downthrown Rio Straits at the western end of the Gulf of Corinth. In this area of high (15–22 mm/yr) extension rates measured with GPS, the ratio of uplift‐rate to extensional velocity is 0.025–0.035, much lower than values of 0.15–0.25 found further east in the gulf. These low values imply that if GPS extension rates are correct then mechanical/kinematic models developed for the eastern and central gulf may not be applicable to the western gulf.
The coherence method using a thin anisotropic elastic plate model
Authors: Swain C. J. , Kirby J. F.
Published: October 2003

The coherence method, based on the statistical correlation between gravity and topography, has been widely used to estimate the effective elastic thickness of the continental lithosphere and its variations. By far the majority of studies have assumed an isotropic lithosphere, but several papers have inferred anisotropy from differences in the observed coherence (or admittance) functions in different directions. However, none have used an anisotropic model to fit the coherence. We show how the simplest model of elastic anisotropy (an orthotropic thin plate) can be incorporated into both forward and inverse modeling algorithms, using an appropriate approximation in the partial differential equation for the flexure of such a plate.
Measurements of near‐bed intra‐wave sediment entrainment above vortex ripples
Authors: Thorne Peter D. , Davies Alan G. , Williams Jon J.
Published: October 2003

In general, descriptions of suspended sediment transport beneath surface waves are based on the turbulent diffusion concept. However, it is recognised that this approach is questionable for the suspension of sediment when the seabed is rippled. In this case, at least if the ripples are sufficiently steep, the entrainment process is likely to be well organised, and associated with vortex formation and shedding from the ripples. To investigate the entrainment process above ripples, a study was carried out in a large‐scale wave flume facility. Utilising acoustic techniques, visualisations of the intra‐wave sediment entrainment above vortex ripples have been generated. The observations provide a detailed description of entrainment, which is interpreted here in relation to the process of vortex formation and shedding. It is anticipated that such measurements will contribute to the development of improved physical process models of sediment transport in the rippled bed regime.
Spatial maps of heliospheric and geocoronal X‐ray intensities due to the charge exchange of the solar wind with neutrals
Authors: Robertson I. P. , Cravens T. E.
Published: October 2003

X‐rays are generated throughout the heliosphere and the terrestrial magnetosheath as a consequence of charge transfer collisions between heavy solar wind ions and interstellar and geocoronal neutrals, respectively. Simple models of this X‐ray emission have been presented in the past, but results from a more sophisticated model are described in this paper. In particular, to obtain the densities of interstellar neutrals our X‐ray model uses to determine X‐ray intensities, we use the Fahr [1971] hot model although with recently determined input parameters. The geocoronal X‐ray model we use in this paper has also been improved, as described in a recent paper by Robertson and Cravens [2003]. In previous papers we demonstrated that there is significant correlation between the “long‐term enhancement” part of the soft X‐ray background measured by the Röntgen Satellite (ROSAT) and the solar wind proton flux. In the current paper we determine the steady‐state X‐ray intensities due to the interaction between the solar wind and both interstellar neutrals and the geocoronal neutrals as a function of look direction and time of year. X‐ray intensity maps are shown for both a spherically symmetric solar wind and for a latitude‐dependent solar wind (i.e., fast and slow solar wind regions). In all cases, the X‐ray intensity is highest when the view direction is towards the Sun, but the intensity is also relatively high for view directions intersecting the gravitational focusing cone of interstellar helium. We also show a heliospheric/geocoronal X‐ray intensity map for the conditions used by Snowden et al. [1995] in producing the 1/4 keV channel soft X‐ray background map in galactic coordinates. Our preliminary conclusion is that very roughly 50% of the total background soft X‐ray intensity in the galactic plane and 25% at high galactic latitudes can be attributed to the charge transfer process operating within the solar system, with the remaining emission coming from outside our heliosphere.
Magnetic helicity analysis of an interplanetary twisted flux tube
Authors: Dasso S. , Mandrini C. H. , Démoulin P. , Farrugia C. J.
Published: October 2003

We compute the magnetic flux and helicity of an interplanetary flux tube observed by the spacecraft Wind on 24–25 October 1995. We investigate how model‐dependent are the results by determining the flux‐tube orientation using two different methods (minimum variance and a simultaneous fit), and three different models: a linear force‐free field, a uniformly twisted field, and a nonforce‐free field with constant current. We have fitted the set of free parameters for the six cases and have found that the two force‐free models fit the data with very similar quality for both methods. Then, both the comparable computed parameters and global quantities, magnetic flux and helicity per unit length, agree to within 10% for the two force‐free models. These results imply that the magnetic flux and helicity of the tube are well‐determined quantities, nearly independent of the model used, provided that the fit to the data is good enough.
Type II radio emission predictions: Multiple shock ripples and dynamic spectra
Authors: Knock S. A. , Cairns Iver H. , Robinson P. A.
Published: October 2003

A recently developed model of type II radio emission from a single ripple on a global shock is extended to (1) investigate the interaction of multiple shock ripples and (2) calculate the dynamic spectra of radio emission for a shock that consists of multiple independent ripples, as it propagates from 10 solar radii to 1 AU. It is found that the interaction of ripples is relatively unimportant, typically changing the predicted emission level by only 20%. It is predicted that dynamic spectra vary with observer location, which implies that different spacecraft observing the same type II event will see different dynamic spectra. Correlations between source location and dynamic spectra predicted for remote observers are thus investigated and a number of characteristic type II features, such as split bands, are found to be produced naturally by a combination of different source locations and propagation effects such as frequency blocking. The results imply a need for large‐scale structure such as large‐scale fluctuations in magnetic field orientations, coronal mass ejections, and corotating interaction regions in order to account for the diversity in type II burst observations.
Investigation of external triggering of substorms with Polar ultraviolet imager observations
Authors: Liou K. , Newell P. T. , Meng C.‐I. , Wu C.‐C. , Lepping R. P.
Published: October 2003

The triggering mechanism(s) for the substorm expansion phase onset is one of the outstanding issues in magnetospheric physics. Previous studies have shown that an impingement of the high solar wind dynamic pressure may lead to the expansion phase onset of a substorm. These previous studies typically used a negative magnetic bay as the main proxy for a substorm, but we now know that some magnetic bays are associated not with substorms but with the enhancement of convection. Therefore it is reasonable to cast doubts on the compression trigger mechanism. In this study we use classical substorm onsets, “auroral breakups,” which are the most reliable substorm onset indicator when identified with global auroral images, to reinvestigate this issue. We examine 43 interplanetary shock events that occurred between 1996 and 1999 with simultaneous global auroral images from the Polar ultraviolet imager images and the auroral electrojet indices. It is found, indeed, that ∼52% of the shocks produce magnetic bays (AL < −100 nT). While most of the shocks enhance auroral luminosities, only 4 events (∼9%) appear to have an auroral breakup preceded by an SSC/SI by 20 min (two events by 10 min). These results strongly indicate interplanetary shocks can produce negative magnetic bays but not auroral breakups (thus christened “compression bays”). An examination of precisely timed interplanetary magnetic field (IMF) during 11 substorms that occurred near the shock‐induced SSCs/SIs indicates that northward turnings of IMF occurred more than 50% of time. Given such a low probability, it is concluded that shock compression is not likely to trigger substorms but enhances magnetospheric currents and auroral particle precipitation. In line with many previous study results, on the other hand, the northward turnings of IMF can be a plausible substorm triggering mechanism.
Acoustic fluidization and the extraordinary mobility of sturzstroms
Authors: Collins Gareth S. , Melosh H. Jay
Published: October 2003

Sturzstroms are a rare category of rock avalanche that travel vast horizontal distances with only a comparatively small vertical drop in height. Their extraordinary mobility appears to be a consequence of sustained fluid‐like behavior during motion, which persists even for driving stresses well below those normally associated with granular flows. One mechanism that may explain this temporary increase in the mobility of rock debris is acoustic fluidization; where transient, high‐frequency pressure fluctuations, generated during the initial collapse and subsequent flow of a mass of rock debris, may locally relieve overburden stresses in the rock mass and thus reduce the frictional resistance to slip between fragments. In this paper we develop the acoustic fluidization model for the mechanics of sturzstroms and discuss the conditions under which this process may sustain fluid‐like flow of large rock avalanches at low driving stresses.
Ekman transport and pumping in the California Current based on the U.S. Navy's high‐resolution atmospheric model (COAMPS)
Authors: Pickett Mark H. , Paduan Jeffrey D.
Published: October 2003

Upwelling in the California Current system due to Ekman transport and pumping was estimated using a high‐resolution (9‐km grid) atmospheric model reanalysis. Model winds, verified with satellite‐measured winds at 13 locations, had weekly averaged wind components within 1.7 m s−1 RMS, and wind gradients within 1.6 m s−1 per 100 km RMS. Model wind hind‐casts from May 1999 to September 2000 revealed narrow bands (about 10 by 50 km) of strong wind stress and wind stress curl parallel to the coast and adjacent to major coastal promontories. These bands, which are sub‐grid scale in operational models, were capable of generating local upwelling greater than 10 m d−1 and downwelling greater than 5 m d−1. Peak summer estimates for the California Current system indicate vertical transport due to Ekman pumping was roughly 1.0 × 10−6 m3 s−1, and Ekman transport from alongshore wind stress was about 0.5 × 10−6 m3 s−1. These estimates suggest that Ekman pumping from wind stress curl is as important as Ekman transport from alongshore winds in the California Current system.
On the angular radiance closure of tropical cumulus congestus clouds observed by the Multiangle Imaging Spectroradiometer
Authors: Zuidema Paquita , Davies Roger , Moroney Catherine
Published: October 2003

Monte Carlo reflectance simulations of three tropical cumulus congestus clouds reconstructed from Multiangle Imaging Spectroradiometer (MISR) data are compared to the domain‐averaged MISR reflectance measurements. The goal of the comparison is to evaluate the nadir‐view pixel cloud optical depth retrievals derived using plane‐parallel radiative transfer theory, and the assumptions for vertically distributing the optical depth. Cloud heights are operationally retrieved using a stereo‐imaging algorithm. The cloud heights and optical depths are at a 275 m spatial resolution, and for most simulations a vertical resolution of 250 m is applied. Five different but common three‐dimensional cloud representations are assessed, using (1) a column vertical‐mean volume extinction coefficient (β) value (the reference case), (2) a volume extinction coefficient proportional to the two‐thirds power of height (the adiabatic assumption), (3) the adiabatic assumption at a 25 m vertical resolution, (4) a vertical‐mean β retrieved from reflectances averaged over a (2.2 km)2 area, and (5) a vertical‐mean β retrieved using off‐nadir reflectances. An asymmetry about nadir in the observed reflectance means and skewnesses is not reproduced by any Monte Carlo simulation. The lack of symmetry can be related to differing proportions of unobscured sunlit and shadowed cloudy areas within the different views, even for these cases with viewing angles close to the perpendicular plane. The Monte Carlo simulations do not appear to capture the observed fraction of unobscured sunlit and shadowed cloudy areas, suggesting that radiatively significant cloud variability is occurring at scales smaller than the height field resolution of ±550 m. Results from the Monte Carlo simulation done at a higher vertical resolution are consistent with this. The cases examined also contain a nadir maximum in the observed reflectance skewnesses and a relative maximum for the observed nadir reflectances, attributed to the solar illumination of some optically thick cloud surfaces and to specular reflection pervading through the optically thin cloudy regions. This contrasts with previous modeling results that assume a Lambertian surface.
Effects of snow physical parameters on shortwave broadband albedos
Authors: Aoki Teruo , Hachikubo Akihiro , Hori Masahiro
Published: October 2003

Snow pit work of several‐day intervals was performed simultaneously with radiation budget observations during two winters in eastern Hokkaido, Japan. From these data we investigated the effects of elapsed time after snowfall (snow aging), air temperature, snow surface temperature, snow grain size, and snow impurities on the visible and the near infrared albedos for improving the snow albedo scheme in the land surface process from an empirical model to a physically based model. The dependence of albedos on elapsed time after snowfall could be clearly classified by dividing the snow‐covered period into a dry snow season and a wet snow season rather than by snow surface temperature. The albedo reduction by snow aging statistically depends on the snow surface temperature, which is often used to predict the snow albedo in the empirical model of land surface process. However, the albedo reduction rate was very scattered for snow surface temperatures above −10°C. This is because the snow albedo reduction essentially depends on the snow grain size and the concentration of snow impurities. Using the radiative transfer model for the atmosphere‐snow system, the effects of these snow physical parameters on broadband albedos are calculated and compared with the observed ones. The measured broadband albedos fell close to the range of theoretically calculated ones as functions of these snow physical parameters. In particular, the measured near infrared albedo agreed well with the theoretically calculated ones both for the dependence of snow grain size and snow impurities but not as well for the visible albedo in detail. In the near infrared region the light absorption by ice is strong, and thus the snow albedo contains the information of snow physical parameters near the surface where these parameters are measured. In contrast, the visible albedo contains the snow information in the deeper layer because the ice is relatively transparent in the visible region. This suggests the necessity of the multiple‐snow‐layer model for the visible region in the physically based snow albedo model.
Time‐dependent response of the tropical atmosphere to a fixed sea surface temperature anomaly
Authors: Zehnder Joseph A. , Reeder Michael J.
Published: October 2003

The time‐dependent response of the tropical atmosphere to a fixed, localized sea surface temperature (SST) anomaly is explored using a highly simplified nonlinear shallow water numerical model. The work builds on that by Webster [1972] and Gill [1980]. The present model has three layers and is formulated on an equatorial beta plane in an atmosphere initially in radiative‐convective equilibrium. Observations suggest that the tropical atmosphere is only marginally unstable to moist convection. Accordingly, the convective parameterization in the model assumes that clouds consume the convective available potential energy at approximately the same rate as large‐scale processes generate it. The convective parameterization allows for both shallow nonprecipitating and deep precipitating clouds. The convection scheme allows the shallow convection to condition the atmosphere for further deep convection, which is an important factor controlling deep convection in the tropics. The model calculations show that shallow convection moistens the middle troposphere, providing favorable conditions for the development of deep convection. In contrast, radiative cooling and drying of the middle troposphere act to suppress deep convection. In the model, these competing processes modulate the deep convection over the localized SST anomaly with a period of about 30 days. The convective heating also excites large‐scale, equatorially trapped normal modes. The response ranges from a steady state flow similar to that by Gill to a periodic generation of Rossby‐Kelvin wave couplets and finally to a transition to chaotic behavior depending on the strength of the forcing.
OH and HO2 concentrations, sources, and loss rates during the Southern Oxidants Study in Nashville, Tennessee, summer 1999
Authors: Martinez M. , Harder H. , Kovacs T. A. , Simpas J. B. , Bassis J. , Lesher R. , Brune W. H. , Frost G. J. , Williams E. J. , Stroud C. A. , Jobson B. T. , Roberts J. M. , Hall S. R. , Shetter R. E. , Wert B. , Fried A. , Alicke B. , Stutz J. , Young V. L. , White A. B. , Zamora R. J.
Published: October 2003

OH and HO2 mixing ratios and total OH reactivity were measured together with photolysis frequencies, NOx, O3, many VOCs, and other trace gases during the midsummer 1999 SOS campaign in Nashville, Tennessee. These measurements provided an excellent opportunity to study OH and HO2 (collectively called HOx), and their sources and sinks in a polluted metropolitan environment. HOx generally showed the expected diurnal evolution, with maxima around noon of up to about 0.8 pptv of OH and 80 pptv of HO2 during sunny days. Overall, daytime observed OH and HO2 were a factor of 1.33 and 1.56 times modeled values, within the combined 2σ instrument and model uncertainties. The chain length of HOx, which is determined from the ratio of the measured total OH reactivity that cycles OH to the total HOx loss, was on average 3–8 during daytime and up to 3 during nighttime, in general agreement with expectations. However, differences occurred between observed HOx behavior and expectations from theory and models. First, HO2 was greater than expected during daytime when NO mixing ratios were high; ozone production did not decrease as expected when NO was greater than 2 ppbv. Ozone production determined by the imbalance of the NOx photostationary state, which was almost twice that from HO2, also shows this dependence on NO. Second, the calculated OH production rate, which should equal the measured OH loss rate because OH is in steady state, is instead less than the measured OH loss rate by (1–2) × 107 molecules cm‐3 s‐1, with low statistical significance during the day and high statistical significance at night. Third, surprisingly high OH and HO2 mixing ratios were often observed during nighttime. The nighttime OH mixing ratio and the HO2/OH ratio cannot be explained by known reaction mechanisms, even those involving O3 and alkenes. Because instrument tests have failed to reveal any instrument artifacts, more exotic chemicals or chemistry, such as OH adducts or other radicals that fall apart into OH inside the instrument, are suspected.
Thermoremanent magnetization of the Martian lithosphere
Authors: Arkani‐Hamed Jafar
Published: October 2003

This paper investigates the thermoremanent magnetization (TRM) of the Martian lithosphere assuming that the upper part of the lithosphere acquired TRM in the early history of the planet and in the presence of the core field (the primary magnetization), whereas the lower part has been gradually magnetized by the magnetic field of the upper part as it has cooled below the Curie temperature (secondary magnetization). The secondary magnetization is relatively weak if the magnetic properties of the lower lithosphere are taken to be similar to that of the extrusive basalt near the oceanic ridge axes on Earth. However, if the Martian lower lithosphere is more magnetic, e.g., by an order of magnitude, the secondary magnetization can be significant, although still weaker than the primary magnetization of the upper part. Such a highly magnetic lower lithosphere does not seem plausible by terrestrial standards, and it remains to be confirmed whether it is geologically plausible for Mars. I also examine a lithospheric model with a strongly magnetic layer beneath the crust, 25 times more magnetic than the extrusive basalt, representing a possible ilmenite‐rich layer with a considerable amount of hematite‐ilmenite lamellae. I assume that the layer was not magnetized by the core field because it was hotter than the Curie temperature of the lamellae when the core dynamo was active. It acquired secondary magnetization later in the presence of the magnetic field of the crust. Despite adopting an extraordinarily high magnetic layer which seems implausible by terrestrial standards, the secondary magnetization of the layer has minor contributions to the observed magnetic anomalies. In all models considered the primary magnetization is ∼20–30 A/m and has the dominant contribution to the observed magnetic anomalies. It is worth noting that the radial components of the primary and secondary magnetization are parallel, whereas the tangential components are in opposite directions. Because the strong magnetic anomalies in the south likely arise from the tangential magnetization, considering the secondary magnetization requires even stronger primary magnetization.
Stardust Imaging Camera
Authors: Newburn Ray L. , Bhaskaran Shyam , Duxbury Thomas C. , Fraschetti George , Radey Tom , Schwochert Mark
Published: October 2003

The Stardust spacecraft is carrying an Imaging Camera, primarily for 81P/Wild 2 approach navigation, but the camera also will provide valuable data for P/Wild 2 nucleus characterization and about its activity. During an engineering readiness test, the camera already has provided useful scientific data about an asteroid, 5535 Annefrank. The camera utilizes spare parts from Cassini and Voyager as well as some inherited designs to provide an excellent, low‐cost imaging system with a 1024 × 1024 pixel CCD detector and an f/3.5 lens with a 202 mm focal length. These yield a 3.5° × 3.5° field of view and, potentially, 12 arc second resolution. Spacecraft roll combined with a movable mirror permits safe autonomous body tracking. This capability was proven on Annefrank and will be used to acquire the desired data on P/Wild 2, with the spacecraft protected by a dust shield (a Whipple bumper) during that flyby. Details of the instrumental design and problems associated with its use make up the bulk of the paper.
Scale effect on geomorphologic and kinematic dispersion
Authors: Botter Gianluca , Rinaldo Andrea
Published: October 2003

Geomorphologic dispersion relates to the fraction of the variance of residence time distributions that can be directly linked to the heterogeneity of the paths available to hydrologic runoff of a river basin in response to suitable rainfall pulses. It thus defines the dispersive characters of geomorphological origin. Hillslope transport processes and systematic variations of advective processes in the channel network define a kinematic component of dispersion. Here we suggest that channel‐borne kinematic effects are likely to be clouded by hillslope dispersion in a surprisingly wide spectrum of basin scales. We find that the signatures of hillslope transport on travel time distributions do not fade away rapidly with the size of the catchment (i.e., when the basin scale becomes much greater than the mean hillslope size), in particular because of their major impact on the skewness of the travel time distribution. We suggest that an appropriate description of hillslope‐channel transitions entails a combination of geomorphic and kinematic effects which plays a decisive role in shaping the main characters of the hydrologic response in cases of practical interest.
Isolation of peptides of the brevinin‐1 family with potent candidacidal activity from the skin secretions of the frog Rana boylii
Authors: Conlon J. M. , Sonnevend Á. , Patel M. , Davidson C. , Nielsen P.F. , Pál T. , Rollins‐ Smith L.A.
Published: October 2003

Abstract: The emergence of strains of the human pathogen Candida albicans with resistance to commonly used antibiotics has necessitated a search for new types of antifungal agents. Six peptides with antimicrobial activity were isolated from norepinephrine‐stimulated skin secretions from the foothill yellow‐legged frog Rana boylii. Brevinin‐1BYa (FLPILASLAA10KFGPKLF CLV20TKKC) was particularly potent against C. albicans [minimal inhibitory concentration (MIC) = 3 μm] and also active against Escherichia coli (MIC = 17 μm) and Staphylococcus aureus (MIC = 2 μm), but its therapeutic potential for systemic use is limited by its strong hemolytic activity (HC50 = 4 μm). The single amino acid substitution (Phe12 → Leu) in brevinin‐1BYb resulted in a fourfold lower potency against C. albicans and the additional amino acid substitutions (Lys11 → Thr, Phe17 → Leu and Val20 → Ile) in brevinin‐1BYc resulted in a ninefold decrease in activity. Two members of the ranatuerin‐2 family and one member of the temporin family were also isolated from the secretions but showed relatively low potency against the three microorganisms tested.
Tachyphylactic properties of angiotensin II analogs with bulky and hydrophobic substituents at the N‐terminus
Authors: Motta S. C. , Poletti E. F. , Souza S. E. G. , Correa S. A. A. , Jubilut G. N. , Paiva A. C. M. , Shimuta S. I. , Nakaie C. R.
Published: October 2003

Abstract:  Tachyphylaxis, defined as the acute loss of response of some smooth muscles upon repeated stimulations with angiotensin II (Ang II), has been shown to be dependent mainly on the N‐terminal region of the ligand. To further study the structural requirements for the induction of tachyphylaxis we have synthesized Ang II analogs containing the bulky and very lipophilic substituents 9‐fluorenylmethyloxycarbonyl (Fmoc) and 9‐fluorenylmethyl ester (OFm) at the α‐amino (Nα‐Fmoc‐Ang II) or the β‐carboxyl ([Asp(OFm)1]‐Ang II) groups of the Asp1 residue, respectively. In binding assays with Chinese hamster ovary cells transfected with the AT1 Ang II receptor, Nα‐Fmoc‐Ang II bound with high affinity, whereas [Asp(OFm)1]‐Ang II showed lower affinity. In biological assays, these two analogs were full agonists and showed 30 and 3%, respectively, of the Ang II potency in contracting the guinea‐pig ileum smooth muscle. The two analogs induced tachyphylaxis, in spite of the lack of a free amino group in Nα‐Fmoc‐Ang II. Thus, analogs with Fmoc‐ or OFm‐type groups coupled to the Asp1 residue, whether at the amino or carboxyl functions, induce tachyphylaxis through an unreported mechanism. Based in these findings and those available from the literature, an alternate molecular interaction mode between Ang II N‐terminal portion and the AT1 receptor is proposed to explain the tachyphylactic phenomenon.
Combined deficiency of iron and other divalent cations mitigates the symptoms of iron deficiency in tobacco plants
Authors: Kobayashi Takanori , Yoshihara Toshihiro , Jiang Tingbo , Goto Fumiyuki , Nakanishi Hiromi , Mori Satoshi , Nishizawa Naoko K.
Published: October 2003

To determine the responses of plants to deficiencies of multiple metals, tobacco plants (Nicotiana tabacum L.) were subjected to treatments that were deficient in combinations of Fe and two other micronutrients, Zn and Mn. The response was measured using macro indices, including plant appearance, FW, chlorophyll concentration, and mineral concentrations, and with a molecular index, the barley (Hordeum vulgare L.) Ids2 promoter/GUS fusion gene system (Yoshihara et al. 2003, Plant Biotech 20: 33–41). Tobacco plants grown in medium with combined deficiencies grew better and had higher chlorophyll concentrations than did plants grown on medium deficient in Fe only, although the measured Fe concentrations in the plant tissues were essentially the same. The Ids2/GUS expression responded to Fe deficiency, but not to Mn or Zn deficiencies in tobacco plants when Fe was present. Tobacco plants grown in medium with combined deficiencies had clearly detectable GUS activity, but the response was significantly lower than that in tobacco plants deficient in Fe only. The Fe‐deficiency symptoms were mitigated at both the visible and molecular levels. Although more precise experimental evidence is needed to explain the mitigation mechanism, the balance of minerals was shown to be an important parameter to consider when estimating iron deficiency based on tobacco plant responses.
Analysing photosynthetic complexes in uncharacterized species or mixed microalgal communities using global antibodies
Authors: Campbell Douglas A. , Cockshutt Amanda M. , Porankiewicz‐Asplund Joanna
Published: October 2003

Photoautotrophs share core pathways for primary productivity and elemental cycling. These paths are generally mediated by abundant protein complexes which are conserved across wide taxonomic ranges, and which quantitatively dominate the proteomes of photoautotrophs. Quantification of key protein pools is a powerful approach to measure resource allocations and maximal catalytic capacities for biological functions, for comparing species or communities, or for tracking change over time within communities. Protein quantification can be more definitive than transcript analyses for functional studies, since changes in transcript levels are often only weakly coupled to pool sizes of functional protein. For field samples protein detections are more generally applicable than enzyme assays which require individually specialized extractions and assays, which are prone to interference by environmental contaminants. We are using bioinformatic analyses to design a series of peptide sequence tags that are conserved in all family members for a well‐characterized subunit from each of the major catalytic complexes mediating photosynthesis and nitrogen metabolism. We use these peptide sequence tags to elicit production of ‘global antibodies’, intended to recognize all members of the target protein family with equal efficiency regardless of the species of origin. Uniform target detection is particularly important for tracking levels of key proteins in mixed communities, or for quantitative comparisons across plant species. In parallel we are creating quantification standards for these key protein pools for functional and (eco)physiological studies.
Different induction patterns of glutamate metabolizing enzymes in ripening fruits of the tomato mutant green flesh
Authors: Bortolotti Santiago , Boggio Silvana B. , Delgado Luciana , Orellano Elena G. , Valle Estela M.
Published: October 2003

The stay‐green mutant of tomato green flesh (gf) is deficient in the chloroplast degradation machinery and displays an altered ripening profile. The ripening process of tomato (Lycopersicon esculentum Mill.) fruit is characterized by a substantial induction in glutamate dehydrogenase (GDH, EC 1.4.1.3) and a decline in glutamine synthetase (GS, EC 6.3.1.2) levels, associated with an increase in the relative glutamate content. In this study the level of free amino acids and enzymes associated with glutamate metabolism were followed in mature gf fruits at green and ripe stages. From these fruits, total RNA, protein extracts and intact plastids were isolated. Specific activities of GDH, GS and NADH‐ or ferredoxin‐dependent glutamate synthase (NADH‐GOGAT, EC 1.4.1.14; Fd‐GOGAT, EC 1.4.7.1) were measured and immunoblot analyses were performed. The total free amino acid contents of gf mature fruits decreased during ripening, contrasting with that observed in several cultivated varieties of tomatoes. The relative glutamate content, however, increased markedly in ripe gf fruits, as in all the tomato cultivars tested so far. Although GDH activity and polypeptides were found in green gf fruits, GDH transcripts were not detected in these fruits. In ripe gf fruits GDH was clearly present. NADH‐ and Fd‐GOGAT activities, on the other hand, were barely measurable in gf fruits whereas Fd‐GOGAT protein was detected in green gf fruits and, to a lower extent in ripe gf fruits. Levels of GS protein and transcripts were correlated in all fruits tested. Collectively, the expression of the enzymes involved in the primary glutamate metabolism seems to be differently regulated during the ripening process.
Logistics in the life cycle of Photosystem II—lateral movement in the thylakoid membrane and activation of electron transfer
Authors: Mamedov Fikret , Styring Stenbjörn
Published: October 2003

Due to its unique ability to split water, Photosystem II (PSII) is easily accessible to oxidative damage. Photoinhibited PSII centres diffuse laterally from the grana core region of the thylakoid membrane to the stroma lamellae in order to allow replacement of damaged proteins and cofactors. The ‘new born’ PSII centres in this region are characterized by the absence of the water splitting capacity and very poor ability to bind the secondary quinone acceptor, QB. After the repair process PSII has to regain the water splitting capacity. This requires a set of well‐defined electron transfer reactions leading to assembly of the Mn‐cluster. In order to minimize the danger of photoinhibition during these earlier stages of photoactivation of PSII, auxiliary donors to the primary donor P680+, such as redox active tyrosine on D2 protein, YD, and cytochrome b559 become involved in the electron transport reactions by providing necessary electrons. Cytochrome b559 may also serve as an electron acceptor to QA– if elevated light intensities occur during the photoactivation process. These reactions lead to activation of QB binding, and finally to the assembly of the Mn‐cluster. All these electron transport events occur simultaneously with the lateral movement of PSII centres back to the appressed regions of the grana core, where the pool of the most active PSII is situated.