bluuebunny/crossref_metadata_2025 huggingface dataset:
A record minimum arctic sea ice extent and area in 2002
Authors: Serreze M. C. , Maslanik J. A. , Scambos T. A. , Fetterer F. , Stroeve J. , Knowles K. , Fowler C. , Drobot S. , Barry R. G. , Haran T. M.
Published: May 2003

Arctic sea ice extent and area in September 2002 reached their lowest levels recorded since 1978. These conditions likely resulted from (1) anomalous warm southerly winds in spring, advecting ice poleward from the Siberian coast (2) persistent low pressure and high temperatures over the Arctic Ocean in summer, promoting ice divergence and rapid melt.
The first 80‐hour continuous lidar campaign for simultaneous observation of mesopause region temperature and wind
Authors: She C. Y. , Sherman Jim , Yuan Tao , Williams B. P. , Arnold Kam , Kawahara T. D. , Li Tao , Xu Li Fang , Vance J. D. , Acott P. , Krueger David A.
Published: May 2003

The Colorado State Sodium lidar has been upgraded to a two‐beam system capable of simultaneous measurement of mesopause region temperature and winds, day and night, weather permitting. This paper reports the initial result of the first campaign, conducted in April 2002, with a total of 145 hours of observation including an 80‐hour continuous data acquisition of temperature and zonal wind. The contour plots of the continuous data set show considerable coherence and activities of upward propagating waves, with a maximum day‐night difference of 15.5 m/s in zonal wind at 88 km and of 10 K in temperature at 92 km. Oscillations at periods of 10‐hour in temperature and 16‐hour in zonal wind, implicating nonlinear interactions, can be identified. Decomposition of the time series into tidal periods, resulted in very good agreement with the GSWM00 predictions of diurnal tide. The observed altitude dependence in diurnal amplitudes and phases is consistent with the presence of a significant upward propagating wave, accompanying and modulating the main diurnal tide.
A modeling study of oceanic nitrous oxide during the Younger Dryas cold period
Authors: Goldstein Beat , Joos Fortunat , Stocker Thomas F.
Published: May 2003

The marine production, cycling, and air‐sea gas exchange of nitrous oxide (N2O) are simulated in a coupled climate‐biogeochemical model of reduced complexity. The model gives a good representation of the large‐scale features of the observed oceanic N2O distribution and emissions to the atmosphere. The transient behavior of the model is tested for the Younger Dryas (Y‐D) cold period (12,700–11,550 BP), which is simulated by releasing a freshwater pulse into the North Atlantic, causing a temporary collapse of the model's Atlantic thermohaline circulation (THC). A temporary drop in atmospheric N2O of about 10 ppb results, while ice‐core measurements show a total drop of 25 to 30 ppb. This suggests that terrestrial changes have also contributed to the observed variations. The main cause of the modeled reduction in atmospheric N2O is increased oceanic storage in the short‐term and a reduction of new production in the long‐term due to increased stratification.
Are CME “interactions” really important for accelerating major solar energetic particle events?
Authors: Richardson Ian G. , Lawrence Gareth R. , Haggerty Dennis K. , Kucera Therese A. , Szabo Adam
Published: May 2003

Recent studies have proposed that the presence or absence of an “interaction” with a preceding coronal mass ejection (CME) or other coronal structure within ∼50 Rs of the Sun discriminates large, fast CMEs associated with major solar energetic particle (SEP) events from those that are not. We conclude that there is no compelling evidence that, if such interactions take place, they play an important role in SEP acceleration. Reasons include: The reported statistical results are consistent with a chance association between interacting CMEs and SEP events; Energetic SEPs are detected at Earth typically before or around the time when the “primary” CME enters the LASCO C2 field of view ‐ interactions higher in the corona cannot play a role in acceleration of these particles; For ∼60% of major SEP events in 1997–2001, the preceding CME fades into the background corona or is relatively narrow (<40°), suggesting any interaction will be weak; Radio signatures attributed to CME interaction occur after SEP acceleration has commenced.
Inverse modeling in the time domain for solving diffusion in a heterogeneous rock matrix
Authors: Delay Frederick , Porel Gilles
Published: May 2003

A Lagrangian method has been developed to solve heterogeneous diffusion. The time domain on which the method rests allows for the coupling with a Gauss‐Newton inversion in which the sensitivity to parameters is derived analytically. This tool has proved very rapid and efficient, even for large computation grids as those extracted from autoradiographs of rock samples. It offers a more comprehensive view of transport by diffusion for many applications, one of them being for instance, the safety of underground repository sites.
Links between flood events in central Europe since AD 1500 and large‐scale atmospheric circulation modes
Authors: Jacobeit J. , Glaser R. , Luterbacher J. , Wanner H.
Published: May 2003

Based on documentary sources incidence variations of flood events can be reconstructed back to AD 1500 for several catchment areas in Central Europe. Links to atmospheric circulation modes, derived from reconstructed large‐scale sea level pressure (SLP) grids for the last 500 years, have been identified on climatic time scales (monthly to seasonal). These relations are expressed in terms of several indices describing the particular importance of atmospheric circulation modes as a dynamical background for the varying incidence of flood events. During winter, the zonal circulation mode covers the largest part of these events, in relation to mode‐frequency, however, other circulation modes become important during historical periods of increased flood frequency, e.g. modes characterised by Atlantic low and Russian high pressure centres. Different subtypes of this mode reached maxima in flood‐association during different climatic periods of the past.
Large solar energetic particle events of cycle 23: A global view
Authors: Gopalswamy N. , Yashiro S. , Lara A. , Kaiser M. L. , Thompson B. J. , Gallagher P. T. , Howard R. A.
Published: May 2003

We report on a study of all the large solar energetic particle (SEP) events that occurred during the minimum to maximum interval of solar cycle 23. The main results are: 1. The occurrence rate of the SEP events, long‐wavelength type II bursts and the fast and wide frontside western hemispheric CMEs is quite similar, consistent with the scenario that CME‐driven shocks accelerate both protons and electrons; major flares have a much higher rate. 2. The SEP intensity is better correlated with the CME speed than with the X‐ray flare class. 3. CMEs associated with high‐intensity SEPs are about 4 times more likely to be preceded by wide CMEs from the same solar source region, suggesting the importance of the preconditioning of the eruption region. We use a specific event to demonstrate that preceding eruption from a nearby source can significantly affect the properties of SEPs and type II radio bursts.
Two distinct seasonal Asian source regions for mineral dust deposited in Greenland (NorthGRIP)
Authors: Bory Aloys J.‐M. , Biscaye Pierre E. , Grousset Francis E.
Published: May 2003

A four‐year, high‐resolution (<2 mo) record of mineralogical and isotopic (Sr and Nd) characteristics of mineral dust deposited at NorthGRIP confirms the seasonal variability in the eastern Asian source regions providing dust to northern Greenland at present. Comparison of the Sr and Nd isotopic compositions of the dust with those of potential source area samples from China and Mongolia support that the Takla Makan desert is the primary source, supplying most if not all of the mineral particles during the dusty spring season. A different source area, however, plays a role during most of year and during the low‐dust season (summer through winter) in particular. Inner Mongolian deserts of northern China, including the Tengger and the Mu Us, are likely candidates but the Mongolian Gobi is ruled out as a significant contributor to Greenland.
Comparison of POLDER apparent and corrected oxygen pressure to ARM/MMCR cloud boundary pressures
Authors: Vanbauce Claudine , Cadet Bertrand , Marchand Roger T.
Published: May 2003

POLDER (POLarization and Directionality of the Earth's Reflectances) cloud oxygen pressures are compared to cloud boundary pressures obtained from the combination of Lidar and Millimeter Wave Cloud Radar ground measurements located at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site. Without ground reflection correction, the apparent pressures are found to be closer to the mean cloud pressure than to the cloud top pressure. Nevertheless, for almost a quarter of our comparison cases the apparent pressure level is found to be below the cloud base level. This problem practically disappears applying a simple correction for the surface reflection effect. The corrected oxygen pressures are then found to be very close (12 hPa on average) to the mean cloud pressure.
Remote estimation of leaf area index and green leaf biomass in maize canopies
Authors: Gitelson Anatoly A. , Viña Andrés , Arkebauer Timothy J. , Rundquist Donald C. , Keydan Galina , Leavitt Bryan
Published: May 2003

Leaf area index (LAI) is an important variable for climate modeling, estimates of primary production, agricultural yield forecasting, and many other diverse studies. Remote sensing provides a considerable potential for estimating LAI at local to regional and global scales. Several spectral vegetation indices have been proposed, but their capacity to estimate LAI is highly reduced at moderate‐to‐high LAI. In this paper, we propose a technique to estimate LAI and green leaf biomass remotely using reflectances in two spectral channels either in the green around 550 nm, or at the red edge near 700 nm, and in the NIR (beyond 750 nm). The technique was tested in agricultural fields under a maize canopy, and proved suitable for accurate estimation of LAI ranging from 0 to more than 6.
Deep convection and brine rejection in the Japan Sea
Authors: Talley Lynne D. , Lobanov V. , Ponomarev V. , Salyuk A. , Tishchenko P. , Zhabin I. , Riser S.
Published: May 2003

Direct water mass renewal through convection deeper than 1000 m and the independent process of dense water production through brine rejection during sea ice formation occur at only a limited number of sites globally. Our late winter observations in 2000 and 2001 show that the Japan (East) Sea is a part of both exclusive groups. Japan Sea deep convection apparently occurs every winter, but massive renewal of bottom waters through brine rejection had not occurred for many decades prior to the extremely cold winter of 2001. The sites for both renewal mechanisms are south of Vladivostok, in the path of cold continental air outbreaks.
Delamination structure imaged in the source area of the 1982 Urakawa‐oki earthquake
Authors: Murai Yoshio , Akiyama Satoshi , Katsumata Kei , Takanami Tetsuo , Yamashina Tadashi , Watanabe Tomoki , Cho Ikuo , Tanaka Masayuki , Kuwano Asako , Wada Naoto , Shimamura Hideki , Furuya Itsuo , Zhao Dapeng , Sanda Ryohei
Published: May 2003

The Kuril arc collides with the northeast Japan arc in the southern part of Hokkaido, Japan. 3‐D tomographic inversion of data from a dense network of sensitive ocean‐bottom seismographs and land stations has allowed imaging of previously unseen details of the arc‐arc collision structure. A low velocity body dips gently southwestward, at depths of 35 to 45 km, from east of the Hidaka Mountains to the source area of the 1982 Urakawa‐oki destructive earthquake (Ms 6.8). The low velocity body is the lower half of the lower crust of the Kuril arc, which must have been delaminated by the collision. We believe that the continuing collision of the delaminated lower crust with the northeast Japan arc resulted as an episode of aseismic slow slip prior to the 1982 Urakawa‐oki earthquake as well being the reason for the high seismic activity in this region.
A new method for determining the meridional wind velocity during an ionospheric storm
Authors: Yuan Zhigang , Ning Baiqi , Liu Libo , Wan Weixing , Zhao Biqiang
Published: May 2003

This paper introduces a new method for determining the meridional wind velocity during an ionospheric storm based on a sequence of Doppler ionograms. By this new method, the height‐ and time‐dependent meridional wind velocity in the F2 layer was obtained during the magnetic substorm on April 17, 2002. The peak velocity of meridional wind at 300 km altitude is about 300 m/s, the deduced propagation velocity of traveling atmospheric disturbances (TADs) is about 520 m/s. Furthermore, not only the amplitude but also the onset time and phase velocity of the TAD‐associated wind perturbation can be explained by the present theories and observations of meridional winds. This work offers a new method to investigate the propagation and morphology of meridional wind during a magnetic substorm by using Digisonde routine observations.
IMF‐driven plasmasphere erosion of 10 July 2000
Authors: Goldstein J. , Sandel B. R. , Forrester W. T. , Reiff P. H.
Published: May 2003

On 10 July 2000, the IMAGE EUV imager observed erosion of the nightside plasmasphere that occurred in two bursts during 5–8 UT. The plasmapause radial velocity Vpp at 2.4 MLT was extracted from the time sequence of EUV images. We show that intervals of Vpp < 0 (i.e., erosion) are correlated with intervals of southward (Swd) interplanetary magnetic field (IMF), if the solar wind and IMF data are time‐delayed by 30 minutes (in addition to a 3.7‐minute delay for propagation to the magnetopause). This suggests that coupling between the solar wind and the plasmapause, involving processes in the ionosphere and magnetotail, takes about 30 minutes. A 6:40 UT magnetosphere compression may have hurried the onset of the second erosion.
A statistical study of CMEs associated with metric type II bursts
Authors: Lara A. , Gopalswamy N. , Nunes S. , Muñoz G. , Yashiro S.
Published: May 2003

We present a statistical study of the characteristics of CMEs which show temporal association with type II bursts in the metric domain but not in the decameter/hectometric (DH) domain. This study is based on a set of 80 metric (m) type II bursts associated with surface events in the solar western hemisphere. It was found that in general, the distribution of the widths and speeds of the CMEs associated with metric (but not DH) type II bursts are shifted towards higher values compared to those of all CMEs observed by LASCO in the 1996–2001 period. We also found that these distributions have lower values than the same distributions of the CMEs associated with DH type II bursts. In terms of energy, this means that the CMEs associated only with metric type II bursts are more energetic (wider and faster) than regular CMEs but less energetic than the CMEs associated with DH type II bursts.
Radiative impacts from biomass burning in the presence of clouds during boreal spring in southeast Asia
Authors: Hsu N. Christina , Herman Jay R. , Tsay Si‐Chee
Published: May 2003

The impact of smoke aerosols generated from biomass burning activities in Southeast Asia on the total (i.e., direct and indirect effects) reflected solar and emitted thermal radiation from clouds was investigated using satellite data. We combine narrowband radiance measurements, from ultraviolet to near‐infrared wavelengths (e.g., SeaWiFS and TOMS), with broadband irradiance measurements (e.g., CERES) to quantify how smoke aerosols modulate the cloud radiative forcing. In Southeast Asia, our results reveal that smoke is frequently present over large areas of cloud‐covered regions during boreal spring. The reflected solar (emitted thermal) radiation from clouds due to smoke aerosols can be reduced (enhanced) by as much as 100 (20) W m−2 over the month of March 2000. We also found that the reduction in cloud spectral reflectance at 670 nm is large enough to lead to significant errors in retrieving cloud properties (e.g., optical thickness and effective radius) from current satellite measurements, such as AVHRR and MODIS.
Coulomb stress changes in the South Iceland Seismic Zone due to two large earthquakes in June 2000
Authors: Árnadóttir Thóra , Jónsson Sigurjón , Pedersen Rikke , Gudmundsson Gunnar B.
Published: May 2003

The South Iceland Seismic Zone experienced the largest earthquakes for 88 years in June 2000, with a MS = 6.6 event on June 17, followed by another MS = 6.6 earthquake on June 21. These events occurred on two parallel N‐S striking, right‐lateral strike slip faults, separated by about 17 km. We calculate the static Coulomb stress change for the June 17 and 21 earthquakes using a distributed slip model derived from joint inversion of InSAR and GPS data. We find that the static stress change caused by the June 17 event is about 0.1 MPa at the location of the June 21 hypocenter, promoting failure on the second fault. Locations of aftershocks agree well with areas of increased Coulomb failure stress. Our calculations indicate that positive stress changes due to the two earthquakes make the area west of the June 21 rupture the most likely site of the next large earthquake in South Iceland.
GPS occultation sensor observations of ionospheric scintillation
Authors: Straus P. R. , Anderson P. C. , Danaher J. E.
Published: May 2003

We present the first globally distributed set of observations of radiowave scintillation by a GPS occultation sensor, the Ionospheric Occultation Experiment on board the PICOSat satellite. Examples of GPS C/A code signal‐to‐noise ratios at the L1 frequency are shown which contain strong fluctuations. The source of the fluctuations is evaluated through a statistical analysis of more than 10,000 occultations obtained during February/March 2002. The geographic and local time distributions of occultations having large values of the S4 scintillation index are consistent with known scintillation climatology, unambiguously identifying the fluctuations as ionospheric scintillation. GPS occultation measurements provide a means of measuring scintillation on a global basis, which can not be done using traditional ground‐based monitoring techniques.
Predictability of decadal variations in the thermohaline circulation and climate
Authors: Collins Matthew , Sinha Bablu
Published: May 2003

Ensemble experiments with a coupled atmosphere‐ocean model show that natural variations in the strength of ocean thermohaline circulation (THC), a key player in the maintenance of the climate of Earth, are potentially predictable one to two decades into the future. In contrast to previous studies, these predictable THC variations lead to predictable variations of the climate of Western Europe that could be of considerable benefit to society. Further model experiments also show that, under certain conditions, variations in the strength of the THC may even be predictable for more than 50 years into the future.
Impact of gas absorption and surface albedo on cloud radiative smoothing
Authors: Schroeder Marc , Bennartz Ralf
Published: May 2003

Using visible and near infrared aircraft observations of stratocumulus clouds over land, the impact of gas absorption and surface albedo on cloud radiative smoothing has been studied. Time series of the observed nadir radiances have been converted into Fourier space, and the scale break as well as the large scale and small scale slopes of the resulting spatial power spectrum have been analyzed. An increase in gas absorption leads to a reduction in radiative smoothing due to a decreased likelihood of horizontal photon transport within the cloud. This can be seen both in the derived scale breaks and in the slope of the power spectrum at high spatial wavenumbers which exhibit a high correlation with cloud single scatter albedo. An increase in surface albedo leads to a radiative smoothing of the observed radiance field at scales proportional to the cloud height and to a decrease in the slope of the large scale spatial power spectrum.
Extremely strong thermohaline sources/sinks generated by diagnostic initialization
Authors: Chu Peter C. , Lan Jian
Published: May 2003

One difficulty for ocean modeling is the lack of velocity data for specifying the initial condition. Diagnostic initialization is widely used; it integrates the model from known temperature (Tc) and salinity (Sc) and zero velocity fields while holding (Tc, Sc) unchanged. After a period (around 30 days) of the diagnostic run, the velocity field (Vc) is established, and (Tc, Sc, Vc) fields are then treated as the initial conditions for the prognostic numerical modeling. During the diagnostic initialization period, the heat and salt ‘source/sink’ terms are generated at each time step. Maximum time rates of absolute change of the monthly mean T, S (0.1°/day, 0.1 ppt/day) are taken as the standard measures to identify the strength of the thermohaline ‘sources/sinks’. Twenty four times of the standard measures (0.1°/hr, 0.1 ppt/hr) represent strong ‘sources/sinks’. Ten times of the strong ‘sources/sinks’ (1°/hr, 1 ppt/hr) represent extremely strong ‘sources/sinks’. The Princeton Ocean Model implemented for the Japan/East Sea is used to demonstrate the existence of extremely strong thermohaline sources and sinks generated by the diagnostic initialization with the annual mean Tc, Sc from the Navy's Global Digital Environmental Model. The effects of extremely strong and spatially nonuniform initial heating/cooling (salting/freshening) rates on thermohaline and velocity fields need to be further investigated.
Vertical distribution of spectral solar irradiance in the cloudless sky: A case study
Authors: Wendisch Manfred , Mayer Bernhard
Published: May 2003

First airborne measurements of spectral solar down‐ and upwelling irradiances with a high spectral resolution (2–3 nm) are presented. The data were gathered in cloudless, hazy conditions over sea and land using a new instrument (called albedometer), which is equipped with a unique sensor head leveling technique. The downwelling irradiances and their spectral slope increase with altitude, illustrating the impact of Rayleigh scattering and boundary layer aerosols. The upwelling spectra reveal typical reflection features of the underlying surface (e.g., vegetation step around 700 nm). The measurements are compared with radiative transfer model results based on simultaneous airborne aerosol observations. The downwelling irradiances mostly agree to ±10% which is within the experimental and modeling uncertainties. The upwelling irradiances are highly sensitive to uncertainties in the spectral surface albedo. Reasonable agreement between measurements and simulations required us to determine the surface albedo from flights at low altitude, rather than adopting literature values.
Coherency of multi‐scale abrupt changes between the NAO, NPI, and PDO
Authors: Schwing Franklin B. , Jiang Jianmin , Mendelssohn Roy
Published: May 2003

A scanning t‐test and coherency detection algorithm is used to analyze and detect multi‐scale abrupt changes in three climate indices; the NAO (North Atlantic Oscillation), PDO (Pacific Decadal Oscillation), and NPI (North Pacific Index). The analysis suggests that decadal fluctuations in atmospheric and ocean circulation are linked between the Atlantic and Pacific Ocean regions. The NPI and PDO are negatively correlated on decadal scales, with change points in about 1915, 1924, 1942, 1961, 1976, and 1988. The longer NAO also displays significant change points around these dates, as well as in 1832, 1865, 1870, and 1881. Decadal changes in the NAO and NPI (PDO) were positively (negatively) correlated prior to the late 1950s, but negatively (positively) correlated during 1962–1988. Although the north Atlantic and north Pacific atmosphere is teleconnected on decadal scales, the change after 1961 suggests it has multiple spatial modes.
High‐temperature seafloor hydrothermal circulation over geologic time and archean banded iron formations
Authors: Lowell Robert P. , Keller Susan M.
Published: May 2003

Under the assumption of simple plate tectonics with a range of continental growth scenarios, we construct models of global lithospheric heat loss, hydrothermal heat loss and hydrothermal iron flux to the ocean as functions of geologic time from 4.0 Ga to present. The models show that lithospheric heat loss scales with the square root of the plate creation rate, whereas hydrothermal heat loss scales linearly with that rate. Thus during the Archean lithospheric and hydrothermal heat losses were ≈3 and ≈10 times greater than present, respectively. Straightforward extrapolation of hydrothermal Fe flux from the present to the Archean using these models indicates that hydrothermal Fe may not have been sufficient to supply the large Superior‐type Banded Iron Formations deposited between 2.7 and 1.8 Ga.
Seasonal variation of mesospheric iron layers at Arecibo: First results from low‐latitudes
Authors: Raizada Shikha , Tepley Craig A.
Published: May 2003

We present the annual variation of the distribution of neutral iron of the low‐latitude mesopause region measured at the Arecibo Observatory using resonance fluorescence lidar. A comparison was made between our low‐latitude measurements and similar mid‐and high‐latitude observations of Fe column abundance, centroid height, and RMS width of the layer. We find that the annual variation of the height and width of the layer are essentially anti‐correlated with previous measurements, while the column abundance lags its midlatitude counterpart by roughly three months. We suggest that the latitudinal differences in Fe layer properties result from variations in the distribution of mesospheric ozone and O2, which in turn affect the iron chemistry at the two latitudes.
Uptake of reactive nitrogen on cirrus cloud particles in the upper troposphere and lowermost stratosphere
Authors: Kondo Y. , Toon O. B. , Irie H. , Gamblin B. , Koike M. , Takegawa N. , Tolbert M. A. , Hudson P. K. , Viggiano A. A. , Avallone L. M. , Hallar A. G. , Anderson B. E. , Sachse G. W. , Vay S. A. , Hunton D. E. , Ballenthin J. O. , Miller T. M.
Published: May 2003

NOy (total reactive nitrogen) contained in ice particles was measured on board the NASA DC‐8 aircraft in the Arctic in January and March 2000. During some of the flights, the DC‐8 encountered widespread cirrus clouds. Large quantities of ice particles were observed at 8–12 km and particulate NOy showed large increases. The data indicate that the amount of NOy covering the cirrus ice particles strongly depended on temperature. Similar measurements were made in the upper troposphere over the tropical Pacific Ocean in August–September 1998 and 1999. The data obtained in the Arctic and tropics show very limited uptake of NOy on ice at temperatures above 215 K.
Novel technique for remote estimation of CO2 flux in maize
Authors: Gitelson Anatoly A. , Verma Shashi B. , Viña Andrés , Rundquist Donald C. , Keydan Galina , Leavitt Bryan , Arkebauer Timothy J. , Burba George G. , Suyker Andrew E.
Published: May 2003

There is considerable interest in assessing the magnitude of carbon sources and sinks for agricultural lands, grasslands, and forests. In this paper, we propose a novel technique to remotely assess CO2 fluxes in maize using reflectances (ρ) in two spectral channels either in the green around 550 nm or in the red edge near 700 nm and the NIR (beyond 750 nm). Differences of reciprocal reflectances [(ρGreen)−1 − (ρNIR)−1] and [(ρRedEdge)−1 − (ρNIR)−1] accounted for more than 90 percent of the variability in mid‐day canopy photosynthesis of irrigated maize. The technique was validated by an independent data set; root mean square error in predicting mid‐day canopy photosynthesis by [(ρRedEdge)−1 − (ρNIR)−1] was 0.17 mg/m2/s and 0.2 mg/m2/s by [(ρGreen)−1 − (ρNIR)−1].
Limits on inference of Mars small‐scale topography from MOLA data
Authors: Campbell Bruce A. , Ghent Rebecca R. , Shepard Michael K.
Published: May 2003

The surface roughness of Mars at scales from ∼1–200 m is of interest for lander hazard and radar‐sounder clutter analysis, but MOLA data are the only current source of global topographic information. We use synthetic fractal profiles to determine the uncertainties associated with deriving self‐affine statistics from detrended segments of MOLA tracks. The mean Hurst exponent derived from such segments is an underestimate of the true value, H, for H > 0.5, and an overestimate for H < 0.5. Values of H from independent samples along a profile are distributed about this biased mean value. The magnitudes of the bias and variance in H increase for shorter segments. Terrestrial topography data show that extrapolation of roughness statistics to smaller scales based on self‐affine relationships is uncertain. Roughness at the 1–15 m scales may be poorly correlated with topography at >100‐m scales. We suggest that any extrapolation be regarded as a lower bound on the true terrain statistics.
A time series based method for estimating relative soil moisture with ERS wind scatterometer data
Authors: Wen Jun , Su Zhongbo
Published: May 2003

The radar backscattering coefficient is mainly determined by surface soil moisture, vegetation and land surface roughness under a given configuration of the satellite sensor. It is observed that the temporal variations of the three variables are different, the variation of vegetation and roughness are at the longer temporal scales corresponding to climate and cultivation practices, while soil moisture varies at a shorter temporal scale in response to weather forcing. Based on this hypothesis, a robust method for the determination of relative soil moisture is proposed for application to the ERS Wind Scatterometer database and the Pathfinder AVHRR dataset. Ground measured soil moisture data collected during GAME/Tibet field experiment are used to validate the proposed method. The results show that the estimated relative soil moisture corresponds closely to local precipitation at two GAME/Tibet field sites. The volumetric soil moisture converted from the Wind Scatterometer estimated relative soil moisture is in good agreement with the measured 0–4 cm topsoil volumetric soil moisture. The regional distributions of relative soil moisture are evaluated and correlated well to the ground measured volumetric soil moisture. It is concluded that the large footprint Wind Scatterometer dataset can capture ground soil wetness variation in arid and semi‐arid zone with the aid of vegetation information derived from other sensors.
The transformation of solid atmospheric particles into liquid droplets through heterogeneous chemistry: Laboratory insights into the processing of calcium containing mineral dust aerosol in the troposphere
Authors: Krueger B. J. , Grassian V. H. , Laskin A. , Cowin J. P.
Published: May 2003

Individual calcium carbonate particles reacted with gas‐phase nitric acid at 293 K have been followed using Scanning Electron Microscopy (SEM) and Energy Dispersive X‐Ray (EDX) analysis as a function of time and relative humidity (RH). The rate of calcium carbonate to calcium nitrate conversion is significantly enhanced in the presence of water vapor. The SEM images clearly show that solid CaCO3 particles are converted to spherical droplets as the reaction proceeds. The process occurs through a two‐step mechanism involving the conversion of calcium carbonate into calcium nitrate followed by the deliquescence of the calcium nitrate product. The change in phase of the particles and the significant reactivity of nitric acid and CaCO3 at low RH are a direct result of the deliquescence of the product at low RH. This is the first laboratory study to show the phase transformation of solid particles into liquid droplets through heterogeneous chemistry.
Freshwater teleconnections and ocean thermohaline circulation
Authors: Seidov Dan , Haupt Bernd J.
Published: May 2003

Asymmetry of the Atlantic and Pacific sea surface salinity (SSS) is recognized as an important element of the global ocean thermohaline circulation. However, a threshold of such asymmetry that may trigger a true global deep‐ocean conveyor has not yet been examined. A combined effect of the Atlantic‐Pacific and the Southern Ocean surface salinity asymmetries also has not yet been clearly shown. We address these issues and conclude that Atlantic‐Pacific SSS asymmetry is one of the most critical elements for maintaining the global ocean conveyor. Our experiments suggest, albeit preliminary, that high‐latitudinal freshwater impacts, as a mechanism of altering global ocean thermohaline circulation, may be less effective than inter‐basin freshwater communications.
Evidence of near‐Earth breakup location
Authors: Dubyagin S. V. , Sergeev V. A. , Carlson C. W. , Marple S. R. , Pulkkinen T. I. , Yahnin A. G.
Published: May 2003

We report a detailed study of an isolated substorm onset with the FAST spacecraft crossing the equatorward = most auroral arc just when/where it starts to break up. Comprehensive ground (optical, riometer and magnetometer) data combined with the space borne field and particle high resolution observations allowed to infer the following properties of the breakup onset region in this well‐documented event: (1) The arc flux tube stays in the region of considerable plasma pressure gradient wherethe pressure values are close to ∼1–2 nPa. The arc was located (2) just 0.4° poleward of the proton isotropic (b2i) boundary (which roughly gives ∼40 nT estimate for the equatorial magnetic field) and (3) close to the peak of the diffuse electron precipitation. (4) Tsyganenko 96 model for these particular solar wind conditions (which correspond well to both the observed b2i boundary and estimated plasma pressure) maps the arc to the equatorial distance of ∼8RE.All these facts in mutual agreement evidence that the auroral breakup in this particular case was launched in the near‐Earth domain of the magnetotail at r ∼8RE.
Arctic/North Atlantic Oscillation signature in Holocene sea surface temperature trends as obtained from alkenone data
Authors: Rimbu N. , Lohmann G. , Kim J.‐H. , Arz H. W. , Schneider R.
Published: May 2003

The variability in alkenone‐derived sea surface temperatures (SSTs) in the North Atlantic realm shows that a continuous SST decrease in the northeast Atlantic from the early to the late Holocene was accompanied by a persistent warming over the western subtropical Atlantic, the eastern Mediterranean Sea and the northern Red Sea. Based on the analysis of the instrumental data and of atmospheric general circulation model experiments, we show that this variation in SSTs during the Holocene can be attributed to a continuous weakening of a Northern Hemisphere atmospheric circulation pattern similar to that of the Arctic/North Atlantic Oscillation.
Solar influence on the spatial structure of the NAO during the winter 1900–1999
Authors: Kodera Kunihiko
Published: May 2003

The solar influence on the North Atlantic Oscillation (NAO), reported in a previous study based on 39 years of data, was confirmed by using 100 years of historical data. During the low solar activity winters, the NAO signal in the sea level pressure is confined in the Atlantic sector, while, during the high solar activity winters, NAO‐related anomalies extend over the northern hemisphere, in particular over the polar region and Eurasian continent. It was also found that the solar influence on the NAO originates from the Eurasian continent in early winter. In addition, two prolonged periods of high NAO index in the early and late 1900s showed spatial structures that were quite different and similar to those that occur during the low and high solar activity winters, respectively.
Super‐deep low‐velocity layer beneath the Arabian plate
Authors: Vinnik L. , Ravi Kumar M. , Kind R. , Farra V.
Published: May 2003

S and P receiver functions reveal indications of a low S velocity layer at 350–410 km depths beneath the Arabian plate. A similar layer was previously found beneath the Kaapvaal craton in southern Africa and Tunguska basin of the Siberian platform. We hypothesize, that the boundary at 350 km depth may separate dry mantle root of the Arabian plate from the underlying wet mantle layer. This boundary is not found beneath the Gulf of Aden, where the root is destroyed by sea‐floor spreading.
Mantle wedge water contents estimated from seismic velocities in partially serpentinized peridotites
Authors: Carlson Richard L. , Miller D. Jay
Published: May 2003

Water carried into subduction zones with the down‐going plate and subsequently released by dehydration reactions at depth affects the composition of the mantle wedge, triggers partial melting and affects subduction zone seismicity. Partially serpentinized peridotite may be a significant reservoir for water in the subducted plate, the mantle wedge and the overriding plate. Here we develop a model that relates the degree of serpentinization and water content of partially serpentinized peridotites to their seismic P‐wave velocities. In partially‐serpentinized ultramafic rocks, a 1% decrease in P‐wave velocity corresponds to a 2.4% increase in serpentine content, and a 0.3% (0.18 moles/m3) increase in H2O content (up to a maximum of 13%). Where there is evidence of serpentinization, mantle serpentine content is typically ∼15%, corresponding to 4–5 wt% H2O (6–10 moles/m3).
Energetic baroclinic super‐tidal oscillations on the southeast Florida shelf
Authors: Soloviev Alexander V. , Luther Mark E. , Weisberg Robert H.
Published: May 2003

Historical and recent data reveal a very energetic regime on the shelf off southeast Florida. In addition to spin off eddies, large‐amplitude tidal velocity fluctuations with amplitudes exceeding 0.5 ms−1 are observed. Recent exploratory measurements conducted as a part of the South Florida Ocean Measurement Center (SFOMC) show that the time scale of these oscillations is about 10 hrs. This period does not coincide either with the inertial period (27 Hrs) or with the semidiurnal M2 (12.42 hrs) or S2 (12 hrs) tidal constituents. In addition, these internal oscillations appear to be modulated seasonally. A possible explanation is that these oscillations are near‐resonant internal seiches generated by barotropic tidal wave in the channel between Florida and Bahamas.
The amplitude and phasing of climate change during the last deglaciation in the Sulu Sea, western equatorial Pacific
Authors: Rosenthal Yair , Oppo Delia W. , Linsley Braddock K.
Published: May 2003

Variations in tropical sea surface temperature patterns and the phasing relative to climate change in higher‐latitudes provide insight into the mechanisms of climate change on both orbital and shorter time‐scales. Here, we present well‐dated, high‐resolution records of planktonic foraminiferal δ18O and Mg/Ca‐based SST spanning the last deglaciation from the Sulu Sea, located in the western equatorial Pacific. The results indicate that the last glacial maximum was 2.3 ± 0.5°C cooler than present in the Sulu Sea with a concomitant decrease in sea surface salinity. The similarity between variations in surface salinity in the Sulu Sea, the western and eastern equatorial Pacific, and the Greenland ice‐core record suggests that the observed changes in salinity reflect large‐scale rearrangement of atmospheric patterns, which were coherent and synchronous throughout the Northern Hemisphere. The results suggest that the glacial equatorial Pacific climate was strongly influenced by both tropical, and extra‐tropical forcing, although it is not clear whether interannual (ENSO) variability is a good analogue of glacial‐interglacial climate change.
Response of streamflow to multiple earthquakes
Authors: Manga Michael , Brodsky Emily E. , Boone Michael
Published: May 2003

We analyze the streamflow response of Sespe Creek, CA, to several large earthquakes. We find that flow increased after three earthquakes, and that the observed changes in flow have the same character. Both those earthquakes that induced static extension and those that induced static contraction cause flow to increase; streamflow thus appears to respond to dynamic strain. We find that all postseismic responses can be explained by a model in which pore pressure increases coseismically without any changes in hydraulic diffusivity. There is a particle velocity threshold in the range of 5–20 cm/s to induce the pore pressure increase.
Long‐duration hectometric type III radio bursts and their association with solar energetic particle (SEP) events
Authors: MacDowall R. J. , Lara A. , Manoharan P. K. , Nitta N. V. , Rosas A. M. , Bougeret J. L.
Published: May 2003

It has recently been suggested by Cane et al. [2002] that a class of type III solar radio bursts, called type III‐l, is reliably associated with intense solar energetic particle (SEP) events. They proposed that the causative electrons for these bursts are accelerated in regions of reconnecting magnetic field in the wakes of coronal mass ejections (CMEs). In this paper, we examine the durations, intensities, and other characteristics of such radio bursts in the hectometric frequency range and compare them to several groups of control events. We conclude that simple criteria, based on hectometric data alone, can identify the majority (∼80%) of type III‐l radio bursts, which are associated with >20 MeV SEP proton events, while excluding almost 100% of the control events. Detailed study of these type III‐l bursts may play a significant role in a better understanding of the acceleration of SEPs and of the magnetic field evolution in the vicinity of CMEs.
Earthquakes series preceding very long period seismic signals, observed during the 2000 Miyakejima volcanic activity
Authors: Kobayashi Tomokazu , Ohminato Takao , Ida Yoshiaki
Published: May 2003

Unusual earthquakes series were observed one to two hours before a very long‐period (VLP) seismic pulse that happened once or twice a day, during the 2000 activity of Miyakejima volcano, Japan. The series on July 11 and 12 have particularly a clear feature. The time intervals of the earthquakes in the series decrease at a constant rate in the manner of geometric progression. The maximum amplitude of each earthquake is initially almost constant, but linearly decreases with time from few minutes before the occurrence of a VLP pulse. Hypocenters of these earthquakes are below the south‐western region of the crater, and near the sea level in depth. We interpret these earthquakes series as repetition of a gradual stress accumulation, and release under the variable critical stress level. The critical stress level is first constant, but linearly decreases later.
Enhancement of cloud cover and suppression of nocturnal drizzle in stratocumulus polluted by haze
Authors: Ackerman A. S. , Toon O. B. , Stevens D. E. , Coakley J. A.
Published: May 2003

Recent satellite observations indicate a significant decrease of cloud water in ship tracks, in contrast to an ensemble of in situ ship‐track measurements showing no average change in cloud water relative to the surrounding clouds, and contrary to the expectation of cloud water increasing in polluted clouds. We find through large‐eddy simulations of stratocumulus that the trend in the satellite data is likely an artifact of sampling only overcast clouds. The simulations instead show cloud cover increasing with droplet concentrations. The simulations also show that increases in cloud water from suppressing drizzle by increasing droplet concentrations are favored at night or at extremely low droplet concentrations.
Overshielding event of 28–29 July 2000
Authors: Goldstein J. , Spiro R. W. , Sandel B. R. , Wolf R. A. , Su S.‐Y. , Reiff P. H.
Published: May 2003

On 29 July 2000, IMAGE EUV observed a shoulder‐like bulge on the plasmapause. Goldstein et al. [2002] showed that plasmaspheric shoulders may be caused by a pre‐dawn concentration of eastward overshielding electric (E) field triggered by a decrease in magnetospheric convection. A simulation by the Magnetospheric Specification Model (MSM) captures the shoulder formation, reproducing its approximate size and location. ROCSAT‐1 ion drift meter data are consistent with the strength, time development and local‐time variation of the MSM eastward penetration E‐field (and associated radial flows) during the shoulder formation on 28 July.
Analysis of satellite imagery for Emiliania huxleyi blooms in the Bering Sea before 1997
Authors: Merico A. , Tyrrell T. , Brown C. W. , Groom S. B. , Miller P. I.
Published: May 2003

The presence of blooms of the coccolithophore Emiliania huxleyi in the Bering Sea shelf has been studied using satellite imagery in order to ascertain whether its first reported appearance in 1997 is really a new phenomenon for the area. Examination for Emiliania huxleyi blooms in Coastal Zone Color Scanner (CZCS) and Advanced Very High Resolution Radiometer (AVHRR) imagery dating from 1978 to 1996 was performed and the relationship between the presence of Emiliania huxleyi and the Pacific Decadal Oscillation and the El Niño Southern Oscillation was investigated. No evidence of the presence of this species was found in CZCS or AVHRR imagery between 1978 and 1995. AVHRR images reveal that a small coccolithophore bloom was present in summer 1996. Although the blooms of 1997 were unprecedented in extension and intensity, it appears that the Bering Sea ecosystem did not respond as abruptly to atmospheric anomalies as initially reported.
Stratospheric and tropospheric response to enhanced solar UV radiation: A model study
Authors: Tourpali K. , Schuurmans C. J. E. , van Dorland R. , Steil B. , Brühl C.
Published: May 2003

The atmospheric response to the 11‐year solar cycle is studied using a fully interactive 3‐D coupled chemistry‐general circulation model with a complete seasonal cycle. The stratosphere‐troposphere system shows partly significant response to a realistic solar cycle enhancement of UV radiation. This response consists of increases in stratospheric ozone and temperature, giving rise to changes in the zonal wind from the stratosphere into the troposphere. Computed changes of stratospheric ozone, temperature, zonal wind and geopotential heights are generally in agreement with observed changes between solar minimum and solar maximum. Observed pattern changes of the stratospheric response between early and late winter are approximately reproduced by the model. Our radiative forcing results show that the 11‐year solar cycle effect on global mean temperature is negligible, but simulated responses of sea level pressure do suggest that regional effects are probably significant, e.g. by affecting the North Atlantic Oscillation.
Initiation of a mesoscale convective complex over the Ethiopian Highlands preceding the genesis of Hurricane Alberto (2000)
Authors: Hill Christopher M. , Lin Yuh‐Lang
Published: May 2003

A tropical disturbance, which would later become Hurricane Alberto (2000), was traced back in time as a mesoscale convective complex (MCC) to the Ethiopian Highlands (EH), where the MCC first developed. Meteosat‐7 imagery indicates that the MCC develops during the late afternoon and evening of 28 July 2000, and that a mesovortex (MV) was evident on the morning of 29 July 2000. A preliminary mesoscale model simulation features the development of two areas of maximum relative vorticity in the middle troposphere, with the maturation of one of the vorticity maxima into a significant MV. The higher‐level vorticity center of the simulated MV tracks westward and is nearly collocated with the vortex signature in satellite imagery, while the lower‐level center remains near the lee side of the EH. The vortex signature in satellite imagery was traceable to the cyclogenesis stage over the eastern Atlantic Ocean.