bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of tropical cirrus properties by simultaneous LIDAR and radiosonde measurements
Authors: Immler Franz , Schrems Otto
Published: December 2002

High‐altitude tropical cirrus (TC) have been observed by lidar during a cruise of the German research vessel ‘Polarstern’ above the Atlantic between 8°S and 12°. The backscatter lidar data give a detailed picture of the vertical structure of the clouds with a high time resolution. Using the data of radiosondes, which were launched twice a day aboard ‘Polarstern,’ the temperature of the clouds as well as the structure of the tropical tropopause is characterized. The clouds are found in an altitude between 14 km and 17 km, with a mean optical depth of τ = 0.02 and a mean temperature of 198 K. Tropical Cirrus appear in two distinct layers which are separated by a change in wind direction. This structure was observed south as well as north of the ITCZ. Cloud tops are often found at the thermal tropopause, in some case these clouds are of the ultra‐thin type.
Effects of ozone and well‐mixed gases on annual‐mean stratospheric temperature trends
Authors: Ramaswamy V. , Schwarzkopf M. D.
Published: December 2002

The effects of changes in ozone and well‐mixed greenhouse gases upon the annual‐mean stratospheric temperatures are investigated using a general circulation model and compared with the observed (1979–2000) trends. In the global‐mean lower stratosphere (50–100 hPa), ozone changes exert the most important influence upon the cooling trend. In the upper stratosphere, where both ozone and greenhouse gas changes influence the temperature trends, the amount of cooling is sensitive to the background ozone climatology. Taking into account the uncertainties in the observed temperature trend estimates and the dynamical variability of the model, the simulated results are in reasonable quantitative agreement with the vertical profile of the observed global‐and‐annual‐mean stratospheric cooling, and with the observed lower stratospheric zonal‐and‐annual‐mean cooling. This affirms the major role of these species in the temperature trend of the stratosphere over the past two decades.
Dissolution finger growth in variable aperture fractures: Role of the tip‐region flow field
Authors: Cheung Wendy , Rajaram Harihar
Published: December 2002

We present high‐resolution computations to demonstrate the influence of the tip‐region flow field on dissolution finger morphology in variable aperture fractures. Linear fingers are observed for small values (<0.1) of the coefficient of variation of the aperture field, whereas for larger values, fingers exhibit significant branching and winding. A consequence of this behavior is that finger breakthrough times vary non‐monotonically with the coefficient of variation of the aperture field. This non‐monotonicity is a robust feature across almost all realizations for in‐plane fracture dimensions > about 25 × 25 correlation lengths.
Modeling the dynamics of terrestrial carbon storage since the Last Glacial Maximum
Authors: Kaplan Jed O. , Prentice I. Colin , Knorr Wolfgang , Valdes Paul J.
Published: December 2002

A dynamic global vegetation model (DGVM) was used to simulate global terrestrial carbon storage and stable carbon isotope composition changes for the last 21000 years. A paleoclimate scenario was provided by interpolation of coupled AGCM/mixed‐layer ocean model experiments; [CO2]atm data were obtained from the Byrd and Taylor Dome ice core records. According to the model results, terrestrial carbon storage at the Last Glacial Maximum (LGM, 21 ka) was 821 Pg C less than today. The modeled isotopic composition (δ13C) of total terrestrial carbon at LGM was enriched by 1.5‰ compared to present. During the deglaciation (17–9 ka), vegetation expanded rapidly into formerly glaciated areas and carbon storage correspondingly increased. Increasing NPP sustained a continuing increase in terrestrial carbon storage through the Holocene. These results do not support the published hypothesis that terrestrial CO2 outgassing drove the ca. 20 ppm increase in [CO2]atm after 8 ka. They are consistent with an alternative explanation based on the oceanic CaCO3 compensation response to the extraction of carbon from the atmosphere‐ocean system during the deglaciation.
Warming trends in the continental shelf of Málaga Bay (ALBORÁN SEA)
Authors: Vargas‐Yáñez Manuel , Ramírez Teodoro , Cortés Dolores , Sebastián Marta , Plaza Francisco
Published: December 2002

Temperature time series from 1992 to 2001 (ECOMÁLAGA Project), show an intense warming trend in deep layers (200m depth) of Málaga Bay (0.02°C/yr). Data from MEDATLAS show that this trend is 0.005°C/yr throughout the whole century. Another striking change in Málaga Bay is the disappearance of the cold Western Intermediate Water (WIW) after 1992. This could be the responsible of temperature changes in the Málaga continental shelf.
GEM reconnection challenge: Implicit kinetic simulations with the physical mass ratio
Authors: Ricci Paolo , Lapenta Giovanni , Brackbill J. U.
Published: December 2002

We extend kinetic simulations of the Geospace Environment Modeling (GEM) magnetic reconnection challenge [Birn et al., J. Geophys. Res., 106, 3715, 2001] to a physical mass ratio, using the implicit Particle‐in‐Cell (PIC) code CELESTE3D which allows the use of a coarser grid and a bigger time step. We compare results for three values of the mass ratio mi/me = 25 (GEM challenge standard mass ratio), mi/me = 180 and the physical mass ratio mi/me = 1836. The results of the three simulations are compared and the scaling laws based on reconnection via nongyrotropic electron pressure are verified.
Diurnal cycle of liquid water path over the subtropical and tropical oceans
Authors: Wood R. , Bretherton C. S. , Hartmann D. L.
Published: December 2002

The diurnal cycle of liquid water path (LWP) over the subtropical and tropical oceans is examined using two complete years of TMI (Tropical Rainfall Measuring Mission Microwave Imager) satellite microwave radiometer data. Diurnal amplitudes are a considerable fraction of the mean, especially in low cloud regions to the west of continents, where values of 15–35% are typical. Early morning maxima occur throughout most of the subtropics, consistent with a diurnal cycle driven largely by cloud solar absorption. In deep convective regions of the west Pacific the diurnal cycle is also strong and peaks slightly later. Interestingly, the diurnal amplitude in the SE Pacific and Atlantic stratus regions is considerably larger than in their northern hemisphere counterparts, suggesting differences in the dynamics and structure of low clouds may exist from region to region. The data provide important constraints for models simulating the diurnal cycle of clouds.
Variations on the concentration of 222Rn in the subsurface of the volcanic island of Tenerife, Canary Islands
Authors: Eff‐Darwich A. , Martín‐Luis C. , Quesada M. , de la Nuez J. , Coello J.
Published: December 2002

A simple theoretical model, based on the assumption that radon is transported by molecular diffusion combined with advective flow induced by barometric pressure, is used to investigate radon exhalation at three subsurface monitoring sites in the volcanic island of Tenerife, Canary Islands. The model is intended to filter out all known contributions to radon flux, in an attempt to find potential precursory signals of seismic and/or volcanic activity. For the period of observations (1 December 2000 to 1 April 2001), variations on radon concentration predicted by the model were in good agreement with those measured, confirming they were induced by atmospheric pressure changes.
Double intertropical convergence zones—a new look using scatterometer
Authors: Liu W. Timothy , Xie X.
Published: December 2002

The high‐resolution wind vectors observed by the space‐based scatterometer QuikSCAT, from 1999 to 2002, show that the double intertropical convergence zones (ITCZ) exist in the Atlantic and the eastern Pacific oceans for most of the annual cycle, and are far more extensive than previously recognized. For most of the time, the southern ITCZ is weaker than the northern one. The stronger ITCZ occurs when the northerly trade winds meet the southerly trade winds over warm water, resulting in deep convection. The weaker ITCZ over cooler water is caused by the deceleration of the surface winds as they approach the cold upwelling water near the equator. Decreases in vertical mixing and increases in vertical wind shear in the atmospheric boundary layer are suggested to be the causes of the deceleration of the trade winds as they move from warmer to colder water.
Anisotropic seismic structure of the lithosphere beneath the Adriatic coast of Italy constrained with mode‐converted body waves
Authors: Levin Vadim , Margheriti Lucia , Park Jeffrey , Amato Alessandro
Published: December 2002

PS converted waves observed near Ancona on the Adriatic coast of central Italy, as revealed by teleseismic receiver functions (RFs), vary with earthquake back‐azimuth and epicentral distance in a manner consistent with a 1‐D anisotropic seismic structure. Using reflectivity calculations, we develop a profile of anisotropic seismic velocity through the Adriatic lithosphere at this locality. We infer crustal thickness of ∼45 km. Anisotropy within the crust appears at ∼15‐km depth, suggesting a decollement between the subducting Adriatic lithosphere and the overriding crustal wedge. Lineation of inferred rock fabric is compatible with simple shear in ENE‐WSW direction. In the upper mantle, we infer an anisotropic layer at 80–90 km depth. If caused by olivine crystals alignment, the nearly north‐south lineation of the inferred rock fabric would be consistent with some nearby shear‐wave splitting observations. This anisotropic layer may be related to mantle deformation induced by the rollback of Adriatic lithosphere.
Array tracking of infrasonic sources at Stromboli volcano
Authors: Ripepe Maurizio , Marchetti Emanuele
Published: December 2002

Infrasonic arrays are a powerful tool for volcanic monitoring and hazard assessment. Explosions were recorded at Stromboli using a small aperture array of 4 infrasonic stations, allowing precise vent location. The acoustic signals were delayed‐and‐summed, revealing the existence of two main groups of infrasonic waves. The NE crater produces short (<3 s) high amplitude (20–80 Pa) pressure waves while the SW crater produces small acoustic pressure (10–30 Pa) with long (5–15 s) coda. The two groups reflect different in explosive styles and similar spectral content, centered on 5–6 Hz. When stacked together, acoustic waveforms for each crater reveal the same pressure pulse, which indicates a common source process. We infer that the acoustic onset at both craters is generated by the burst of a large gas bubble while the acoustic coda is controlled by a sustained pressure release.
A comparison of variable solar total and ultraviolet irradiance outputs in the 20th century
Authors: Foukal Peter
Published: December 2002

Differences in time‐ variation between total and ultraviolet solar irradiance could help in separating their influence on climate. We present the first models based on area measurements of magnetic plages from CaK spectroheliograms obtained between 1915–1999. Correlation of our time series of UV irradiance with global temperature, T, accounts for only 20% of the global temperature variance during the 20th century. Correlation of our total irradiance time series with T accounts statistically for 80% of the variance in global temperature over that period, although the irradiance variation amplitude is insufficient to influence global warming in present‐day climate models. This interesting difference has been obscured in past modelling by additional components introduced to represent secular variations, which are no longer supported by current observational evidence. Future irradiance models emphasizing the more securely‐ based contributions of photospheric magnetic structures seem to provide better prospects for improved physical understanding of sun‐climate links.
River discharge measurements by using helicopter‐mounted radar
Authors: Melcher N. B. , Costa J. E. , Haeni F. P. , Cheng R. T. , Thurman E. M. , Buursink M. , Spicer K. R. , Hayes E. , Plant W. J. , Keller W. C. , Hayes K.
Published: December 2002

The United States Geological Survey and the University of Washington collaborated on a series of initial experiments on the Lewis, Toutle, and Cowlitz Rivers during September 2000 and a detailed experiment on the Cowlitz River during May 2001 to determine the feasibility of using helicopter‐mounted radar to measure river discharge. Surface velocities were measured using a pulsed Doppler radar, and river depth was measured using ground‐penetrating radar. Surface velocities were converted to mean velocities, and horizontal registration of both velocity and depth measurements enabled the calculation of river discharge. The magnitude of the uncertainty in velocity and depth indicate that the method error is in the range of 5 percent. The results of this experiment indicate that helicopter‐mounted radar can make the rapid, accurate discharge measurements that are needed in remote locations and during regional floods.
The likelihood of winter sprites over the Gulf Stream
Authors: Price Colin , Burrows William , King Patrick
Published: December 2002

With the recent introduction of the Canadian Lightning Detection Network (CLDN), it was revealed that during the winter months every year, the highest lightning activity within the network occurs over the Gulf Stream, southeast of Nova Scotia. These storms over the Gulf Stream, in addition to being of importance to trans‐Atlantic shipping and aviation, have an unusually high fraction of positive polarity lightning, with unusually large peak currents. Such intense positive lightning flashes are known to generate transient luminous events (TLEs) such as sprites and elves in the upper atmosphere. It is found that many of these large positive discharges produce extremely low frequency (ELF) electromagnetic radiation detected at a field station in the Negev Desert, Israel, 8000 km away, in agreement with previously documented sprite observations. Since these winter storms occur in the same location every year, it provides a good opportunity for field experiments focused on studying winter sprites and oceanic thunderstorms.
The potassium density and temperature structure in the mesopause region (80–105 km) at a low latitude (28°N)
Authors: Fricke‐Begemann C. , Höffner J. , von Zahn U.
Published: December 2002

By means of a groundbased lidar we have measured potassium layer parameters and the temperature structure in the mesopause region during 55 nights in 1999 at Tenerife (28°N). The potassium density shows a seasonal variation similar to that at midlatitudes. We also study the nocturnal mean temperatures and their seasonal variations and derive new evidence for the global two‐level structure of the mesopause. About midsummer we observed the mesopause close to 86 km with about 183 K for a period of four weeks. Transition periods between the regular (high) and the low altitude state of the mesopause were two weeks each.
The potential vorticity flux through the Yucatan Channel and the Loop Current in the Gulf of Mexico
Authors: Candela Julio , Sheinbaum Julio , Ochoa José , Badan Antoine , Leben Robert
Published: December 2002

Two‐year‐long time series of current and density structure measurements across the Yucatan Channel's main section allow the calculation of the time‐dependent potential vorticity flux between the Gulf of Mexico and the Caribbean Sea, which is characterized by alternating periods of positive (cyclonic) and negative (anti‐cyclonic) vorticity influx. Periods of negative cumulative vorticity influx are related to the Loop Current extending into the Gulf of Mexico, whereas periods of positive cumulative vorticity influx relate to a Loop Current retraction, sometimes coincident with the shedding of an anti‐cyclonic eddy.
Dust deposition and provenance at the Last Glacial Maximum and present day
Authors: Lunt D. J. , Valdes P. J.
Published: December 2002

Ice and ocean core data suggest an increase in atmospheric dust loading at the Last Glacial Maximum, 21,000 years ago, relative to the present day. We present results from a new dust model; in contrast to previous modelling studies, we correctly simulate the observed provenance data in both Antarctica and Greenland, and obtain reasonable agreement with the dust deposition data. The observed increases are attributable to decreases in vegetation, increased surface wind strength, and increased particle lifetime (due to the drier LGM climate). The Patagonian provenance of Antarctic LGM dust is linked to a decrease in soil moisture and an extension in area of the source region, and a high transport efficiency between the two regions. The results show a high degree of interannual variability, which must be taken into account when interpreting previous modelling results.
Aerosol black carbon over a tropical coastal station in India
Authors: Babu S. Suresh , Moorthy K. Krishna
Published: December 2002

Extensive ground based measurements of aerosol Black Carbon (BC) and size segregated aerosol mass concentration (total) were carried out (during August 2000 to October 2001) for the first time at a tropical coastal station, Trivandrum, India. BC depicted diurnal (with a nocturnal peak and mid‐after noon low) and seasonal variations (highest during local winter and lowest during monsoon). The diurnal variations were closely associated with the boundary‐layer dynamics. Daily mean BC concentration as high as ∼6 μg m−3 was observed on several occasions. Mass apportionment showed a BC share ranging from ∼3% to as high as ∼12% to the total aerosol mass, depending on the season. The presence of such large amount of BC over land might influence the regional aerosol forcing.
Trace metal fluxes to the ocean: The importance of high‐standing oceanic islands
Authors: Carey Anne E. , Nezat Carmen A. , Lyons W. Berry , Kao Shuh‐Ji , Hicks D. Murray , Owen Jeffrey S.
Published: December 2002

Trace metal analyses of river channel sediments from Taiwan and New Zealand provide new estimates for global budgets of trace metal inputs to the world's ocean. Mean trace metal values from high standing island river sediments are less chemically weathered than observed in sediments collected from large, continental, rivers and more similar to upper continental crust (UCC) values. Our mean values for Cu, Mn, Co and Pb are similar to the UCC; Zn, Ni and Cr are more highly enriched, compared to UCC values. Our new estimates of global trace metal budgets, combining previous estimates with these new data, show that geochemical fluxes of metals into the oceans are lower than previous estimates, ranging from 9% lower for Co to 24% lower for Cu.
Experimental simulation of a double return‐stroke lightning flash by lasers
Authors: Sobral Hugo , Villagrán‐Muniz Mayo , Navarro‐González Rafael , Camps Enrique
Published: December 2002

A lightning flash is composed of various energetic discharges called return‐strokes which are believed to be responsible for the natural formation NOX in the atmosphere. We report the first experimental attempt in the simulation of such a process. The temporal evolution of electric breakdown in air at atmospheric pressure of two synchronized Nd:YAG nanosecond laser pulses was studied to understand the physical behavior of a double return‐stroke lightning flash by shadowgraphy and interferometry techniques. The temperature of the second return‐stroke reaches about 20,000 K after 1 μs of laser ignition of the second pulse and cools off more rapidly than the first discharge. The cooling rate of the heated gas is about a factor of two faster for the second simulated return‐stroke. The estimated production of nitric oxide of two synchronized laser induced plasmas seems to be not substantially modified as compared with the sum of the isolated single pulses.
A new method for the quantitative identification of the composition, size and density of stratospheric aerosols from high resolution IR satellite measurements
Authors: Zasetsky A. Yu. , Sloan J. J. , Escribano R. , Fernandez D.
Published: December 2002

We describe a new method for the rapid and quantitative determination of the composition, size and density of atmospheric aerosols from broadband high resolution IR spectra recorded by remote sensing instruments. This method uses a novel technique for the separation of the aerosol spectrum from that of the gas phase. It is fast enough to permit the analysis of high resolution IR satellite measurements in real time, yielding aerosol composition, size distribution and volume density. The method is applied to spectra measured by the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument during flights in March 1992, shortly after the eruption of Mount Pinatubo, and again in November 1994. We report the chemical and physical characteristics of the stratospheric aerosols as a function of the tangent height.
A model for complex slip behavior on a large asperity at subduction zones
Authors: Hirose Hitoshi , Hirahara Kazuro
Published: December 2002

3‐D numerical simulations for rupture process of a large asperity on a subduction fault are carried out in order to examine whether the whole area of an asperity always breaks at once or not during an earthquake. Our quasi‐static simulation in an elastic half‐space includes a rate‐ and state‐dependent friction. We examine the effect of lateral dimension of an asperity which extends the whole seismogenic width in dip direction on the slip behavior. In cases of the asperity with comparable dimension to the seismogenic width, the whole area of the asperity can break at once and its seismic cycle shows a regular periodic behavior. However, in cases with much larger lateral dimension, the asperity does not break its whole area at once. In addition, its slip behavior becomes complex within a certain range. This suggests that the slip complexity in earthquake fault may be an intrinsic property in the system.
Origin of intraseasonal variability in Lake Tanganyika
Authors: Naithani Jaya , Deleersnijder Eric , Plisnier Pierre‐Denis
Published: December 2002

Intraseasonal thermocline oscillations in Lake Tanganyika are analysed using observations near Mpulungu and simple analytical/numerical models, in order to understand their origin. The region around the lake is characterised by strong and persistent southeast winds during the four months dry season, lasting from May to August. The associated wind‐stress causes the tilting of the thermocline which oscillates for the whole year. The wavelet transform spectra of temperature at 30 m depth of the lake near Mpulungu indicates the presence of various scales of motion, localised in frequency and time. The dominant modes of thermocline oscillations are intraseasonal variability with 3–4 weeks periods. Similar results are obtained from a reduced‐gravity model with various wind forcing, including the observed forcing, and a simple analytical solution. In addition, the model results indicates that the dominant mode of oscillation exhibits one node only. From the study, it is inferred that the free modes of oscillations of the lake are in resonance with wind pulses.
Influence of a tropical cyclone on Chlorophyll‐a Concentration in the Arabian Sea
Authors: Subrahmanyam Bulusu , Rao K. H. , Srinivasa Rao N. , Murty V. S. N. , Sharp Ryan J.
Published: December 2002

The effect of a tropical cyclone on the variation of phytoplankton biomass in terms of surface chlorophyll‐a is brought out based on satellite observations and mixed layer model simulations in the Arabian Sea during 21 May–3 June 2001. Along the cyclone's passage, chlorophyll‐a was high with extreme values (5–8 mg m−3) in the blooms of phytoplankton. The model simulations indicate deepening of mixed layer on the southeastern edge of the cyclone. This forced mixed layer deepening, due to intense wind stirring and cyclone‐induced divergent geostrophic currents, has lead to the injection of nutrients into the surface layer, resulting in higher chlorophyll‐a. This study suggests that the short‐lived tropical cyclones would alter the generally prevailing oligotrophic (nutrient depleted) conditions into a productive surface layer in the Arabian Sea during spring intermonsoon.
Impact of geoengineering schemes on the terrestrial biosphere
Authors: Govindasamy B. , Thompson S. , Duffy P. B. , Caldeira K. , Delire C.
Published: December 2002

Climate stabilization via “Geoengineering” schemes seek to mitigate climate change due to increased greenhouse gases by compensating reduction in solar radiation incident on earth's surface. In this paper, we address the impact of these climate stabilization schemes on terrestrial biosphere using equilibrium simulations from a coupled atmosphere‐terrestrial biosphere model. Climate stabilization would tend to limit changes in vegetation distribution brought on by climate change, but would not prevent CO2‐induced changes in Net Primary Productivity (NPP) or biomass; indeed, if CO2 fertilization is significant, then a climate‐stabilized world could have higher NPP than our current world. Nevertheless, there are many reasons why geoengineering is not a preferred option for climate stabilization.
Shear stress at the base of shield lithosphere
Authors: Bokelmann Götz H. R. , Silver Paul G.
Published: December 2002

One of the basic unresolved issues regarding plate tectonics is the degree of coupling between surface plates and convecting mantle below. Are the plates effectively decoupled from the mantle flow field by a low viscosity asthenosphere, or are they strongly coupled to mantle flow? While these two views are essentially incompatible, they both do a reasonably good job of predicting the motions of the surface plates, and cannot therefore be distinguished on this basis. The significant distinguishing feature for these models is the magnitude of basal shear stress that is applied to the base of the plate. While it is difficult to measure this stress directly, it is possible, in principle, to measure the corresponding deformation of the plate through observations of seismic anisotropy and to infer stress. Here we focus on the Canadian Shield, for which we expect strong plate‐mantle interaction. We show that seismic anisotropy can be used to constrain the magnitude of the stress level applied to the base of the plate, and to document the level of interaction between tectonic plates and the mantle below.
Scaling of solar wind ϵ and the AU, AL and AE indices as seen by WIND
Authors: Hnat B. , Chapman S. C. , Rowlands G. , Watkins N. W. , Freeman M. P.
Published: December 2002

We apply the finite size scaling technique to quantify the statistical properties of fluctuations in AU, AL and AE indices and in the ϵ parameter that represents energy input from the solar wind into the magnetosphere. We find that the exponents needed to rescale the probability density functions (PDF) of the fluctuations are the same to within experimental error for all four quantities. This self‐similarity persists for time scales up to ∼4 hours for AU, AL and ϵ and up to ∼2 hours for AE. Fluctuations on shorter time scales than these are found to have similar long‐tailed (leptokurtic) PDF, consistent with an underlying turbulent process. These quantitative and model‐independent results place important constraints on models for the coupled solar wind‐magnetosphere system.
Treating clouds with a grain of salt
Authors: Rudich Yinon , Khersonsky Olga , Rosenfeld Daniel
Published: December 2002

High concentrations of small atmospheric aerosols are known to reduce the size of cloud droplets, increase cloud albedo and suppress precipitation formation. In contrast, cloud simulations suggest that even low concentrations of large soluble aerosols should promote droplets' growth and rainfall. Until now, though, no observational evidence of such microphysical effects in natural circumstance over land has been presented. By using NOAA‐AVHRR retrievals on cases where salt‐dust from the Aral Sea interacts with clouds we show that large salt‐containing dust particles increase cloud drops to sizes that promote precipitation. These findings are in line with the findings of the microphysical models and recent results from hygroscopic cloud seeding experiments for rain enhancement.
Observed interannual oscillations of planetary wave forcing in the Northern Hemisphere winter
Authors: Chen Wen , Graf Hans‐F. , Takahashi Masaaki
Published: December 2002

Using NCEP‐NCAR reanalysis data from 1958 to 1998, two interannual oscillations in the eddy forcing due to planetary waves (wavenumbers 1–3) are found in the Northern Hemisphere winter, called as the stratospheric interannual oscillation (SIO) and the tropospheric interannual oscillation (TIO). The temporal evolutions are different between the SIO and the TIO, suggesting different dynamic mechanisms. The planetary waves tend to be bent equatorward in the troposphere during a positive TIO phase, and in the mid‐ and upper stratosphere during a positive SIO phase. The result also suggests that upward propagation of planetary waves into the polar waveguide across the tropopause is closely associated with the TIO. Further regression and correlation analyses suggest that the TIO is closely linked to the Northern Annular Mode (NAM), whereas the SIO is closely associated with the El Niño/Southern Oscillation (ENSO).
Filling and emptying of the plasma sheet: Remote observations with 1–70 keV energetic neutral atoms
Authors: McComas D. J. , Valek P. , Burch J. L. , Pollock C. J. , Skoug R. M. , Thomsen M. F.
Published: December 2002

This paper shows the first energetic neutral atom (ENA) observations of the extended plasma sheet, taken with the Medium Energy Neutral Atom (MENA) imager on the IMAGE spacecraft. We show that ENA emissions can be routinely observed back to several tens of RE deep in the magnetotail when IMAGE is in an appropriate orbital position. Enhanced emissions (high plasma sheet densities) are associated with high solar wind densities and with super dense plasma sheet observations at geosynchronous orbit. We examine two magnetospheric storm intervals where plasma sheet loading begins prior to the storms and continues under all IMF BZ orientations, reaching its maximum during the peaks of the storms. For several days following these storms ENA emissions are weak, indicating that the plasma sheet is depleted after the storms. This study indicates that routine ENA observations of the plasma sheet content could become an important part of space weather monitoring.
Lifetimes of atmospheric species: Integrating environmental impacts
Authors: Prather Michael J.
Published: December 2002

The environmental damage caused by atmospheric pollutants is proportional to the duration of their effects. The global impacts of greenhouse gases (as measured by global warming potential) and ozone depleting substances (as measured by ozone depletion potential) have traditionally been calculated using the atmospheric lifetime of the source gas as a quantitative measure of the impact's duration, assuming that the gas quickly reaches a steady‐state pattern which decays exponentially according to the lifetime. This assumed behavior obviously does not match the true rise and fall of impacts, particularly secondary ones like ozone depletion, that can be seen in numerical integrations or chemical mode decomposition. Here, the modes decomposition is used to prove that: (a) the steady‐state pattern of impacts caused by specified emissions, multiplied by (b) the steady‐state lifetime of the source gas for that emission pattern, is exactly equal to (c) the integral of all impacts ‐ independent of the number and atmospheric residence times of secondary impacts.
2.5D Particle and MHD simulations of mini‐magnetospheres at the Moon
Authors: Harnett Erika M. , Winglee Robert M.
Published: December 2002

2.5D Particle simulations of the solar wind interaction with the magnetized regions on the surface of the Moon confirm the earlier 2D MHD result that mini‐magnetospheres can form around the magnetic anomalies. A dipole buried 100 km below the surface with a field strength equal to 50 nT at the surface and 10 nT at 100 km above the surface held the solar wind off of the surface and caused a bow shock and a magnetopause to form. However, the boundary separating the bow shock and magnetopause becomes ambiguous as the two structures merge due to the small‐scale size of the mini‐magnetospheres. Acceleration of solar wind particles occurs at the shock. Inside the magnetopause, the Lunar electrons remained highly magnetized and exhibited fluid‐like behavior. The Lunar ions, on the other hand, become demagnetized. Outside of the magnetopause, the solar wind ions and electrons exhibited fluid‐like behavior. Small‐scale and nonideal MHD effects can be included into fluid simulations by adding Hall and pressure gradient terms in Ohm's Law, creating a magnetoplasma dynamics (MPD) model. The small‐scale effects allow for field‐aligned currents and electric fields that look qualitatively similar to those in the particle simulations, but they do not appear to change the overall shape of the mini‐magnetosphere. The extra components of the electric field indicate the presence of charge separation at the shock surface, due to the momentum difference between ions and electrons, and the near the Lunar surface, due to nonideal MHD behavior inside the mini‐magnetosphere. The 2.5D MPD model can replicate the ion demagnetization seen in the 2.5D particle simulations.
Universal time variation of the Dst index and the relationship between the cumulative AL and Dst indices during geomagnetic storms
Authors: Ahn B.‐H. , Moon Ga‐Hee , Sun Wei , Akasofu S.‐I. , Chen G. X. , Park Y. D.
Published: December 2002

The nonuniform distribution in longitude of the four Dst stations provides an unexpected opportunity to examine the storm‐substorm relationship. This is because any asymmetry of the ring current with the longitudinal scale size less than or comparable to the spacing between the two closely located stations, Honolulu and Kakioka, 62°, would result in UT variation of the Dst index. In this paper, prominent UT variations in Dst are found with the index being 23% lower than the daily mean around 0700 UT and 28% higher around 1200 UT during the main phase of magnetic storms. Since the midpoints between the two stations are around dusk (1800 MLT) and midnight (2330 MLT) at 0700 and 1200 UT respectively, the deviations from the daily average Dst can be interpreted as the development of a partial ring current around dusk and a substorm wedge current in the midnight sector. Interestingly, the UT variation is only noticeable during the main phase of a storm, thus suggesting a possibility that substorm expansive activity is closely associated with storm development. The causal relationship between substorm and storm is further investigated by comparing the AL and Dst indices, assuming that the AL index carries partly the substorm expansive signature. Admitting that a substorm is a transient phenomenon while a storm is a longer period one, an integrated index over a given interval is helpful in examining the contribution of substorms to the development of the storm‐time ring current. For this purpose, the cumulative AL and Dst indices are devised. The two indices thus defined are highly correlated with each other regardless of storm phases. More importantly, it is shown that for a given level of Dst, almost twice of the cumulative AL index is needed during the main phase than during the recovery phase. This indicates that a higher level of substorm activity in terms of the cumulative AL index is required to maintain a given level of the Dst index before the maximum phase of a storm than afterwards. It may also have an important implication in understanding the causal relationship between magnetospheric substorms and geomagnetic storms.
Large‐scale speed fluctuations at 1 AU on scales from 1 hour to ≈1 year: 1999 and 1995
Authors: Burlaga L. F. , Forman Miriam A.
Published: December 2002

This paper describes the solar wind speed fluctuations, V(τi), observed on a wide range of scales (from 1 hour to ≈1 year) at 1 AU, both during 1999 approaching solar maximum and during 1995 during the descending phase of solar activity. The fluctuations extend from the inertial turbulence range, throughout the scales dominated by interaction regions and streams, and through the largest scales where the fluctuations reflect the variability of the characteristics of the streams. The general properties of the fluctuations of the speed differences, dVn, on all of these scales, τn, are described by the three functions: skewness S(τn), kurtosis K(τn), and standard deviation SD(τn). These three functions have the same qualitative form for both the 1999 data and the 1995 data, in the range of scales of τn= 10.7–341 days (the “Gaussian range”), S(τn) ≈ 0, and K(τn) ≈ 3, consistent with Gaussian distribution functions for both 1999 and 1995. The skewness is positive for τn< 10.7 days and is maximum at a characteristic scale, which is 4 hours for the 1999 data and ≈8 hours for the 1995 data. A more detailed description of the fluctuations is provided by the probability distribution functions (PDFs) for dVn. In the range τn> 10.7 days, the PDFs are Gaussian for the 1999 data and approximately Gaussian for the 1995 period. For scales defined by streams, the PDFs are like Gaussians but fatter on the dVn > 0 side. The PDFs are cubic on a semilog scale for the 1999 data and are approximately cubic for the 1995 data. At scales characteristic of the sizes of interaction regions, the PDFs have a large tail for dVn > 0 that is produced by the large positive dVn at leading edges of streams. At the smallest scales, the PDFs have a form that is characteristic of intermittent turbulence. The power spectra for the 1999 and 1995 data are power laws in frequency throughout the interaction region range and the stream range, the slopes being β = −2.02 ± 0.01 and −2.12 ± 0.04, respectively, consistent with the dominance of shocks and jumps over turbulence. The fluctuations of V(τn) have a multifractal scaling structure, described by a function s(q), the exponent of the structure function versus moment number q in the inertial range, the interaction region range, and extending to the stream range. In the interaction region and stream ranges, s(3) > 1.
Experimental levitation of dust grains in a plasma sheath
Authors: Sickafoose A. A. , Colwell J. E. , Horányi M. , Robertson S.
Published: December 2002

Dust grains have been observed to levitate above the surface of the Moon and as spokes in Saturn's rings. In order to gain a better understanding of these observations, we have performed levitation experiments on dust grains in a low‐density plasma. Plasma sheath potential profiles, measured by an emissive probe, are used to determine the spatial dependence of the electric force on a grain in the sheath. The observed levitation height agrees with the values calculated using orbital‐motion‐limited charging theory and force balance equations. Levitating grains were also exposed to an ultraviolet light source to induce photoemission. Three types of dust were investigated: polystyrene divinylbenzene microspheres 10.0 ± 0.5 μm in diameter, glass microballoons <38 μm in diameter, and JSC‐1 (lunar regolith simulant) <25 μm in diameter. Our experimental results show that (1) various types and sizes of grains can levitate in a plasma sheath above a conducting surface; (2) levitating grains of a standard size float at a height corresponding to that predicted by theory; (3) exposure to UV light causes the grain levitation height to decrease slightly as a result of less negative charge; and (4) a mechanism to inject grains into the sheath is not necessary if the electric field is sufficiently strong.
Characterization of acoustic–gravity waves in the upper thermosphere using Dynamics Explorer 2 Wind and Temperature Spectrometer (WATS) and Neutral Atmosphere Composition Spectrometer (NACS) data
Authors: Innis J. L. , Conde M.
Published: December 2002

Data obtained by the Neutral Atmosphere Composition Spectrometer (NACS) and the Wind and Temperature Spectrometer (WATS) instruments on Dynamics Explorer 2 (DE 2) show examples of large wave‐like events in composition, vertical wind, and temperature, particularly (perhaps almost exclusively) at high geomagnetic latitudes. These events are believed to arise due to atmospheric gravity waves (AGWs). If so, the various perturbation quantities of mass density, pressure, temperature, horizontal wind, and vertical wind should be related in a manner consistent with the AGW theory. An analysis of a subset of the WATS (vertical and horizontal wind and temperature) and NACS data (number density and, hence, mass density) and pressure (as a derived quantity, from number density and temperature) was performed to investigate whether such perturbations could be clearly shown to be due to AGWs by comparing quantitatively the various simultaneous data sets with AGW theory. Seven examples of wave‐like events in the vertical wind were studied, together with the accompanying variations in mass density, pressure, temperature, and horizontal wind. The pressure (acoustic) component of the density variation was calculated and then subtracted from the total density variation, allowing the wave‐induced vertical displacement amplitude to be found. This was compared to the vertical wind amplitude, via a spectral analysis, to yield estimates of the possible AGW frequency. The observed variation in the ratio of O/N2 number densities during the course of the oscillations was found to be consistent with the calculated altitude displacements. Phase lags in the number density perturbations between different species also appeared consistent with the AGW theory. Horizontal velocity perturbations in phase with the pressure perturbations were also seen. It is concluded that the oscillations are consistent with acoustic–gravity waves, where the pressure perturbation is nonnegligible. Phase relationships between the various observables can define the direction of wave travel to within 90° of azimuth, relative to the direction of spacecraft motion. For the seven cases detailed here, the derived (intrinsic) wave frequencies are close to, but slightly less than, the estimated local Brunt–Vaisala frequency, while the vertical displacement amplitudes were typically around ±25 km. All of the wave events studied in this work were located at high latitudes, poleward of the nominal location of the auroral oval.
Correlative study of ultraviolet aurora and low‐latitude Pi2 pulsations
Authors: Takahashi Kazue , Liou Kan , Yumoto Kiyohumi
Published: December 2002

We study the relationship between auroras observed by the ultraviolet imager (UVI) on the Polar spacecraft and Pi2 pulsations detected by the Circum‐pan Pacific Magnetometer Network at magnetic latitudes lower than 55°. Instead of focusing on the few minutes around auroral breakups, we treat both auroral power and pulsation parameters as continuous time series in an effort to quantify the relationship between the two phenomena. A 3‐hour interval on 3 April 1996 is selected for the present study because it includes several episodes of auroral intensification. The auroral power is represented by electron precipitation energy (PUVI) that is inferred from the observed 170‐nm photon emission over the 2000–0200 magnetic local time sector in 36‐s time windows separated by ∼5 min. Parameters characterizing Pi2 signals in the magnetometer data are computed in a moving 5‐min time window using the autoregressive spectral analysis technique. The parameters include the amplitude APi2 in the Pi2 band (7–25 mHz), the frequency, the ellipticity, and azimuth of the major axis of polarization for oscillations with a well‐defined spectral peak. Overall, there is a high degree of similarity between the temporal profiles of PUVI and APi2. The pulsation amplitude varied from ∼0.1 nT for a PUVI change of <1 GW to ∼1 nT for a PUVI change of >20 GW; although due to different decay timescales, ∼10 min for APi2 and ∼80 min for PUVI, the linear cross‐correlation coefficient between the two parameters remained at a modest level (∼0.75). In one instance, APi2 was enhanced without auroral intensification, and for this pulsation the azimuth of the major axis of polarization was oriented in the east‐west direction instead of the north‐south direction that is the norm for Pi2 pulsations associated with auroral intensifications. Examination of solar wind plasma data from the Geotail spacecraft suggests that this particular event was directly driven by changes in the solar wind dynamic pressure. We conclude that low‐latitude magnetic pulsations are a sensitive indicator of changes of auroral intensity and that pulsations that are not associated with aurora could be distinguished by examining their polarization properties.
Effect of the orientation of interplanetary shock on the geomagnetic sudden commencement
Authors: Takeuchi T. , Russell C. T. , Araki T.
Published: December 2002

The rise time of the geomagnetic sudden commencement (SC) in low latitudes generally lies within a range from 2 to 10 min. An SC observed on 15 December 1995 was remarkable because it had an extremely long rise time of ∼30 min, although as seen by Wind, the interplanetary shock responsible for the SC was sharp as usual. The amplitude of the SC was consistent with the estimated value experimentally deduced from the increase in the solar wind dynamic pressure, implying that a complete compression of the magnetosphere occurred. However, the in situ measurement of the magnetotail by Geotail exhibited this event as an unusually gradual compression compared with a typical SC. Even this gradual compression of the magnetosphere produced a preliminary impulse on the ground that was lengthy, small, but detectable at auroral latitudes. The multisatellite observations of the interplanetary shock and the SC signals indicate that the shock normal was highly inclined duskward. Thus the orientation of the interplanetary shock or discontinuity is important in determining the SC field observed on the ground. Even if the local measurement of the solar wind dynamic pressure at a spacecraft appears to be rapid, a tilted pressure front could require many minutes to compress the forward part of the magnetosphere, producing a long rise time. Thus we can not predict the speed of the magnetospheric responses on the basis of the real‐time solar wind observations without knowing the orientation of the causative shock/discontinuity.
Cloud processing of aerosol as modeled by a large eddy simulation with coupled microphysics and aqueous chemistry
Authors: Feingold Graham , Kreidenweis Sonia M.
Published: December 2002

Cloud processing of aerosol through both drop collision coalescence and aqueous chemistry is simulated with the aid of a large eddy simulation model and fully coupled components that represent (1) size‐resolved aerosol, (2) size‐resolved microphysics, and (3) the conversion of SO2 to sulfate via aqueous chemistry. Prior work with cloud parcel models has shown that the outcome of processing in a stratocumulus‐capped marine boundary layer depends strongly on the cloud liquid water content, aerosol concentrations, trace gas concentrations, and contact time with a cloud. The current model represents spatial and temporal variability of these parameters at large eddy scales on the order of a few hundred meters and timescales on the order of a few seconds. A number of scenarios are presented here: (1) a case with relatively low aerosol concentrations in which aqueous chemistry processing does not substantially affect drizzle, (2) a case with intermediate aerosol concentrations of relatively large size in which drizzle is suppressed by aqueous chemistry, and (3) a case with intermediate aerosol concentrations of relatively small size in which drizzle is enhanced by aqueous chemistry. The simulations indicate that aqueous chemistry can modify the dynamics and microphysics of stratocumulus clouds and illustrate the complexity of the coupled system. This work suggests that parameterizations of the effects of cloud processing of aerosol require careful consideration of the myriad feedbacks in the cloudy boundary layer.