bluuebunny/crossref_metadata_2025 huggingface dataset:
Understanding the evolution of the Sun's open magnetic flux
Authors: Wang Y. ‐M. , Sheeley N. R. , Lean J.
Published: September 2002

The large‐scale magnetic field of the Sun, including the open flux that extends into the interplanetary medium, originates in active regions but is redistributed over the photosphere by differential rotation, supergranular convection, and poleward meridional flow. We use simulations to clarify the role of the surface transport processes in the evolution of the total open flux, Φopen, which determines the strength of the radial interplanetary field component. Representing the initial photospheric field configuration by one or more bipolar magnetic regions (BMRs), we show that Φopen varies approximately as the net dipole strength, determined by vectorially summing the dipole moments of the individual BMRs. As meridional flow carries the BMR flux to higher latitudes, the equatorial dipole component is annihilated on a timescale ∼1 yr by the combined effect of rotational shearing and supergranular diffusion. The remaining flux becomes concentrated around the poles, and Φopen approaches a limiting value that depends on the axisymmetric dipole strength of the original active regions. We discuss the implications of these results for the solar cycle evolution of Φopen.
Poleward‐moving HF radar flow bursts in the cusp: Transient changes in flow speed or direction?
Authors: Chisham G. , Pinnock M. , Rodger A. S.
Published: September 2002

Poleward‐moving line‐of‐sight velocity “flow bursts” have been observed in the cusp by two southern hemisphere SuperDARN HF radars with overlapping fields‐of‐view. This has allowed the estimation of unambiguous two‐dimensional velocity vectors in the vicinity of the “flow bursts”. Rather than showing enhancements in the flow magnitude, the velocity vectors suggest that the line‐of‐sight velocity enhancements are a result of a change in the direction of the flow associated with latitudinal motion of the convection reversal boundary. These observations may have important implications for understanding the ionospheric footprint of flux transfer events, and also illustrate that caution is needed when interpreting line‐of‐sight velocity data from single radars.
Trapped energetic electron curtains produced by thunderstorm driven relativistic runaway electrons
Authors: Lehtinen N. G. , Inan U. S. , Bell T. F.
Published: September 2002

Relativistic runaway electron beams driven upward by intense lightning‐generated quasielectrostatic (QE) fields undergo intense interactions with the background magnetospheric plasma, leading to rapid nonlinear growth of Langmuir waves. The beam electrons are strongly scattered by the waves in both pitch angle and energy, within one interhemispheric traverse along the Earth's magnetic field lines. While those electrons within the loss cone precipitate out, most of the electrons execute bounce and drift motions, forming detectable trapped curtains of energetic electrons.
Detection of daytime sprites via a unique sprite ELF signature
Authors: Stanley Mark , Brook Marx , Krehbiel Paul , Cummer Steven A.
Published: September 2002

On August 14, 1998, 3 separate daytime sprite events were detected via a unique extremely low frequency (ELF) sprite signature. The onset of the sprite ELF signatures was delayed by 11.0–13.2 ms from positive cloud‐to‐ground strokes which had attained exceptionally large charge moment (charge times height) changes of 3900–6100 C·km. It is shown that a charge moment change of 6100 C·km may have been sufficient for conventional breakdown at ≃54 km altitude, assuming an experimentally measured ion conductivity profile of Holzworth et al., [1985]. The daytime sprites themselves contained unusually large charge moment changes of ≃2800 C·km, ≃1200 C·km, and ≃910 C·km.
Influence of electrophilic species on the lower ionosphere of Titan
Authors: Molina‐Cuberos G. J. , López‐Moreno J. J. , Rodrigo R.
Published: September 2002

The galactic cosmic rays induced ionosphere of Titan is studied from 0 to 70 km. We resent here a new model developed for calculating the concentration of cations, anions, and electrons depending on the mixing ratio of electrophilic species present in the atmosphere of Titan. The existence of neutral species in which electrons can be attached by the three‐body process produces anions and, depending on the abundance of electrophilic specie, reduces, even very strongly, the concentration of electrons. We also discuss the effect of the electron detachment of negative ions by absorption of solar radiation, which could produce a decrease in the anions density and, consequently, an increase in the electron density.
Coincident POLAR/UVI and WIND observations of pseudobreakups
Authors: Fillingim M. O. , Parks G. K. , Chen L. J. , Brittnacher M. , Germany G. A. , Spann J. F. , Larson D. , Lin R. P.
Published: September 2002

Using POLAR/UVI global images, we have identified a period of successive minor auroral activations during which WIND was making a perigee pass (X ∼ −11 RE). These auroral brightenings are interpreted to be pseudobreakups due to the lack of global expansion. Large magnetic field fluctuations and high earthward ion velocity moments measured by the WIND spacecraft show a nearly one‐to‐one correspondence with the auroral intensifications. Analysis of the plasma parameters indicates that there is no difference in the behavior of the plasma during pseudobreakups as compared to substorm expansive phase onset. Inspection of the ion distribution functions during high velocity moment events reveals the presence of a two component plasma. The particles contributing to the large mean velocities are energetic ions with energies from ∼ 2 to 27 keV. We conclude that pseudobreakups are the ionospheric signature of high velocity moment events.
Microphysical properties of mixed‐phase & Ice clouds retrieved from In Situ airborne “polar nephelometer” measurements
Authors: Oshchepkov Sergey , Isaka Harumi , Gayet Jean‐Francois , Sinyuk Alexander , Auriol Frederique , Havemann Stephan
Published: September 2002

In this paper we present microphysical properties of natural clouds retrieved from an airborne “Polar Nephelometer” measurements. The retrieval was done by means of an iterative inversion method, which is based on the bi‐component (water droplets and ice crystals) representation of ice and mixed phase cloud composition. The present study shows that experimental scattering phase functions of ice crystals are characterized by high information content with respect to the aspect ratio of ice crystals which can be estimated in addition to their effective size distributions.
Observations of the breakdown of an atmospheric gravity wave near the cold summer mesopause at 54N
Authors: Hecht James H. , Fricke‐Begemann Cord , Walterscheid Richard L. , Höffner Josef
Published: September 2002

Recently, it was shown from a single set of airglow/lidar observations in Urbana, Illinois (40N) that some small‐scale wave‐like structure seen in OH airglow images can be associated with the breakdown, via a convective instability, of an atmospheric gravity wave. A second set of simultaneous airglow/lidar observations, showing wave breakdown, has been obtained over Kühlungsborn, Germany (54N) during a period when noctilucent clouds (NLCs) were also observed. This showed that the wave breakdown process can occur under the same cold, low altitude summer mesopause conditions that support the occurrence of NLCs. This new set of data shows that the first observations were not a unique event, and give credence to the suggestion that some of the small scale structure seen in NLC displays may be due to wave breakdown.
Aerosol production over remote marine areas‐A new route
Authors: Leck Caroline , Bigg E. Keith
Published: September 2002

We report on enhanced levels of 3–5 nm particles in the remote summer Arctic. Simultaneous increases in particle number occurred in certain size ranges <50nm. Particles >100nm, marine in origin, were also present. Stable airmasses with at least 4 days residence over the ice, a surface mixed layer <140m deep, capped by a temperature inversion and cloud‐free stable layer ∼1km in depth excluded a tropospheric source. Instead a surface source was indicated. The most vigorous nucleation was associated with sudden reductions of humidity (<80%) causing rapid dissipation of fogs. However, particles <50nm contained no detectable H2SO4 implying recent formation or growth from material other than the acid. It is proposed that the marine particles were derived from bubbles bursting on open leads and provided the material for both nucleation and larger particle formation. Nucleation is attributed to oxidation of an amino acid, L‐methionine.
Vertical air motion and raindrop size distributions in convective systems using a 94 GHz radar
Authors: Kollias Pavlos , Lhermitte R. , Albrecht B. A.
Published: September 2002

This paper presents a method for the observation of air vertical velocity and raindrop size distribution in convective storms, based on the interpretation of Mie backscattering oscillations seen in the Doppler spectrum observed at vertical incidence with a 94 GHz Doppler radar. The location of the first minimum allows an accurate determination of vertical air motion, which is used to shift the spectrum so that it relates to the raindrops terminal velocity alone. The drop size distribution is then retrieved from the shifted Doppler spectrum. An example of the structure of two‐dimensional updrafts and downdrafts observed in the low levels of a convective storm is presented. Drop size distributions can also be estimated and evidence of small drop removal by the updraft is presented.
Structure of the terdiurnal tide at 95 km
Authors: Smith Anne K.
Published: September 2002

Satellite wind observations from the High Resolution Doppler Interferometer (HRDI) instrument on the Upper Atmosphere Research Satellite (UARS) are used to describe the latitudinal structure and seasonal variation of the terdiurnal (8 hour) atmospheric tide at 95 km. The amplitude of the annual average tide is 5 m/s (meridional) and 15 m/s (zonal). Within the range observed (60°S to 60°N), the maximum amplitudes are found during fall and winter at midlatitudes. Only weak temporal correlations with the diurnal and semidiurnal tides are seen on the monthly time scales resolved.
Polar mesosphere summer echoes and noctilucent clouds: Simultaneous and common‐volume observations by radar, lidar and CCD camera
Authors: Stebel K. , Barabash V. , Kirkwood S. , Siebert J. , Fricke K. H.
Published: September 2002

Simultaneous and common‐volume VHF radar and lidar measurements of polar mesospheric summer echoes (PMSEs) and noctilucent clouds (NLCs) have been successfully performed during August 10/11 and 13/14, 1997 from Esrange in northern Sweden (68°N, 21°E). There was no one‐to‐one correlation of PMSEs and NLCs in the observed volume during these observations. Rather, regions of PMSE, separated in altitude and time, showed an apparent evolution from PMSE alone to NLC alone to combined PMSE/NLC. A CCD camera observed the night sky above Esrange at the same time from Lycksele, 372km south of Esrange. While the first lidar NLC on August 10/11 was also detected by the camera, the second lidar NLC remained invisible to the camera in spite of clear skies. For the first NLC the altitude and the optical thickness are anticorrelated, showing a periodicity of 20.5±2.5 min. We associate this modulation with the NLC band structure seen on the camera images. We can show that the modulation, the radar winds, and the band orientation form a consistent data set. The change in orientation of the visual NLC bands during this night, the two distinct lidar NLCs, in combination with the change in mesospheric winds give evidence for advection of different airmasses over our volume of measurements.
A GPS‐based three‐dimensional lightning mapping system: Initial observations in central New Mexico
Authors: Rison W. , Thomas R. J. , Krehbiel P. R. , Hamlin T. , Harlin J.
Published: September 2002

A GPS‐based system has been developed that accurately locates the sources of VHF radiation from lightning discharges in three spatial dimensions and time. The observations are found to reflect the basic charge structure of electrified storms. Observations have also been obtained of a distinct type of energetic discharge referred to as positive bipolar breakdown, recently identified as the source of trans‐ionospheric pulse pairs (TIPPs) observed by satellites from space. The bipolar breakdown has been confirmed to occur between the main negative and upper positive charge regions of a storm and found to be the initial event of otherwise normal intracloud discharges. The latter is contrary to previous findings that the breakdown appeared to be temporally isolated from other lightning in a storm. Peak VHF radiation from the energetic discharges is observed to be typically 30 dB stronger than that from other lightning processes and to correspond to source power in excess of 100 kW over a 6 MHz bandwidth centered at 63 MHz.
Changing methane lifetime: Possible cause for reduced growth
Authors: Karlsdóttir S. , Isaksen I. S. A.
Published: September 2002

We present a 3‐D model study, where the focus is on CH4 lifetime and variations related to changes in the global distribution of OH. The observed CH4 concentration and estimates of the anthropogenic emissions of CO, NOx and NMHC's, for the period 1980–96 is used to calculate changes in OH and in CH4 lifetime. The model suggests that CH4 lifetime has decreased by 0.49%/yr, while the annual global average OH concentration has increased by 0.43%/yr. Combining the calculated change in CH4 lifetime and the observed CH4 concentration the yearly average CH4 emission from 1980–96 is calculated to increase by 0.67%/yr. A moderate decrease in CH4 emissions is obtained towards the end of the period, 0.53%/yr from 1993–96 compared to 0.69%/yr from 1980–90. The key to the changing oxidation of CH4 is the increasing anthropogenic emissions in SE‐Asia, which more than compensate for the declining emissions seen over Europe and N‐America.
A stratospheric “drain” over the maritime continent
Authors: Sherwood Steven C.
Published: September 2002

Operational wind data are used to show that the time‐averaged mass flux near the tropopause is downward over the maritime continent (Indonesia) region during both summer and winter. The air descends within a layer above the convective level of neutral buoyancy (despite mean upward motion below and above this layer) and must rise through the mean tropopause elsewhere, contradicting the common view that the entry occurs over strongly‐convecting regions. Closing the energy budget in the sinking regions requires an energy sink; one possibility is that overshooting convective clouds are irreversibly injecting cold, heavy air at great heights.
The record breaking global temperatures of 1997 and 1998: Evidence for an increase in the rate of global warming?
Authors: Karl Thomas R. , Knight Richard W. , Baker Bruce
Published: September 2002

During the time between May of 1997 and September of 1998, for sixteen consecutive months, each month broke the previous monthly all‐time record high temperature. Using autoregressive intervention moving average (ARMA) models in a series of Monte Carlo experiments the probability of such an event was analyzed for various rates of temperature change. The string of record‐breaking global temperatures could not be readily explained by the best fit linear increase of temperature since the late 1970's (2°C/Century), although the event was not implausible (probabilities slightly less than 5%). The 1997–98 event could signal yet another change point in the rate of global temperature increase, but the warming rate over the past few decades is already comparable to that projected during the 21st Century based on IPCC business as usual scenarios of anthropogenic climate change (Kattenberg et al., 1996).
Tracer correlations in the northern high latitude lowermost stratosphere: Influence of cross‐tropopause mass exchange
Authors: Fischer H. , Wienhold F. G. , Hoor P. , Bujok O. , Schiller C. , Siegmund P. , Ambaum M. , Scheeren H. A. , Lelieveld J.
Published: September 2002

We present an analysis of trace gas correlations in the lowermost stratosphere. In‐situ aircraft measurements of CO, N2O, NOy and O3, obtained during the STREAM 1997 winter campaign, have been used to investigate the role of cross‐tropopause mass exchange on tracer‐tracer relations. At altitudes several kilometers above the local tropopause, undisturbed stratospheric air was found with NOy/NOy* ratios close to unity, NOy/O3 about 0.003–0.006 and CO mixing ratios as low as 20 ppbv (NOy* is a proxy for total reactive nitrogen derived from NOy–N2O relations measured in the stratosphere). Mixing of tropospheric air into the lowermost stratosphere has been identified by enhanced ratios of NOy/NOy* and NOy/O3, and from scatter plots of CO versus O3. The enhanced NOy/O3 ratio in the lowermost stratospheric mixing zone points to a reduced efficiency of O3 formation from aircraft NOx emissions.
Ice nucleation in cirrus clouds: A model study of the homogeneous and heterogeneous modes
Authors: Sassen Kenneth , Benson Sally
Published: September 2002

Parcel cloud model simulations have explored the feasibility of a unified approach to describe the homogeneous and heterogeneous ice nucleation mechanisms in cirrus clouds. It was assumed that the ice crystal generation process involved the freezing of ammonium sulfate haze particles, as modulated by an effective temperature proportional to molality in both cases. Treated as variables in the ‐36° to ‐60°C model domain are the updraft velocity, and the terms in a modified Fletcher equation used to approximate heterogeneous freezing. Parameterizations drawn from the homogeneous freezing runs are provided for the threshold relative humidity and number of crystals nucleated, as functions of both temperature and updraft velocity. We find that heterogeneous nucleation can compete or dominate at relatively weak updrafts, but only for unusually high ice nuclei concentration and temperature activation terms.
Latitudinal distribution of atmospheric methyl bromide: Measurements and modeling
Authors: Yokouchi Y. , Machida T. , Barrie L. A. , Toom‐Sauntry D. , Nojiri Y. , Fujinuma Y. , Inuzuka Y. , Li H. ‐J. , Akimoto H. , Aoki S.
Published: September 2002

The global distribution of atmospheric methyl bromide (CH3Br) obtained from extensive new measurements of atmospheric CH3Br from latitude 82.5°N to 69.1°S, showed a small decrease from mid‐ to high‐latitudes, a gradient between the northern and southern hemispheres with a ratio of 1.2 to 1.3, and occasional high concentrations in the tropics. The observed data and modeled distributions of industrial CH3Br were used to apportion CH3Br between natural and industrial components for both hemisphere. We obtained an estimated man‐made contribution of 4.3 pptv and 2.3 pptv in the northern and southern hemispheres, respectively and a natural (non‐industrial) background concentration in both hemispheres of 6 pptv with a slight increase in the tropics.
The impact of greenhouse gases and halogenated species on future solar UV radiation doses
Authors: Taalas Petteri , Kaurola Jussi , Kylling Arve , Shindell Drew , Sausen Robert , Dameris Martin , Grewe Volker , Herman Jay , Damski Juhani , Steil Benedikt
Published: September 2002

The future development of stratospheric ozone layer depends on the concentration of chlorine and bromine containing species. The stratosphere is also expected to be affected by future enhanced concentrations of greenhouse gases. These result in a cooling of the winter polar stratosphere and to more stable polar vortices which leads to enhanced chemical depletion and reduced transport of ozone into high latitudes. One of the driving forces behind the interest in stratospheric ozone is the impact of ozone on solar UV‐B radiation. In this study UV scenarios have been constructed based on ozone predictions from the chemistry‐climate model runs carried out by GISS, UKMO and DLR. Since cloudiness, albedo and terrain height are also important factors, climatological values of these quantities are taken into account in the UV calculations. Relative to 1979–92 conditions, for the 2010–2020 time period the GISS model results indicate a springtime enhancement of erythemal UV doses of up to 90% in the 60–90 °N region and an enhancement of 100% in the 60–90 °S region. The corresponding maximum increases in the annual Northern Hemispheric UV doses are estimated to be 14% in 2010–20, and 2% in 2040–50. In the Southern Hemisphere 40% enhancement is expected during 2010–20 and 27% during 2040–50.
Vertical profiling of the Indian aerosol plume with six‐wavelength lidar during INDOEX: A first case study
Authors: Ansmann Albert , Althausen Dietrich , Wandinger Ulla , Franke Kathleen , Müller Detlef , Wagner Frank , Heintzenberg Jost
Published: September 2002

During the Intensive Field Phase (IFP) of the Indian Ocean Experiment (INDOEX) lasting from 15 February to 26 March 1999, a large number of pollution outbreaks from India and southeast Asia were observed with a unique six‐wavelength aerosol lidar at Maldives International Airport, Hulule (4.1°N, 73.3°E). An example is presented here. Above the polluted marine boundary layer a 3‐km deep aerosol layer was advected from the Indian subcontinent. The aerosol optical depths of the marine boundary layer and the free‐troposphere layer were approximately 0.2 and 0.4 at 532 nm, respectively. Inversions using spectrally resolved particle backscatter and extinction data indicate an effective particle radius of 0.17 µm, volume and surface concentrations around 13 µm³ cm−3 and 600 µm² cm−3, respectively, and considerable absorption by the free‐tropospheric particles.
Enhanced NOx by lightning in the upper troposphere and lower stratosphere inferred from the UARS Global NO2 measurements
Authors: Zhang Renyi , Sanger Neil T. , Orville Richard E. , Tie Xuexi , Randel William , Williams Earle R.
Published: September 2002

This paper reveals a possible connection between lightning activity and the UARS NO2 data on a global scale. NO2 measured by the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS) is analyzed for the entire year of 1993 and compared to the seasonal and global lightning distributions inferred from the Optical Transient Detector (OTD). The results suggest a link between lightning activity and observed high levels of NO2 in the upper troposphere and lower stratosphere. Enhanced NO2 mixing ratios significantly above the background level are consistently found in areas of elevated lightning activity. This relation is strongest in the tropical regions during the summer and spring months of the Northern and Southern Hemispheres. Moreover, the results show that background levels of NO2 mixing ratios generally correspond to areas of little or no lightning activity.
Convective boundary layer evolution to 4 km asl over High‐alpine terrain: Airborne lidar observations in the Alps
Authors: Nyeki S. , Kalberer M. , Colbeck I. , De Wekker S. , Furger M. , Gäggeler H. W. , Kossmann M. , Lugauer M. , Steyn D. , Weingartner E. , Wirth M. , Baltensperger U.
Published: September 2002

Mountain ranges have important influences on the structure and composition of the convective boundary layer (CBL) and free troposphere (FT). Evolution of the summer CBL, measured over the European Alps using airborne lidar, was clearly observed to attain a near‐uniform height up to 4.2 km asl by early afternoon. A climatology of in‐situ high‐alpine aerosol measurements suggests that such substantial growth, corresponding to ∼ 0.3 of the mid‐latitude tropopause height, often occurs during summer months. Subsequent nocturnal collapse of the CBL was estimated to result in the venting of ∼ 0.8 ± 0.3 (SO44) Gg day−1 into a FT residual layer, leeward of the Alps.
Size distribution and estimated optical properties of carbonate, water soluble organic carbon, and sulfate in aerosols at a remote high altitude site in western China
Authors: Li Shao‐Meng , Tang Jie , Xue Husheng , Toom‐Sauntry Desiree
Published: September 2002

Measurements at the GAW station in western China reveal the levels and size distributions of chemical components in aerosols. The results indicate similarly high levels of three components, water‐soluble organic carbon (WSOC), Ca2++CO3=, and NH4++SO4=. Both WSOC and SO4= show a dominant accumulation mode, with a geometric mean mode diameter Dg of 0.41 and 0.34 µm and geometric standard deviation σsgof 0.31 and 0.33, respectively. This mode makes up >70% of the total mass of both species. In comparison, Ca2+and CO3= show a prominent coarse mode with Dg of 2.98 and 1.76 µm and σsg of 0.29 and 0.22, respectively, that accounts for >60% of the mass. Based on these characteristics, estimates of the volume scatter coefficient β, direct back scatter coefficient βπ, and mass scattering efficiency ϕ for each component were made, assuming external mixing and optical and growth characteristics of corresponding pure chemical compounds. The results show that NH4++SO4= has the largest β, βπ, and ϕ (median 1760×10−8 m−1, 79×10−8 m−1 sr−1, and 6.9 m² g−1, respectively). It is followed by WSOC with 1470×10−8 m−1, 30×10−8 m−1 sr−1, and 5.3 m² g−1 for β, βπ, and ϕ, respectively. Ca2++CO3= has only about 10% of the β and ϕ values but 20% of the βϕ of NH4++SO4= respectively. For both NH4++SO4= and WSOC, the mass scattering efficiency ϕ is inversely related to their Dg between the size range of 0.2–0.45 µm.
An assessment of southern hemisphere stratospheric NOx enhancements due to transport from the upper atmosphere
Authors: Siskind D. E. , Nedoluha G. E. , Randall C. E. , Fromm M. , Russell J. M.
Published: September 2002

Data from the Halogen Occultation Experiment (HALOE) are used to evaluate the contribution of upper atmospheric NOx to the stratospheric polar vortex. Using CH4 and potential vorticity as tracers, an isolated region of enhanced NOx is shown to occur in the Southern Hemisphere (SH) polar vortex almost every spring from 1991–1996. The magnitude of this enhancement varies according to the Ap auroral activity index. Up to half of the NOx in the mid‐stratospheric SH polar vortex may be due to particle precipitation. The peak enhancement occurred in 1991 with a magnitude of 3–5% of the NOy, source due to N2O oxidation.
Tropical cirrus cloud properties derived from TOGA/COARE airborne polarization lidar
Authors: Sassen Kenneth , Benson Randall P. , Spinhirne James D.
Published: September 2002

During the January–February 1993 TOGA/COARE intensive field program, airborne polarization lidar data were collected from cirrus clouds generated by thunderstorm anvils over the western Pacific Ocean. The cirrus cloud tops typically extended to near the 16.85 km average tropical tropopause. Average lidar linear depolarization ratios δ show a consistent increase with height, with the maximum δ ≈ 0.52 values found at the tropopause. This finding can be interpreted in terms of a fundamental dependence of ice crystal habit or axis ratio on temperature. Although similar δ trends have been observed elsewhere, a complication in this case is that the cirrus may have been affected by the Pinatubo volcanic aerosol, which midlatitude research indicates could alter ice crystal shapes.
Six‐moment representation of multiple aerosol populations in a sub‐hemispheric chemical transformation model
Authors: Wright D. L. , McGraw R. , Benkovitz C. M. , Schwartz S. E.
Published: September 2002

This letter describes the first application of the Quadrature Method of Moments (QMOM) [McGraw, 1997] in a 3‐D chemical transformation and transport model. The QMOM simultaneously tracks an arbitrary (even) number of moments of a particle size distribution directly in space and time without the need for explicitly representing the distribution itself. The host 3‐D model, the Global Chemistry Model driven by Observation‐derived meteorological data (GChM‐O), has been previously described [Benkovitz et al., 1994]. The present implementation evolves the six lowest‐order radial moments for each of several externally‐mixed aerosol populations. From these moments we report modeled geographic distributions of several aerosol properties, including a shortwave radiative forcing obtained using the Multiple Isomomental Distribution Aerosol Surrogate (MIDAS) technique [Wright, 2000]. These results demonstrate the capabilities of these moment‐based techniques to simultaneously represent aerosol nucleation, condensation, coagulation, dry deposition, wet removal, cloud activation, and transport processes in a large scale model, and to yield aerosol optical properties and radiative influence from the modeled aerosol.
Wave‐guide effects in subduction zones: Evidence from three‐dimensional modeling
Authors: Shapiro N. M. , Olsen K. B. , Singh S. K.
Published: September 2002

We have simulated seismic wave propagation in models of the subduction zone off the Pacific coast of Mexico using a three‐dimensional finite difference method. The results show that a significant part of the energy generated by earthquakes in the subduction zone can be trapped inside a wave‐guide generated by the low‐velocity material of the accretionary prism. The trapped waves in the simulations appear as long‐duration wave‐trains that follow the onset of the surface waves, similar to the signature of broadband seismograms recorded by stations along the Pacific coast of Mexico for subduction earthquakes.
TRMM satellite estimates of convective processes in central Africa during September, October, November 1998: Implications for elevated Atlantic tropospheric ozone
Authors: Jenkins Gregory S.
Published: September 2002

The recent launch of the Tropical Rainfall Measuring Mission (TRMM) allows for new understanding of convective processes in remote areas of Equatorial Africa. Time averaged rainfall statistics during September, October and November of 1998 for TRMM merged data and TRMM Precipitation Radar data are compared to long‐term averages. The TRMM precipitation radar data shows the highest convective rainfall rates and mean storm heights in October occurring west of the East African Highlands. This area is downstream of savanna fires and could serve as an important region for the vertical transport of pollutants, which are then transported westward in the upper troposphere contributing to the high ozone values over the Tropical eastern Atlantic ocean.
The relative impact of observed change in land cover and carbon dioxide as simulated by a climate model
Authors: Pitman Andrew J. , Zhao Mei
Published: September 2002

The relative impact on temperature of a change in land use compared to a change in carbon dioxide was investigated using the Community Climate Model. We performed two 17 year equilibrium simulations, one using an estimate of natural land use at carbon dioxide levels of 280 ppmv, and a second simulation using an estimate of current land use. An identical pair of experiments, but at 355 ppmv, were also performed. Regionally, land use change causes air temperature changes of 50% to 100% of the size induced by the carbon dioxide perturbation although globally averaged the effect of land use change is negligible. The regional impacts of land cover change provides an avenue for improving modeling efforts to simulate recent global change. Including land cover change in transitory simulations may make detecting human‐induced climate change easier by permitting a more accurate simulation of regional patterns of change across the Northern Hemisphere.
Isothermal compressibility of hydrous ringwoodite and its relation to the mantle discontinuities
Authors: Yusa Hitoshi , Inoue Toru , Ohishi Yasuo
Published: September 2002

High pressure X‐ray diffraction experiments of hydrous ringwoodite, containing 2.8 ± 0.2 wt% H2O, have been carried out by using X‐rays from a synchrotron radiation source with a diamond anvil cell under hydrostatic pressure up to 6 GPa. The isothermal bulk modulus (K0) was determined to be 148 ± 1 GPa with the pressure derivative (K′0) fixed to 5 using the Birch‐Murnaghan equation of state. This value is almost 80% of that of anhydrous ringwoodite. The relations of the bulk modulus and zero pressure volumes (V0) with H2O content are estimated within the solid solution range. Combining the present results with recent seismological data, the nature of the 520 km and 660 km seismic discontinuities is discussed.
CO2 and SF6 as stratospheric age tracers: Consistency and the effect of mesospheric SF6‐loss
Authors: Strunk M. , Engel A. , Schmidt U. , Volk C. M. , Wetter T. , Levin I. , Glatzel‐Mattheier H.
Published: September 2002

Mixing ratios of the conserved tracers SF6 and CO2 in air samples collected with cryogenic whole‐air samplers during two balloon flights in the Arctic and mid‐latitude stratosphere up to 30 km altitude in 1997 are presented. The data are used to derive the mean age of stratospheric air. The calculated CO2‐ages agree with the corresponding SF6‐ages to within 0.5 years. These results do not confirm the findings previously reported by Harnisch et al. [1998] but rather suggest that SF6 and CO2 can be regarded as equivalent age tracers. However, evidence is presented that this general agreement may not be valid for polar stratospheric air parcels that comprise fractions of mesospheric air.
Fracture permeability and in situ stress to 7 km depth in the KTB scientific drillhole
Authors: Ito Takatoshi , Zoback Mark D.
Published: September 2002

To better understand the mechanisms that control fluid flow and hydraulic conductivity at significant depth in the brittle crust, we have examined the relationship between fracture permeability and in situ stress in the German continental deep drillhole (the KTB main hole) through analysis of high resolution temperature profiles. Our analysis shows that over the entire 3–7 km depth range studied, permeable fractures and faults (i.e., those associated with distinct thermal anomalies) lie close to the Coulomb failure line for a coefficient of friction of about 0.6. This indicates that critically‐stressed faults in the crust are also the most permeable faults. This includes a major Mesozoic thrust fault at 7.1 km that is being reactivated as a strike‐slip fault in the current stress field. Conversely, non‐critically stressed fractures and faults do not appear to be permeable as they are not associated with identifiable thermal anomalies.
Comparison of simultaneous rain drop size distributions estimated from two surface disdrometers and a UHF profiler
Authors: Williams Christopher R. , Kruger Anton , Gage Kenneth S. , Tokay Ali , Cifelli Robert , Krajewski Witold F. , Kummerow Christian
Published: September 2002

In support of the NASA Tropical Rainfall Measuring Mission (TRMM) Ground Validation Program, a suite of surface instruments and vertical pointing Doppler radar profilers were deployed in central Florida to quantify the number and size of the rain drops reaching the surface. Analyzing 276 minutes of simultaneous observations from two surface disdrometers and one profiler revealed good agreement among the instruments for drop sizes >1.5 mm diameter but poor agreement for smaller drop sizes. The magnitude of the difference in small drop estimation was proportional to the reflectivity (and rainrate). At reflectivities greater than 40 dBZ, the differences in the estimation of the number of small drops yielded differences in estimates of mass‐weighted diameter of > 13% and of rainrate >25%. The combined effect of these uncertainties impact the interpretation of the precipitation processes and the development and validation of space‐based precipitation retrieval algorithms.
Methanesulfonic acid in a Svalbard Ice Core as an indicator of ocean climate
Authors: O'Dwyer Jane , Isaksson Elisabeth , Vinje Torgny , Jauhiainen Tauno , Moore John , Pohjola Veijo , Vaikmäe Rein , van de Wal Roderik S. W.
Published: September 2002

Methanesulfonic acid (MSA) is an atmospheric oxidation product of dimethyl sulfide, produced by marine biota. MSA preserved in a Svalbard glacier between 1920 and 1996 is compared with the sea surface temperature (SST) and sea‐ice extent of the surrounding ocean over the same period. On decadal timescales high MSA concentrations are found to be associated with warm SST and reduced sea‐ice extent. MSA appears to be influenced by climatic changes related to variations in the import of warm Atlantic Water to the Barents Sea. Atlantic Water plays an important role in the Arctic climate system, therefore MSA concentrations may indirectly reflect larger‐scale changes in the region and may be useful as a proxy for past climate.
Satellite observation of El Niño effects on Amazon Forest phenology and productivity
Authors: Asner Gregory P. , Townsend Alan R. , Braswell Bobby H.
Published: September 2002

Climate variability may affect the functioning of Amazon moist tropical forests, and recent modeling analyses suggest that the carbon dynamics of the region vary interannually in response to precipitation and temperature anomalies. However, due to persistent orbital and atmospheric artifacts in the satellite record, remote sensing observations have not provided quantitative evidence that climate variation affects Amazon forest phenology or productivity. We developed a method to minimize and quantify non‐biological artifacts in NOAA AVHRR satellite data, providing a record of estimated forest phenological variation from 1982–1993. The seasonal NDVI amplitude (a proxy for phenology) increased throughout much of the basin during El Niño periods when rainfall was anomalously low. Wetter La Niña episodes brought consistently smaller NDVI amplitudes. Using radiative transfer and terrestrial biogeochemical models driven by these satellite data, we estimate that canopy energy absorption and net primary production of Amazon forests varied interannually by as much as 21% and 18%, respectively. These results provide large‐scale observational evidence for interannual sensitivity to El Niño of plant phenology and carbon flux in Amazon forests.
Density and porosity of the upper oceanic crust from seafloor gravity measurements
Authors: Johnson H. Paul , Pruis M. J. , Van Patten D. , Tivey M. A.
Published: September 2002

The exposure of 1300 meters of upper oceanic crust at the Blanco Fracture Zone allows near‐bottom gravity measurements to determine the in situ density of the seafloor as a function of depth. Gravity measurements along the north wall of the Blanco Depression indicate an outcrop density of 2530 ± Kg/m³ for the upper 800 meters of crust and a calculated porosity of 23%. The lower 500 meters of crust (800 to 1300 meters below the sea floor) has a measured density of 2710 ± 130 Kg/m³ and a porosity of 14%. These data indicate that most of the extrusive volcanic oceanic crust is highly porous and can act as an aquifer and large‐scale reservoir for hydrothermal fluids. These direct crustal density measurements also support previous interpretations that low seismic velocities observed in Layer 2 are due to the high porosity of the upper extrusive section.
Seasonal modeling of regional ozone pollution in the eastern United States
Authors: Kasibhatla P. , Chameides W. L.
Published: September 2002

In this study, we report on the results from a comprehensive model simulation of regional ozone (O3) throughout a season in the eastern United States. The model is shown to perform better in terms of simulating seasonal, rather than episodic, characteristics of the regional surface O3 distribution. This finding suggests that it may be more appropriate to use models of this type to assess seasonal O3 patterns rather than following the current paradigm of developing regional control strategies based on event‐specific simulations.
Atmospheric vortex streets on a RADARSAT SAR image
Authors: Li Xiaofeng , Clemente‐Colón Pablo , Pichel William G. , Vachon Paris W.
Published: September 2002

We analyze the sea surface imprint of two atmospheric vortex streets (AVS's) observed on a RADARSAT, a Canadian earth observation satellite, Synthetic Aperture Radar (SAR) image of the Aleutian Islands in the western Gulf of Alaska acquired on May 5, 1999. The RADARSAT SAR instrument is operated in C‐band with HH polarization. These AVS's are interpreted as the atmosphere analog of classic Von Kármán vortex streets. The SAR image, along with radiosonde data and surface weather charts, reveal that the AVS lengths are 196 km and 111 km for AVS‐1 and AVS‐2, respectively. There are five and two pairs of vortices within each AVS. The vortex shedding period is estimated to be between 35 and 48 minutes. The vortex shedding started approximately 4.6 and 2.6 hours prior to the SAR imaging time for AVS‐1 and AVS‐2, respectively. There are seven and three pairs of vortices within the respective AVS's. The vortex tangential velocity is estimated to be between 1.7 and 2.3 m/s and the energy dissipated during the vortex lifetime is estimated to be between 24.9 and 23.6 J/m³.
Insights into the importance of cloud vertical structure in climate
Authors: Weare Bryan C.
Published: September 2002

Multi‐year surface and satellite observations of cloud amounts have been combined to estimate the full three‐dimensional structure of clouds for a three‐layer atmosphere. This analysis provides new insight into the vertical structure of clouds and the interactions with atmospheric radiation. For instance, a simple vertical overlap parameter has been derived which is very consistent with general climatology. In addition radiative transfer model calculations show that both the mean net heating rates within the atmosphere and the perturbations of cloud radiative forcing at the top are very sensitive to variations in the overlap parameter.
Diurnal temperature range and rainfall probability over the United Kingdom
Authors: Tomsett Ashley C. , Toumi Ralf
Published: September 2002

Daily data from five stations in the United Kingdom covering the period 1900–1993 were used to explore the relationship between diurnal temperature range (DTR) and precipitation. A strong dependency between the probability of future rainfall and the magnitude of the previous day's DTR was found. The form of this relationship seems to be independent of location and season. DTRs greater than approximately 10°C are associated with reduced probabilities of rainfall. It is argued that DTR is a good proxy for cloud base height, which, in turn, is critical in determining the probability of precipitation.
Photofragmentation two‐photon laser‐induced fluorescence detection of NO2 and NO: Comparison of measurements with model results based on airborne observations during PEM‐Tropics A
Authors: Bradshaw J. , Davis D. , Crawford J. , Chen G. , Shetter R. , Müller M. , Gregory G. , Sachse G. , Blake D. , Heikes B. , Singh H. , Mastromarino J. , Sandholm S.
Published: September 2002

Measurements of NO and NO2 are reported using a highly modified photofragmentation two‐photon laser‐induced fluorescence (PF‐TP‐LIF) instrument. Available evidence suggests that the changes made substantially reduced wall decomposition of labile NOy species. In sharp contrast to the results reported from NASA's 1991 PEM‐West A program where the median value for the ratio (NO2)meas/(NO2)calc was 3.36, the PEM‐Tropics A observations produced a value for this ratio of 0.93. This represents the first time that remote upper tropospheric NO‐NO2 data have shown a high degree of correspondence with current photochemical mechanisms.
Cosmic ray modulation and the solar magnetic field
Authors: Cane H. V. , Wibberenz G. , Richardson I. G. , von Rosenvinge T. T.
Published: September 2002

We show that the variations of the interplanetary magnetic field strength (B) over a 22‐year period are tracked by the inverted profile of the cosmic ray density measured by neutron monitors. We suggest that global changes in the Sun's magnetic field are more important for long‐term modulation than magnetic field enhancements resulting from the merging of high‐speed flows and coronal mass ejections in the outer heliosphere. The unexpectedly close relationship that we find between the “tilt angle” of the heliospheric current sheet and the cosmic ray density away from solar minimum for both polarity states of the solar magnetic field may be accounted for by the anticorrelation between the cosmic ray density and field strength variations.
August 4, 1972 revisited: A new look at the geomagnetic disturbance that caused the L4 cable system outage
Authors: Boteler D. H. , van Beek G. Jansen
Published: September 2002

Space weather effects on the ground are produced by magnetic field changes associated with electric currents resulting from the solar wind/magnetosphere interaction. For most ground events the principal currents involved are the auroral electrojet systems. However, on August 4, 1972, there was a major magnetic disturbance and an outage of the L4 cable system in the mid‐western US that was thought to be caused by currents on the magnetopause. New model calculations now show that the observed magnetic disturbance was too localised to have been caused by magnetopause currents. Contour plots of the disturbance are instead consistent with an ionospheric current as the source. Equivalent current plots derived from the observed magnetic field variations show that a rapid intensification of an eastward electrojet was responsible for the magnetic disturbance and the cable system outage.
A possible influence of the North Atlantic Oscillation on the circulation of the western Mediterranean Sea
Authors: Vignudelli S. , Gasparini G. P. , Astraldi M. , Schiano M. E.
Published: September 2002

A current time series spanning from 1985 to 1996 in the Corsica Channel shows that seasonal and interannual variabilities are stable components of the circulation of the northern part of the Western Mediterranean Sea. For the first time these characteristics are related to the state of the North Atlantic Oscillation during winter. We have found that this large‐scale control is mainly maintained through the air‐sea interaction processes which take place in the Northern Basin. These results provide new elements for a consistent explanation of the major features of the basin circulation, such as the seasonal increase of the boundary current and Deep Water Formation.
Current rates of convergence across the central Andes : Estimates from continuous GPS observations
Authors: Kendrick Eric C. , Bevis M. , Smalley R. F. , Cifuentes O. , Galban F.
Published: September 2002

We present velocity solutions for 16 continuous GPS (CGPS) stations located in South America in a geodetic reference frame that nominally fixes the craton or stable core of this continent. The RMS horizontal velocity of 8 stations located within the craton is 1.3 mm/yr. Three CGPS stations located in Chile between about 33° S and 20° S have velocities in the range 19–24 mm/yr. These motions manifest current rates of convergence across the southern limb of the Central Andes. The IGS station in Arequipa, Peru (at 16.5°S) in the northern limb of the orocline, however, has a velocity of just 10 mm/yr.
Aircraft measurements of ozone, NOx, CO, and aerosol concentrations in biomass burning smoke over Indonesia and Australia in October 1997: Depleted ozone layer at low altitude over Indonesia
Authors: Tsutsumi Yukitomo , Sawa Yousuke , Makino Yukio , Jensen Jørgen B. , Gras John L. , Ryan Brian F. , Diharto Sri , Harjanto Hery
Published: September 2002

The 1997 El Niño unfolded as one of the most sever El Niño Southern Oscillation (ENSO) events in this century and it coincided with massive biomass burning in the equatorial western Pacific region. To assess the influence on the atmosphere, aircraft observations of trace gases and aerosol were conducted over Kalimantan in Indonesia and Australia. Over Kalimantan in Indonesia, high concentrations of O3, NOx, CO, and aerosols were observed during the flight. Although the aerosol and NOx decreased with altitude, the O3 had the maximum concentration (80.5 ppbv) in the middle layer of the smoke haze and recorded very low concentrations (∼20 ppbv) in the lower smoke layer. This feature was not observed in the Australian smoke. We proposed several hypotheses for the low O3 concentration at low levels over Kalimantan. The most likely are lack of solar radiation and losses at the surface of aerosol particles.