bluuebunny/crossref_metadata_2025 huggingface dataset:
Winter North Atlantic low cloud anomalies associated with the northern hemisphere annular mode
Authors: Park Sungsu , Leovy Conway B.
Published: February 2004

Ship observations of low cloud anomalies over the Atlantic Ocean from Jan. 1956 through Mar. 1995 are linearly related to the Northern Hemisphere annular mode (NAM) and to the corresponding anomalies of surface pressure, surface wind and sea surface temperature (SST). Positive NAM anomalies are associated with coherent cloud anomaly patterns: a band of increased bad weather stratiform cloud along the storm track between 40°N and 50°N, positive anomalies of precipitating stratiform and convective clouds together with negative anomalies of fair weather stratiform clouds north of this band, and negative anomalies of cumulonimbus with weak increases in fair weather stratiform clouds south of this band. Near 10°N, positive NAM anomalies are associated with increased trade winds and increases in both fair weather and bad weather stratiform clouds, resulting in an increase of total low cloud amount. Low cloud anomalies are also related to anomalies in SST and surface wind divergence.
Correlation approaches to detection
Authors: Wigley T. M. L. , Santer B. D. , Taylor K. E.
Published: February 2004

Criticisms leveled at the use of pattern correlation methods in climate‐change detection studies are addressed. We first explain how spatial autocorrelation effects are accounted for. We then show why it is important to consider both pattern similarity and spatial‐mean results in detection studies, and evaluate a mean‐square‐error statistic in this context. We also show that the use of changes in climate, as opposed to absolute climate states, does not lead to spurious trends in the pattern correlation statistic R(t). In doing this, we explain how previous pattern correlation studies account for “time arrow” effects in considering changes relative to an arbitrary reference year. We conclude that criticisms of the pattern correlation method are without substance.
Supercooling of single H2SO4/H2O aerosols to 158 K: No evidence for the occurrence of the octrahydrate
Authors: Krieger U. K. , Colberg C. A. , Weers U. , Koop T. , Peter Th.
Published: February 2004

Polar stratospheric clouds (PSCs) are important for the chemical activation of chlorine compounds and subsequent ozone depletion. However, how solid PSCs form is still subject to controversial discussion. Recently, the octahydrate of sulfuric acid (H2SO48H2O) has been proposed as a solid phase for PSC particles. In our experiment single H2SO4/H2O aerosols levitated in an electrodynamic balance are cooled to 158 K along the ice‐liquid equilibrium line. This coexistence curve has been measured for the first time in the temperature interval between 200 K and 158 K. Three independent methods are used for measuring the H2SO4 concentration of the aerosol. No phase transition is observed over a time period of 24 hours and longer at these or higher temperatures. There is no indication for the occurrence of the octahydrate in our experiments. Since the product of experimental volume and suspension time is equal to that of stratospheric droplets over an entire winter, the homogeneous formation of the octahydrate at quasi‐thermodynamic equilibrium can be practically excluded.
A case study on middle atmospheric water vapor transport during the February 1998 stratospheric warming
Authors: Seele Cord , Hartogh Paul
Published: February 2004

We present the first analysis of water vapor measurements made during a stratospheric warming using ground‐based microwave spectroscopy. The measurements were made from the ALOMAR observatory (69°N, 16°E) between January 31 and February 10, 1998. The data show an increased mixing ratio between ≈ 45 and 70 km throughout the warming. The analysis uses temperature data obtained by lidar measurements from the same location. A comparison with results obtained using standard temperature data reveals the importance of ‘good’ temperature measurements for water vapor retrieval from remote sensing data during such events in order to separate temperature effects from atmospheric dynamics.
Realistic quasi‐biennial oscillations in a simulation of the global climate
Authors: Scaife Adam A. , Butchart Neal , Warner Christopher D. , Stainforth David , Norton Warwick , Austin John
Published: February 2004

The tropical quasi‐biennial oscillation is one of the most spectacular examples of low frequency variability observed in the Earth's atmosphere, yet the oscillation is noted for its absence from numerical simulations of the global climate. Recent studies suggest that much of the required wave forcing for the oscillation is likely to come from buoyancy (gravity) waves [Sato and Dunkerton, 1997; Dunkerton, 1997] that are not well resolved in the numerical models currently used for climate prediction and global weather forecasting. Here we show that when the effects of these missing waves are parametrized in a comprehensive numerical model of the atmosphere, the simulation of the climate is improved by the generation of a realistic quasi‐biennial oscillation in the stratosphere.
A dual‐wavelength radar technique for measuring the turbulent energy dissipation rate ε
Authors: VanZandt T. E. , Clark W. L. , Gage K. S. , Williams C. R. , Ecklund W. L.
Published: February 2004

We used the ratio of simultaneous observations of radar reflectivity by S‐ and UHF‐band radars together with Hill's model of refractivity fluctuations due to turbulence to infer ε, the rate of viscous dissipation of turbulent kinetic energy per unit mass. Observations were made for 25 days from November 13 to December 7, 1995, at 11.4°S, 130.4°E (about 100 km northwest of Darwin, Australia) during the Maritime Continent Thunderstorm Experiment (MCTEX). The 500 m pulse length data covered the height range 872 to 3032 m MSL. The observed distribution of ε has a strong diurnal variation, with mean daytime and nighttime values of ε of the order of 10−3 and 10−5 m²s−3, respectively. With the dual‐wavelength technique most non‐turbulent echoes (including particulate echoes) are identified and filtered out, since the ensemble of turbulent observations is identified by its conformity to Hill's model. The technique is self‐calibrating, requiring only the relative calibration of the two radars using observations during rain, and does not require precise absolute calibration of either radar.
Currents in the Celebes and Maluku Seas, February 1999
Authors: Kashino Yuji , Firing Eric , Hacker Peter , Sulaiman A. , Lukiyanto
Published: February 2004

Upper ocean currents in the Celebes Sea, the northern Maluku Sea, and the adjacent region to the east were measured during February 1999 using a shipboard acoustic Doppler current profiler (ADCP) on R/V Kaiyo. The new data provide the first quasisynoptic observations of the circulation within the central Celebes Sea. South of Mindanao, the Mindanao Current split into three branches. Only the westernmost branch entered the Celebes Sea, where part retroflected around a cyclonic eddy in the western Celebes Sea and part took a shorter route through the eastern basin before the two paths joined and returned to the Pacific. The remainder of the Celebes Sea branch of the Mindanao Current continued toward Makassar Strait. In the central and eastern Celebes Sea, the circulation pattern below 150 m differed substantially from that at the surface. The strongest feature was a northward flow that exceeded 60 cm s−1 near 230 m in the center of the basin, where shallower currents were weak. A northward transport of 6 Sv in the top 300 m was measured across 1.75°N in the Maluku Sea, carrying Indonesian Seas waters northeast toward the Pacific. Water properties and other current sections in the northern Maluku Sea confirm shallow northeastward flow.
Variability of accumulation in northwest Greenland over the past 250 years
Authors: Bales R. C. , Mosley‐Thompson E. , McConnell J. R.
Published: February 2004

During summer 1996, a 120‐m firn and ice core was drilled to determine annual accumulation rates at a northwest Greenland site (GITS, 77.1392°N, 61.0422°W, 1910 m elevation). Annual layers were identified in the core using multiple parameters: δ18O and concentrations of dust, hydrogen peroxide, ammonium, calcium and nitrate. Using all parameters together to define annual layers resulted in a 251‐year record with a dating uncertainty of one year within that period. Annual accumulation over the period of record averaged about 0.37 m water equivalent. Comparing this record with four other multi‐century long records from the west central and northwest portion of the ice sheet shows many periods when decadal‐scale fluctuations in accumulation at the different sites are in phase. Overall variations in accumulation in this portion of the ice sheet were ±8–9% per decade, versus ±25% for individual cores. Annual accumulation at GITS showed a significant correlation with a 12‐month North Atlantic Oscillation index (Pearson's R=−0.32 with a significance level of >99%), though the correlation was slightly lower than for two cores roughly 350 and 700 km south.
Transtensional basins in the Western Sunda Strait
Authors: Lelgemann Heidrun , Gutscher Marc‐André , Bialas Jörg , Flueh Ernst R. , Weinrebe Wilhelm , Reichert Christian
Published: February 2004

In 1999 a marine geophysical survey collected bathymetric imagery, seismic reflection and refraction data to investigate the crustal structure and evolution of the Sunda Strait, which is linked to the obliquely convergent geodynamic setting of the Sumatran trench. The transtensional character of the study area is manifested in faulted blocks of arc basement and active normal faults detected on both sides of a large graben at the western entrance to the Sunda Strait. The combined interpretation of reflection and wide‐angle data reveals over 6 km of sediment graben fill associated with substantial crustal thinning. The southern part of the study region is only 50 km from the trench and the Moho of the downgoing plate is found at a depth of 28 km.
Seismic moments of major earthquakes and the rate of shortening across the Tien Shan
Authors: Molnar Peter , Ghose Sujoy
Published: February 2004

Three Twentieth Century earthquakes that Richter assigned M ≥ 8 and two of comparable magnitude in the Nineteenth Century imply rapid deformation within the Tien Shan. Seismic moment tensors of major earthquakes in this century suggest an average shortening rate of 7 (± 2) mm yr−1 across the Tien Shan. In the western part, however, where three of the five largest earthquakes occurred, the calculated rate is consistent with the value of ∼20 mm yr−1 measured using GPS in that area by Abdrakhmatov et al. As Avouac et al. suggested, the high rate in the western part apparently is a manifestation of counter‐clockwise rotation of the Tarim Basin relative to Eurasia about an axis near the east end of the Tien Shan.
Lower stratospheric organic and inorganic bromine budget for the Arctic winter 1998/99
Authors: Pfeilsticker K. , Sturges W. T. , Bösch H. , Camy‐Peyret C. , Chipperfield M. P. , Engel A. , Fitzenberger R. , Müller M. , Payan S. , Sinnhuber B.‐M.
Published: February 2004

In the Arctic winter 1998/99, two balloon payloads were launched in a co‐ordinated study of stratospheric bromine. Vertical profiles (9–28 km) of all known major organic Br species (CH3Br, C2H5Br, CH2BrCl, CHBrCl2, CH2Br2, CHBr2Cl, CHBr3, H1301, H1211, H2402, and H1202) were measured, and total organic Br (henceforth called Bryorg) originating from these organic precursors was inferred as a function of altitude. This was compared with total inorganic reactive Br (henceforth called Bryin) derived from spectroscopic BrO observations, after accounting for modeled stratospheric Bry partitioning. Within the studied altitude range the two profiles differed by less than the estimated accumulated uncertainties. This good agreement suggests that the lower stratospheric budget and chemistry of Br is well understood for the specified conditions. For early 1999 our data suggest a Bryin mixing ratio of 1.5 ppt in air just above the local Arctic tropopause (∼9.5 km), whilst at 25 km in air of 5.6 yr mean age it was estimated to be 18.4(+1.8/−1.5) ppt from organic precursor measurements, and (21.5±3.0) ppt from BrO measurements and photochemical modelling, respectively. This suggests a Bryin influx of 3.1(−2.9/+3.5) ppt from the troposphere to the stratosphere.
Evidence of lunar phase influence on global surface air temperature
Authors: Anyamba Ebby K. , Susskind Joel
Published: February 2004

Intraseasonal oscillations appearing in a newly available 20‐year record of satellite‐derived surface air temperature are composited with respect to the lunar phase. The daily surface air temperature is one of the geophysical fields derived from the TOVS data processed at the NASA Goddard Laboratory for Atmospheres. Polar regions exhibit strong lunar phase modulation with higher temperatures occurring near full moon and lower temperatures at new moon, in agreement with previous studies. The polar response to the apparent lunar forcing is most robust in winter when solar influence is at minimum. In addition, the response appears to be influenced by ENSO events. The highest mean temperature range between full moon and new moon in the region between 60° and 90° latitude was recorded in 1983, 1986/87, and 1990/91. Although the largest signal is in the polar regions, anomalies tend to progress equartoward in both hemispheres so that the warming in the tropics occurs at the time of the new moon.
The influence of soil moisture anomalies on variability of the North American Monsoon System
Authors: Small Eric E.
Published: February 2004

We examine the influence of land‐atmosphere interactions, as moderated by soil moisture anomalies, on variability of the North American Monsoon System (NAMS). Sensitivity experiments, in which soil moisture was prescribed to field capacity, were completed with the MM5 mesoscale model linked to the OSU land surface scheme. Our results demonstrate that the NAMS precipitation response to soil moisture forcing depends critically on the location of anomalous surface conditions. Wet soil in the southern Rocky Mountains (SRM) during July, which could result from the melt of an above‐normal snowpack, inhibits precipitation in the NAMS region. This is consistent with the observed negative correlation between SRM spring snowcover and NAMS summer precipitation [Gutzler and Preston, 1997]. In contrast, wet soil in the NAMS region enhances July precipitation within that area—a positive soil moisture‐rainfall feedback exists. Our findings must be tested with experiments that incorporate anomalies constrained by regional‐scale soil moisture observations.
Western Mediterranean sea‐level rise: Changing exchange flow through the Strait of Gibraltar
Authors: Ross Tetjana , Garrett Chris , Le Traon Pierre‐Yves
Published: February 2004

Sea‐level data from tide gauges and satellite altimetry show a decrease of nearly 40% in the sea‐level drop between the Atlantic and the Mediterranean from 1994 to 1997, coming mainly from a rapid rise of western Mediterranean sea‐level by more than 10 mm/year. A decrease in the sea‐level difference across the Strait, coincident with this Mediterranean rise, indicates that the surface inflow is reduced by an amount dynamically consistent with the change along the strait. These secular changes are accompanied by a seasonal cycle in the sea‐level drop between the Atlantic and the Mediterranean, which indicates a seasonal flipping of hydraulic exchange states in the Strait of Gibraltar. Thus, we suggest the sea‐level rise in the Mediterranean is a consequence of a changing exchange flow through the Strait of Gibraltar, driven indirectly by changing conditions in the Mediterranean.
On the impact of heterogeneous chemistry on ozone in the tropopause region
Authors: Meilinger S. K. , Kärcher B. , von Kuhlmann R. , Peter Th.
Published: February 2004

We examine the impact of heterogeneous chemistry involving liquid aerosol and ice particles on net ozone (O3) production rates under conditions representative of the midlatitude upper troposphere (UT) and lowermost stratosphere (LS). We demonstrate that heterogeneous effects are controlled by nitrogen oxides (NOx) and by the location of the air masses relative to the tropopause (TP). The net effect of heterogeneous chemistry is to decrease net O3 production below the TP (via heterogeneous HO2 loss) and to cause O3 destruction above the TP (via heterogeneous chlorine (Cl) activation). In the UT, gas phase chemistry due to non‐methane hydrocarbons (NMHCs) can become as important for O3 chemistry as heterogeneous reactions, and removal of HO2 by particles can become more important than changes of hydrogen oxides (HOx) through heterogeneous bromine (Br) chemistry. In the humid LS, Cl activation can become sufficiently large, so that O3 depletion occurs at all conceivable values of NOx. Such cold and humid conditions occur frequently enough to reduce the average ozone production rates in the midlatitude LS by more than 10%.
Estimation of dynamic rupture parameters from the radiated seismic energy and apparent stress
Authors: Pulido N. , Irikura K.
Published: February 2004

We propose a new procedure for estimating the critical slip weakening distance, Dc, by evaluating the spatio‐temporal distribution of the apparent stress calculated from the spatio‐temporal distribution of the slip velocity function on the fault plane obtained from a kinematic inversion of the earthquake source. The idea is based on the fact that the apparent stress can be related to the difference between the earthquake average stress and the frictional dynamical stress on the fault plane during the rupture process. From the cumulative slip‐apparent stress relationship we estimate the critical slip, Dc, of the 1992 Landers earthquake. We find that the critical slip weakening plays an important role in controlling the rupture velocity. In the case of the Landers earthquake the very low rupture velocity in the central segment could be explained by the large Dc‐value obtained for the main asperity on that segment.
The dependence of AABW transport in the Atlantic on vertical diffusivity
Authors: Kamenkovich Igor V. , Goodman Paul J.
Published: February 2004

Simple theoretical arguments are employed to study the dependence of the volume and transport of the Antarctic Bottom Water (AABW) in the Atlantic Ocean on the vertical diffusivity. We have found that while the vertical extent of the AABW cell decreases with the intensification and deepening of the North Atlantic overturning cell, the transport of AABW into the Atlantic increases. The latter fact is explained by the increase in the deep meridional pressure gradient, which drives the flow. An estimate of the AABW transport is then derived from the density balance in the deep western boundary layer.
The relationship between atmospheric water vapor and temperature in simulations of climate change
Authors: Hu Haijun , Oglesby Robert J. , Saltzman Barry
Published: February 2004

Atmospheric moisture (Q) and temperature (T) relationships simulated by two general circulation models (GCMs) and that of a recent operational analysis are intercompared. The GCMs represent two important stages of model development, with the earlier one using a simplistic convective adjustment scheme and the more recent one employing a more physically‐realistic convective parameterization. While the models agree in some fundamental qualitative aspects of the Q‐T relationship, they differ quantitatively in the correlations of Q with T, and in the vertical dependencies of moistening to increasing CO2. As the sophistication of convective parameterizations has increased, model sensitivity to changes in atmospheric CO2 has decreased markedly. This study indicates the reduction in sensitivity is primarily due to a reduction in simulated moisture amount along with changes in vertical distributions. While the more recent model shows clear signs of improvements, there is also indication that it may have underestimated the Q‐T correlations, leading to a somewhat lower climate sensitivity with increasing CO2.
The effect of clouds on enhancing UVB irradiance at the Earth's surface: A one year study
Authors: Sabburg J. , Wong J.
Published: February 2004

The most extensive study of frequency, magnitude and sky properties associated with UVB enhancement is reported. The first integrated automatic sky camera and irradiance measurement system was used for simultaneous data collection over the solar zenith angle range of 4.2 to 64.3°. It is reported that 3% of UVB irradiance measurements collected at intervals of 6 minutes, over a one‐year period, were cloud enhanced. It was found that 85% of possible UVB enhancements occurred for solar zenith angles ranging from 40 to 63°. The study was undertaken during September 1997 to August 1998 at Toowoomba, Australia (27.6°S, 151.9°E). The maximum UVB enhancement was found to have an irradiance of 8% greater than that of an equivalent clear‐sky. A mechanism for UVB enhancement for cases of solar obstruction by cirrus cloud is postulated. Analysis showed that 86% of enhancement occurred under hazy/cirrus skies.
Periodic loading on a creeping fault: Implications for tides
Authors: Perfettini Hugo , Schmittbuhl Jean
Published: February 2004

We study the effect of time varying normal and shear stress perturbations on a creeping fault and in which inertia is neglected. When interpreted in terms of earthquake triggering by earth tides, our results suggest that tidal triggering may exist but be very difficult to detect. We use a spring‐block model with a rate‐and state dependent friction law, loaded at constant velocity, and in which inertia is neglected. When a periodic stress is applied, a resonance exists which can destabilize sliding (i.e. earthquakes). However, when factional parameters slightly vary along the fault, the observed phase lag between the response of the fault and the perturbating stresses close to resonance shows a broad and uncorrelated scattering.
Frictional sinking of the dense water overflow in a z‐Coordinate OGCM of the Mediterranean Sea
Authors: Stratford Kevin , Haines Keith
Published: February 2004

The overflow and subsequent spreading of dense water formed in the Adriatic Sea is studied in a high resolution z‐coordinate ocean general circulation model (OGCM) of the Mediterranean Sea via simulations of chlorofluorocarbons (CFC12). Frictional sinking is investigated using different parametrisations of the mean bottom stress in term of the mean currents. A series of model integrations shows that increasing the strength of the bottom stress allows the dense overflow to descend the continental slope at a steeper angle, as would be expected on the basis of theoretical streamtube models. The use of a linear drag, which can be thought of as parametrising unresolved time‐varying motions, greatly improves the model's ability to capture a realistic dense water pathway and hence realistic CFC12 distributions.
Global distribution of cloud droplet effective radius from POLDER polarization measurements
Authors: Bréon François‐Marie , Colzy Stéphane
Published: February 2004

Polarization measurements from the spaceborne POLDER instrument are used to estimate the droplet effective radius of liquid‐phase clouds. Eight months of measurements have been processed. Seasonal averages have been generated and are discussed here. The measurements confirm that, on average, droplets are 2 to 3 µm smaller over land than over the oceans. The smaller droplets are found over highly polluted regions and in areas affected by smoke from biomass burning activity. The influence of land masses is apparent downwind of the continents. Largest droplets are found in remote tropical oceans, away from major aerosol sources. A large zonal gradient is also apparent in the southern oceans, with very small droplets close to the Antarctic continent.
Photochemical transformations in ice: Implications for the fate of chemical species
Authors: Dubowski Yael , Hoffmann Michael R.
Published: February 2004

A quantum yield of ϕice = 2.3 × 10−4 (±4 × 10−5) was determined for the photochemical degradation of 4‐nitrophenol over the wavelength range of 300 to 370 nm in ice pellets (pH 5.6). Five reaction products were identified: hydroquinone, benzoquinone, 4‐nitrosophenol, nitrate, nitrite, and the likely formation of organic polymers. The similarities of these results to the observations from 4‐nitrophenol photolysis in aqueous solutions indicate that similar mechanisms are operative in both phases. The photochemical decomposition of 4‐nitrophenol under conditions similar to those in polar snow and ice suggests that other direct and indirect photochemical process can occur in the polar ice/snow during spring and summer.
Gravitational braking of inner‐core rotation in geodynamo simulations
Authors: Buffett Bruce A. , Glatzmaier Gary A.
Published: February 2004

The effects of gravitational coupling between the inner core and the mantle are incorporated into numerical simulations of the geodynamo. Differential rotation between the inner core and the mantle is permitted by allowing the inner core to viscously deform. Calculations with a deformation time scale of 1 yr, corresponding to an average viscosity of 5 × 1016 Pa s, predict eastward rotation of the inner core with a mean rate of 0.02deg/yr relative to the mantle. Fluctuations about this mean rate of rotation occur with a typical period of 75 yr and have sufficient amplitude to explain observed changes in length of day at decadal periods. When gravitational coupling is removed, or viscous coupling is added by imposing no‐slip boundary conditions, the mean inner core rotation rate is almost an order of magnitude greater.
Long period interferograms reveal 1992–1998 steady rate of deformation at Krafla Volcano (North Iceland).
Authors: Henriot Oliver , Villemin Thierry , Jouanne François
Published: February 2004

We formed interferograms of ERS‐SAR scenes covering the area of Krafla (N. Iceland) with time span values of up to six years (1992–1998). Our data reveals a steady deformation rate at Krafla and within its fissure swarm, with values reaching +2.1 cm/y in the ground to satellite direction, at the volcano. The area affected by deformation extends 20 km both north and south of the volcano. The best fit dislocation model consists of sills, to the north and south of the volcano, and a magma chamber, located below the volcano, all of them undergoing contraction.
Variability of core layer temperature (CLT) of the North Pacific Subtropical Mode Water
Authors: Hanawa Kimio , Kamada Jun
Published: February 2004

A time series of the core layer temperature (CLT) of the North Pacific subtropical mode water for the 40‐year period from 1957 to 1996 is constructed using all available temperature profiles archived in World Ocean Database 1998. CLT is defined as the temperature of the layer having the minimum vertical temperature gradient at a single profile, with temperature ranging from 15 to 19°C. Annual mean CLT is calculated using all CLT data taken from May to December for four 5° × 10° (lat. × Ion.) regions from 30° to 35°N and from 140°E to 180°. The CLT time series shows decadal to interdecadal variation, as well as interannual variation. This time series correlates very well with that of wintertime (February and March) sea surface temperature in the same region. Relationships are investigated among several atmospheric circulation indices, the Kuroshio transport, and CLT. As a result, it is suggested that CLT might be crucially influenced by the Kuroshio transport in a time frame longer than ten years, and by the wintertime East Asian Monsoon in shorter time frames.
Compaction localization in porous rock
Authors: Olsson W. A. , Holcomb D. J.
Published: February 2004

Experimental work on shear localization in porous sandstone led to the observation of nonuniform compaction. By analogy with shear localization, the process is referred to as compaction localization. To gain insight into the process of compaction localization, acoustic emission locations were used to define and track the thicknesses of localized zones of compaction during axisymmetric compression experiments. Zones of acoustic emission, demarcating the boundaries between the uncompacted and compacted regions, developed and moved parallel to the sample axis at velocities an order of magnitude higher than the imposed specimen shortening rate. Thus tabular zones of compaction were found to grow (thicken) in the direction of maximum compressive stress. These structures may form due to tectonic stresses or as a result of local stresses induced during production of fluids from wells, resulting in barriers to fluid (oil, gas, water) movement in sandstone reservoirs.
Upper limits for the rate coefficients for reactions of BrO with formaldehyde and HBr
Authors: Orlando John J. , Ramacher Bjoern , Tyndall Geoffrey S.
Published: February 2004

The reactions of the BrO radical with hydrogen bromide, BrO + HBr → HOBr + Br (R4) and with HCHO, BrO + HCHO → HOBr + HCO (R5) have been studied at 298 K, 1 atm. pressure in an environmental chamber. No conclusive evidence for the occurrence of either reaction was found and upper limits for both reaction rate coefficients are reported (k4, k5 <4 × 10−15 cm³ molecule−1 s−1). These upper limits are about 4–5 times lower than recent estimates [Hansen et al., 1999a,b].
Will the North Atlantic Ocean thermohaline circulation weaken during the 21st century?
Authors: Gent Peter R.
Published: February 2004

The North Atlantic Ocean thermohaline circulation is examined in three experiments using the Climate System Model. They are a control integration for 1870 conditions, and particular emission scenarios for the 20th and 21st centuries. It is found that the strength of the thermohaline circulation does not change significantly over the 21st century. This is in contrast to several other recent studies, which have projected a significant reduction over the 21st century. The reason for the difference is that the Northwest Atlantic becomes warmer and more saline in the Climate System Model. These changes combine to make little change to the surface ocean density in this region, and hence to the rate of deep water formation. Caveats about the Climate System Model and other coupled climate models are then discussed.
System of Gigantic Valleys northwest of Tharsis, Mars: Latent catastrophic flooding, northwest watershed, and implications for Northern Plains Ocean
Authors: Dohm J. M. , Anderson R. C. , Baker V. R. , Ferris J. C. , Hare T. M. , Strom R. G. , Rudd L. P. , Rice J. W. , Casavant R. R. , Scott D. H.
Published: February 2004

Mars Orbiter Laser Altimeter (MOLA) reveals a system of gigantic valleys to the northwest of the huge martian shield volcano, Arsia Mons, in the western hemisphere of Mars. These newly identified northwestern slope valleys (NSVs) potentially signify previously undocumented martian catastrophic floods and may corroborate the northern ocean hypotheses. These features, which generally correspond spatially to gravity lows, were previously obscured in Mariner and Viking Orbiter imagery by veneers of materials, including volcanic lava flows and air fall deposits. Geologic investigations of the Tharsis region suggest that the NSVs were mainly carved prior to the construction of Arsia Mons and its associated Late Hesperian and Amazonian age lava flows, concurrent with the early development of the outflow channels that debouch into Chryse Planitia.
Evaluation of the simulations of the North American Monsoon in the NCAR CCM3
Authors: Yang Zong‐Liang , Gochis Dave , Shuttleworth William James
Published: February 2004

The six‐year average of a ten‐year integration of the National Center for Atmospheric Research (NCAR) Community Climate Model version 3 (CCM3), forced with prescribed, climatological sea surface temperatures, was compared with the Legates‐Willmott precipitation climatology and the National Centers for Environmental Prediction (NCEP)‐NCAR reanalysis product. Summertime precipitation associated with the North American Monsoon (NAM) circulation is largely underrepresented in simulations using the CCMS. The CCM3 simulates excessive amounts of tropical eastern Pacific and Caribbean precipitation, depressed precipitation over Mexico and the southwestern United States, and largely misrepresents the summertime circulation pattern over North America as compared to the reanalysis climatology fields. Basic diagnostic analyses suggest that excessive convection over tropical waters in the eastern Pacific and the Caribbean alters the summertime circulation pattern which produces excess subsidence over much of Northern Mexico and the southwestern U.S. and prohibits the northward transport of atmospheric moisture into the NAM region. The vertically integrated moisture flux and precipitable water estimated by the CCM3 are significantly different in amount and direction (in the case of fluxes) than those observed in the reanalysis data. Introducing anomalously wet land‐surface conditions over the NAM region at model initialization yields minimal improvement. Suspected causes for the erroneous simulation of the summertime circulation in the CCM3 are discussed.
Precipitation changes in a GCM resulting from the indirect effects of anthropogenic aerosols
Authors: Rotstayn Leon D. , Ryan Brian F. , Penner Joyce E.
Published: February 2004

An atmospheric GCM coupled to a mixed‐layer ocean model is used to study changes in rainfall due to the indirect effects of anthropogenic aerosols. The model includes treatments of both the first and second indirect effects. The most striking feature of the equilibrium rainfall response to the indirect effects of anthropogenic aerosols is a southward shift of the equatorial rainfall. We hypothesize that this is caused by a hemispheric asymmetry in the cooling of the sea surface. This is supported by another pair of experiments, in which the model is run with prescribed present‐day SSTs. In one experiment the standard model is used, and in the other the SSTs in the Northern Hemisphere are increased by 1 K in the calculation of the surface fluxes, to mimic the effect of a return to pre‐industrial conditions. Compared to the run with increased NH SST, the standard run shows a southward shift of equatorial rainfall, similar to that obtained as a response to anthropogenic aerosols.
UARS Microwave Limb Sounder observations of denitrification and ozone loss in the 2000 Arctic late winter
Authors: Santee M. L. , Manney G. L. , Livesey N. J. , Waters J. W.
Published: February 2004

The UARS Microwave Limb Sounder obtained measurements of ClO, HNO3, and O3 inside the Arctic lower stratospheric vortex during two intervals in February and March 2000. The data show evidence of significant chemical processing in February, consistent with the exceptionally cold conditions that prevailed earlier in the winter. Ozone at 465 K decreased by 0.04±0.01 ppmv/day in early February, implying chemical loss rates greater than those observed during the 1995–1996 winter, which was also unusually cold in the lower stratosphere. A persistent depression in the HNO3 abundances in late March, well after polar stratospheric cloud activity had ceased, suggests a moderate degree (∼20%) of denitrification around the 465 K level at 70°N and higher equivalent latitudes. This is the strongest evidence yet seen for the occurrence of denitrification in the Arctic over spatial scales large enough to be detected in satellite measurements.
Numerical modeling of Jupiter's moist convection layer
Authors: Nakajima Kensuke , Takehiro Shin‐ichi , Ishiwatari Masaki , Hayashi Yoshi‐Yuki
Published: February 2004

Moist convection of Jupiter's atmosphere is examined using a large‐domain two‐dimensional fluid dynamical model with simplified cloud microphysics of water. The result shows that the water condensation level acts as a dynamical and compositional boundary. The convection below the condensation level is characterized by a steady regular cellular structure and a homogeneous distribution of water mixing ratio. Above the condensation level, cloud elements accompanied by the upward motion develop and disappear irregularly but successively, and water mixing ratio is highly inhomogeneous. The horizontal average of mixing ratio decreases rapidly with height just above the condensation level, resulting in a distinctive stable layer at 5 bar. The stable layer prevents the air masses above and below it from mixing with each other. As a result, the upper dry air does not reach 20 bar level, where the Galileo probe observed low humidity.
Origin of carbonaceous aerosols over the tropical Indian Ocean: Biomass burning or fossil fuels?
Authors: Novakov T. , Andreae M. O. , Gabriel R. , Kirchstetter T. W. , Mayol‐Bracero O. L. , Ramanathan V.
Published: February 2004

We present an analysis of the carbon, potassium and sulfate content of the extensive aerosol haze layer observed over the tropical Indian Ocean during the Indian Ocean Experiment (INDOEX). The black carbon (BC) content of the haze is as high as 17% of the total fine particle mass (the sum of carbonaceous and soluble ionic aerosol components) which results in significant solar absorption. The ratio of black carbon to organic carbon (OC) (over the Arabian Sea and equatorial Indian Ocean) was a factor of 5 to 10 times larger than expected for biomass burning. This ratio was closer to values measured downwind of industrialized regions in Japan and Western Europe. These results indicate that fossil fuel combustion is the major source of carbonaceous aerosols, including black carbon during the events considered. If the data set analyzed here is representative of the entire INDOEX study then fossil fuel emissions from South Asia must have similarly contributed to aerosols over the whole study region. The INDOEX ratios are substantially different from those reported for some source regions of South Asia, thus raising the possibility that changes in composition of carbonaceous aerosol may occur during transport.
Increasing background ozone in surface air over the United States
Authors: Cynthia Lin C.‐Y. , Jacob Daniel J. , Munger J. William , Fiore Arlene M.
Published: February 2004

The long‐term trend of background O3 in surface air over the United States from 1980 to 1998 is examined using monthly probability distributions of daily maximum 8‐hour average O3 concentrations at a large ensemble of rural sites. Ozone concentrations have decreased at the high end of the probability distribution (reflecting emission controls) but have increased at the low end. The cross‐over takes place between the 30th and 50th percentiles in May–August and between the 60th and 90th percentiles during the rest of the year. The increase is statistically significant at a 5% level in spring and fall, when it is 3–5 ppbv. The maximum increase is in the Northeast. A possible explanation is an increase in the O3 background transported from outside the United States. Better understanding of the causes of the increase is needed because of its implications for meeting O3 air quality standards.
Wave propagation in the 1999–2000 Arctic early winter stratosphere
Authors: Sabutis J. L. , Manney G. L.
Published: February 2004

Stratospheric wave propagation during the unusually cold NH early winter 99–00 is studied and compared to the recent cold winters of 94–95, 95–96 (the previous coldest NH winter) and 96–97. EP fluxes reveal less wave activity entered the stratosphere in 95–96 and 99–00, substantial temperature decreases during long periods of little wave activity in 94–95 and 99–00, and little wave propagation into the upper stratosphere in Nov 99–Jan 00 and Nov 95–mid‐Jan 96. 2‐D and 3‐D EP fluxes for 95–96 and 99–00 show both that wave activity was inhibited from propagating upward and poleward through the middle stratosphere until mid–Jan, and there was large horizontal propagation of wave activity in the middle and lower stratosphere during Nov and Dec. Thus, both less wave activity entering the stratosphere, and a background structure that prevented wave activity from propagating into the upper stratosphere, were important factors in producing unusually cold early winters in 95–96 and 99–00.
Frost flowers as a source of fractionated sea salt aerosol in the polar regions
Authors: Rankin A. M. , Auld V. , Wolff E. W.
Published: February 2004

Frost flowers collected from the surface of new sea ice near the Brunt Ice Shelf, Antarctica, show depletion in sulphate and sodium relative to other sea water ions. This is consistent with loss of mirabilite (Na2SO4) during formation of the brine from which the frost flowers grow. Aerosol generated from frost flowers would have higher sodium:sulphate ratios than aerosol generated from sea water. This would explain low values of non‐sea‐salt sulphate encountered in winter aerosol, and winter layers in ice cores, at coastal Antarctic sites. Calculations confirm that the frost flower source should be significant compared to an open water source for coastal regions.
Large loss of total ozone during the Arctic winter of 1999/2000
Authors: Sinnhuber B.‐M. , Chipperfield M. P. , Davies S. , Burrows J. P. , Eichmann K.‐U. , Weber M. , von der Gathen P. , Guirlet M. , Cahill G. A. , Lee A. M. , Pyle J. A.
Published: February 2004

Three‐dimensional model calculations are used together with total ozone observations from the Global Ozone Monitoring Experiment (GOME) and ozone sonde measurements at Ny‐Ålesund, Spitsbergen to quantify the chemical ozone loss inside the Arctic polar vortex in winter 1999/2000. GOME shows March 2000 mean Arctic total ozone values of 365 DU, about 100 DU less than the 1980–1989 mean from TOMS data, well reproduced by the model calculations. A comparison of the modeled ozone with a passive ozone tracer and ozone sonde observations at Ny‐Ålesund shows that by the end of March 2000 about 2.5 ppmv of ozone are chemically depleted in the lower stratosphere, corresponding to more than 70% ozone loss. At the same time, the inferred loss in total ozone inside or at the edge of the polar vortex is between 90 and 140 DU. The large ongoing loss during March 2000 is likely to be due to widespread denitrification, which maintains high chlorine activation during this period.
Variability in the Deep Western Boundary Current in the equatorial Atlantic at 44°W
Authors: Stramma Lothar , Rhein Monika
Published: February 2004

The variability of the North Atlantic Deep Water (NADW) was studied by ten hydrographic repeat sections taken along 44°W off Brazil between September 1989 and March 1994. This data set allowed for the first time to describe the seasonal signal in the Deep Western Boundary Current at the equator from hydrographic data. Annual and semiannual layer thickness modulations were observed similar to such signals in transport time series, however with a time lag of 2 months. A comparison of the interannual variability of the Labrador Sea Water component of the NADW at 44°W at the equator with the formation region indicated a time lag of 13 to 17 years. The effective spreading velocities in the Labrador Sea Water are in the range 2 to 5 cms−1 for the tropical Atlantic Ocean.
Committed warming and its implications for climate change
Authors: Wetherald Richard T. , Stouffer Ronald J. , Dixon Keith W.
Published: February 2004

Time lags between changes in radiative forcing and the resulting simulated climate responses are investigated in a set of transient climate change experiments. Both surface air temperature (SAT) and soil moisture responses are examined. Results suggest that if the radiative forcing is held fixed at today's levels, the global mean SAT will rise an additional 1.0K before equilibrating. This unrealized warming commitment is larger than the 0.6K warming observed since 1900. The coupled atmosphere‐ocean GCM's transient SAT response for the year 2000 is estimated to be similar to its equilibration response to 1980 radiative forcings—a lag of ∼20 years. Both the time lag and the warming commitment are projected to increase in the future, and depend on the model‧s climate sensitivity, oceanic heat uptake, and the forcing scenario. These results imply that much of the warming due to current greenhouse gas levels is yet to be realized.
Forward and reverse modeling of the three‐dimensional viscous Rayleigh‐Taylor instability
Authors: Kaus Boris J. P. , Podladchikov Yuri Y.
Published: February 2004

A combined finite‐difference/spectral method is used to model the 3D viscous Rayleigh‐Taylor instability. Numerically calculated growth rate spectra are presented for an initial sinusoidal perturbation of the interface separating two fluids with amplitude 10−3H and 0.2H, where H is the height of the system. At small initial amplitude, growth rate spectra closely follow linear theory, whereas the calculation with higher initial amplitude shows wavelength selection towards 3D perturbations. Numerical simulations and analytical theory are used to evaluate the applicability of previous 2D numerical models, which is shown to depend on (1) the wavelength and amplitude of an initially 2D sinusoidal perturbation and (2) the amplitude of background noise. It is also shown that reverse (backward) modeling is capable of restoring the initial geometry as long as overhangs are not developed. If overhangs are present, the possibility of restoring the initial conditions is largely dependent on the stage of overhang development.
Deformation of Earth's inner core by electromagnetic forces
Authors: Buffett Bruce A. , Bloxham Jeremy
Published: February 2004

A recent study of Karato (1999) suggests that deformation induced in the inner core by electromagnetic (Lorentz) forces may account for the development of seismic anisotropy. The viability of this proposal depends on whether Lorentz forces can sustain persistent flow within the inner core. We explore this question by establishing the conditions for static equilibrium when Lorentz forces are present. We find that the requirements for thermodynamic and hydrostatic equilibrium are incompatible at the surface of the inner core. However, the resulting deformation redistributes mass in the interior so as to minimize steady flow. Numerical calculations show that the flow becomes vanishingly weak and is confined to the top of the inner core. Strains in the interior are small and the alignment of crystals is insufficient to explain the anisotropy inferred from seismological observations.
Cloud photochemistry and its effect on the composition of the upper atmosphere of Venus
Authors: Rowland Glenn A. , Phillips Leon F.
Published: February 2004

Laboratory studies of the 248 nm photooxidation of Fe(II) to Fe(III) in concentrated sulfuric acid solutions indicate that photochemical reactions in the sulfuric acid clouds of Venus are capable of affecting the composition of the atmosphere at high altitudes, by removing O2 and CO and regenerating CO2. Major primary processes are the production of SO3− radical ions by photolysis of solvated SO2, and of SO4− radical ions by photolysis of complex ions containing Fe(III), if traces of iron salts are present. Secondary processes are similar to those which result in the formation of acid rain in Earth's troposphere.
Vertical profiles of nitrous oxide isotopomer fractionation measured in the stratosphere
Authors: Griffith David W. T. , Toon Geoffrey C. , Sen Bhaswar , Blavier Jean‐François , Toth Robert A.
Published: February 2004

We have measured the vertical profiles of several isotopomers of nitrous oxide, N2O, in the stratosphere by balloon‐borne infrared remote sensing between 15 and 35 km. In particular we distinguish the individual profiles and relative enrichments of the positional isotopomers15N14N16O and14N15N16O for the first time. We find a distinct and reproducible relative enrichment of the isotopomers which is in general agreement with measured photolysis rates in the laboratory and theoretical predictions. The results confirm photolysis as the dominant stratospheric loss process for N2O and argue against suggestions that additional chemical sources of N2O in the stratosphere are required to explain the observed heavy isotopic enrichments there.