Showing papers in "Geophysical Research Letters in 1996"
TL;DR: The authors used multivariate linear regression to show that nearly all the cooling in the northwest Atlantic and the warming across Europe and downstream over Eurasia since the mid-1970s results from the changes in the North Atlantic Oscillation (NAO), and the NAO accounts for 31% of the hemispheric interannual variance over the past 60 winters.
Abstract: Pronounced changes in the wintertime atmospheric circulation have occurred since the mid-1970s over the ocean basins of the Northern Hemisphere, and these changes have had a profound effect on surface temperatures. The variations over the North Atlantic are related to changes in the North Atlantic Oscillation (NAO), while the changes over the North Pacific are linked to the tropics and involve variations in the Aleutian low with teleconnections downstream over North America. Multivariate linear regression is used to show that nearly all of the cooling in the northwest Atlantic and the warming across Europe and downstream over Eurasia since the mid-1970s results from the changes in the NAO, and the NAO accounts for 31% of the hemispheric interannual variance over the past 60 winters. Over the Pacific basin and North America, the temperature anomalies result in part from tropical forcing associated with the El Nino-Southern Oscillation phenomenon but with important feedbacks in the extratropics. The changes in circulation over the past two decades have resulted in a surface temperature anomaly pattern of warmth over the continents and coolness over the oceans. This pattern of temperature change has amplified the observed hemispheric-averaged warming because of it interaction with land and ocean;more » temperature changes are larger over land compared to the oceans because of the small heat capacity of the former. 13 refs., 5 fig., 2 tab.« less
1,002 citations
TL;DR: In this article, the authors carried out several statisticaJ tests to assess the likelihood that the recent behavior of the Southern Oscillation (SO) is part of a natural decadal timescae variation.
Abstract: The tendency for more frequent E1 Nifio events America to the International Dateline. It is the basin-scale and fewer La Nifia events since the late 1970's has been phenomenon, however, that is linked to globaJ atmospheric linked to decadl changes in climate throughout the Pacific circulation and associated weather anomalies. The primary basin. Aspects of the most recent warming in the tropical response in the atmosphere coupled to EN is the SO and, Pacific from 1990 to 1995, which are connected to but not together, the tropical Pacific warm events are often referred synonymous with E1 Nifio, are unprecedented in the climate to as ENSO events. record of the past 113 years. There is a distinction between E1 Nifio (EN), the Southern Oscillation (SO)in the atmo- sphere, and ENSO, where the two are strongly linked, that emerges clearly on decadal time scaJes. In the traditional E1 Nifio region, sea surface temperature anomalies (SSTAs) have waxed and waned, while SSTAs in the centraequatorial Pa- cific, which are better linked to the SO, remained positive from 1990 to June 1995. We carry out several statisticaJ tests to assess the likelihood that the recent behavior of the SO is part of a natural decadal-timescae variation. One test fits an autoregressive-moving average (ARMA) model to a measure of the SO given by the first hundred years of the pressures at Darwin, Australia, beginning in 1882. Both the recent trend for more ENSO events since 1976 and the prolonged 1990- 1995 ENSO event are unexpected given the previous record, with a probability of occurrence about once in 2,000 years. This opens up the possibility that the ENSO changes may be partly caused by the observed increases in greenhouse gases.
801 citations
TL;DR: In this article, the authors measured the surface tension and subsumption properties of difunctional organic acids in various concentrations of (NH4)2SO4 and NH4HSO4 aqueous solutions.
Abstract: Solubilities and surface tensions were measured for difunctional organic acids in various concentrations of (NH4)2SO4 and NH4HSO4 aqueous solutions. Model results using these data indicate that the organic compounds affect cloud droplet growth by two mechanisms: by gradual dissolution in the growing droplet which affects the shape of the Kohler growth curve, and by lowering of surface tension which decreases the critical supersaturation.
451 citations
TL;DR: In this article, the authors show that the horizontal motion of slope had an important contribution to the tsunami generation in the case of the 1994 June 2 Java, Indonesia, earthquake, the focal mechanism was a shallow dipping thrust and the source was near a very steep trench slope.
Abstract: Tsunami generation by an earthquake is generally modeled by water surface displacement identical to the vertical deformation of ocean bottom due to faulting. The effect of horizontal deformation is usually neglected. However, when the tsunami source is on a steep slope and the horizontal displacement is large relative to the vertical displacement, the effect becomes significant. We show this for two recent earthquakes which generated much larger tsunamis than expected from seismic waves. In the case of the 1994 June 2 Java, Indonesia, earthquake, the focal mechanism was a very shallow dipping thrust and the source was near a very steep trench slope. In the case of the 1994 Nov. 14 Mindoro, Philippines, earthquake, strike-slip faulting extended from ocean to land perpendicular to the coast line. In both cases, we found that the horizontal motion of slope had an important contribution to the tsunami generation.
444 citations
TL;DR: In this paper, a method was developed to derive the electric potentials in the high-latitude ionosphere resulting from any arbitrary combination of the interplanetary magnetic field (IMF) magnitude and orientation, solar wind velocity, and dipole tilt angle.
Abstract: A method has been developed to derive the electric potentials in the high-latitude ionosphere resulting from any arbitrary combination of the interplanetary magnetic field (IMF) magnitude and orientation, solar wind velocity, and dipole tilt angle. This model is based on spherical harmonic coefficients that were derived by a least error fit of measurements from multiple satellite passes. These harmonic coefficients have been found to have systematic variations that can be reproduced by a combination of a Fourier series and a multiple linear regression formula. Examples of the model output are shown. In principal, this technique could be used as a fundamental building block to forecast geomagnetic disturbances, or “space weather”, from satellite measurements in the upstream solar wind.
357 citations
TL;DR: The first oceanographic measurements across a deep channel beneath the calving front of Pine Island Glacier reveal a sub-ice circulation driven by basal melting of 10−12 m yr−1 as mentioned in this paper.
Abstract: The first oceanographic measurements across a deep channel beneath the calving front of Pine Island Glacier reveal a sub-ice circulation driven by basal melting of 10–12 m yr−1. A salt box model described here gives a melt rate similar to that of ice balance and numerical models, 5–50 times higher than averages for the George VI and Ross Ice Shelves. Melting is fueled by relatively warm Circumpolar Deep Water that floods the deep floor of the Amundsen and Bellingshausen Sea continental shelves, reaching the deep draft of this floating glacier. A revised melt rate for ice shelves in the Southeast Pacific sector raises circumpolar ice shelf melting to 756 Gt yr−1. Given prior estimates of surface accumulation and iceberg calving, this suggests that the Antarctic Ice Sheet is currently losing mass to the ocean.
336 citations
TL;DR: In this paper, the results of measurements of ultra-low-frequency magnetic noise during a large earthquake (Ms=7.1) at Guam of 8 August, 1993 (depth ∼60 km).
Abstract: We report the results of measurements of ultra-low-frequency magnetic noise during a large earthquake (Ms=7.1) at Guam of 8 August, 1993 (depth ∼60 km). The ULF observing system is located in the Guam Island, about 65 km from the epicenter. Several distinct features of this analysis are summarized. (1) We have proposed rather sophisticated statistical analyses (monthly mean, standard deviation) in order to estimate the wave intensity and polarization (i.e. ratio Z/H). (2) A comparison between the ULF wave activity and ΣKp, is useful in distinguishing between the space geomagnetic pulsations and non-space emissions. (3) Then, the use of the ratio (Z/H) is found to be of essential importance in discrimating the emissions presumably of seismic origin from space plasma waves. (4) The statistical analysis of the temporal evolution of this ratio, has yielded that it shows a broad maximum only about one month before the earthquake, and this suggests that the emissions during this period are very likely to be magnetic precursors. (5) The temporal variation of Z component is similar to that for the Loma Prieta earthquake such that it shows a broad maximum ten days ∼ two weeks before the earthquake and another increase a few days before the earthquake. (6) The emissions presumably associated with the earthquake are of noise-like nature, and their main frequency is 0.02 ∼ 0.05 Hz (with maximum intensity ∼0.1 nT).
327 citations
TL;DR: In this paper, a methodology is presented for generating surrogate climate-change scenarios with a regional climate model, which can be used for process and parameterization studies, to calibrate the regional response to a putative global climate change, and to intercompare different models.
Abstract: A methodology is presented for generating surrogate climate-change scenarios with a regional climate model. The procedure is simple to implement and dynamically consistent. It entails (i) adopting a realized or simulated atmospheric flow evolution and (ii) prescribing specific thermodynamic modifications of this realization to a regional model's initial fields and externally-specified time-dependent lateral boundaries fields. The resulting scenarios can be used for process and parameterization studies, to calibrate the regional response to a putative global climate change, and to intercompare different models. The approach is illustrated with two month-long regional climate model simulations. The experiment is designed to explore the response within Europe to a pseudo-global warming of 2 K with an accompanying increase in atmospheric water vapor content. Analysis reveals that there is a spatially-differentiated preciptation increase consonant with the domain-averaged increase of about 16% in the water vapor content.
289 citations
TL;DR: In this article, a multichannel high-speed photometer and image intensified CCD cameras were carried out at Yucca Ridge Field Station (40040'N, 104o.56'W) in Colorado as part of the SPRITES'95 campaign from 15 June to August 6, 1995.
Abstract: Observations of optical phenomena at. high alti- tude a, bove thunderstorms using a multichannel high-speed photometer and image intensified CCD cameras were carried out at Yucca Ridge Field Station (40040 ' N, 104o.56 ' W), Colorado as part of the SPRITES'95 campaign from 15 June to August 6, 1995. These newneasurements indicate that diffuse optical flashes with a duration of < I ms and a hori- zontal scale of-.- 100-300 km occur at 75-105 km altitude in the lower ionosphere just after the onset of cloud-to-ground lightning discharges, but preceding the onset of sprites. Here we designate these events as 'alves" to distinguish them from 'i'ed sprites" . This finding is consistent with the production of diffuse optical emissions due to the heating of the lower ionosphere by electromagnetic pulses generated by lightning discharges as suggested by several authors.
287 citations
TL;DR: In this paper, a significant fraction of the semidiurnal internal tide generated at the Hawaiian Ridge is evidently phase-locked to the astronomical potential and can modulate the amplitude of the surface tide by ∼5 cm.
Abstract: Analysis of Topex/Poseidon satellite altimetry reveals short-wavelength fluctuations in the ocean surface tide that are attributable to internal tides. A significant fraction of the semidiurnal internal tide generated at the Hawaiian Ridge is evidently phase-locked to the astronomical potential and can modulate the amplitude of the surface tide by ∼5 cm. The internal tide is thus easily mapped along satellite groundtracks, and it is found to be spatially coherent over great distances, with waves propagating well over 1000 km from the Hawaiian Ridge before decaying below noise level. Both first and second baroclinic modes are observed in both the M 2 (lunar) and S 2 (solar) tides. The high space-time coherence is in sharp contrast to what is often inferred from current-meter observations, but it confirms recent speculations from an acoustic experiment north of Hawaii.
282 citations
TL;DR: In this paper, a linear least squares fit to the monthly and annual increases in UV exposure since 1979 are given for 3 wavelengths (300 nm, 310 nm, and 320 nm) that are strongly, moderately, and weakly absorbed by ozone.
Abstract: Increases in ultraviolet fluxes (300 nm to 340 nm) reaching the ground between 1979 and 1992 are estimated using measured stratospheric ozone amounts and reflectivity data from Nimbus-7/TOMS (Total Ozone Mapping Spectrometer). The UV-increases are estimated from an ozone data set obtained using a new algorithm incorporating improved in-flight instrument calibration. The 380 nm radiance data are used to show that there were no changes in ultraviolet atmospheric albedo due to clouds and aerosols from 1979 to 1992 within the 1% uncertainty of the measurements. Linear least squares fits to the monthly and annual increases in UV exposure since 1979 are given for 3 wavelengths (300 nm, 310 nm, and 320 nm) that are strongly, moderately, and weakly absorbed by ozone. The estimated linear changes for the 3 wavelengths become significant (2 standard deviations) poleward of about 40° latitude. In the 45°±5° latitude band, the slope of linear fits to the annual zonally averaged changes for these wavelengths are about 13%, 3%, and 1% per decade in the southern hemisphere, and 10%, 3%, and 1% per decade in the northern hemisphere. Similarly derived values are estimated for DNA, plant, and erythema action spectra. Monthly values of exposure changes are larger towards higher latitudes and during the spring and winter months (e.g., 8.6%, 9.8%, and 5.1% per decade during April at 45°N). Erythemal UV-increases obtained from TOMS data disagree with previously determined ground based UV-decreases from an average of 8 U.S. Robertson-Berger sites.
TL;DR: In this article, the authors show that summer ice coverage has been below normal in recent years, with extreme minima in 1990, 1993, and 1995, and linkages are proposed between these ice anomalies and a sharp increase since 1989 in the frequency of low pressure systems over the central Arctic.
Abstract: Sea ice data from November 1978 through September 1995 for the Arctic Ocean and peripheral seas indicate that summer ice coverage has been below normal in recent years, with extreme minima in 1990, 1993, and 1995. The net trend in summer ice cover over the 17-year period is −0.6% per year, with the extent of the perennial ice pack reduced by 9% in 1990–1995 compared with 1979–1989. The reductions are greatest in the Siberian sector of the Arctic Ocean. Linkages are proposed between these ice anomalies and a sharp increase since 1989 in the frequency of low pressure systems over the central Arctic.
TL;DR: In this paper, the authors draw attention to the potential importance of ozone with alkenes in the primary production of Hox (HOx = OH, HO2 and RO2) radicals in various regions of the boundary layer.
Abstract: The reactions of ozone with alkenes have been shown recently to lead to the direct production of OH radi- cals. Organic peroxy radicals (RO2) probably accompany the production of OH. In this paper, we draw attention to the potential importance of these reactions in the primary production of HOx (HOx = OH, HO2 and RO2) radicals in various regions of the boundary layer. The reactions of ozone with anthropogenic alkenes are shown to be the most important source of HOx in many urban settings during the day and evening, and a significant source at night. The majority of HO x comes from trace quantities of alkenes with internal double bonds. Reaction of 03 with isoprene and terpenes can be an important source of HOx in forested regions; we show that these reactions are the dominant radical source in the late afternoon and into the night. This additional HOx source is expected to increase predicted OH concentrations compared to those calculated by models that do not include the O3-alkene source.
TL;DR: In this article, an intertropical Atlantic zonal divergent circulation anomaly is forced by the difference of sea surface temperature (SST) anomalies between the eastern equatorial parts of Pacific and Atlantic.
Abstract: Correlations between summer Sahel rainfall and Southern Oscillation Index has increased during the last thirty years. At high frequency time scale (periods lower than 8 years), an intertropical Atlantic zonal divergent circulation anomaly is forced by the difference of sea surface temperature (SST) anomalies between the eastern equatorial parts of Pacific and Atlantic. This zonal connection worked well during most of the E1 Nino/Southern Oscillation (ENSO) events occurring after 1970; positive/negative SST anomalies in the eastern Pacific/Atlantic led to rainfall deficits over the whole West Africa. At low frequency time scale (periods greater than 8 years), positive SST anomalies in the Indian ocean and in equatorial Pacific existing after 1970 have been associated with decreasing rainfall intensity over West Africa through another zonal divergent circulation. These different time scales remote SST forcings are combined to provide a global zonal divergent circulation anomaly pattern which could explain the strong association between Sahel drought and ENSO dynamics after 1970.
TL;DR: In this paper, high-resolution imaging of the microstructure of Fontainebleau sandstone allows a direct comparison between theoretical calculations and laboratory measurements, and they find that electrical resistivity and wetting phase residual saturation are both overestimated.
Abstract: High resolution imaging of the microstructure of Fontainebleau sandstone allows a direct comparison between theoretical calculations and laboratory measurements. While porosity, pore-volume-to-surface ratio, permeability, and end point relative permeability are well predicted by our calculations, we find that electrical resistivity and wetting phase residual saturation are both overestimated.
TL;DR: In this paper, it was shown that large-scale compound pahoehoe lava flows can thicken by at least an order of magnitude through gradual inflation and the same mechanism has been proposed for larger (10-20 km3) phoehoe flows in Iceland.
Abstract: Extensive flows of the Columbia River Basalt (CRB) Group in Washington, Oregon, and Idaho are dominantly inflated compound pahoehoe sheet lavas. Early studies recognized that CRB lavas are compound pahoehoe flows, with textures suggesting low flow velocities, but it was thought that the great thickness and extent of the major flows required very rapid emplacement as turbulent floods of lava over a period of days or weeks. However, small volume (< 1 km³) compound pahoehoe flows on Kilauea, Hawai'i, demonstrate that such flows can thicken by at least an order of magnitude through gradual inflation and the same mechanism has been proposed for larger (10–20 km3) pahoehoe flows in Iceland. The vertical distribution of vesicles and other morphologic features within CRB lava flows indicate that they grew similarly by inflation. Small pahoehoe lobes at the base and top of many CRB pahoehoe lava flows indicate emplacement in a gradual, piecemeal manner rather than as a single flood. We propose that each thick CRB sheet flow was active for months to years and that each group of flows produced by a single eruption (a flow field) was emplaced slowly over many years.
TL;DR: In this paper, the authors reported the mantle C flux in subduction zones based on He and C isotopes and CO 2 / 3 He ratios of high-temperature volcanic gases and medium and low-time temperature fumaroles in circum-Pacific volcanic regions.
Abstract: The potential impact of increases in atmospheric CO 2 is a topic of considerable controversy. Even though volcanic emission of CO 2 may be very small as compared to anthropogenic emissions, evaluation of natural degassing of CO 2 is important for any model of the geochemical C cycle and evolution of the Earth's atmosphere. We report here the mantle C flux in subduction zones based on He and C isotopes and CO 2 / 3 He ratios of high-temperature volcanic gases and medium- and low-temperature fumaroles in circum-Pacific volcanic regions. The calculated volcanic C flux of 3.1 x 10 12 moVa from subduction zones is larger than the flux of 1.5 x 10 12 mol/a from mid-ocean ridges, while contributions from the mantle in subduction zone is only 0.30 x 10 12 mol/a, equivalent to about 20 % of the C flux in mid-ocean ridges. Since the estimated mantle C flux in hot spot regions is insignificant, 0.029 x 10 12 mol/a, we propose that the global mantle C flux is 1.8 x 10 12 mol/a in total. The flux, if accumulated over 4.5 billion year of geological time, amounts to 8.3 x 10 21 mol which agrees well with 9 x 10 21 mol of the present inventory of C at the Earth's surface. This may support a continuous degassing model of C or the idea that subducted C is recycled into the lower mantle.
TL;DR: A 145 year gridded data set of tropospheric absorbing aerosol index was derived from the Nimbus-7 Total Ozone Mapping Spectrometer (TOMS) reflectivity difference between 340 and 380 nm channels based upon radiative transfer calculations.
Abstract: A 145 year gridded data set of tropospheric absorbing aerosol index was derived from the Nimbus-7 Total Ozone Mapping Spectrometer (TOMS) reflectivity difference between 340 and 380 nm channels Based upon radiative transfer calculations, the reflectivity anomaly between these two UV wavelength channels is very sensitive to smoke and soot aerosols from biomass burning and forest fires, volcanic ash clouds as well as desert mineral dust We demonstrate the ability of the TOMS instrument to detect and track smoke and soot aerosols generated by biomass burning in South America TOMS data can clearly distinguish between absorbing particles (smoke and dust) and non-absorbing aerosols (clouds and haze) For South American fires, comparisons of TOMS data are consistent with the limited amount of ground-based observations (Porto Nacional, Brazil) and show generally good agreement with other satellite imagery TOMS data shows large-scale transport of smoke particulates generated by the burning fires in the South America, which subsequentially advects smoke aerosols as far as the Atlantic Ocean east of Uruguay
TL;DR: In this paper, area-averaged anomalies of sea surface temperature (SSTA) and rainfall, developed from large scale data sets, have been used to explore the relative importance of Pacific versus Atlantic SST variability for inter-American climate variability at interannual time scales.
Abstract: Area-averaged anomalies of sea surface temperature (SSTA) and rainfall, developed from large scale data sets, have been used to explore the relative importance of Pacific versus Atlantic SST variability for inter-American (50°S–50°N) climate variability at interannual time scales. SSTA in the tropical Pacific and tropical North Atlantic are comparably related to rainfall north of 15°S, with clear associations distributed between the southeastern United States (US) in the north and northern South America in the south. Although NINO3 explains 25% of the variance of the North Atlantic SSTA index, the rainfall correlations with North Atlantic SSTA are for the most part opposite in sign to those with NINO3. Hence, a significant part of the Atlantic SSTA probably has a direct association with rainfall, rather than being merely an indirect proxy for Pacific ENSO linkages. In contrast to the North Atlantic, South Atlantic SSTA appear to be only related to rainfall in northeast (NE) Brazil. The entire region between Venezuela and NE Brazil appears to be sensitive to both the ITCZ and to antisymmetric configurations of SSTA across the ITCZ, in a manner consistent with the relationships between SST, surface wind and surface wind divergence fields, and with previous studies.
TL;DR: The ATMOS Fourier transform spectrometer was flown for a fourth time on the Space Shuttle as part of the ATLAS-3 instrument payload in November 1994 as discussed by the authors, where more than 190 sunrise and sunset occultation events provided measurements of more than 30 atmospheric trace gases at latitudes 3-49°N and 65-72°S, including observations both inside and outside the Antarctic polar vortex.
Abstract: The ATMOS Fourier transform spectrometer was flown for a fourth time on the Space Shuttle as part of the ATLAS-3 instrument payload in November 1994. More than 190 sunrise and sunset occultation events provided measurements of more than 30 atmospheric trace gases at latitudes 3–49°N and 65–72°S, including observations both inside and outside the Antarctic polar vortex. The instrument configuration, data retrieval methodology, and mission background are described to place in context analyses of ATMOS data presented in this issue.
TL;DR: In this paper, it is argued that approximately half of all 40Ar produced within the Earth since its formation is retained within the solid Earth and that this additional 40Ar is located principally in the lower mantle.
Abstract: The 40Ar budget of the Earth offers a powerful and straightforward argument in favour of the existence of a layered structure to the mantle.
Whereas K-Ar-isotope systematics have been included as part of various discussions of mantle structure previously a simple and straightforward argument is presented here. Because 40Ar is produced by 40K the amount of K in the Earth may be constrained from 40Ar budgets. The atmospheric 40Ar budget implies that approximately half of all 40Ar produced within the Earth since its formation is retained within the solid Earth. It is argued that this additional 40Ar is located principally in the lower mantle.
TL;DR: In this paper, four Antarctic marine mollusc shells, collected alive between 1917 and 1940, were analyzed by accelerator mass spectrometry to provide the first pre-bomb radiocarbon measurements of biogenic carbonates from the Southern Ocean.
Abstract: Four Antarctic marine mollusc shells, which were collected alive between 1917 and 1940, were analyzed by accelerator mass spectrometry to provide the first pre-bomb radiocarbon measurements of biogenic carbonates from the Southern Ocean. After correcting for the impact of fossil fuel combustion (Suess Effect), radiocarbon activities of the pre-bomb shells averaged −149.8±10.4‰. In contrast, the Δ 14C values for post-bomb molluscs, echinoderms, brachiopods and foraminifera averaged −96.1±25.2‰. These biogenic carbonate Δ 14C values are nearly identical to pre-bomb estimates (-148‰ to −152‰) and post-bomb measurements (−98.4±22.0‰) of the surface waters in the Southern Ocean. Average radiocarbon ages of the biogenic carbonates before and after 1950 (1303±84 years and 811±205 years, respectively), along with those from seals and penguins, indicate that the Antarctic marine radiocarbon reservoir has decreased in age by nearly 500 years during the second half of the 20th century. Marine species and seawater measurements firmly place the radiocarbon reservoir correction at 1300±100 years for calcareous marine fossils which are widespread, abundant and well-preserved organic materials for interpreting ice-sheet, climate and sea level impacts on the Antarctic marine ecosystem during the Holocene.
TL;DR: In this paper, the authors investigated if seismicity patterns following 1857 could be due to static stress changes generated by the 1857 earthquake and found that the correlation disappears around 1907, suggesting that tectonic loading began to overwhelm the effect of the 18 57 earthquake early in the 20 century.
Abstract: The great 1857 Fort Tejon earthquake is the largest earthquake to have hit southern California during the historic period. We investigated if seismicity patterns following 1857 could be due to static stress changes generated by the 1857 earthquake. When post-1857 earthquakes with unknown focal mechanisms were assigned strike-slip mechanisms with strike and rake determined by the nearest active fault, 13 of the 13 southern California M≥5.5 earthquakes between 1857 and 1907 were encouraged by the 1857 rupture. When post-1857 earthquakes in the Transverse Ranges with unknown focal mechanisms were assigned reverse mechanisms and all other events were assumed strike-slip, 11 of the 13 earthquakes were encouraged by the 1857 earthquake. These results show significant correlations between static stress changes and seismicity patterns. The correlation disappears around 1907, suggesting that tectonic loading began to overwhelm the effect of the 1857 earthquake early in the 20th century.
TL;DR: This article found that tropical cyclone rains have distinctly lower stable isotope ratios than rains in other tropical and summer precipitation systems, with a mean value slightly above that of water vapor near the sea surface.
Abstract: Tropical cyclone rains have distinctly lower stable isotope ratios than rains in other tropical and summer precipitation systems, with a mean value slightly above that of water vapor near the sea surface. The isotope ratios also decrease radially inward to the eye wall, but appear to be anomalously low even near the periphery of the rain shield. These findings indicate that tropical cyclones are highly efficient precipitation systems and suggest the use of stable isotope ratios as dynamic tracers of a tropical cyclone's water and energy budgets.
TL;DR: In this article, the authors analyzed precipitation and temperature trends in nine dryland regions for the period 1900 to 1994 and found no widespread desiccation in dryland climates, the African Sahel being the only region to demonstrate a significant drying trend, with the majority of the warming probably being unrelated to regional dryland effects.
Abstract: Precipitation and temperature trends in nine dryland regions are analysed for the period 1900 to 1994. No widespread desiccation in dryland climates is found, the African Sahel being the only region to demonstrate a significant drying trend. All dryland regions have warmed, however, with the majority of the warming probably being unrelated to regional dryland effects. This warming may have contributed to a worsening of the P/PE ratio in many of these dryland regions. Three African dryland regions are alone in showing a significant negative correlation between precipitation and temperature, contrasting with the relationship for global land areas of warmer years/decades being also wetter years/decades. The relative lack of warming in the Sahel is noted and increased atmospheric dust resulting from the increased desiccation of the region is suggested as a possible explanation.
TL;DR: In this article, the authors report results of laboratory experiments on smoke particles produced by combustion of eucalyptus, redwood, and cellulose which show that their water-soluble organic fraction is principally derived from smoldering combustion of the cellulosic fuel content.
Abstract: Natural and anthropogenic water-soluble inorganic aerosol species are efficient cloud condensation nuclei (CCN). Biomass smoke particles, although composed mostly of organic material, are also known to be efficient CCN. However, because smoke particles consist of mixtures of organic and inorganic species, it has not been established whether the organic component is intrinsically CCN active or is intrinsically inactive and rendered CCN active only through association with water-soluble inorganic species. Here we report results of laboratory experiments on smoke particles produced by combustion of eucalyptus, redwood, and cellulose which show that their water-soluble organic fraction is principally derived from smoldering combustion of the cellulosic fuel content. Because cellulose smoke particles are entirely organic, water soluble, and CCN active (at 0.5% and 0.3% supersaturation), we conclude that the water-soluble organic species in smoke particles from smoldering biomass combustion are responsible for their intrinsic CCN activity.
TL;DR: In this paper, the authors estimate the fault parameters of the 1896 Sanriku tsunami by numerically computing the tsunami and comparing the waveforms with those recorded at three tide gauge stations in Japan.
Abstract: The June 15, 1896 Sanriku earthquake generated devastating tsunamis with the maximum run-up of 25 m and caused the worst tsunami disaster in the history of Japan, despite its moderate surface wave magnitude (Ms=7.2) and weak seismic intensity. This is a typical tsunami earthquake, which generates anomalously larger tsunamis than expected from its seismic waves. Previously proposed mechanisms of tsunami earthquakes include submarine slumping and slow rupture in the accretionary wedge or in the subducted sediments. In this paper, we estimate the fault parameters of the 1896 tsunami earthquake by numerically computing the tsunami and comparing the waveforms with those recorded at three tide gauge stations in Japan. The result indicates that the tsunami source is very close to the Japan trench and the fault strike is parallel to the trench axis. The fault width is about 50 km, suggesting that the tsunami earthquake is a slow rupture in the subducted sediments beneath the accretionary wedge.
TL;DR: The authors coupled a global biome model iteratively with an atmospheric general circulation model to study the possible role of vegetation in the climate system, at the time of glacial inception 115,000 years ago.
Abstract: We coupled a global biome model iteratively with an atmospheric general circulation model to study the possible role of vegetation in the climate system, at the time of glacial inception 115,000 years ago. Orbital forcing alone was not sufficient to initiate glaciation when other components of the climate system were kept as present (atmospheric composition, oceans, biosphere and cryosphere). Summers were however cold enough to induce major vegetation shifts in high northern latitudes. Southward migration of the boreal forest/tundra limit helped to create favourable conditions for continental ice-sheet growth, with increasing snow depth and duration in Labrador, Arctic Canada and northern/western Fennoscandia. These results support a role for biogeophysical feedback in initiating glaciations.
TL;DR: In this article, the authors perform joint inversions for mantle viscosity of geophysical observables associated with both mantle convection and glacial isostatic adjustment (GIA).
Abstract: We perform joint inversions for mantle viscosity of geophysical observables associated with both mantle convection and glacial isostatic adjustment (GIA). Our data include coefficients of the non-hydrostatic geoid (up to degree 8) and decay times associated with post-glacial relative sea level (RSL) variations in Hudson Bay and Fennoscandia. We find that both data sets may be reconciled using a single profile of mantle viscosity which is characterized by a significant increase, with depth, across this region. This result weakens previous arguments that the mantle rheology has significant transient effects. The viscosity profiles we obtain are found to reconcile the observed free air gravity anomaly over Hudson Bay.
TL;DR: The most recent years of 1991 through 1994 have experienced the quietest tropical cyclone activity on record in terms of frequency of tropical storms, hurricanes, and intense hurricanes, while the maximum intensity attained by the strongest hurricane each year has not shown significant change as mentioned in this paper.
Abstract: There is concern that the enhanced greenhouse effect may be affecting extreme weather events such as tropical cyclones. The North Atlantic basin offers a reliable, long-term record of tropical cyclone activity, though it may not be representative of tropical cyclones throughout the rest of the tropics. The most recent years of 1991 through 1994 have experienced the quietest tropical cyclone activity on record in terms of frequency of tropical storms, hurricanes, and intense hurricanes. This was followed by the 1995 hurricane season, one of the busiest in the past 50 years. Despite 1995's activity, a long-term (five decade) downward trend continues to be evident primarily in the frequency of intense hurricanes. In addition, the mean maximum intensity (i.e., averaged over all cyclones in a season) has decreased, while the maximum intensity attained by the strongest hurricane each year has not shown a significant change.