scispace - formally typeset
Search or ask a question

Showing papers in "Geophysical Research Letters in 2001"


Journal ArticleDOI
TL;DR: The Atlantic Multidecadal Oscillation (AMO) as mentioned in this paper is a 65-80 year cycle with a 0.4 C range, referred to as the AMO by Kerr (2000).
Abstract: North Atlantic sea surface temperatures for 1856-1999 contain a 65-80 year cycle with a 0.4 C range, referred to as the Atlantic Multidecadal Oscillation (AMO) by Kerr (2000). AMO warm phases occurred during 1860- 1880 and 1940-1960, and cool phases during 1905-1925 and 1970-1990. The signal is global in scope, with a posi- tively correlated co-oscillation in parts of the North Pa- cic, but it is most intense in the North Atlantic and cov- ers the entire basin there. During AMO warmings most of the United States sees less than normal rainfall, including Midwest droughts in the 1930s and 1950s. Between AMO warm and cool phases, Mississippi River outflow varies by 10% while the inflow to Lake Okeechobee, Florida varies by 40%. The geographical pattern of variability is influenced mainly by changes in summer rainfall. The winter patterns of interannual rainfall variability associated with El Ni~no- Southern Oscillation are also signicantly changed between AMO phases.

2,582 citations


Journal ArticleDOI
TL;DR: The influence of the Indian Ocean Dipole (IOD) on the interannual variability of Indian summer monsoon rainfall (ISMR) has been investigated for the period 1958-1997.
Abstract: The influence of the recently discovered Indian Ocean Dipole (IOD) on the interannual variability of the Indian summer monsoon rainfall (ISMR) has been investigated for the period 1958-1997. The IOD and the El Nino/Southern Oscillation (ENSO) have complementarily affected the ISMR during the last four decades. Whenever the ENSO-ISMR correlation is low (high), the IOD-ISMR correlation is high (low). The IOD plays an important role as a modulator of the Indian monsoon rainfall, and influences the correlation between the ISMR and ENSO. We have discovered that the ENSO-induced anomalous circulation over the Indian region is either countered or supported by the IOD-induced anomalous meridional circulation cell, depending upon the phase and amplitude of the two major tropical phenomena in the Indo-Pacific sector.

920 citations


Journal ArticleDOI
TL;DR: In this article, the connection between Arctic Oscillation (AO) and variability of East Asian winter monsoon is investigated, and the correlation coefficient between the AO and the Siberian High intensity index is −0.48 for period 1958-98.
Abstract: In this study, the connection between Arctic Oscillation (AO) and variability of East Asian winter monsoon is investigated. Two indices are chosen to describe the winter monsoon. One is the intensity of the Siberian High, defined as the average SLP over the center region, and the other is the temperature of eastern China, averaged over 76 surface stations. These are two tightly related components, correlate at −0.62 for period 1951–99. Temperature drops by 0.64 degrees Celsius in association with a one standard deviation increase in Siberian High intensity. It is found that there are significant out-of-phase relationships between the AO and the East Asian winter monsoon. The correlation coefficient between the AO and the Siberian High intensity index is −0.48 for period 1958–98. AO is also significantly correlated with the temperature of eastern China at 0.34. However, when the linear trend is removed, the correlation between AO and temperature is no longer significant. But the strong connection between the AO and Siberian High, and between the Siberian High and temperature are still significant. These results reveal that the AO influences the East Asian winter monsoon through the impact on the Siberian High. Negative phase of the AO is concurrent with a stronger East Asian Trough and an anomalous anticyclonic flow over Urals at the middle troposphere (500hPa). Both the AO and the Eurasian pattern play important roles in changes of the Siberian High and/or East Asian winter monsoon. They account for 13.0% and 36.0% of the variance in the Siberian High respectively.

659 citations


Journal ArticleDOI
TL;DR: In this article, a recent version of the CCCma climate model exhibits a much more symmetric warming, compared to an earlier version, and agrees somewhat better with observed 20th century trends.
Abstract: Climate change simulations made with coupled global climate models typically show a marked hemispheric asymmetry with more warming in the northern high latitudes than in the south. This asymmetry is ascribed to heat uptake by the ocean at high southern latitudes. A recent version of the CCCma climate model exhibits a much more symmetric warming, compared to an earlier version, and agrees somewhat better with observed 20th century trends. This is associated with an improved parameterization of ocean mixing which results in a decrease in heat penetration into the Southern Ocean, in accord with earlier ocean-only and simple coupled model investigations. The global average warming and the net penetration of heat into the global ocean (and hence its thermal expansion) are essentially unchanged. Observed trends in sea-ice extent over the past two decades exhibit hemispheric asymmetry with a statistically significant decrease in northern but not in southern ice cover. Both model versions are consistent with these observations implying that observed ice extent is not yet an indicator of asymmetry in future global warming. Taken together, these results suggest that southern hemisphere climate warming at a rate comparable to that in the northern hemisphere should be considered a realistic possiblity.

500 citations


Journal ArticleDOI
TL;DR: In this article, the authors used synthesis inversion to compare the uncertainties in regional sources calculated from a moderate-sized surface network and either global or oceanic coverage of column-integrated pseudodata.
Abstract: This paper aims to establish the required precision for column-integrated CO2 concentration data to be useful in constraining surface sources. We use the method of synthesis inversion and compare the uncertainties in regional sources calculated from a moderate-sized surface network and either global or oceanic coverage of column-integrated pseudodata. With a simple measure of total uncertainty, we require precision of monthly averaged column data better than 2.5 ppmv on a 8° × 10° footprint for comparable performance with the existing surface network. If coverage is only oceanic we require 1.5 ppmv precision. We recommend more detailed studies on the feasibility of obtaining such observations from current and future satellite instruments.

477 citations


Journal ArticleDOI
TL;DR: The first radio occultation measurements of the CHAMP (CHAllenging Minisatellite Payload) satellite using Global Positioning System (GPS) signals have been performed on February 11, 2001.
Abstract: The first radio occultation measurements of the CHAMP (CHAllenging Minisatellite Payload) satellite using Global Positioning System (GPS) signals have been performed on February 11, 2001. By the end of April 2001 more than 3000 occultations were recorded. Globally distributed vertical profiles of dry temperature and specific humidity are derived, of which a set of 438 vertical dry temperature profiles is compared with corresponding global weather analyses. The observed temperature bias is less than ∼1 K above the tropopause and even less than 0.5 K in the altitude interval from 12 to 20 km at latitudes >30°N. About 55% of the compared profiles reached the last kilometer above the Earth's surface. In spite of the activated anti-spoofing mode of the GPS system the state-of-the-art GPS flight receiver aboard CHAMP combined with favorable antenna characteristics allows for atmospheric sounding with high accuracy and vertical resolution.

467 citations


Journal ArticleDOI
TL;DR: In this paper, a short climate simulation with a 2D cloud resolving model (CRM) installed into each grid column of an NCAR Community Climate System Model (CCSM) is presented.
Abstract: Preliminary results of a short climate simulation with a 2-D cloud resolving model (CRM) installed into each grid column of an NCAR Community Climate System Model (CCSM) are presented. The CRM replaces the conventional convective and stratiform cloud parameterizations, and allows for explicit computation of the global cloud fraction distribution for radiation computations. The extreme computational cost of the combined CCSM/CRM model has thus far limited us to a two-month long climate simulation (December-January) using 2.8° × 2.8° resolution. The simulated geographical distributions of the total rainfall, precipitable water, cloud cover, and Earth radiation budget, for the month of January, look very reasonable.

454 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used InSAR data to derive continuous maps for three orthogonal components of the co-seismic surface displacement field due to the 1999 M_w7.1 Hector Mine earthquake in southern California.
Abstract: We use Interferometric Synthetic Aperture Radar (InSAR) data to derive continuous maps for three orthogonal components of the co-seismic surface displacement field due to the 1999 M_w7.1 Hector Mine earthquake in southern California. Vertical and horizontal displacements are both predominantly antisymmetric with respect to the fault plane, consistent with predictions of linear elastic models of deformation for a strike-slip fault. Some deviations from symmetry apparent in the surface displacement data may result from complexity in the fault geometry.

452 citations


Journal ArticleDOI
TL;DR: In this article, an adjustment factor was proposed to account for the probabilistic missing energy and apply it to three previously studied data sets with limited recording bandwidth to eliminate much of the moment dependence of radiated energy found previously.
Abstract: Seismic energy is distributed across a wide fre- quency band so that limited bandwidth recording can lead tosubstantialunderestimates oftheradiatedseismic energy or introduce an articial upper bound of radiated energy. We estimate an adjustment factor to account for the proba- ble missing energy and apply it to three previously studied data sets with limited recording bandwidth. We nd that thisadjustment,togetherwithaccountingforpossibly miss- ing events, eliminates much of the moment dependence of radiated energy found previously. We obtain a nearly con- stant ratio of radiated energy to seismic moment, 310 5 , or 1 MPa of apparent stress drop, over 17 orders of seismic moment. This suggests that deviation from similarity of the energy radiation for seismic events essentially the entire observablerangeofearthquakesizemaynotyetberesolved.

414 citations


Journal ArticleDOI
TL;DR: In this paper, a connection between the mid-latitude and tropical Pacific is identified in a coupled general circulation model (CGCM) by a seasonal coupling between winter midlatitude atmospheric circulation anomalies, and summer equatorial wind stress anomalies.
Abstract: A connection between the mid-latitude and tropical Pacific is identified in a coupled general circulation model (CGCM) The connection involves a seasonal coupling between winter mid-latitude atmospheric circulation anomalies, and summer equatorial wind stress anomalies The seasonal coupling results from a “footprinting” mechanism, in which the summer tropical atmosphere responds to subtropical sea surface temperature (SST) anomalies that are generated by the mid-latitude atmospheric variability during the previous winter Details of the connection, and of the footprinting mechanism are presented Implications for interannual ENSO and decadal ENSO-like variability are discussed

413 citations


Journal ArticleDOI
TL;DR: In this article, an interannual dipole event that is seasonally phase-locked to the austral summer was found to produce above normal rainfall over many regions in south-central Africa.
Abstract: Sea surface temperature (SST) anomalies in the subtropical southern Indian Ocean show interannual dipole events that are seasonally phase-locked to the austral summer. A positive phase of the event is characterized by cold SST anomalies in the eastern part i.e. off Australia and warm SST anomalies in the southwestern part, south of Madagascar. Such an event is found to produce above normal rainfall over many regions in south-central Africa. The cooling of SST in the eastern part is mainly caused by the enhanced evaporation. This is associated with stronger winds along the eastern edge of the subtropical high, which is strengthened and shifted slightly to the south during the event. On the other hand, relative decrease in the seasonal latent heat loss due to reduced evaporation dominates the warming in the southwestern part. Evolution of such subtropical dipole events shows quite a contrast to that of the tropical dipole events discovered recently in the Indian Ocean.

Journal ArticleDOI
TL;DR: In this article, the authors show that landslide data sets from New Zealand and Taiwan exhibit two scaling regimes, separated by a crossover scale that is purely an artefact of mapping resolution, and propose a general model for the size distribution of observed landslides which can account for the whole population of mapped slope failures.
Abstract: Landslide size distributions generally exhibit power-law scaling over a limited scale range. The range is set by the mapping resolution, by the number of observed events, and by the slope failure process itself. This property of self-similarity is an important insight into the physics of hillslope failure. Typically, however, a large proportion of the landslide data does not fit a simple power law. These data are always ignored in order to characterize the scaling. We show that landslide data sets from New Zealand and Taiwan exhibit two scaling regimes, separated by a crossover scale that is purely an artefact of mapping resolution. Below this scale the landslide data are undersampled. We propose a general model for the size distribution of observed landslides which can account for the whole population of mapped slope failures. The model quantifies the undersampling of smaller landslides and provides an improved estimation of the power-law scaling of larger landslides. Estimates of this scaling suggest that the area disturbed by landsliding, and perhaps the landslide sediment yield, are essentially dependent on the frequency of smaller landslides. Higher resolution landslide maps will be required in order to quantify these fluxes. Our results also indicate that the probability of extreme landslide events is less than previous studies would predict.

Journal ArticleDOI
TL;DR: In this paper, the column aerosol particle number and low cloud microphysical parameters derived from AVHRR remote sensing were compared over ocean for four months in 1990, and the satellite data/model comparison range from −0.7 to −1.7 Wm−2.
Abstract: The column aerosol particle number and low cloud microphysical parameters derived from AVHRR remote sensing are compared over ocean for four months in 1990. There is a positive correlation between cloud optical thickness and aerosol number concentration, whereas the effective particle radius has a negative correlation with aerosol number. The cloud liquid water path (LWP), on the other hand, tends to be constant with no large dependence on aerosol number. This result contrasts with results from recent model simulations which imply that there is a strong positive feedback between LWP and aerosol number concentration. Estimates for indirect forcing over oceans derived from the satellite data/model comparison range from −0.7 to −1.7 Wm−2.

Journal ArticleDOI
TL;DR: Horizontal transport through this cold trap region causes air parcels that reach the tropopause at other longitudes to be dehydrated to the very low saturation mixing ratios characteristic of the cold trap, and hence can explain why observed tropical stratospheric water vapor mixing ratios are often lower than the saturation mixing ratio at the mean Tropopause temperature as discussed by the authors.
Abstract: The coldest tropopause temperatures occur over the equatorial West Pacific during Northern Hemisphere winter. Horizontal transport through this “cold trap” region causes air parcels that reach the tropopause at other longitudes to be dehydrated to the very low saturation mixing ratios characteristic of the cold trap, and hence can explain why observed tropical stratospheric water vapor mixing ratios are often lower than the saturation mixing ratio at the mean tropopause temperature. Horizontal transport of water vapor can also explain how a persistent layer of subvisible cirrus can exist near the tropopause in the cold trap even though observations suggest that there is diabatic cooling and subsidence, rather than diabatic heating and rising through the tropopause in this region. Thus, horizontal transport in the tropical transition layer in the vicinity of the tropopause plays an important role in the water balance of the stratosphere.

Journal ArticleDOI
TL;DR: In this article, the effects of long-wavelength (> 100 km), seasonal variability in continental water storage on vertical crustal motions are assessed, and the modeled vertical displace-ments (ARM) have root-mean-square (RMS) values for 1994-1998 as large as 8 mm, with ranges up to 30 mm, and are predominantly annual in character.
Abstract: The effects of long-wavelength (> 100 km), seasonal variability in continental water storage on vertical crustal motions are assessed. The modeled vertical displace- ments (ARM) have root-mean-square (RMS) values for 1994- 1998 as large as 8 mm, with ranges up to 30 mm, and are predominantly annual in character. Regional strains are on the order of 20 nanostrain for tilt and 5 nanostrain for hori- zontal deformation. We compare ArM with observed Global Positioning System (GPS) heights (Aro) (which include ad- justments to remove estimated effects of atmospheric pres- sure and annual tidal and non-tidal ocean loading) for 147 globally distributed sites. When the Aro time series are ad- justed by ArM, their variances are reduced, on average, by an amount equal to the variance of the ArM. Of the Aro time series exhibiting a strong annual signal, more than half

Journal ArticleDOI
TL;DR: In this paper, a parameterization for the internal wave drag over rough topography is included as a dissipative mechanism in a model for the barotropic tides, which substantially increases the amount of modeled tidal dissipation in the deep ocean, bringing dissipation levels there into agreement with recent estimates from TOPEX/Poseidon altimetry data.
Abstract: The traditional model of tidal dissipation is based on a frictional bottom boundary layer, in which the work done by bottom drag is proportional to a drag coefficient and the velocity cubed. However, away from shallow, coastal regions the tidal velocities are small, and the work done by the bottom boundary layer can account for only weak levels of dissipation. In the deep ocean, the energy flux carried by internal waves generated over rough topography dominates the energy transfer away from barotropic flow. A parameterization for the internal wave drag over rough topography is included as a dissipative mechanism in a model for the barotropic tides. Model results suggest that the inclusion of this dissipation mechanism improves hydro-dynamical models of the ocean tide. It also substantially increases the amount of modeled tidal dissipation in the deep ocean, bringing dissipation levels there into agreement with recent estimates from TOPEX/Poseidon altimetry data.

Journal ArticleDOI
TL;DR: In this article, the authors present the first analysis of global and hemispheric surface warming trends that attempts to quantify the major sources of uncertainty, such as urbanization, changing land-based observing practices and SST bias corrections.
Abstract: We present the first analysis of global and hemispheric surface warming trends that attempts to quantify the major sources of uncertainty. We calculate global and hemispheric annual temperature anomalies by combining land surface air temperature and sea surface temperature (SST) through an optimal averaging technique. The technique allows estimation of uncertainties in the annual anomalies resulting from data gaps and random errors. We add independent uncertainties due to urbanisation, changing land-based observing practices and SST bias corrections. We test the accuracy of the SST bias corrections, which represent the largest source of uncertainty in the data, through a suite of climate model simulations. These indicate that the corrections are likely to be fairly accurate on an annual average and on large space scales. Allowing for serial correlation and annual uncertainties, the best linear fit to annual global surface temperature gives an increase of 0.61 ± 0.16°C between 1861 and 2000.

Journal ArticleDOI
TL;DR: In this paper, it is shown that bacteria in cloud droplets collected at high altitudes are actively growing and reproducing at temperatures at or below 0°C, and that since ∼60% of the earth surface is covered by clouds, cloud water should be considered as a microbial habitat.
Abstract: It is well known that the atmosphere is a conveyor of microorganisms, and that bacteria can act as ice or cloud condensation nuclei, but clouds have not been considered as a site where organisms can live and reproduce. Here we show that bacteria in cloud droplets collected at high altitudes are actively growing and reproducing at temperatures at or below 0°C. Since ∼60% of the earth surface is covered by clouds, cloud water should be considered as a microbial habitat.

Journal ArticleDOI
TL;DR: P-wave and S-wave delay times from the broadband data of the southern Africa seismic experiment have been inverted to obtain three-dimensional images of velocity perturbations in the mantle beneath southern Africa as discussed by the authors.
Abstract: P-wave and S-wave delay times from the broadband data of the southern Africa seismic experiment have been inverted to obtain three-dimensional images of velocity perturbations in the mantle beneath southern Africa. High velocity mantle roots appear to extend to depths of at least 250 km, and locally to depths of 300 km beneath the Kaapvaal and Zimbabwe cratons. Thick roots are confined to the Archean cratons, with no evidence for similar structures beneath the adjacent Proterozoic mobile belts. The Kaapvaal craton was modified ca. 2.05 Ga by the Bushveld magmatic event, which affected a broad swath of cratonic mantle beneath and to the west of the exposed Bushveld Complex. The mantle beneath the extended Bushveld province is characterized by seismic velocities lower than those observed in regions of undisturbed cratonic mantle. The mantle beneath the Limpopo Belt, an Archean collisional zone sandwiched between the Kaapvaal and Zimbabwe cratons, exhibits a cratonic signature.

Journal ArticleDOI
TL;DR: In this article, the authors used a linear velocity analysis for forearc locations in Nicaragua and Guatemala to predict 14 2m m yr 1 of northwestward trench-parallel slip of the forearc relative to the Cocos-Caribbean plate, possibly decreasing inmagnitude inEl Salvador and Guatemala, where extension east of the volcanic arc complicates the tectonic setting.
Abstract: Velocities from 153 continuously-operatingGPS sites on the Caribbean, North American, and Pacic plates arecombinedwith61newlyestimatedPacic-Cocosseafloor spreading rates and additional marine geophysical data to deriveanewestimate of present-dayCocos-Caribbean plate motion. AcomparisonofthepredictedCocos-Caribbean di- rectiontoslipdirectionsofnumerousshallow-thrustsubduc- tion earthquakes from the Middle America trench between Costa Rica and Guatemala shows the slip directions to be deflected 10 clockwise from the plate convergence direc- tion, supporting thehypothesisthatfrequentdextralstrike- slip earthquakes along the Central American volcanic arc result from partitioning of oblique Cocos-Caribbean plate convergence. Linear velocity analysis for forearc locations in Nicaragua and Guatemala predicts 14 2m m yr 1 of northwestward trench-parallel slip of the forearc relative to theCaribbean plate, possibly decreasing inmagnitude inEl Salvador and Guatemala, where extension east of the vol- canic arc complicates the tectonic setting.

Journal ArticleDOI
TL;DR: The upwelling along the Java-Sumatra Indian Ocean coasts is a response to regional winds associated with the monsoon climate as discussed by the authors, which migrates westward and toward the equator during the southeast monsoon (June to October).
Abstract: Upwelling along the Java-Sumatra Indian Ocean coasts is a response to regional winds associated with the monsoon climate The upwelling center with low sea surface temperature migrates westward and toward the equator during the southeast monsoon (June to October) The migration path depends on the seasonal evolution of alongshore winds and latitudinal changes in the Coriolis parameter Upwelling is eventually terminated due to the reversal of winds associated with the onset of the northwest monsoon and impingement of Indian Ocean equatorial Kelvin waves Significant interannual variability of the Java-Sumatra upwelling is linked to ENSO through the Indonesian throughflow (ITF) and by anomalous easterly wind During El Nino episodes, the Java-Sumatra upwelling extends in both time (into November) and space (closer to the equator) During El Nino (La Nina), the ITF carries colder (warmer) water shallowing (deepening) thermocline depth and enhancing (reducing) upwelling strength

Journal ArticleDOI
TL;DR: In this paper, the authors used satellite spectral measurements and ground-based sky measurements to demonstrate that Saharan dust absorption of solar radiation is several times smaller than the current international standards.
Abstract: Dust absorption of solar radiation is not well known due to limitations in the accuracy of in situ measurements. Here we report two new independent remote sensing techniques that provide sensitive measurements of dust absorption. One uses satellite spectral measurements, the second ground based sky measurements. Both techniques demonstrate that Saharan dust absorption of solar radiation is several times smaller than the current international standards. For example, at wavelength of 0.64 µm the dust single scattering albedo is reported here as 0.97±0.02 rather than 0.87±0.04 in recent review.

Journal ArticleDOI
TL;DR: In this article, the authors show that there is a positive feedback between the climate system and the carbon cycle, and that the gain of this climate-carbon cycle feedback to be 10% at 2 × CO2 and 20% at 4 × CO 2.
Abstract: Future climate change due to increased atmo- sphericCO 2 may affect land and ocean efficiency to absorb atmosphericCO 2. Here, using climate and carbon three- dimensional models forced by a 1% per year increase in at- mosphericCO 2, we show that there is a positive feedback between the climate system and the carbon cycle. Climate change reduces land and ocean uptake of CO2 ,r espec tively by 54% and 35% at 4 × CO2 . This negative impact im- plies that for prescribed anthropogenic CO2 emissions, the atmosphericCO 2 would be higher than the level reached if climate change does not affect the carbon cycle. We esti- mate the gain of this climate-carbon cycle feedback to be 10% at 2 × CO2 and 20% at 4 × CO2 . This translates into a 15% higher mean temperature increase.

Journal ArticleDOI
TL;DR: In this article, the authors examined the ionospheric total electron content (TEC) served by a network of the global positioning system (GPS) receivers in Taiwan area.
Abstract: On 20 September1999 UT (21 Septemberin local time, LT) a large earthquake Mw=7.7 struck central Taiwan nearthe small town of Chi-Chi. The greatest plasma frequency in the ionosphere, foF2, observed by the Chung- Li ionosonde (25.0 ◦ N, 121.2 ◦ E) reveals three clear precur- sors at 1, 3, and 4 days prior to the earthquake. This paper examines the ionospheric total electron content (TEC) ob- served by a network of the global positioning system (GPS) receivers in Taiwan area. It is found that variations in foF2 and overhead TEC recorded at Chung-Li have a similar ten- dency. Combining the data of the network of 13 GPS re- ceivers, time, and spatial variations of TEC prior to the Chi- Chi earthquake are examined. Results show that the equa- torial anomaly crest moves equatorward and its TEC value significantly decreases 1, 3, and 4 days before the earth- quake. A comparison between the disturbed and reference (previous 15-day median) days confirms that TEC decreases significantly around the epicenter in the afternoons of these days. Finally, possible mechanisms are proposed and dis- cussed.

Journal ArticleDOI
TL;DR: In this paper, it was shown that both the magnitude and spectral dependence of light absorption are controlled by the size of graphitic clusters within the material, and can be described using the optical band-gap theory.
Abstract: Optical characteristics of particles that absorb visible light are needed to model their effects on atmospheric radiation. Light absorption by particles emitted from low-technology coal combustion has exhibited a strong spectral dependence. I investigate various explanations for this phenomenon and conclude that a spectrally dependent imaginary refractive index is the most plausible. Following previous work on the structure of amorphous carbon, I propose that both the magnitude and spectral dependence of light absorption are controlled by the size of graphitic clusters within the material, and can be described using the optical band-gap theory. This hypothesis is an alternative to the current measurement divisions of light-absorbing “black carbon” and non-absorbing “organic carbon,” and offers an explanation for preferential absorption at blue wavelengths that may extend to ultraviolet wavelengths.

Journal ArticleDOI
TL;DR: A transect of climate sensitive tree ring-width chronologies from coastal western North America provides a useful proxy index of North Pacic ocean-atmosphere variability since 1600 AD.
Abstract: A transect of climate sensitive tree ring-width chronologies from coastal western North America provides a useful proxy index of North Pacic ocean-atmosphere variability since 1600 AD. Here we use this high-resolution record to identify intervals of an enhanced interdecadal cli- mate signal in the North Pacic, and to assess the timing and magnitude of abrupt shifts in this system. In the con- textofthisrecord,thestep-likeclimateshiftthatoccurredin 1976-1977 is not a unique event, with similar events having occurredfrequentlyduringthepast400years. Furthermore, most of the pre-instrumental portion of this record is char- acterized by pronounced interdecadal variability, while the secularportionismorestronglyinterannualinnature. Ifthe 1976-1977 event marks a return to this mode of variability there may be signicant consequences for natural resources management in the North Pacic Sector.

Journal ArticleDOI
TL;DR: In this paper, the phase center of the interferometric depth, or penetration depth, was estimated using InSAR data in Greenland and Alaska at the C- (5.6 cm wave length) and L-band (24 cm) frequencies.
Abstract: Digital elevation models of glaciated terrain produced by the NASA/Jet Propulsion Laboratory (JPL) airborne interferometric synthetic-aperture radar (InSAR) instrument in Greenland and Alaska at the C- (5.6 cm wave-length) and L-band (24-cm) frequencies were compared with surface elevation measured from airborne laser altimetry to estimate the phase center of the interferometric depth, or penetration depth, δp. On cold polar firn at Greenland summit, δp = 9±2m at C- and 14±4m at L-band. On the exposed ice surface of Jakobshavn Isbrae, west Greenland, δp = 1±2 m at C- and 3±3 m at L-band except on smooth, marginal ice where δp = 15±5 m. On colder marginal ice of northeast Greenland, δp reaches 60 to 120 m at L-band. On the temperate ice of Brady Glacier, Alaska, δp is 4±2 m at C- and 12±6 m at L-band, with little dependence on snow/ice conditions. The implications of the results on the scientific use of InSAR data over snow/ice terrain is discussed.

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed ten data sets covering the period 1954-2000 to show a 1% per year increase in stratospheric water vapor, which is unlikely the result of a single event but rather indicative of long-term climate change.
Abstract: Ten data sets covering the period 1954-2000 are analyzed to show a 1% per year increase in stratospheric water vapor. The trend has persisted for at least 45 years, hence is unlikely the result of a single event but rather indicative of long-term climate change. A long-term change in the transport of water vapor into the stratosphere is the most probable cause.

Journal ArticleDOI
TL;DR: In this article, a coupled atmosphere-biosphere-ocean model of intermediate complexity was used to quantify the relative magnitude of these processes as well as their synergisms by using a coupled model.
Abstract: Large-scale changes in land cover affect near- surface energy, moisture and momentum fluxes owing to changes in surface structure (referred to as biogeophysical effects) and the atmospheric CO2 concentration owing to changes in biomass (biogeochemical effects). Here we quan- tify the relative magnitude of these processes as well as their synergisms by using a coupled atmosphere-biosphere-ocean model of intermediate complexity. Our sensitivity studies show that tropical deforestation tends to warm the planet because the increase in atmospheric CO2 and hence, at- mospheric radiation, outweighs the biogeophysical effects. In mid and high northern latitudes, however, biogeophysi- cal processes, mainly the snow-vegetation-albedo feedback through its synergism with the sea-ice-albedo feedback, win over biogeochemical processes, thereby eventually leading to a global cooling in the case of deforestation and to a global warming, in the case of afforestation.

Journal ArticleDOI
TL;DR: In this paper, the authors suggest that a positive ocean-atmosphere feedback operating through longwave radiation and associated cloudiness is responsible for the Western Hemisphere warm pool (WHWP) SST anomalies.
Abstract: The Western Hemisphere warm pool (WHWP) of water warmer than 285°C extends from the eastern North Pacific to the Gulf of Mexico and the Caribbean, and at its peak, overlaps with the tropical North Atlantic It has a large seasonal cycle and its interannual fluctuations of area and intensity are significant Surface heat fluxes warm the WHWP through the boreal spring to an annual maximum of SST and areal extent in the late summer/early fall, associated with eastern North Pacific and Atlantic hurricane activities and rainfall from northern South America to the southern tier of the United States SST and area anomalies occur at high temperatures where small changes can have a large impact on tropical convection Observations suggest that a positive ocean-atmosphere feedback operating through longwave radiation and associated cloudiness is responsible for the WHWP SST anomalies Associated with an increase in SST anomalies is a decrease in atmospheric sea level pressure anomalies and an anomalous increase in atmospheric convection and cloudiness The increase in convective activity and cloudiness results in less longwave radiation loss from the surface, which then reinforces SST anomalies