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Showing papers in "Geophysical Research Letters in 2003"


Journal ArticleDOI
TL;DR: Wang et al. as mentioned in this paper explored the relationship between column aerosol optical thickness (AOT) derived from the Moderate Resolution Imaging SpectroRadiometer (MODIS) on the Terra/Aqua satellites and hourly fine particulate mass (PM2.5) measured at the surface at seven locations in Jefferson county, Alabama for 2002.
Abstract: [1] We explore the relationship between column aerosol optical thickness (AOT) derived from the Moderate Resolution Imaging SpectroRadiometer (MODIS) on the Terra/Aqua satellites and hourly fine particulate mass (PM2.5) measured at the surface at seven locations in Jefferson county, Alabama for 2002. Results indicate that there is a good correlation between the satellite-derived AOT and PM2.5 (linear correlation coefficient, R = 0.7) indicating that most of the aerosols are in the well-mixed lower boundary layer during the satellite overpass times. There is excellent agreement between the monthly mean PM2.5 and MODIS AOT (R > 0.9), with maximum values during the summer months due to enhanced photolysis. The PM2.5 has a distinct diurnal signature with maxima in the early morning (6:00 8:00AM) due to increased traffic flow and restricted mixing depths during these hours. Using simple empirical linear relationships derived between the MODIS AOT and 24hr mean PM2.5 we show that the MODIS AOT can be used quantitatively to estimate air quality categories as defined by the U.S. Environmental Protection Agency (EPA) with an accuracy of more than 90% in cloud-free conditions. We discuss the factors that affect the correlation between satellite-derived AOT and PM2.5 mass, and emphasize that more research is needed before applying these methods and results over other areas. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 3300 Meteorology and Atmospheric Dynamics. Citation: Wang, J., and S. A. Christopher, Intercomparison between satellitederived aerosol optical thickness and PM2.5 mass: Implications for air quality studies, Geophys. Res. Lett., 30(21), 2095, doi:10.1029/ 2003GL018174, 2003.

796 citations



Journal ArticleDOI
TL;DR: In this article, the ice nucleating ability of aerosol particles in air masses over Florida having sources from North Africa has been measured, and the concentrations of ice nuclei within dust layers at particle sizes below 1 pn exceeded 1/cu cm.
Abstract: Measurements of the ice nucleating ability of aerosol particles in air masses over Florida having sources from North Africa support the potential importance of dust aerosols for indirectly affecting cloud properties and climate. The concentrations of ice nuclei within dust layers at particle sizes below 1 pn exceeded 1/cu cm; the highest ever reported with our device at temperatures warmer than homogeneous freezing conditions. These measurements add to previous direct and indirect evidence of the ice nucleation efficiency of desert dust aerosols, but also confirm their contribution to ice nuclei populations at great distances from source regions.

745 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present reconstructions of Northern and Southern Hemisphere mean surface temperature over the past two millennia based on high-resolution "proxy" temperature data which retain millennial-scale variability.
Abstract: [1] We present reconstructions of Northern and Southern Hemisphere mean surface temperature over the past two millennia based on high-resolution ‘proxy’ temperature data which retain millennial-scale variability. These reconstructions indicate that late 20th century warmth is unprecedented for at least roughly the past two millennia for the Northern Hemisphere. Conclusions for the Southern Hemisphere and global mean temperature are limited by the sparseness of available proxy data in the Southern Hemisphere at present.

718 citations


Journal ArticleDOI
TL;DR: In this paper, a global simulation of the ocean response to atmospheric wind and pressure forcing has been run during the Topex/Poseidon (T/P) period (1992-2002), using a new hydrodynamic finite element (FE) model, MOG2D-G.
Abstract: [1] A global simulation of the ocean response to atmospheric wind and pressure forcing has been run during the Topex/Poseidon (T/P) period (1992–2002), using a new hydrodynamic finite element (FE) model, MOG2D-G. Model outputs are compared to in situ observations with tide gauge data (TG) and bottom pressure gauge data (BPR), and also with T/P altimetric cross over points (noted CO). Intercomparisons were performed over the 1993–1999 period. The model correction reduces the sea level variance by more than 50% at TG locations, and by more than 15% at T/P CO, when compared to the classical inverse barometer correction (IB). The model impact differs between high and low latitudes: in the very energetic high latitudes areas, MOG2D-G is efficient in reducing the variance, while at low latitudes, the results are similar to the IB static response. In shallow water, the model shows an oceanic response very different from the IB response. In conclusion, MOG2D-G models the high frequency (HF) atmospheric forced variability of the global ocean with unprecedented accuracy.

621 citations


Journal ArticleDOI
TL;DR: In this article, the authors show that the late Holocene drought cycles following the 4.2 ka BP event vary between 200 and 800 years and are coherent with the evolution of cosmogenic 14C production rates, suggesting that solar variability is one fundamental cause behind Holocene rainfall changes over south Asia.
Abstract: [1] Planktonic oxygen isotope ratios off the Indus delta reveal climate changes with a multi-centennial pacing during the last 6 ka, with the most prominent change recorded at 4.2 ka BP. Opposing isotopic trends across the northern Arabian Sea surface at that time indicate a reduction in Indus river discharge and suggest that later cycles also reflect variations in total annual rainfall over south Asia. The 4.2 ka event is coherent with the termination of urban Harappan civilization in the Indus valley. Thus, drought may have initiated southeastward habitat tracking within the Harappan cultural domain. The late Holocene drought cycles following the 4.2 ka BP event vary between 200 and 800 years and are coherent with the evolution of cosmogenic 14C production rates. This suggests that solar variability is one fundamental cause behind Holocene rainfall changes over south Asia.

522 citations


Journal ArticleDOI
TL;DR: In this paper, the climate of the North Pacific underwent a rapid and striking transition in late 1998 following a strong El Nino, upwelling-favorable winds strengthened over the California Current (CC), and winds weakened in the Gulf of Alaska (GOA).
Abstract: [1] Following a strong El Nino, the climate of the North Pacific underwent a rapid and striking transition in late 1998. Upwelling-favorable winds strengthened over the California Current (CC), and winds weakened in the Gulf of Alaska (GOA). Coastal waters of the CC and GOA cooled by several degrees, and the Pacific Decadal Oscillation (PDO) reversed sign and remained negative through summer 2002. Zooplankton biomass in the northern CC doubled and switched from warm to cold water species dominance, coho and chinook salmon stocks rebounded, and anchovy and osmeriids increased. Persistent changes in atmosphere and upper ocean fields and ecosystem structure suggest a climate regime shift has occurred, similar (opposite) to shifts observed in 1947 (1925 and 1976). If the 1998 regime shift in the northern CC is completely analogous to earlier shifts, then ecosystem structure should have changed in the GOA. Recent surveys indicate this ecosystem has transformed as well.

521 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed a technique to estimate LAI and green leaf biomass remotely using reflectances in two spectral channels either in the green around 550 nm, or at the red edge near 700 nm, and in the NIR (beyond 750 nm).
Abstract: [1] Leaf area index (LAI) is an important variable for climate modeling, estimates of primary production, agricultural yield forecasting, and many other diverse studies. Remote sensing provides a considerable potential for estimating LAI at local to regional and global scales. Several spectral vegetation indices have been proposed, but their capacity to estimate LAI is highly reduced at moderate-to-high LAI. In this paper, we propose a technique to estimate LAI and green leaf biomass remotely using reflectances in two spectral channels either in the green around 550 nm, or at the red edge near 700 nm, and in the NIR (beyond 750 nm). The technique was tested in agricultural fields under a maize canopy, and proved suitable for accurate estimation of LAI ranging from 0 to more than 6.

519 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed a new model for magma genesis: slab steepening and breakoff beneath a large subduction-accretion complex, which holds that a northward subducting oceanic lithosphere beneath the Eastern Anatolia Accretionary Prism gets steepened and eventually detached from the continental lithosphere of the Bitlis-Poturge Massif.
Abstract: [1] Eastern Anatolia is regarded as one of the best examples of continental collision, represented by a 2 km high plateau. It displays shallow and diffuse seismicity, indicating that the crust is still being actively deformed. Perhaps the most striking aspect of Eastern Anatolia is the volume and compositional variability of collision-related volcanic products erupted during the Neogene and Quaternary time. A number of models have been proposed for the genesis of this volcanism in the region. However, recent geophysical studies have revealed that a mantle lithosphere is almost completely absent beneath a greater portion of the region, which makes us question the validity of the previous models. In this paper, we propose a new model for magma genesis: slab steepening and breakoff beneath a large subduction-accretion complex. This model holds that a northward subducting oceanic lithosphere beneath the Eastern Anatolia Accretionary Prism gets steepened and eventually detached from the continental lithosphere of the Bitlis-Poturge Massif, following the continent-accretionary complex collision. This brings the asthenospheric mantle in contact with the accretionary complex at shallow depths (e.g., around 50 km), resulting in rapid regional uplift and extensive melting which leads to collisional volcanism.

518 citations


Journal ArticleDOI
TL;DR: In this paper, the authors studied the Cenozoic history of the Neotethyan ocean between Arabia and Eurasia and found that the convergence rate of the Arabia-Eurasia convergence has been fairly constant at 2 to 3 cm/yr since 56 Ma with a slowing of Africa-Eurusia motion to < 1 cm/r near 25 Ma, coeval with the opening of the Red Sea.
Abstract: Africa-North America-Eurasia plate circuit rotations, combined with Red Sea rotations and new estimates of crustal shortening in Iran define the Cenozoic history of the Neotethyan ocean between Arabia and Eurasia. The new constraints indicate that Arabia-Eurasia convergence has been fairly constant at 2 to 3 cm/yr since 56 Ma with slowing of Africa-Eurasia motion to <1 cm/yr near 25 Ma, coeval with the opening of the Red Sea. Ocean closure occurred no later than 10 Ma, and could have occurred prior to this time only if a large amount of continental lithosphere was subducted, suggesting that slowing of Africa significantly predated the Arabia-Eurasia collision. These kinematics imply that Africa's disconnection with the negative buoyancy of the downgoing slab of lithosphere beneath southern Eurasia slowed its motion. The slow, steady rate of northward subduction since 56 Ma contrasts with strongly variable rates of magma production in the Urumieh-Dokhtar arc, implying magma production rate in continental arcs is not linked to subduction rate.

514 citations


Journal ArticleDOI
TL;DR: Sengor et al. as discussed by the authors published an edited version of this paper by the American Geophysical Union (AGU) Copyright 2003, AGU, Inc. The paper was published by the AGU.
Abstract: An edited version of this paper was published by the American Geophysical Union (AGU). Copyright 2003, AGU. See also: http://www.agu.org/pubs/crossref/2003.../2003GL017858.shtml; http://atlas.geo.cornell.edu/turkey/publications/Sengor-et-al_2003.htm

Journal ArticleDOI
TL;DR: Bond et al. as mentioned in this paper showed that recent major changes in the ecosystems off the west coast of the United States and continued conditions similar to those of the early 1990s in the Gulf of Alaska, Bering Sea, and Sea of Okhotsk are consistent with these SLPA and SSTA patterns.
Abstract: [1] The winters of 1999–2002 for the North Pacific were characterizedbyspatialpatternsinsealevelpressureanomaly (SLPA) and sea surface temperature anomaly (SSTA) with little resemblance to those of the leading pattern of North Pacific climate variability, the Pacific Decadal Oscillation (PDO). In essence, the southeastern (northern) portion of the North Pacific was subject to atmospheric forcing characteristic of that before (after) the major regime shift of 1976–77. Recent major changes in the ecosystems off the west coast of the United States and continued conditions similar to those of the early 1990s in the Gulf of Alaska, Bering Sea, and Sea of Okhotsk are consistent with these SLPA and SSTA patterns. Our result illustrates that a single indicator such as the PDO is incomplete in characterizing North Pacific climate. INDEX TERMS: 1635 Global Change: Oceans (4203); 1610 Global Change: Atmosphere (0315, 0325); 4215 Oceanography: General: Climate and interannual variability (3309); 3339 Meteorology and Atmospheric Dynamics: Ocean/ atmosphere interactions (0312, 4504).Citation: Bond, N. A., J. E. Overland, M. Spillane, and P. Stabeno, Recent shifts in the state of the North Pacific, Geophys. Res. Lett., 30(23), 2183, doi:10.1029/ 2003GL018597, 2003.

Journal ArticleDOI
TL;DR: In this paper, a 3-D transport model was used to predict a decrease in CH4 emissions of ∼10 Tg CH4 from north of 50°N in the early 1990s, which may have accelerated the global methane budget towards steady state.
Abstract: [1] The globally-averaged atmospheric methane abundance determined from an extensive network of surface air sampling sites was constant at ∼1751 ppb from 1999 through 2002. Assuming that the methane lifetime has been constant, this implies that during this 4-year period the global methane budget has been at steady state. We also observed a significant decrease in the difference between northern and southern polar zonal annual averages of CH4 from 1991 to 1992. Using a 3-D transport model, we show that this change is consistent with a decrease in CH4 emissions of ∼10 Tg CH4 from north of 50°N in the early-1990s. This decrease in emissions may have accelerated the global methane budget towards steady state. Based on current knowledge of the global methane budget and how it has changed with time, it is not possible to tell if the atmospheric methane burden has peaked, or if we are only observing a persistent, but temporary pause in its increase.

Journal ArticleDOI
TL;DR: In this article, the authors presented simulations of Asian dust emissions over the past 43 years based on a size-dependent soil dust emission and transport model (NARCM) along with supporting data from a network of surface stations.
Abstract: [1] Simulations of Asian dust emissions over the past 43 years are presented based on a size-dependent soil dust emission and transport model (NARCM) along with supporting data from a network of surface stations. The deserts in Mongolia and in western and northern China (mainly the Taklimakan and Badain Juran, respectively) contribute ∼70% of the total dust emissions; non-Chinese sources account for ∼40% of this. Several areas, especially the Onqin Daga sandy land, Horqin sandy land, and Mu Us Desert, have increased in dust emissions over the past 20 years, but efforts to reduce desertification in these areas may have little effect on Asian dust emission amount because these are not key sources. The model simulations indicate that meteorology and climate have had a greater influence on the Asian dust emissions and associated Asian dust storm occurrences than desertification.

Journal ArticleDOI
TL;DR: In this article, a robust 2D joint inversion scheme incorporating the new concept of cross-gradients of electrical resistivity and seismic velocity as constraints was developed to investigate more precisely the resistivity-velocity relationships in complex near-surface environments.
Abstract: [1] We have developed a robust 2D joint inversion scheme incorporating the new concept of cross-gradients of electrical resistivity and seismic velocity as constraints so as to investigate more precisely the resistivity-velocity relationships in complex near-surface environments. The results of joint inversion of dc resistivity and seismic traveltime data from collocated experiments suggest that one can distinguish between different types or facies of unconsolidated and consolidated materials, refining a previously proposed resistivity-velocity interrelationship derived from separate inversions of the respective data sets. A consistent interpretive structural model can be obtained from the joint inversion models.

Journal ArticleDOI
TL;DR: In this article, the influence of the Indian Ocean Dipole (IOD) on the Australian winter rainfall was studied using an atmospheric general circulation model and observed datasets of sea surface temperature and rainfall.
Abstract: [1] Using an atmospheric general circulation model and observed datasets of sea surface temperature and rainfall, we studied the influence of the Indian Ocean Dipole (IOD) on the Australian winter rainfall. The IOD has significant negative partial correlations with rainfall over the western and southern regions of Australia. These negative partial correlations extend south-eastward from Indonesia all the way to south east Australia. Our atmospheric general circulation model sensitivity experiments indicate that cold sea surface temperature anomalies prevailing west of the Indonesian archipelago during the positive IOD events introduce an anomalous anticyclonic circulation at lower levels over the eastern tropical and subtropical Indian Ocean, and over much of the Australian continent. It is also apparent that the response of the atmosphere to the IOD in this region is baroclinic, causing anomalous subsidence and anomalous reduction in the rainfall over the affected regions of Australia.

Journal ArticleDOI
TL;DR: In this article, the long-neglected contribution of tropical cyclones to ocean primary production may be as much as 20-30% with an average of 14 cyclones passing over the South China Sea.
Abstract: [1] New evidence based on recent satellite data is presented to provide a rare opportunity in quantifying the long-speculated contribution of tropical cyclones to enhance ocean primary production. In July 2000, moderate cyclone Kai-Tak passed over the South China Sea (SCS). During its short 3-day stay, Kai-Tak triggered an average 30-fold increase in surface chlorophyll-a concentration. The estimated carbon fixation resulting from this event alone is 0.8 Mt, or 2–4% of SCS's annual new production. Given an average of 14 cyclones passing over the SCS annually, we suggest the long-neglected contribution of tropical cyclones to SCS's annual new production may be as much as 20–30%.

Journal ArticleDOI
TL;DR: In this article, a composite time series (1993-2000) of sea surface height anomaly from several satellites is used to identify eddies in the South China Sea (SCS), and the eddy lifetime, radius, strength, and straight-line travel distance are estimated.
Abstract: [1] A composite time series (1993–2000) of sea surface height anomaly from several satellites is used to identify eddies in the South China Sea (SCS). The eddy lifetime, radius, strength, and straight-line travel distance are estimated. Altogether 58 anticyclonic eddies and 28 cyclonic eddies are identified for this period. They are grouped into four geographical zones according to known eddy generation mechanisms, and their statistics are discussed accordingly. Our geographical classification is a useful first step in gaining an overview of their generation.

Journal ArticleDOI
TL;DR: In this article, secondary aerosol formation of atmospheric polymers occurs by heterogeneous reaction of isoprenoid or terpenoid emissions in the presence of a sulfuric acid aerosol catalyst.
Abstract: [1] Water-soluble macromolecular substances with spectral properties of “humic-like substances” (HULIS) were recently found to form the major identified fraction of the organic aerosol at urban and rural sites in Europe. With primary sources identified so far (e.g., biomass combustion) it is not possible to explain the observed HULIS levels in Europe, therefore there is an ongoing search for other sources - which form HULIS in situ in the atmosphere. Here we show that secondary aerosol formation of atmospheric polymers occurs by heterogeneous reaction of isoprenoid or terpenoid emissions in the presence of a sulfuric acid aerosol catalyst. Competing oxidants such as ozone or the presence of humidity decreased the reaction yield, but the formation of humic–like substances was not disabled. Calculations indicate that the presented reaction pathway could be an additional source for HULIS in the continental aerosol.

Journal ArticleDOI
TL;DR: In this paper, the authors present a dataset on CH4 flux rates totaling 12 measurement years at sites from Greenland, Iceland, Scandinavia and Siberia, and find that temperature and microbial substrate availability (expressed as the organic acid concentration in peat water) combined explain almost 100% of the variations in mean annual CH4 emissions.
Abstract: [1] Global wetlands are, at estimate ranging 115-237 Tg CH4/yr, the largest single atmospheric source of the greenhouse gas methane (CH4). We present a dataset on CH4 flux rates totaling 12 measurement years at sites from Greenland, Iceland, Scandinavia and Siberia. We find that temperature and microbial substrate availability (expressed as the organic acid concentration in peat water) combined explain almost 100% of the variations in mean annual CH4 emissions. The temperature sensitivity of the CH4 emissions shown suggests a feedback mechanism on climate change that could validate incorporation in further developments of global circulation models.

Journal ArticleDOI
TL;DR: A recent field experiment in southern Florida using aircraft and polarization lidar shows that mineral dust particles transported from Saharan Africa are effective ice nuclei, apparently capable of glaciating a mildly supercooled (−5.2° to −8.8°C) altocumulus cloud as mentioned in this paper.
Abstract: [1] A recent field experiment in southern Florida using aircraft and polarization lidar shows that mineral dust particles transported from Saharan Africa are effective ice nuclei, apparently capable of glaciating a mildly supercooled (−5.2° to −8.8°C) altocumulus cloud. These results are similar to those from Asian dust storm particles observed over the western US, suggesting that in the northern hemisphere major dust storms play a role in modulating climate through the indirect aerosol effect on cloud properties. If this is true of desert dusts in general, then even minor aeolian emissions could have an effect on regional weather and climate.

Journal ArticleDOI
TL;DR: In this paper, the variability of flood risk across NSW is analyzed with respect to the observed increase in the magnitude of ENSO event magnitude and the frequency of their occurrence, using the Pacific Oscillation (IPO) index.
Abstract: Recent research has highlighted the persistence of multi-decadal epochs of enhanced/reduced flood risk across New South Wales (NSW), Australia. Recent climatological studies have also revealed multi-decadal variability in the modulation of the magnitude of El Nin椀/Southern Oscillation (ENSO) impacts. In this paper, the variability of flood risk across NSW is analysed with respect to the observed modulation of ENSO event magnitude. This is achieved through the use of a simple index of regional flood risk. The results indicate that cold ENSO events (La Nin和) are the dominant drivers of elevated flood risk. An analysis of multidecadal modulation of flood risk is achieved using the interdecadal Pacific Oscillation (IPO) index. The analysis reveals that IPO modulation of ENSO events leads to multi-decadal epochs of elevated flood risk, however this modulation appears to affect not only the magnitude of individual ENSO events, but also the frequency of their occurrence. This dual modulation of ENSO processes has the effect of reducing and elevating flood risk on multi-decadal timescales. These results have marked implications for achieving robust flood frequency analysis as well as providing a strong example of the role of natural climate variability.

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed a time series of 21-yr satellite data for three bioclimate subzones in northern Alaska and confirmed a long-term trend of increase in vegetation greenness for the Alaskan tundra that has been detected globally for the northern latitudes.
Abstract: [1] Here we analyzed a time series of 21-yr satellite data for three bioclimate subzones in northern Alaska and confirmed a long-term trend of increase in vegetation greenness for the Alaskan tundra that has been detected globally for the northern latitudes. There was a 16.9% (±5.6%) increase in peak vegetation greenness across the region that corresponded to simultaneous increases in temperatures. We also examined the changes for four specific vegetation types using an 11-yr finer resolution (1-km) satellite data and found that the temporal changes in peak and time-integrated greenness were greatest in areas of moist nonacidic tundra. These changes in greenness between 1981 and 2001 correspond approximately to a 171 g/m2 (±81 g/m2) increases in aboveground plant biomass for Alaskan tundra. This remotely sensed interpretation is conducted in the absence of long-term biomass records in the region.

Journal ArticleDOI
TL;DR: In this article, satellite-in situ blended ocean chlorophyll records indicate that global ocean annual primary production has declined more than 6% since the early 1980's and nearly 70% of the global decadal decline occurred in the high latitudes.
Abstract: [1] Satellite-in situ blended ocean chlorophyll records indicate that global ocean annual primary production has declined more than 6% since the early 1980's. Nearly 70% of the global decadal decline occurred in the high latitudes. In the northern high latitudes, these reductions in primary production corresponded with increases in sea surface temperature and decreases in atmospheric iron deposition to the oceans. In the Antarctic, the reductions were accompanied by increased wind stress. Three of four low latitude basins exhibited decadal increases in annual primary production. These results indicate that ocean photosynthetic uptake of carbon may be changing as a result of climatic changes and suggest major implications for the global carbon cycle.

Journal ArticleDOI
TL;DR: In this paper, observations of snow water equivalent (SWE) in the Pacific Northwest were examined and compared with variability and trends in temperature and precipitation at nearby climate stations at most locations, especially below about 1800 m.
Abstract: [1] Observations of snow water equivalent (SWE) in the Pacific Northwest are examined and compared with variability and trends in temperature and precipitation at nearby climate stations. At most locations, especially below about 1800 m, substantial declines in SWE coincide with significant increases in temperature, and occur in spite of increases in precipitation.

Journal ArticleDOI
TL;DR: In this paper, the authors modified the avalanche mode of runaway breakdown to include positive feedback from gamma-rays and positrons, and found that enormous bursts of energetic radiation can be produced in strong electric fields in air, with peak fluxes up to one billion times greater than from conventional models.
Abstract: [1] By modifying the avalanche mode of runaway breakdown to include positive feedback from gamma-rays and positrons, it is found that enormous bursts of energetic radiation can be produced in strong electric fields in air, with peak fluxes up to one billion times greater than from conventional models. These bursts generate so many runaway electrons that the electric field is very rapidly discharged, resulting in a fundamental upper limit on the electric field strength achievable in air. This limit has important implications for the electrification of thunderstorms and the production of lightning.

Journal ArticleDOI
TL;DR: In this paper, anomalous warm southerly winds in spring, advecting ice poleward from the Siberian coast, and persistent low pressure and high temperatures over the Arctic Ocean in summer, promoting ice divergence and rapid melt.
Abstract: [1] Arctic sea ice extent and area in September 2002 reached their lowest levels recorded since 1978. These conditions likely resulted from (1) anomalous warm southerly winds in spring, advecting ice poleward from the Siberian coast (2) persistent low pressure and high temperatures over the Arctic Ocean in summer, promoting ice divergence and rapid melt.

Journal ArticleDOI
TL;DR: Frohlich et al. as mentioned in this paper showed that the lower PMOD trend and lower TSI at the maxima of solar cycles 22 and 23 are artifacts of ERBS degradation.
Abstract: [1] A series of satellite total solar irradiance (TSI) observations can be combined in a precise solar magnetic cycle length composite TSI database by determining the relationship between two non-overlapping components: ACRIM1 and ACRIM2. [Willson and Hudson, 1991; Willson, 1994] An ACRIM composite TSI time series using the Nimbus7/ERB results [Hoyt et al., 1992] to relate ACRIM1 and ACRIM2 demonstrates a secular upward trend of 0.05 percent-per-decade between consecutive solar activity minima. [Willson, 1997] A PMOD TSI composite using ERBS [Lee et al., 1995] comparisons to relate ACRIM1 and ACRIM2 [Frohlich and Lean, 1998] differs from the ACRIM composite in two significant respects: a negligible trend between solar minima and lower TSI at solar maxima. Our findings indicate the lower PMOD trend and lower PMOD TSI at the maxima of solar cycles 22 and 23 are artifacts of ERBS degradation. Lower PMOD TSI during the maximum of cycle 21 results from modifications of Nimbus7/ERB and ACRIM1 published results that produces better agreement with a TSI/solar proxy model [Foukal and Lean, 1988; Lean et al., 1995; Frohlich and Lean, 1998].

Journal ArticleDOI
TL;DR: Li et al. as discussed by the authors presented a 2326-year tree-ring chronology of Sabina przewalskii Kom. for the Dulan area of northeastern Qinghai-Tibetan Plateau.
Abstract: [1] High-resolution climate proxy records covering the last two millennia on the Qinghai-Tibetan Plateau are scarce yet essential to evaluation of the patterns, synchroneity and spatial extent of past climatic changes including those in the Medieval Warm Period (MWP) and the Little Ice Age (LIA). Here we present a 2326-year tree-ring chronology of Sabina przewalskii Kom. for Dulan area of northeastern Qinghai-Tibetan Plateau. We find that the annual growth rings mainly reflect variations in regional spring precipitation. The greatest change in spring precipitation during the last two millennia seems to occur in the second half of the 4th century. The North Atlantic MWP was accompanied by notable wet springs in the study region during A.D. 929–1031 with the peak occurring around A.D. 974. Three intervals of dry springs occurred in the period of LIA. Our tree-ring data will facilitate intercontinental comparisons of large-scale synoptic climate variability for the last two millennia.

Journal ArticleDOI
TL;DR: In this paper, changes in the frequency of some extreme temperature events were studied with a focus on trends, and increasing trends were detected in the frequencies of warm days and warm nights in China.
Abstract: [1] Based on the daily surface air temperature data from about 200 stations during 1951-1999 in China, changes in the frequency of some extreme temperature events were studied with a focus on trends. For China as a whole, the number of hot days (Tmax over 35°C) displays a slightly decreasing trend, while the number of frost days (Tmin below 0°C) exhibits a significant decreasing trend. Meanwhile, increasing trends were detected in the frequencies of warm days and warm nights. In addition, decreasing trends was found in the frequencies of cool days and even stronger decreasing trend was found in frequencies of cool nights in China.