STATE OF THE CLIMATE IN 2010 Blunden, J.; Arndt, D. S.; Baringer, M. O. ...
Bulletin of the American Meteorological Society,
06/2011, Letnik:
92, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Several large-scale climate patterns influenced climate conditions and weather patterns across the globe during 2010. The transition from a warm El Niño phase at the beginning of the year to a cool ...La Niña phase by July contributed to many notable events, ranging from record wetness across much of Australia to historically low Eastern Pacific basin and near-record high North Atlantic basin hurricane activity. The remaining five main hurricane basins experienced below- to well-below-normal tropical cyclone activity. The negative phase of the Arctic Oscillation was a major driver of Northern Hemisphere temperature patterns during 2009/10 winter and again in late 2010. It contributed to record snowfall and unusually low temperatures over much of northern Eurasia and parts of the United States, while bringing above-normal temperatures to the high northern latitudes. The February Arctic Oscillation Index value was the most negative since records began in 1950.
The 2010 average global land and ocean surface temperature was among the two warmest years on record. The Arctic continued to warm at about twice the rate of lower latitudes. The eastern and tropical Pacific Ocean cooled about 1°C from 2009 to 2010, reflecting the transition from the 2009/10 El Niño to the 2010/11 La Niña. Ocean heat fluxes contributed to warm sea surface temperature anomalies in the North Atlantic and the tropical Indian and western Pacific Oceans. Global integrals of upper ocean heat content for the past several years have reached values consistently higher than for all prior times in the record, demonstrating the dominant role of the ocean in the Earth’s energy budget. Deep and abyssal waters of Antarctic origin have also trended warmer on average since the early 1990s. Lower tropospheric temperatures typically lag ENSO surface fluctuations by two to four months, thus the 2010 temperature was dominated by the warm phase El Niño conditions that occurred during the latter half of 2009 and early 2010 and was second warmest on record. The stratosphere continued to be anomalously cool.
Annual global precipitation over land areas was about five percent above normal. Precipitation over the ocean was drier than normal after a wet year in 2009. Overall, saltier (higher evaporation) regions of the ocean surface continue to be anomalously salty, and fresher (higher precipitation) regions continue to be anomalously fresh. This salinity pattern, which has held since at least 2004, suggests an increase in the hydrological cycle.
Sea ice conditions in the Arctic were significantly different than those in the Antarctic during the year. The annual minimum ice extent in the Arctic—reached in September—was the third lowest on record since 1979. In the Antarctic, zonally averaged sea ice extent reached an all-time record maximum from mid-June through late August and again from mid-November through early December. Corresponding record positive Southern Hemisphere Annular Mode Indices influenced the Antarctic sea ice extents.
Greenland glaciers lost more mass than any other year in the decade-long record. The Greenland Ice Sheet lost a record amount of mass, as the melt rate was the highest since at least 1958, and the area and duration of the melting was greater than any year since at least 1978. High summer air temperatures and a longer melt season also caused a continued increase in the rate of ice mass loss from small glaciers and ice caps in the Canadian Arctic. Coastal sites in Alaska show continuous permafrost warming and sites in Alaska, Canada, and Russia indicate more significant warming in relatively cold permafrost than in warm permafrost in the same geographical area. With regional differences, permafrost temperatures are now up to 2°C warmer than they were 20 to 30 years ago. Preliminary data indicate there is a high probability that 2010 will be the 20th consecutive year that alpine glaciers have lost mass.
Atmospheric greenhouse gas concentrations continued to rise and ozone depleting substances continued to decrease. Carbon dioxide increased by 2.60 ppm in 2010, a rate above both the 2009 and the 1980–2010 average rates. The global ocean carbon dioxide uptake for the 2009 transition period from La Niña to El Niño conditions, the most recent period for which analyzed data are available, is estimated to be similar to the long-term average. The 2010 Antarctic ozone hole was among the lowest 20% compared with other years since 1990, a result of warmer-than-average temperatures in the Antarctic stratosphere during austral winter between mid-July and early September.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
STATE OF THE CLIMATE IN 2009 ARNDT, D.S; BARINGER, M.O; JOHNSON, M.R ...
Bulletin of the American Meteorological Society,
07/2010, Letnik:
91, Številka:
7
Journal Article
Recenzirano
Odprti dostop
The year was characterized by a transition from a waning La Niña to a strengthening El Niño, which first developed in June. By December, SSTs were more than 2.0°C above average over large parts of ...the central and eastern equatorial Pacific. Eastward surface current anomalies, associated with the El Niño, were strong across the equatorial Pacific, reaching values similar to the 2002 El Niño during November and December 2009. The transition from La Niña to El Niño strongly influenced anomalies in many climate conditions, ranging from reduced Atlantic basin hurricane activity to large scale surface and tropospheric warmth.
Global average surface and lower-troposphere temperatures during the last three decades have been progressively warmer than all earlier decades, and the 2000s (2000–09) was the warmest decade in the instrumental record. This warming has been particularly apparent in the mid- and high-latitude regions of the Northern Hemisphere and includes decadal records in New Zealand, Australia, Canada, Europe, and the Arctic. The stratosphere continued a long cooling trend, except in the Arctic.
Atmospheric greenhouse gas concentrations continued to rise, with CO₂ increasing at a rate above the 1978 to 2008 average. The global ocean CO₂ uptake flux for 2008, the most recent year for which analyzed data are available, is estimated to have been 1.23 Pg C yr−1, which is 0.25 Pg C yr−1smaller than the long-term average and the lowest estimated ocean uptake in the last 27 years. At the same time, the total global ocean inventory of anthropogenic carbon stored in the ocean interior as of 2008 suggests an uptake and storage of anthropogenic CO₂ at rates of 2.0 and 2.3 ±0.6 Pg C yr−1for the decades of the 1990s and 2000s, respectively. Total-column ozone concentrations are still well below pre-1980 levels but have seen a recent reduction in the rate of decline while upper-stratospheric ozone showed continued signs of ongoing slow recovery in 2009. Ozone-depleting gas concentrations continued to decline although some halogens such as hydrochlorofluorocarbons are increasing globally. The 2009 Antarctic ozone hole was comparable in size to recent previous ozone holes, while still much larger than those observed before 1990. Due to large interannual variability, it is unclear yet whether the ozone hole has begun a slow recovery process.
Global integrals of upper-ocean heat content for the last several years have reached values consistently higher than for all prior times in the record, demonstrating the dominant role of the oceans in the planet’s energy budget. Aside from the El Niño development in the tropical Pacific and warming in the tropical Indian Ocean, the Pacific Decadal Oscillation (PDO) transitioned to a positive phase during the fall/winter 2009. Ocean heat fluxes contributed to SST anomalies in some regions (e.g., in the North Atlantic and tropical Indian Oceans) while dampening existing SST anomalies in other regions (e.g., the tropical and extratropical Pacific). The downward trend in global chlorophyll observed since 1999 continued through 2009, with current chlorophyll stocks in the central stratified oceans now approaching record lows since 1997.
Extreme warmth was experienced across large areas of South America, southern Asia, Australia, and New Zealand. Australia had its second warmest year on record. India experienced its warmest year on record; Alaska had its second warmest July on record, behind 2004; and New Zealand had its warmest August since records began 155 years ago. Severe cold snaps were reported in the UK, China, and the Russian Federation. Drought affected large parts of southern North America, the Caribbean, South America, and Asia. China suffered its worst drought in five decades. India had a record dry June associated with the reduced monsoon. Heavy rainfall and floods impacted Canada, the United States, the Amazonia and southern South America, many countries along the east and west coasts of Africa, and the UK. The U.S. experienced its wettest October in 115 years and Turkey received its heaviest rainfall over a 48-hr period in 80 years.
Sea level variations during 2009 were strongly affected by the transition from La Niña to El Niño conditions, especially in the tropical Indo-Pacific. Globally, variations about the long-term trend also appear to have been influenced by ENSO, with a slight reduction in global mean sea level during the 2007/08 La Niña event and a return to the long-term trend, and perhaps slightly higher values, during the latter part of 2009 and the current El Niño event. Unusually low Florida Current transports were observed in May and June and were linked to high sea level and coastal flooding along the east coast of the United States in the summer. Sea level significantly decreased along the Siberian coast through a combination of wind, ocean circulation, and steric effects. Cloud and moisture increased in the tropical Pacific. The surface of the western equatorial Pacific freshened considerably from 2008 to 2009, at least partially owing to anomalous eastward advection of fresh surface water along the equator during this latest El Niño. Outside the more variable tropics, the surface salinity anomalies associated with evaporation and precipitation areas persisted, consistent with an enhanced hydrological cycle.
Global tropical cyclone (TC) activity was the lowest since 2005, with six of the seven main hurricane basins (the exception is the Eastern North Pacific) experiencing near-normal or somewhat below-normal TC activity. Despite the relatively mild year for overall hurricane activity, several storms were particularly noteworthy: Typhoon Morakot was the deadliest typhoon on record to hit Taiwan; Cyclone Hamish was the most intense cyclone off Queensland since 1918; and the state of Hawaii experienced its first TC since 1992.
The summer minimum ice extent in the Arctic was the third-lowest recorded since 1979. The 2008/09 boreal snow cover season marked a continuation of relatively shorter snow seasons, due primarily to an early disappearance of snow cover in spring. Preliminary data indicate a high probability that 2009 will be the 19th consecutive year that glaciers have lost mass. Below normal precipitation led the 34 widest marine terminating glaciers in Greenland to lose 101 km² ice area in 2009, within an annual loss rate of 106 km² over the past decade. Observations show a general increase in permafrost temperatures during the last several decades in Alaska, northwest Canada, Siberia, and Northern Europe. Changes in the timing of tundra green-up and senescence are also occurring, with earlier green-up in the High Arctic and a shift to a longer green season in fall in the Low Arctic.
The Antarctic Peninsula continues to warm at a rate five times larger than the global mean warming. Associated with the regional warming, there was significant ice loss along the Antarctic Peninsula in the last decade. Antarctic sea ice extent was near normal to modestly above normal for the majority of 2009, with marked regional contrasts within the record. The 2008/09 Antarctic-wide austral summer snowmelt was the lowest in the 30-year history.
This 20th annualState of the Climatereport highlights the climate conditions that characterized 2009, including notable extreme events. In total, 37 Essential Climate Variables are reported to more completely characterize theState of the Climatein 2009.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Hydrographic and current profiler data taken during the 1988 Gulf of Cadiz Expedition have been analyzed to diagnose the mixing, spreading, and descent of the Mediterranean outflow. The theta -S ...properties and the thickness and width of the outflow were similar to that seen in earlier surveys. The transport of pure Mediterranean Water (i.e., water with S greater than or equal to 38.4 psu) was estimated to be about 0.4 x 10 super(6) m super(3) s super(-1), which is lower than historical estimates - most of which were indirect - but comparable to other recent estimates made from direct velocity observations. The outflow transport estimated at the west end of the Strait of Gibraltar was about 0.7 x 10 super(6) m super(3) s super(-1) of mixed water, and the transport increased to about 1.9 x 10 super(6) m super(3) s super(-1) within the eastern Gulf of Cadiz. This increase in transport occurred by entrainment of fresher North Atlantic Central Water, and the salinity anomaly of the outflow was consequently reduced. The velocity-weighted salinity decreased to 36.7 psu within 60 km of the strait and decreased by about another 0.1 before the deeper portion of the outflow began to separate from of the bottom near Cape St. Vincent. Entrainment appears to have been correlated spatially with the initial descent of the continental slope and with the occurrence of bulk Froude numbers slightly greater than 1. In the western Gulf of Cadiz, where entrainment was much weaker, Froude numbers were consistently well below 1. The outflow began in the eastern Strait of Gibraltar as a narrow (10 km wide) current having a very narrow range of theta -S properties. The outflow broadened as it descended the continental slope of the northern Gulf of Cadiz and reached a maximum width of 80 km in the western Gulf of Cadiz. The descent of the outflow was very asymmetric: The southern (offshore) edge of the outflow descended about 1000 m from Gibraltar to Cape St. Vincent, while the northern (onshore) edge of the outflow descended only a few hundred meters. The northern, onshore side thus remained considerably higher in the water column and thus entrained relatively warm North Atlantic Central Water. This caused the outflow to develop horizontal theta -S variability and, by about 140 km downstream, the across-stream variation in temperature on an isopycnal was more than 2 degree C. Much of the volume transport in the western Gulf of Cadiz was contained within two preferred modes or cores. The deeper, offshore core had a central sigma sub( theta ) = 27.8 kg m super(-3), and the shallower onshore core, which was still in contact with the bottom in the Gulf of Cadiz, had a central sigma sub( theta ) = 27.5 kg m super(-3). These two cores develop as a result of the spreading and horizontally varying entrainment noted above, combined with topographic steering.
Fourteen temperature sections collected between July 2002 and May 2006 are analyzed to obtain estimates of the meridional heat transport variability of the South Atlantic Ocean. The methodology ...proposed in Part I is used to calculate the heat transport from temperature data obtained from high-density XBT profiles taken along transects from Cape Town, South Africa to Buenos Aires, Argentina. Salinity is estimated from Argo profiles and CTD casts for each XBT temperature observation using statistical relationships between temperature, latitude, longitude, and salinity computed along constant-depth surfaces. Full-depth temperature/salinity profiles are obtained by extending the profiles to the bottom of the ocean using deep climatological data. The meridional transport is then determined by using the standard geostrophic method, applying NCEP-derived Ekman transports, and requiring that salt flux through the Bering Straits be conserved. The results from the analysis indicate a mean meridional heat transport of 0.54
PW (PW=10
15
W) with a standard deviation of 0.11
PW. The geostrophic component of the heat flux has a marked annual cycle following the variability of the Brazil Malvinas Confluence Front, and the geostrophic annual cycle is 180° out of phase with the annual cycle observed in the Ekman fluxes. As a result, the total heat flux shows significant interannual variability with only a small annual cycle. Uncertainties due to different wind products and locations of the sections are independent of the methodology used.
Heat transports estimated CTD data collected during the World Ocean Circulation Experiment (WOCE) along the January 1993 30°S hydrographic transect (A10) and the output from a numerical model show a ...mean heat transport of 0.40 and 0.55±0.24
PW (standard deviation), respectively. The model shows a large annual cycle in heat transport (more than 30% of the variance) with a maximum (minimum) heat transport in July (February) of 0.68 (0.41)
PW. Using these data, a method is proposed and evaluated to calculate the heat transport from temperature data obtained from a trans-basin section of expendable bathythermographs (XBTs) profiles. In this method, salinity is estimated from Argo profiles and CTD casts for each XBT temperature observation using statistical relationships between temperature, latitude, longitude and salinity computed along constant-depth surfaces. Full-depth temperature/salinity profiles are obtained by extending the profiles to the bottom of the ocean using deep climatological data. The meridional transport is then determined by using the standard geostrophic method, applying NCEP-derived Ekman transports, and requiring that the salt flux through the Bering Straits be conserved. The results indicate that the methods described here can provide heat transport estimates with a maximum uncertainty of ±0.18
PW (1
PW=10
15
W). Most of this uncertainty is due to the climatology used to estimate the deep structure and issues related to not knowing the absolute velocity field and most especially characterizing barotropic motions. Nevertheless, when the methodology is applied to temperatures collected along 30°S (A10) and direct model integrations, the results are very promising. Results from the numerical model suggest that ageostrophic non-Ekman motions can contribute less than 0.05
PW to heat transport estimates in the South Atlantic.
Recently there has been discussion about the metabolic state of the ocean, with arguments questioning whether the open ocean is net autotrophic or net heterotrophic. Accurately determining the ...metabolic balance of a marine system depends on fully defining the system being evaluated and on quantifying the inputs and outputs to that system. Here, a net northward transport of dissolved organic carbon (DOC) (across 24.5°N) of 3.3 ± 1.9 Tmol C yr-1 was determined using basin-wide transport estimates of DOC. This flux, coupled with DOC inputs from the Arctic Ocean (2.2 ± 0.8 Tmol C yr-1 the atmosphere (0.6 ± 0.08 Tmol C yr-1) and rivers (3.1 ± 0.6 Tmol C yr-1), indicates net heterotrophy in the North Atlantic (full depth, 24.5-72°N) of 9.2 ± 2.2 Tmol C yr-1. This rate is small (<2%) compared to autochthonous production (∼494 Tmol C yr-1) and consumption (production:respiration of 0.98), indicating that the North Atlantic is essentially metabolically balanced and that autochthonous production is remineralized within the basin. The upper layer of the subtropical gyre has previously been reported to exhibit high rates of net heterotrophy, but our analysis does not support those findings. Instead, allochthonous inputs of organic carbon to the upper subtropical gyre are an order of magnitude less than required by the elevated rates of net heterotrophy reported. We find, too, that net mineralization of allochthonous DOC within the basin could account for 10% of the preindustrial inorganic carbon exported from the basin to the south. Two factors, the import of organic matter and the unique thermohaline circulation pattern of the North Atlantic, are primary in ensuring net heterotrophy in the basin.
Mediterranean Outflow Mixing and Dynamics Price, James F.; Molly O'Neil Baringer; Lueck, Rolf G. ...
Science (American Association for the Advancement of Science),
02/1993, Letnik:
259, Številka:
5099
Journal Article
Recenzirano
The Mediterranean Sea produces a salty, dense outflow that is strongly modified by entrainment as it first begins to descend the continental slope in the eastern Gulf of Cadiz. The current ...accelerates to 1.3 meters per second, which raises the internal Froude number above 1, and is intensely turbulent through its full thickness. The outflow loses about half of its density anomaly and roughly doubles its volume transport as it entrains less saline North Atlantic Central water. Within 100 kilometers downstream, the current is turned by the Coriolis force until it flows nearly parallel to topography in a damped geostrophic balance. The mixed Mediterranean outflow continues westward, slowly descending the continental slope until it becomes neutrally buoyant in the thermocline where it becomes an important water mass.
The physical oceanography of the Mediterranean Sea is reviewed with particular emphasis on the Mediterranean outflow in the Gulf of Cadiz. In this region the dense Mediterranean water forms a high ...velocity bottom current that interacts strongly with the sea floor. The major energy source for the plume comes from the release of potential energy as the plume descends the continental slope, and the major energy sink is work against bottom stress, which is as large as 4 Pa where the plume begins to descend the continental slope. In this region the current makes a nearly inertial turn that would otherwise appear to be steered by the underlying topography. The Mediterranean plume entrains the overlying North Atlantic Central Water and thereby loses much of its density anomaly. The mixed Mediterranean water becomes neutrally buoyant in the lower portion of the North Atlantic thermocline near Cape St. Vincent. There are then two preferred transport modes having somewhat different temperature and salinity whose distinct characteristics can be found far into the open North Atlantic. The temperature, salinity and volume of the Mediterranean water in the Strait of Gibraltar and in the Gulf of Cadiz appear to be roughly constant since modern measurements have been made. The estimated westward transport of Mediterranean water has gone down considerably as direct measurement techniques have been applied. A recent estimate is that the westward transport of pure Mediterranean water is only about a half a Sv (1 Sv = 10
6 m
3 s
−1); the transport of mixed Mediterranean water in the western Gulf of Cadiz is larger by about a factor of three or four because of the entrainment of North Atlantic water.
As part of a newly funded international program to monitor ocean heat transport at mid‐latitudes in the North Atlantic, a continuous estimate of the temperature transport of the Florida Current is ...required. Since 1982, volume transports have been inferred from voltage measurements monitored by submarine telephone cables across the Straits of Florida. Electromagnetic induction theory suggests that the cable voltage should actually give a more direct measure of conductivity transport than pure volume transport. Due to the strong dependence of conductivity on temperature, this would in theory result in a direct and continuous estimate of the Florida Current temperature transport. This hypothesis is investigated using data from a large number of temperature and velocity sections (58) across the Florida Current at the cable location, leading to a new calibration of the voltage signal for the temperature transport of the Florida Current, crucial for trans‐basin heat flux estimates.
Three temperature sections that cross the tropical Atlantic obtained from high density XBT transects are used to identify the major surface currents and to compute their water mass transports. The ...dynamic heights are computed using XBT temperature profiles with salinity derived from historical T‐S relationships. The values of dynamic height estimated from altimeter data used in conjunction with climatological dynamic height fields are within 3 cm of the XBT‐derived values. The error in XBT‐derived dynamic height introduced by using historical T‐S relationships instead of actual salinity values are estimated to be of the order of 1.5 cm. Dynamic height estimates using the actual salinity values underestimate those obtained using historical T‐S relationships. The structure exhibited in the dynamic height and altimeter‐derived sea height fields do not reveal all the upper ocean currents, making these temperature sections presented here critical for computing transports and identifying currents in this region.
PDF
