| 1. |
- Blunden, Jessica, et al.
(författare)
-
State of the Climate in 2012
- 2013
-
Ingår i: Bulletin of The American Meteorological Society - (BAMS). - 0003-0007 .- 1520-0477. ; 94:8, s. S1-S258
-
Tidskriftsartikel (refereegranskat)abstract
- For the first time in serveral years, the El Nino-Southern Oscillation did not dominate regional climate conditions around the globe. A weak La Ni a dissipated to ENSOneutral conditions by spring, and while El Nino appeared to be emerging during summer, this phase never fully developed as sea surface temperatures in the eastern conditions. Nevertheless, other large-scale climate patterns and extreme weather events impacted various regions during the year. A negative phase of the Arctic Oscillation from mid-January to early February contributed to frigid conditions in parts of northern Africa, eastern Europe, and western Asia. A lack of rain during the 2012 wet season led to the worst drought in at least the past three decades for northeastern Brazil. Central North America also experienced one of its most severe droughts on record. The Caribbean observed a very wet dry season and it was the Sahel's wettest rainy season in 50 years. Overall, the 2012 average temperature across global land and ocean surfaces ranked among the 10 warmest years on record. The global land surface temperature alone was also among the 10 warmest on record. In the upper atmosphere, the average stratospheric temperature was record or near-record cold, depending on the dataset. After a 30-year warming trend from 1970 to 1999 for global sea surface temperatures, the period 2000-12 had little further trend. This may be linked to the prevalence of La Ni a-like conditions during the 21st century. Heat content in the upper 700 m of the ocean remained near record high levels in 2012. Net increases from 2011 to 2012 were observed at 700-m to 2000-m depth and even in the abyssal ocean below. Following sharp decreases in to the effects of La Ni a, sea levels rebounded to reach records highs in 2012. The increased hydrological cycle seen in recent years continued, with more evaporation in drier locations and more precipitation in rainy areas. In a pattern that has held since 2004, salty areas of the ocean surfaces and subsurfaces were anomalously salty on average, while fresher areas were anomalously fresh. Global tropical cyclone activity during 2012 was near average, with a total of 84 storms compared with the 1981-2010 average of 89. Similar to 2010 and 2011, the North Atlantic was the only hurricane basin that experienced above-normal activity. In this basin, Sandy brought devastation to Cuba and parts of the eastern North American seaboard. All other basins experienced either near-or below-normal tropical cyclone activity. Only three tropical cyclones reached Category 5 intensity-all in Bopha became the only storm in the historical record to produce winds greater than 130 kt south of 7 N. It was also the costliest storm to affect the Philippines and killed more than 1000 residents. Minimum Arctic sea ice extent in September and Northern Hemisphere snow cover extent in June both reached new record lows. June snow cover extent is now declining at a faster rate (-17.6% per decade) than September sea ice extent (-13.0% per decade). Permafrost temperatures reached record high values in northernmost Alaska. A new melt extent record occurred on 11-12 July on the Greenland ice sheet; 97% of the ice sheet showed some form of melt, four times greater than the average melt for this time of year. The climate in Antarctica was relatively stable overall. The largest maximum sea ice extent since records begain in 1978 was observed in September 2012. In the stratosphere, warm air led to the second smallest ozone hole in the past two decades. Even so, the springtime ozone layer above Antarctica likely will not return to its early 1980s state until about 2060. Following a slight decline associated with the global 2 emissions from fossil fuel combustion and cement production reached a record 9.5 +/- 0.5 Pg C in 2011 and a new record of 9.7 +/- 0.5 Pg C is estimated for 2012. Atmospheric CO2 concentrations increased by 2.1 ppm in 2012, to 392.6 ppm. In spring 2012, 2 concentration exceeded 400 ppm at 7 of the 13 Arctic observation sites. Globally, other greenhouse gases including methane and nitrous oxide also continued to rise in concentration and the combined effect now represents a 32% increase in radiative forcing over a 1990 baseline. Concentrations of most ozone depleting substances continued to fall.
|
|
| 2. |
- Khosrawi, Farahnaz, et al.
(författare)
-
Denitrification and polar stratospheric cloud formation during the Arctic winter 2009/2010
- 2011
-
Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 11:16, s. 8471-8487
-
Tidskriftsartikel (refereegranskat)abstract
- The sedimentation of HNO3 containing PolarStratospheric Cloud (PSC) particles leads to a permanent re-moval of HNO3 and thus to a denitrification of the strato-sphere, an effect which plays an important role in strato-spheric ozone depletion. The polar vortex in the Arctic win-ter 2009/2010 was very cold and stable between end of De-cember and end of January. Strong denitrification between 475 to 525 K was observed in the Arctic in mid of Januaryby the Odin Sub Millimetre Radiometer (Odin/SMR). Thiswas the strongest denitrification that had been observed inthe entire Odin/SMR measuring period (2001–2010). Lidarmeasurements of PSCs were performed in the area of Kiruna,Northern Sweden with the IRF (Institutet för Rymdfysik) li-odar and with the Esrange lidar in January 2010. The measurements show that PSCs were present over the area of Kirunaduring the entire period of observations. The formation ofPSCs during the Arctic winter 2009/2010 is investigated using a microphysical box model. Box model simulationsare performed along air parcel trajectories calculated sixdays backward according to the PSC measurements with the ground-based lidar in the Kiruna area. From the temperaturehistory of the backward trajectories and the box model simulations we find two PSC regions, one over Kiruna accordingto the measurements made in Kiruna and one north of Scandinavia which is much colder, reaching also temperatures below Tice. Using the box model trajectories together with the observations of Odin/SMR,Aura/MLS (Microwave Limb Sounder), CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations)and the ground-based lidar we investigate how and by whichtype of PSC particles the denitrification that was observedduring the Arctic winter 2009/2010 was caused. From ouranalysis we find that due to an unusually strong synopticcooling event in mid January, ice particle formation on NATmay be a possible formation mechanism during that particu-lar winter that may have caused the denitrification observed in mid January. In contrast, the denitrification that was observed in the beginning of January could have been caused by the sedimentation of NAT particles that formed on moun-tain wave ice clouds.
|
|
