The First Issue of the WMO Arctic Ozone Bulletin for the 2015/16 Winter/Spring Season

Executive Summary, Arctic Ozone Bulletin no. 1, 2016 Temperatures cold enough for the formation of nitric acid trihydrate (NAT) clouds have existed since early December, and the area of the region with temperatures below the NAT formation temperature increased rapidly during the first weeks of December. Data from NASA show that from 26 December until now (22 January) the NAT area at the 460 K isentropic surface has been higher than any year during the 1978/79-2014/15 time period. At the 50 hPa isobaric level temperatures have been below the 1978/79-2014/15 average since early November. On several days in December and January the 50 hPa minimum temperature was below the 1978/79-2014/15 minimum. According to the forecast, the minimum temperature will first fall and then rise by about 10 K towards the end of the forecast period. At 50 and 100hPa, the temperature will oscillate but remain close to the long term minimum towards the end of the forecast period. Temperatures averaged over the 60-90°N region at the levels of 10, 50 and 100 hPa have been below the long term mean since November. On some days the average temperature has been below the long term minimum. The average temperature is forecast to increase during the next week and get close to the long term average. From 26 December until now (22 January) the NAT area at the 460 K isentropic surface has been higher than any year during the 1978/79-2014/15 time period. Forecasts show that the NAT area will decline somewhat over the course of the next week, but remain close to the long term maximum. Since early November, the longitudinally averaged heat flux between 45°N and 75°N has been lower than the long term average. During December and January it has increased gradually, while remaining well below the long term average. It is forecast to increase during the next few days. Over the course of the next week, the polar vortex will take on a very elongated shape and seems to be near a split, but towards the end of the forecast period it seems that it will contract and remain intact. Nitric acid (HNO3) has almost completely disappeared from the gas phase inside the polar vortex at several levels and is now bound up in polar stratospheric clouds. Also hydrochloric acid (HCl) has almost completely disappeared from the vortex at several levels. On the other hand, active chlorine (ClO + 2Cl2O2) is now present in considerable amounts (above 3 ppb) at several levels. If such mixing ratios persist, ozone depletion will set in as soon as the sun is back to the Arctic region after the polar night. Contact: Dr. Geir O. Braathen, Senior Scientific Officer, Atmospheric Environment Research Division (AER) Research Department (RES) World Meteorological Organization The World Meteorological Organization, January 2016