Airborne remote sensing of NO sub(2) in the Arctic winter of 1994-1995 and comparison with a three-dimensional chemical transport model

In the winter of 1994-1995, for the first time NO sub(2) was observed by the Michelson Interferometer for Passive Atmospheric Sounding-Flugzeug Transall (MIPAS-FT). We present the NO sub(2) data of MIPAS and of a Differential Optical Absorption Spectroscopy (DOAS) instrument, which was also operated on the Transall, and compare the measurements with the Single Layer Isentropic Model for Chemistry And Transport (SLIMCAT). The daytime midlatitude NO sub(2) column amounts of MIPAS and DOAS increased from 1 x 10 super(1) super(5) cm super(-) super(2) in December to similar to 3 x 10 super(1) super(5) cm super(-) super(2) in March. After sunset MIPAS observed strong NO sub(2) increases, up to 3.2 x 10 super(1) super(5) cm super(-) super(2) on December 20, up to 7.2 x 10 super(1) super(5) cm super(-) super(2) on January 17 and up to 6.4 x 10 super(1) super(5) cm super(-) super(2) on March 27. These high nighttime values, showing considerable amounts of NO sub(x) in the midlatitude stratosphere, were qualitatively reproduced by SLIMCAT. The NO sub(2) columns measured inside the Arctic vortex, less than or equal to 1 x 10 super(1) super(5) cm super(-) super(2) from December until mid-January with no substantial increase after sunset, displayed strong denoxification. From the end of January the Arctic daytime NO sub(2) columns grew to similar to 2 x 10 super(1) super(5) cm super(-) super(2) , and after sunset MIPAS observed similar strong increases as at midlatitudes, up to 3.4 x 10 super(1) super(5) cm super(-) super(2) on January 24 and up to 4.8 x 10 super(1) super(5) cm super(-) super(2) in March and April. The renoxification of the vortex was also shown by SLIMCAT. On April 5, MIPAS NO sub(2) column amounts decreased by 1.5 x 10 super(1) super(5) cm super(-) super(2) after reaching the maximum, caused by N sub(2) O sub(5) and ClONO sub(2) formation and encounter of less renoxified air masses.