ASUR measurements of 23 January 2000.

ClO and HNO3 were measured during a DC-8 flight on 23 January. Figure 1 shows the increase in ClO with the rising sun as the aircraft flew south inside the polar vorex. Later on, a decrease is observed as the aircraft left the vortex flying westwards at constant solar zenith angle.

ClO at the altitude of 20 km is given in Figure 2 as a function of the solar zenith angle. The steep gradient at sunrise will be subject to a comparison with in-situ measurements done simultaneously on-board the ER-2 aircraft. There will also be comparison with model calculations.

HNO3 (nitric acid) measured on the same flight (Figure 3) shows high variability mainly due to polar stratospheric cloud formation, which occurs at low temperatures in the lower stratosphere.



	Activation observed with the ASUR instrument of the University of Bremen during the 23 January flight ClO and HNO3 were measured during a DC-8 flight on 23 January. Figure 1 shows the increase in ClO with the rising sun as the aircraft flew south inside the polar vorex. Later on, a decrease is observed as the aircraft left the vortex flying westwards at constant solar zenith angle. ClO at the altitude of 20 km is given in Figure 2 as a function of the solar zenith angle. The steep gradient at sunrise will be subject to a comparison with in-situ measurements done simultaneously on-board the ER-2 aircraft. There will also be comparison with model calculations. HNO3 (nitric acid) measured on the same flight (Figure 3) shows high variability mainly due to polar stratospheric cloud formation, which occurs at low temperatures in the lower stratosphere.


			Figure 1. Vertical section of the ClO (chlorine monoxide) mixing ratio (pppb) measured on 23 January 2000 with the ASUR microwave radiometer on-board the DC-8 aircraft. Click on the plot to see it in high resolution.

		Figure 2. The ClO mixing ratio (ppb) as a function of solar zenith angle (SZA) during the 23 January flight. Click on the plot to see it in high resolution.

		Figure 3. The HNO₃ (nitric acid) mixing ratio (ppb) as a function of altitude and time during the 23 January flight. Click on the plot to see it in high resolution.
This page was updated on 8 February 2000 by Geir Braathen, NILU.

Activation observed with the ASUR instrument of the University of Bremen during the 23 January flight