Arctic stratospheric ozone loss as observed over Kiruna, Sweden, during winter/spring 2004/05

Arctic stratospheric ozone loss as observed over Kiruna, Sweden, during winter/spring 2004/05

1 2 2 3U. Raffalski , G. Hochschild , G. Kopp , J. Urban ,

Swedish Institute of Space Physics, Kiruna, Sweden, E-mail: Uwe.Raffalski@irf.se2Institute of Meteorology and Climate Research, Forschungszentrum and University Karlsruhe,

3 Chalmers University of Technology, Gothenburg, Sweden

Forschungszentrum Karlsruhe In der Helmholtz-Gemeinschaft

CHALMERSwww.irf.se

Introduction

IRF Kiruna is located above the polar circle (67.8 N/20.4 E) investigating the peculiar processes in the atmosphere such as the aurora and the ozone layer within the polar vortex during Arctic winter. The ground-based observations of stratospheric trace-gases by the IRF millimetre wave radiome-ter KIMRA cover the altitude range from 15 up to 55 km. Here we present observations of stratospheric ozone covering the entire winter/spring period 2004/2005. KIMRA was operated almost continuously and from the measurements we calculated ozone profiles and column densities. For the estimated ozone loss we considered only measurements well within the polar vortex defined by the 'Equivalent Latitude' method described by Nash et al. [1996]*. In order to discriminate dynamic effects we deploy N O data from the Odin satellite.2

* Nash, E. R., P. A. Newmann, J. E. Rosenfield, and M. R.

Schoeberl, An objective determination of the polar vortex using Ertel's potential vorticity, J. Geophys. Res., 101, 9471 - 9478, 1996.

Acknowledgements

We would like to thank the ECMWF for the PV and temperature data and NCEP for providing temperature and pressure data used for the retrievals via the Goddard automailer system.

This work has been supported by the the European Community DG 12.

KIMRA was partly funded by the Swedish Knut and Alice Wallenberg foundation and the former Swedish Natural Research Council (NFR).

Figure 1: Evolution of the polar vortex in terms of equivalent latitudes.

The white lines describe the inner and outer edge of the vortex, respectively, while the black line describes the mean vortex edge, i.e. the strongest gradient in PV for the particular day. The colour coding shows the strength of the vortex in PVU. The open circles depict the PV over Kiruna on the particular measurement days and refer to the underlying PV colour coding, showing how far away from or how deep inside the vortex a measurement has been taken at IRF.

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 9040

50

60

70

80

90

PV [PVU]

Day of year 2005

19.25 -- 20.00 18.50 -- 19.25 17.75 -- 18.50 17.00 -- 17.75 16.25 -- 17.00 15.50 -- 16.25 14.75 -- 15.50 14.00 -- 14.75 13.25 -- 14.00 12.50 -- 13.25 11.75 -- 12.50 11.00 -- 11.75 10.25 -- 11.00 9.500 -- 10.25 8.750 -- 9.500 8.000 -- 8.750

400 K

40

50

60

70

80

90

34.50 -- 36.00 33.00 -- 34.50 31.50 -- 33.00 30.00 -- 31.50 28.50 -- 30.00 27.00 -- 28.50 25.50 -- 27.00 24.00 -- 25.50 22.50 -- 24.00 21.00 -- 22.50 19.50 -- 21.00 18.00 -- 19.50 16.50 -- 18.00 15.00 -- 16.50 13.50 -- 15.00 12.00 -- 13.50

435 K

40

50

60

70

80

90

475 K

53.50 -- 56.00 51.00 -- 53.50 48.50 -- 51.00 46.00 -- 48.50 43.50 -- 46.00 41.00 -- 43.50 38.50 -- 41.00 36.00 -- 38.50 33.50 -- 36.00 31.00 -- 33.50 28.50 -- 31.00 26.00 -- 28.50 23.50 -- 26.00 21.00 -- 23.50 18.50 -- 21.00 16.00 -- 18.50

40

50

60

70

80

90

550 K

123.8 -- 130.0 117.5 -- 123.8 111.3 -- 117.5 105.0 -- 111.3 98.75 -- 105.0 92.50 -- 98.75 86.25 -- 92.50 80.00 -- 86.25 73.75 -- 80.00 67.50 -- 73.75 61.25 -- 67.50 55.00 -- 61.25 48.75 -- 55.00 42.50 -- 48.75 36.25 -- 42.50 30.00 -- 36.25

40

50

60

70

80

90

675 K

360.0 -- 380.0 340.0 -- 360.0 320.0 -- 340.0 300.0 -- 320.0 280.0 -- 300.0 260.0 -- 280.0 240.0 -- 260.0 220.0 -- 240.0 200.0 -- 220.0 180.0 -- 200.0 160.0 -- 180.0 140.0 -- 160.0 120.0 -- 140.0 100.0 -- 120.0 80.00 -- 100.0 60.00 -- 80.00

40

50

60

70

80

90-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90

950 K

Equ

ival

entl

atitu

de[°

]

1988 -- 2100 1875 -- 1988 1763 -- 1875 1650 -- 1763 1538 -- 1650 1425 -- 1538 1313 -- 1425 1200 -- 1313 1088 -- 1200 975.0 -- 1088 862.5 -- 975.0 750.0 -- 862.5 637.5 -- 750.0 525.0 -- 637.5 412.5 -- 525.0 300.0 -- 412.5

Results

The Arctic winter 2004/05 has started with very low temperatures in December and January. The minimum temperatures for this winter period were reached in January when also polar stratospheric clouds have been observed. The upper panel of figure 3 shows the ECMWF temperatures on the 475 K isentropic level along with the measured ozone vmr values on the same level. Part of the total ozone loss is covered by the diabatic subsidence inside the vortex. In order to correct for the diabatic subsidence Odin vortex mean values of N O are used. All measurements shown in 2

the lower panel of figure 3 are taken inside the vortex and show a clear decrease in the volume mixing ratio of about 21% during January. The much higher vortex averaged temperature in February and March stopped the initially strong ozone depletion. The somewhat unusual vmr increase at the beginning of the winter has also been observed in former winters. The estimated vortex averaged ozone loss amounts to about 25 - 30%.

Figure 2: Time series of ozone during winter/spring 2004/05 (upper panel). The contour plot shows the volume mixing ratio in ppmv. The lower panel presents the partial ozone column density from 10 to 60 km.

120

160

200

240

280

32010

20

30

40

50

60 O3 vmr

[ppmv]

altit

ude

[km

]

7.5 -- 8.0 7.0 -- 7.5 6.5 -- 7.0 6.0 -- 6.5 5.5 -- 6.0 5.0 -- 5.5 4.5 -- 5.0 4.0 -- 4.5 3.5 -- 4.0 3.0 -- 3.5 2.5 -- 3.0 2.0 -- 2.5 1.5 -- 2.0 1.0 -- 1.5 0.5 -- 1.0 0.0 -- 0.5

- 40 - 20 0 60 8020- 60 40

Day of year 2005

O3pa

rtia

lcol

umn

[DU

]

Figure 3: The ECMWF temperature over Kiruna and ozone volume mixing ratio on the 475 K isentropic surface (upper panel). Data points depict inside vortex measurements only. In the lower panel the same vmr data are calculated for N O isopleths provided 2

by Odin data in order to eliminate effects of diabatic subsidence.

-40 -20 0 20 40 60 801,6

1,8

2,0

2,2

2,4

2,6

2,8

3,0

3,2

3,4

3,6

3,8

4,0

4,2

4,4

Ozo

nem

ixin

gra

tio[p

pmv]

Day of Year 2005

N2O 150 ppbv

N2O 125 ppbv

N2O 100 ppbv

N2O 75 ppbv

N2O 50 ppbv

N2O 25 ppbv

-40 -20 0 20 40 60 801,5

2,0

2,5

3,0

3,5

180

190

200

210

220 ozone @ 475 K over Kiruna Temperature @ 475 K over Kiruna

Tem

perature@

475K

[K]

Ozo

nevm

r@

475

K[p

pmv]

Day of year 2005

Measurements

KIMRA is a heterodyne radiometer with a cryogenically cooled Schottky mixer. It measures thermal emission lines of strato-spheric trace gases like ozone in the fre-quency range 195-224 GHz. Continuous ozone observations with KIMRA have started in January 2002 providing a time series of almost uninterrupted ozone data. The data in figure 2 present the period November 2004 to March 2005.For the retrieval a modified ‘Optimal Esti-mation Method’ (Rodgers, 1976)** is used.Deploying the FWHM of the averaging ker-nels we can obtain a vertical resolution of the ozone profiles of at best 7 km (at 25 km altitude). Contributions from the measure-ments to the retrieved profile are typically higher than 75% in the altitude range from 15 to 55 km. However the partial column densities are calculated for 10 to 60 km. ** Rodgers, C.D., Retrieval of Atmospheric Temperature and

Com-position from Remote Measurements of Thermal Radiation, Reviews of Geophysics and Space Physics, 14, 609--624, 1976.