Optimal Estimation Method [Rodgers, 2000]. Ground-based millimeter-wave Spectrometer (GBMS) designed and built at the Stony Brook University [de Zafra, ...
Polar vortex dynamics observed by means of stratospheric and mesospheric CO ground-based measurements carried out at Thule (76.5 N, 68.8 W), Greenland I.Fiorucci1, G. Muscari1, P. P. Bertagnolio1, C. Di Biagio2, P. Eriksen3, and R. de Zafra4
1Istituto
Nazionale di Geofisica e Vulcanologia, 2ENEA/UTMEA-TER, 3Danish Meteorological Institute, 4State University of New York at Stony Brook
European Geosciences Union General Assembly 2012 Vienna , Austria, 22 – 27 April 2012
Outline • Brief description of the observing technique and sample results
• Comparison with satellite observations
• Results from 4 winter measurement campaigns • Estimate of air masses subsidence rates inside the polar vortex
Motivation useful tool for studying:
CO is a useful tracer in the polar winter middle atmosphere due to:
1) Subsidence of mesospheric air inside the polar vortex with
1) long photochemical lifetime (≈ time scale for many dynamical processes)
2) latitudinal and vertical gradient
significant effects on ozone chemistry 2) Cross-vortex fast dynamical MLS CO zonal mean (in log ppmv) for the NH winter (from “Aura Microwave Limb Sounder Observations of the Polar Middle Atmosphere: Dynamics and Transport of CO and H2O” Lee et al., 2011)
processes driven by planetary wave
Observing technique Ground-based millimeter-wave Spectrometer (GBMS) designed and built at the Stony Brook University [de Zafra, 1995] • Rotational emission spectra of stratospheric and mesospheric trace gases (O3, HNO3, CO and N2O) between 230 and 280 GHz (tunable). • Deconvolution technique (to retrieve mixing ratio vertical profiles from the emission spectra): Optimal Estimation Method [Rodgers, 2000].
Observing site Thule Air Base, Greenland (76.5° N 68.8° W)
NDACC (Network for the Detection of Atmospheric Composition Change) Arctic station
CO observations • Bandwidth: 50 MHz
•Maximum resolution: 65 kHz •Integration time: 15-60 min
Long-term observation plan of the polar middle atmosphere for tracking long term trends and for bridging between global satellite-based measurements. Four winter campaigns: January-March 2009-2010-2011-2012
Sample CO spectra observed by GBMS Feb 16 Feb 18 Feb 22 Feb 24 Feb 25
8 6 4 2 0 0
100 200 300 400 500 600 700 800 900 1000
Channel Number [0.049 MHz/chan] 80 75 70
Altitude [km]
Brightness Temp [K]
10
65
Altitude sensitivity range: 35-80 km
60 55 50 45
Theoretical vertical resolution: 11-14 km
40 35 30 -0.8
-0.4
0
0.4
0.8
Averaging Kernels
1.2
Satellite comparison EOS Aura MLS • Near-polar orbit • Useful Range: 215-0.0046 hPa • Vertical resolution (mesosphere): 6-7 km
Coincidence criteria:
8 longitude, 1 latitude, 12 h
Column Content 30-80 km MLS Column Dens.[x10-20]
15
12
NTOT = 102
r = 0.88 m = 0.95
2009
9
2010
6
*
3
0 0
3
6
9
GBMS Column Dens.[x10
12 -20
]
15
2011
2012
Mean profiles 4 winters – 102 coincidences
80
Altitude [km]
70 60 50 40 30 0
GBMS MLS conv 5
10
15
20
Mixing Ratio [ppmv]
25
-6
-4
-2
0
2
4
6
Difference [ppmv]
MLS profiles (higher resolution) have been “convolved” using the GBMS Averaging Kernels before the comparison
3
r = 0.84 0.5
MLS CO [ppmv]
MLS CO [ppmv]
1
m = 0.69
0
35 km 0 0.5 GBMS CO [ppmv]
2
m = 0.75
1
45 km
0
1
0
1 2 GBMS CO [ppmv]
NTOT = 102 3
2009 2010
10
8
r = 0.95
6
m = 0.62
MLS CO [ppmv]
10
MLS CO [ppmv]
r = 0.93
4 2
55 km
0 0
2 4 6 8 GBMS CO [ppmv]
8
r = 0.91
6
m = 0.88
4 2
65 km
0 10
*
0
2 4 6 8 GBMS CO [ppmv]
10
2011 2012
Timeseries of CO mixing ratio profiles
2009
2011
2010
2012
Altitude [km]
Estimate of subsidence rates inside the vortex 80
80
75
75
70
70
65
65
60
60
55
55
50
50
45
45
40
40
35 30
2009 15 20 25 30 35 40 45 50 55 60 65 70
Day number
descent rate=0.17±0.04 km/day
35 30
2012 15 20 25 30 35 40 45 50 55 60 65 70
Day number
descent rate=0.18±0.01 km/day
12 11 10 9 8 7 6 5 4 3 2 1 0
Conclusions • GBMS allows retrieval of CO vertical profile between ≈35-70 km with vertical resolution of 11-14 km • Good agreement of GBMS and MLS column content between 30 and 80 km • GBMS and MLS profiles are well correlated at altitudes between 35 and 65 km although GBMS values display a high bias (1.5 ppmv) around 60 km • Estimated descent rates inside the polar vortex of about 0.18 km/day
References de Zafra, R. L., and G. Muscari (2004), CO as an important high-altitude tracer of dynamics in the polar stratosphere and mesosphere, J. Geophys. Res., 109, D06105, doi:10.1029/2003JD004099. de Zafra, R. L. (1995), The ground-based measurement of stratospheric gases using quantitative millimeter wave spectroscopy, in Diagnostic Tools in Atmospheric Physics, Proceedings of the international school of physics “Enrico Fermi”, 23-54, Società italiana di fisica, Bologna. Fiorucci, I., Muscari, G., and de Zafra, R. L. (2011), Revising the retrieval technique of a long-term stratospheric HNO3 data set: from a constrained matrix inversion to the optimal estimation algorithm, Ann. Geophys., 29, 1317-1330, doi:10.5194/angeo-29-1317-2011. Rodgers, C. D. (2000), Inverse method for atmospheric sounding, Series on atmospheric, oceanic and Planetary Physics - vol.2, Taylor, F. W., World Scientific Publishing Co. Pte LTd, Singapore. Lee, J.N., D.L. Wu, G.L. Manney, M.J. Schwartz, A. Lambert, N.J. Livesey, K.R. Minschwaner, H.C. Pumphrey, and W.G. Read (2011), Aura Microwave Limb Sounder Observations of the Polar Middle Atmosphere: Dynamics and Transport of CO and H2O, J. Geophys. Res. 116, D05110, doi:10.1029/2010JD014608.
