Dynamics of the middle atmosphere at low, mid and high latitudes observed by the microwave wind radiometer WIRA Rolf Rüfenacht, Niklaus Kämpfer, Klemens Hocke, Ansgar Schanz Institute of Applied Physics, University of Bern, Switzerland ARISE final meeting 2014
Reasons for developing microwave Doppler wind radiometry
The measurement principle Doppler effect: ν = v LOS c ν 0 where v LOS = v cos ɛ with ɛ: elevation angle Frequency ν 0 = 142.17504 GHz from the rotational transition of the ozone molecule 6 khz ˆ 13 m/s
The measurement principle Doppler effect: ν = v LOS c ν 0 where v LOS = v cos ɛ with ɛ: elevation angle Frequency ν 0 = 142.17504 GHz from the rotational transition of the ozone molecule 6 khz ˆ 13 m/s Observations from west and east zonal wind Observations from north and south meridional wind Ozone emission line is pressure broadened altitude information
The instrument
The instrument Backend (in lab) Frontend (outdoors) AFFTS spectrometer Board 1 3.649 GHz resolution: 6.1 khz bandwidth: 100 MHz x8 10 MHz ref. active mult. 9.117 GHz Board 2 10 MHz ref. 2.950 GHz resolution: 183 khz bandwidth: 1500 MHz
The instrument Backend (in lab) Frontend (outdoors) AFFTS spectrometer Board 1 3.649 GHz resolution: 6.1 khz bandwidth: 100 MHz x8 10 MHz ref. active mult. 9.117 GHz Board 2 10 MHz ref. 2.950 GHz resolution: 183 khz bandwidth: 1500 MHz 154 west east 152 150 Brightness temperature [K] 148 146 144 142 140 138 142.13 142.14 142.15 142.16 142.17 142.18 142.19 142.2 142.21 142.22 Frequency [GHz]
The retrieval principle 154 152 west east 150 Brightness temperature [K] 148 146 144 142 140 138 142.13 142.14 142.15 142.16 142.17 142.18 142.19 142.2 142.21 142.22 Frequency [GHz] Atmospheric emission spectra 20 30 40 50 60 70 80 90 Zonal wind [m/s] Wind profile
The retrieval principle 154 152 west east 150 Brightness temperature [K] 148 146 144 142 140 138 142.13 142.14 142.15 142.16 142.17 142.18 142.19 142.2 142.21 142.22 Frequency [GHz] Atmospheric emission spectra 20 30 40 50 60 70 80 90 Zonal wind [m/s] Wind profile
The retrieval principle 154 152 west east 150 Brightness temperature [K] 148 146 144 142 140 138 142.13 142.14 142.15 142.16 142.17 142.18 142.19 142.2 142.21 142.22 Frequency [GHz] Atmospheric emission spectra Optimal estimation technique 20 30 40 50 60 70 80 90 Zonal wind [m/s] Wind profile Based on the measurement, a priori knowledge and uncertainties
Altitude resolution and accuracy 80 75 70 Altitude resolution [km] Altitude accuracy [km] Measurement response 10 65 60 55 50 45 Approx. altitude [km] 40 0 2 4 6 8 2 14 16 18 20 35
Error analysis 10 3 Noise level 0.1 K 10 3 True wind profile Standard retrieval Peak frequency Line intensity Pressure broad. coeff. p broad. T dependence Temperature profile Noise level 0.2 K 10 2 0 50 100 10 2 0 50 100
Zonal wind measured in Sodankylä (Oct 2011 - Jul 2012) Polar latitudes (67 22 N / 26 38 E) Zonal wind WIRA 1 2 150 100 50 0 24 Oct 13 Dec 01 Feb 22 Mar 11 May 30 Jun Zonal wind ECMWF 50 150 100 50 0 24 Oct 13 Dec 01 Feb 22 Mar 11 May 30 Jun 50
Zonal wind measured in Bern (Sep 2010 - Jul 2011) Mid latitudes (46 57 N / 7 26 E) Zonal wind WIRA 1 2 3 150 100 50 0 19 Sep 08 Nov 28 Dec 16 Feb 07 Apr 27 May 16 Jul 50 Zonal wind ECMWF 150 100 50 0 19 Sep 08 Nov 28 Dec 16 Feb 07 Apr 27 May 16 Jul 50
Zonal wind measured in Provence (Nov 2012 - May 2013) Mid latitudes (43 56 N / 5 43 E) Zonal wind WIRA 150 100 50 0 27 Nov 17 Dec 06 Jan 26 Jan 15 Feb 07 Mar 27 Mar 16 Apr 06 May Zonal wind ECMWF 50 150 100 50 0 27 Nov 17 Dec 06 Jan 26 Jan 15 Feb 07 Mar 27 Mar 16 Apr 06 May 50
Meridional wind measured in Provence (Nov 12 - May 13) Mid latitudes (43 56 N / 5 43 E) Meridional wind WIRA 27 Nov 17 Dec 06 Jan 26 Jan 15 Feb 07 Mar 27 Mar 16 Apr 06 May Meridional wind ECMWF 27 Nov 17 Dec 06 Jan 26 Jan 15 Feb 07 Mar 27 Mar 16 Apr 06 May 50 0 50 50 0 50
Zonal wind measured on La Réunion (Sep 13 - Nov 14) Tropical latitudes (21 04 S / 55 23 E) Zonal wind WIRA 100 50 0 50 23 Sep 12 Nov 01 Jan 20 Feb 11 Apr 31 May 20 Jul 08 Sep 28 Oct 100 Zonal wind ECMWF 100 50 0 50 23 Sep 12 Nov 01 Jan 20 Feb 11 Apr 31 May 20 Jul 08 Sep 28 Oct 100
27 day wave and link to solar activity? Zonal wind on La Réunion correlated with solar Lyman-alpha irradiance 0.5 0.4 0.3 0.2 0.1 0 0.1 0.2 Correlation coefficient 0.3 0.4 60 40 20 0 20 40 60 Time lag [days] 0.5
27 day wave and link to solar activity? Meridional wind on La Réunion correlated with solar Lyman-alpha irradiance 0.5 0.4 0.3 0.2 0.1 0 0.1 0.2 Correlation coefficient 0.3 0.4 60 40 20 0 20 40 60 Time lag [days] 0.5
Conclusions and outlook Continuous middle-atmospheric wind measurements (by microwave radiometry) offer a number of opportunities for atmospheric research: Direct observations of dynamical phenomena: Seasonal cycle Sudden stratospheric warmings Behaviour of the polar vortex Tropical patterns like semi-annual oscillation and potentially quasi-biennial oscillation Studies of atmospheric waves (like the 27 day wave)
Conclusions and outlook Continuous middle-atmospheric wind measurements (by microwave radiometry) offer a number of opportunities for atmospheric research: Direct observations of dynamical phenomena: Seasonal cycle Sudden stratospheric warmings Behaviour of the polar vortex Tropical patterns like semi-annual oscillation and potentially quasi-biennial oscillation Studies of atmospheric waves (like the 27 day wave) New compact WIRA-C is under construction to be used in ARISE-2
Averaging kernels 10 3 Averaging kernels Measurement response / 2 10 2 0.1 0 0.1 0.2 0.3 0.4 0.5 0.6
Error analysis 10 3 Noise level 0.1 K 10 3 True wind profile Standard retrieval O3 variation O3 var. large O3 var. small Baseline 1 Baseline 2 Baseline 10 3 1 Baseline 4 Noise level 0.2 K 10 2 0 50 100 10 2 0 50 100
Dependence from a priori information 10 3 90 A priori profile 0 m/s 10 m/s 10 m/s 20 m/s 20 m/s 30 m/s 30 m/s 40 m/s 40 m/s 50 m/s 50 m/s 80 70 60 50 40 Approx. altitude [km] 30 20 10 2 60 40 20 0 20 40 60 80 100 120 Zonal wind speed [m/s]
Position of polar vortex edge vs Sodankylä (winter 2011/12) Figure from Dominik Scheiben
Strength of polar vortex (winter 2011/12) Figure from Dominik Scheiben