Page 1 MIPAS QWG#12 14/16 February 2007 Retrieval of 15 N/ 14 N isotopic ratio from MIPAS spectra Feasibility of 15 N/ 14 N isotopic ratio profile retrieval from MIPAS spectra G. Brizzi, M. Carlotti, M. Ridolfi, E. Papandrea Bologna University J.-M. Flaud Laboratoire Interuniversitaire des Systèmes Atmosphériques B.M. Dinelli ISAC-CNR

Page 2 MIPAS QWG#12 14/16 February 2007 Retrieval of 15 N/ 14 N isotopic ratio from MIPAS spectra Detection of H 15 NO 3 in the atmosphere Spectral interval 870 – cm -1 (MIPAS band A) G. Brizzi, M. Carlotti, J.-M. Flaud, A. Perrin, M. Ridolfi, First observation of H 15 NO 3 in atmospheric spectra, Geophys. Res. Lett., Vol. 34, No. 3, Signal of H 15 NO 3 evident in residual spectra ! Low S / N → use of average MIPAS spectra T.H. range km Based on the comparison of averaged residuals

Page 3 MIPAS QWG#12 14/16 February 2007 Retrieval of 15 N/ 14 N isotopic ratio from MIPAS spectra Retrieval strategy 1 - Using retrieval software based on UNIBO GMTR software, modified to retrieve isotopic ratio. Subsequent scans: optimal estimation with a-priori profile = profile retrieved in the previous scan with its own error (full VCM). H 14 NO 3 → optimal estimation with a-priori profile retrieved at step N/ 14 N → First scan: optimal estimation with a-priori profile = double of natural isotopic ratio (error = 50%) and Tikhonov first derivative regularization (strength tuned on the basis of a suitable trade-off between noise error and vertical resolution). 2 - First retrieving MIPAS main targets with classical GMTR approach. 3 - Scan by scan (homogeneous atmosphere) joint retrieval of H 14 NO 3 and 15 N/ 14 N.

Page 4 MIPAS QWG#12 14/16 February 2007 Retrieval of 15 N/ 14 N isotopic ratio from MIPAS spectra Tests with simulated observations - MIPAS simulated observations for 72 scans from orbits (HR 17 sweeps) 15 N/ 14 N natural isotopic ratio Assumed True-value Fitted profile - 3 MWs:MW1 H15N cm -1 MW2 HNO cm -1 MW3 HNO cm -1 - Tangent altitude range from 12 to 42 km (maximum HNO 3 VMR around 20 km) Used in OFL HNO 3 retrieval Retrieval assumptions

Page 5 MIPAS QWG#12 14/16 February 2007 Retrieval of 15 N/ 14 N isotopic ratio from MIPAS spectra A-priori profile Retrieved profile In-guess and a-priori profile of scan 1: R = 2±1 True value: R = 1 R profiles retrieved from simulated observations Medium-strength regularization 15 N/ 14 N profile – sequence 1 15 N/ 14 N profile – sequence 2 15 N/ 14 N profile – sequence 3 15 N/ 14 N profile – sequence 4 15 N/ 14 N profile – sequence 5 15 N/ 14 N profile – sequence N/ 14 N profile – sequence N/ 14 N profile – sequence N/ 14 N profile – sequence N/ 14 N profile – sequence 72 Retrieved profile moves towards true value ESD reduction Retrieved profile still on the initial guess (scan 1) R No information !

Page 6 MIPAS QWG#12 14/16 February 2007 Retrieval of 15 N/ 14 N isotopic ratio from MIPAS spectra R profiles retrieved from simulated observations (2) Strong regularization 15 N/ 14 N profile – sequence 1 15 N/ 14 N profile – sequence 2 15 N/ 14 N profile – sequence 3 15 N/ 14 N profile – sequence 4 15 N/ 14 N profile – sequence 5 15 N/ 14 N profile – sequence N/ 14 N profile – sequence N/ 14 N profile – sequence N/ 14 N profile – sequence N/ 14 N profile – sequence 72 A-priori profile Retrieved profile In-guess and a-priori profile of scan 1: R = 2±1 True value: R = 1 R Retrieved profile moves towards true value ESD reduction Retrieved profile still on the initial guess (scan 1) No information !

Page 7 MIPAS QWG#12 14/16 February 2007 Retrieval of 15 N/ 14 N isotopic ratio from MIPAS spectra How many spectra have to be processed ? ESD of R decreases with increasing number of processed scans

Page 8 MIPAS QWG#12 14/16 February 2007 Retrieval of 15 N/ 14 N isotopic ratio from MIPAS spectra Error budget estimation - Using MWMAKE (Oxford University) 1 MW (H15N0001) H 14 NO 3 H 15 NO 3 Preliminary results !

Page 9 MIPAS QWG#12 14/16 February 2007 Retrieval of 15 N/ 14 N isotopic ratio from MIPAS spectra Error budget estimation (2) Preliminary results ! 3 MWs H 14 NO 3 H 15 NO 3

Page 10 MIPAS QWG#12 14/16 February 2007 Retrieval of 15 N/ 14 N isotopic ratio from MIPAS spectra Future work 4 - Establish an acceptable trade-off between the noise error (number of scans to be processed for the retrieval of an individual R profile) and the strength of the regularization. 1 - Estimate the error budget of the isotopic ratio profile (R). 5 - Carry out the analysis using real measurements (HR 17 sweeps). 3 - Based on the resulting number of scans to be processed for the retrieval of an individual R profile, establish suitable latitudinal and time windows from which MIPAS measurement should be selected. 2 - Calculate the vertical resolution (AK).