1. Maria Cadeddu, Jim Liljegren Argonne National Laboratory, 9700 S. C ass Avenue, Argonne, IL 60439, USA Vivienne Payne, Karen Cady-Pereira, Jean-Luc Moncet, Shepard. A. Clough Atmospheric and Environmental Research Inc., 131 Hartwell Ave., Lexington, MA, 02421-3626, USA vpayne@aer.com Assessment of microwave line parameters for oxygen: Comparisons between models and atmospheric measurements Introduction Improved spectroscopic parameters for oxygen have recently been published for the 60 GHz band. These parameters are an update of the MPM92 line parameters widely used in the remote sensing community. They include updated line widths, temperature dependence of the widths and line-coupling coefficients. The 60 GHz region is widely used for retrievals of atmospheric temperature profiles. Accurate spectroscopic parameters are crucial for accurate retrievals of atmospheric temperature and composition. Here we compare calculated brightness temperatures from a monochromatic radiative transfer model, MonoRTM, with measurements from a twelve- channel ground-based microwave radiometer (MWRP), situated at the Atmospheric Radiation Measurement (ARM) site on the North Slope of Alaska (NSA). Oxygen spectrum -Group of lines around 0 GHz Horizontal/vertical lines show -Group of lines around 60 GHz frequencies of instrument - Single line at 118 GHz channels -Line mixing effects are important Measurement/model comparisons Measurements: MWRP: Ground-based microwave radiometer Used to retrieve profiles of temperature, PWV and LWP 7 channels in the 60GHz band (3 are opaque) Situated at ARM site at North Slope of Alaska (NSA) 2 years of data Model: MonoRTM: Microwave radiative transfer model Use sonde profiles to calculate simulated T b T b comparisons for 4 non-opaque channels Retrievals of semi-empirical corrections to line parameters Retrieve scaling factors for -Line width -Temperature dependence of width -Line mixing coefficients Maximum likelihood retrieval 2 cases: 1.H04 as prior information 2.T05 as prior information H04 parameters as prior: retrieval moves towards T05 T05 parameters as prior: retrieval moves little References Boukabara, S.A., S.A. Clough and R. N. Hoffman, MonoRTM; a monochromatic radiative transfer model for microwave and laser calculation. In Programs and Abstracts: Specialist Meeting on Microwave Remote Sensing, 158, November 2001 Caddedu, M.P, V.H. Payne, S.A. Clough, K. Cady-Pereira and J. Liljegren, Efffect of the oxygen line parameter modelling on temperature and humidity retrievals from ground-based microwave radiometers, submitted to Transactions in Geoscience and Remote Sensing, June 2006 Hoke, M.L., S.A. Clough, W.J. Lafferty and B.W. Olsen, Line coupling in oxygen and carbon dioxide. In J. Lenoble and J.F Geleyn, editors, IRS 88: Current Problems in Atmospheric Radiation, 368- 371. A. Deepak Hampton, VA, 1989. H.J. Liebe, P.W. Rosenkranz and G.A. Hufford, J. Quant. Spectrosc. Radiat. Transfer 48, 629-643 (1992) Tretyakov, M.Yu., M.A. Koshelev, V.V. Dorovskikh, D.S. Marakov and P.W. Rosenkranz, 60 GHz oxygen band: precise broadening and central frequencies of fine-structure lines, absolute absorption profile at atmospheric pressure, and revision of mixing coefficients, J. Molec. Spec. 231, 1-14 (2005) Set of parameters Line Intensities Line widths Temp. dep. of widths Line mixing coefficients H04 HITRAN 2004 Hoke et al 1992 TO5 HITRAN 2004 Tretyakov et al, 2005 Liebe et al, 1992 Tretyakov et al, 2005 Summary New microwave oxygen parameters from Tretyakov et al (2005) improve agreement between measurement and model. New parameters also result in improved ground-based temperature retrievals Measurement/model comparisons suggest that HITRAN microwave oxygen parameters should be updated. Oxygen parameters from Tretyakov et al (2005) show good agreement with atmospheric measurements Model/measurement agreement can be improved by increasing the temperature dependence of the line width used by Tretyakov et al (2005) Line parameters Line intensities: Line widths Mixing coefficients Known within ~2% Temperature dependence of widths: H04: 0.71 T05: 0.8 Effect on temperature retrievals Dotted: prior. Solid: T05. Dashed: H04. A priori parametersScaling for line widths Scaling for temperature dependence Scaling for line mixing coefficients H04 +4%+16%+10% T05 -0.2%+4%+1% Temperature dependence of widths: H04_ret: 0.82 T05_ret: 0.83