Sciences and Exploration Directorate

Stephen E Cohn


Stephen E Cohn's Contact Card & Information.
Phone: 301.614.6168
Org Code: 610.1
Mail Code 610.1
Greenbelt, MD 20771

Research Interests

Data Assimilation for Earth System Science, Atmospheric Dynamics and Stochastics, Numerical Weather Prediction, Estimation Theory, Partial Differential Equations

Earth Science: Theory & Modeling


Research Meteorologist, Computer Scientist, Mathematician

NASA Goddard Space Flight Center - Greenbelt, Maryland

1991 - Present

Research Scientist

Universities Space Research Association - Greenbelt, Maryland

1991 - 1991

UCAR Senior Fellow

National Meteorological Center - Camp Springs, Maryland

1990 - 1991

Visiting Professor

Universidade Federal do Rio de Janeiro - Rio de Janeiro, Brazil

1988 - 1988

Visiting Professor

Universita di Catania - Catania, Italy

1987 - 1987

Visiting Professor

Pontificia Universidade Catolica do Rio de Janeiro - Rio de Janeiro, Brazil

1983 - 1985

Assistant Research Scientist through Research Assistant Professor

Courant Institute of Mathematical Sciences, New York University - New York, New York

1982 - 1991


Ph.D., Mathematics, Courant Institute of Mathematical Sciences, New York University, 1982. Thesis Title: Methods of Sequential Estimation for Determining Initial Data in Numerical Weather Prediction

M.S., Mathematics, Courant Institute of Mathematical Sciences, New York University, 1978

B.S., Physics and Mathematics, Drexel University, 1976 

Professional Societies

American Meteorological Society

1978 - Present

American Mathematical Society

1976 - Present

Society for Industrial and Applied Mathematics

1976 - Present

Professional Service

2016 - 2021: Assistant Chief, Global Modeling and Assimilation Office

2014 - 2021: Member, GMAO Strategic Management Team

2008 - 2009: Member, International Scientific Organizing Committee, Fifth WMO International Symposium on Data Assimilation, Melbourne, Australia

2005: Guest Editor, Quarterly Journal of the Royal Meteorological Society

2004 - 2005: Co-Chair, International Program Committee, Fourth WMO International Symposium on Assimilation of Observations in Meteorology and Oceanography, Prague, Czech Republic

2003 - 2008: Editor, Monthly Weather Review

2002 - 2003: Member, Scientific Committee, Roger Daley Memorial Symposium, Montreal, Canada

2002: Lecturer, NATO Advanced Study Institute (ASI) on Data Assimilation for the Earth System, Maratea, Italy

2000 - 2002: Chief Scientist for Analysis, Data Assimilation Office, GSFC

2000 - 2001: Ph.D. Thesis Supervisor (Tijana Janjic), University of Maryland College Park

2000 - 2001: Special Faculty, University of Maryland College Park

1998 - 2000: Associate Editor, Monthly Weather Review

1995: Member, Scientific Committee, Second UNAM-Cray Supercomputing Conference on Numerical Simulations in the Environmental and Earth Sciences, Mexico City, Mexico

1993 - 1998: Lead Scientist for GEOS Data Assimilation System Development, GSFC

1993 - 1995: Fellow, Joint Center for Earth System Science

1992, 2002: Branch Representative, Summer Institute on Atmospheric and Hydrospheric Sciences

1992 - 1998: Chair, GSFC Library Committee

1992 - 1994: Chair and Founding Member, Goddard Mathematics Group


Other Professional Information

As of October 2022:

Total Citations: 5,190

Total Publications: 108

H-Index: 25

I10-Index: 35

Special Experience

2020 - 2021: Lead, PDT, SAMDA II Contract

2017 - 2021: Alt-COR, SAMDA Contract

2016: COR, Remote Sensing Systems (RSS) Contract

2015 - 2016: Member, PDT, Support for Atmospheres, Modeling and Data Assimilation (SAMDA) Contract

2012 - 2013: Member, SEB, Information Sciences and Library Services (ISLS) Contract

2011 - 2012: Member, SEB, Support for Atmospheric Sciences (SAS) Contract

2011: Member, SEB, Global Modeling and Assimilation Office (GMAO) Contract

2006 - 2017: COTR, Global Modeling and Assimilation Office (GMAO) Contract

2005: Chair, SEB, Global Modeling and Assimilation Office (GMAO) Contract

2000: Member, SEB, Laboratory for Atmospheres (LAS) Contract

Selected Publications


2023. "A generalized, compactly supported correlation function for data assimilation applications." Quarterly Journal of the Royal Meteorological Society 149 (754): 1953-1989 [10.1002/qj.4490] [Journal Article/Letter]

2023. "M2‐SCREAM: A Stratospheric Composition Reanalysis of Aura MLS Data With MERRA‐2 Transport." Earth and Space Science 10 (2): e2022EA002632 [10.1029/2022ea002632] [Journal Article/Letter]

2022. "Continuum Covariance Propagation for Understanding Variance Loss in Advective Systems." SIAM/ASA Journal on Uncertainty Quantification 10 (3): 886-914 [10.1137/21m1442449] [Journal Article/Letter]

2021. "Sub‐City Scale Hourly Air Quality Forecasting by Combining Models, Satellite Observations, and Ground Measurements." Earth and Space Science 8 (7): [10.1029/2021ea001743] [Journal Article/Letter]

2020. "The Anomalous 2019 Antarctic Ozone Hole in the GEOS Constituent Data Assimilation System With MLS Observations." Journal of Geophysical Research: Atmospheres 125 (18): [10.1029/2020jd033335] [Journal Article/Letter]

2017. "On the representation error in data assimilation." Quarterly Journal of the Royal Meteorological Society 144 (713): 1257-1278 [10.1002/qj.3130] [Journal Article/Letter]

2014. "Conservation of Mass and Preservation of Positivity with Ensemble-Type Kalman Filter Algorithms." Mon. Wea. Rev. 142 (2): 755-773 [10.1175/MWR-D-13-00056.1] [Journal Article/Letter]

2012. "Numerical treatment of degenerate diffusion equations via Feller's boundary classification, and applications." Numerical Methods for Partial Differential Equations 28 (3): 807-833 [10.1002/num.20657] [Journal Article/Letter]

2010. "The principle of energetic consistency in data assimilation." Data Assimilation: Making Sense of Observations Chapter 7 137--216 [10.1007/978-3-540-74703-1] [Article in Book]

2009. "Energetic Consistency and Coupling of the Mean and Covariance Dynamics." Handbook of Numerical Analysis Vol. XIV, Special Volume: Computational Methods for the Atmosphere and the Oceans Chapter 10 443-478 [10.1016/s1570-8659(08)00210-x] [Article in Book]

2006. "Treatment of Observation Error due to Unresolved Scales in Atmospheric Data Assimilation." Monthly Weather Review 134 (10): 2900-2915 [10.1175/mwr3229.1] [Journal Article/Letter]

2006. "Construction and application of covariance functions with variable length-fields." Q.J.R. Meteorol. Soc. 132 (619): 1815-1838 [10.1256/qj.05.08] [Journal Article/Letter]

2004. "A Lagrangian trajectory filter for constituent data assimilation." Q. J. R. Meteorol. Soc. 130 (601): 2315-2334 [10.1256/qj.02.234] [Journal Article/Letter]

2003. "Tangent linear analysis of the Mosaic land surface model." J. Geophys. Res. 108 (D2): 4054 [10.1029/2002JD002410] [Journal Article/Letter]

2003. "The GEOS-3 Retrospective Data Assimilation System: The 6-Hour Lag Case." Mon. Weather Rev. 131 (9): 2129-2150 [10.1175/1520-0493(2003)131<2129:TGRDAS>2.0.CO;2] [Journal Article/Letter]

2003. "Tangent linear analysis of the Mosaic land surface model." J Geophys Res 108 (D2): 12-1 - 12-16 [Journal Article/Letter]

2001. "Adjoints and low-rank covariance representation." Nonlinear Processes in Geophysics 8 (6): 331-340 [10.5194/npg-8-331-2001] [Journal Article/Letter]

2000. "Low-dimensional representation of error covariance." Tellus 52A (5): 533-553 [Journal Article/Letter]

2000. "Conditioning of the Stable, Discrete-Time Lyapunov Operator." SIAM. J. Matrix Anal. & Appl. 22 (1): 56-65 [10.1137/S0895479899354822] [Journal Article/Letter]

2000. "Assimilation of stratospheric chemical tracer observations using a Kalman filter. Part I: Formulation." Monthly Weather Review 128 (8): 2654--2671 [Journal Article/Letter]

1999. "Construction of correlation functions in two and three dimensions." Quarterly Journal of the Royal Meteorological Society 125 (554): 723-757 [10.1256/smsqj.55416] [Journal Article/Letter]

1998. "Suboptimal Schemes for Retrospective Data Assimilation Based on the Fixed-Lag Kalman Smoother." Monthly Weather Review 126 (8): 2274-2286 [<2274:] [Journal Article/Letter]

1998. "A study on assimilating potential vorticity data." Tellus A 50 (4): 490-506 [10.1034/j.1600-0870.1998.t01-2-00008.x] [Journal Article/Letter]

1998. "The use of spline interpolation in semi-Lagrangian transport models." Monthly weather review 126 (7): 2008--2016 [Journal Article/Letter]

1998. "Assessing the Effects of Data Selection with the DAO Physical-Space Statistical Analysis System*." Monthly Weather Review 126 (11): 2913--2926 [Journal Article/Letter]

1997. "An introduction to estimation theory." JOURNAL-METEOROLOGICAL SOCIETY OF JAPAN SERIES 2 75 147--178 [Journal Article/Letter]

1997. "Data assimilation in the ocean and in the atmosphere: what should be next?." Journal of the Meteorological Society of Japan 75 (1B): 489--496 [Journal Article/Letter]

1997. "Parallel implementation of a Kalman filter for constituent data assimilation." Monthly weather review 125 (7): 1674--1686 [Journal Article/Letter]

1996. "Approximate data assimilation schemes for stable and unstable dynamics." JOURNAL-METEOROLOGICAL SOCIETY OF JAPAN SERIES 2 74 63--75 [Journal Article/Letter]

1994. "Suboptimal Schemes for Atmospheric Data Assimilation Based on the Kalman Filter." Monthly Weather Review 122 (11): 2530-2557 [<2530:] [Journal Article/Letter]

1994. "A fixed-lag Kalman smoother for retrospective data assimilation." Monthly Weather Review 122 (12): 2838-2867 [<2838:] [Journal Article/Letter]

1993. "Dynamics of short-term univariate forecast error covariances." Monthly weather review 121 (11): 3123--3149 [Journal Article/Letter]

1991. "Eliminating grid-orientation errors in alternating-direction implicit schemes." Applied Numerical Mathematics 8 (1): 1-10 [10.1016/0168-9274(91)90094-g] [Journal Article/Letter]

1991. "The behavior of forecast error covariances for a Kalman filter in two dimensions." Monthly Weather Review 119 (8): 1757--1785 [Journal Article/Letter]

1989. "An analysis of the vertical structure equation for arbitrary thermal profiles." Quarterly Journal of the Royal Meteorological Society 115 (485): 143-171 [10.1002/qj.49711548508] [Journal Article/Letter]

1988. "Observability of Discretized Partial Differential Equations." SIAM Journal on Numerical Analysis 25 (3): 586-617 [10.1137/0725037] [Journal Article/Letter]

1985. "An efficient algorithm for estimating noise covariances in distributed systems." IEEE Transactions on Automatic Control 30 (11): 1057-1065 [10.1109/tac.1985.1103837] [Journal Article/Letter]

1985. "A factored implicit scheme for numerical weather prediction." Comm. Pure Appl. Math. 38 (5): 503-517 [10.1002/cpa.3160380504] [Journal Article/Letter]

1985. "A fully implicit scheme for the barotropic primitive equations." Monthly weather review 113 (4): 436--448 [Journal Article/Letter]