1. NASA, CGMS-44, 7 June 2016 Coordination Group for Meteorological Satellites - CGMS SURFACE PRESSURE MEASUREMENTS FROM THE ORBITING CARBON OBSERVATORY-2 (OCO-2): A PROGRESS REPORT Presented to CGMS-44 Working Group II session, agenda item WGII/8 In response to CGMS action A43.15 Presenter: Jack Kaye, NASA HQ Report prepared by David Crisp 1, Christopher O’Dell 2, W. McCarty 3, M. Chattopadhyay 3,4, M. Sienkiewicz 3,4, S. Pawson 3, and Kenneth W. Jucks 5 1 Jet Propulsion Laboratory, California Institute of Technology, 2 Colorado State University, 3 NASA Goddard Space Flight Center, 4 Science Systems and Applications, Inc., 5 NASA Headquarters

2. NASA, CGMS-44, 7 June 2016 Coordination Group for Meteorological Satellites - CGMS Slide: 2 OVERVIEW The Orbiting Carbon Observatory-2 (OCO-2) is the first NASA mission designed to measure atmospheric carbon dioxide (CO 2 ) with the precision, accuracy, resolution, and coverage needed to quantify the “sources” emitting this gas into the atmosphere, and the “sinks” at the surface that are absorbing it. OCO-2 was successfully launched in July of 2014 and was inserted into the 705 km Afternoon Constellation (A-Train) one month later. Since September of 2014, OCO-2 has been returning over 100,000 cloud-free, full- column estimates of the column averaged CO 2 dry air mole fraction, X CO 2, surface pressure, total water column, and other variables. Comparisons of these preliminary surface pressure estimates with those from the European Center for Medium Range Weather Forecasts (ECMWF) and other standards indicate a global bias of 1.4 to 3 hPa and a single sounding random error of about 1 hPa. Recent improvements in the OCO-2 retrieval algorithm are expected to reduce biases. Work is ongoing to assimilate the OCO-2 surface pressure data into the Goddard Earth Observing System (GEOS) atmospheric data assimilation system (ADAS) to assess how they interact with the existing conventional surface pressure observations in the assimilation procedure.

3. NASA, CGMS-44, 7 June 2016 Coordination Group for Meteorological Satellites - CGMS Slide: 3 OCO-2 Sampling Approach OCO-2 orbits the Earth 14.5 times each day, collecting 24 soundings each second along a narrow measurement track as it flies over the sunlit hemisphere, yielding almost 1 million soundings each day 3 frames per second 14 - 15 orbits per day 12 seconds of data O 2 A-Band CO 2 1.61  m Band CO 2 2.06  m Band

4. NASA, CGMS-44, 7 June 2016 Coordination Group for Meteorological Satellites - CGMS Slide: 4 Differences between OCO-2 and ECMWF Pressures Monthly average differences between surface pressure estimates from the OCO-2 version 7 algorithm and ECMWF predictions for September 2014 (top left), December 2014 (top right), March 2015 (bottom left) and June 2015 (bottom right). A global bias of 2.5 hPa has been removed from these results, and the differences have been binned into 2  by 2  bins.

5. NASA, CGMS-44, 7 June 2016 Coordination Group for Meteorological Satellites - CGMS Slide: 5 Overall Bias Correction Background departure distributions without (left) and with (right) bias correction for 12-17 July 2015 for the land/nadir (top), land/glint (middle), and ocean/glint (bottom) OCO-2 surface pressure retrievals. The red lines represent the calculated normal distribution.

6. NASA, CGMS-44, 7 June 2016 Coordination Group for Meteorological Satellites - CGMS Slide: 6 Overall Bias Correction Spatial distribution of background departure for 1800 UTC on 12 July 2015 for all assimilated surface pressure observations (left) and the assimilated OCO surface pressure retrievals (right).

7. NASA, CGMS-44, 7 June 2016 Coordination Group for Meteorological Satellites - CGMS Other OCO-2 Variables: Total Column Water Vapor (TCWV) Slide: 7 Motivation: Atmospheric water vapor measurements are useful Water vapor information is contained in the OCO-2 near-infrared lines Could OCO-2 provide accurate, global obs. of water vapor? Results: OCO-2 is able to retrieve a more precise TCWV relative to its ECMWF* Integrated Forecasting System estimates, when compared to SuomiNet Variance reduction of ~55-70% (retrieved vs. prior) (see below figure) Results not spatially biased (see right figure) Significance: Shows that OCO-2-retrieved TCWV can be used to constrain atmospheric reanalysis data sets (e.g., ECMWF and MERRA) and to tell the OCO-2 algorithm whether to trust the reanalysis used as a test for surface pressure (which correlates to H 2 O column). ECMWF* TCWV (OCO-2 Prior) OCO-2 Retrieved TCWV *European Center for Medium range Weather Forecasting

8. NASA, CGMS-44, 7 June 2016 Coordination Group for Meteorological Satellites - CGMS Slide: 8 CONCLUSIONS The OCO-2 mission is returning estimates of surface pressure for each of the ~100,000 clear-sky soundings that it collects each day. Comparisons of these preliminary surface pressure estimates with the ECMWF results and other standards indicate a global bias of about 2.4 hPa and a single sounding random error of about 1 hPa. Ongoing improvements in the OCO-2 retrieval algorithm are expected to increase the overall accuracy of this product substantially in the next data product release. A preliminary effort to assimilate the OCO-2 surface pressure estimates into the GMAO GEOS ADAS has been initiated to assess their impact on a 6-hour numerical weather prediction. This effort is already yielding useful insight into how remotely sensed pressure measurements interact with the existing conventional surface pressure observations in the assimilation procedure. The utility of other OCO-2 variables of meteorological significance, such as total column water vapor (TCWV) is also being studied.