Decadal Forecasting of UV Dosage Levels at the Surface Aura Airborne Ground Based and Modeling

Decadal Forecasting Of UV Dosage Levels at the Surface: Aura, Airborne, Ground-based, and Modeling EOS Aura Science Team Meeting Pasadena, CA February 28─March 3, 2005 Jim Anderson Rick Stimpfle, Dave Wilmouth, Jasna Pittman, Tom Hanisco, Liz Moyer, Frank Keutsch, Ryan Spackman Elliot Weinstock, Dave Sayres, Harvard University NRC Decadal Report Requested by NASA and NOAA PHASE I Earth Science and Applications from Space: Urgent Needs and Opportunities to Serve the Nation Explicitly Identify the Critical Importance of Societal Objectives Emphasize the Required Decision Support Structure Presidential Initiatives • US Climate Change Science Program: Strategic Plan 1. Reduce uncertainty in projections of how the Earth’s climate and related systems may change in the future; 2. Understand the sensitivity and adaptability of different natural and managed ecosystems and human systems to climate and related global changes; and 3. Explore the uses and identify the limits of evolving knowledge to manage risks and opportunities related to climate variability and change • Global Earth Observation Initiative: 2003 • Vision for Space Exploration ADDRESSING THE SOCIETAL OBJECTIVE OF FORECASTING UV DOSAGE REQUIRES: • Restructuring the connection between forecast modeling, satellite observations and in situ and ground based observations: common coordinate system, high accuracy observations, data assimilation, systematic testing of forecast output, workshop structure that joins to an operational plan to deliver required input to the decision process. • Reassessment of the sophistication and credibility of the observations that are required to develop a picture of this system – to understand the specific mechanisms responsible for S/T exchanges, the coupling of the tropics to the sub-tropics, the role of the middle world in meridional exchange, the dominant rate limiting catalytic cycles, the convective coupling of troposphere to the TTL,etc. – that is tested and trusted leading to a forecast that is credible. Central tenet in the latest WMO report: Scientific Assessment of Ozone Depletion: 2002 In the Scientific Summary for the key Chapter 4, under, “Attribution of Past Changes in Ozone,” on page 4.2, it is stated: “The vertical, latitudinal, and seasonal characteristics of changes in mid-latitude ozone are broadly consistent with the understanding that halogens are the primary cause of these changes, in line with similar conclusions from the 1998 Assessment.” Sensitivity of Ozone Trends to Bromine BryTROP = 8 ppt model accounts for ~94% of observed O3 depletion in the N.H. Enhanced Bromine:  increase in computed ozone depletion  better agreement with observation Ozone Photochemistry AER Model Time Slice: 47°N, March 1993 BryTROP = 0 ppt BryTROP = 8 ppt Enhanced Bromine:   ozone depletion due mainly to BrO+ClO cycle  BrO+HO2 cycle becomes significant O3 sink below 16 km (BrO+HO2 does not drive O3 depletion if BryTROP is constant over time) David Wilmouth’s Poster Images Sensitivity of Ozone Trends to Bromine BryTROP = 8 ppt model accounts for ~94% of observed O3 depletion in the N.H. Enhanced Bromine:  increase in computed ozone depletion  better agreement with observation Solomon et al., “Heterogeneous chlorine chemistry in the tropopause region,” J. Geophys. Res. 102, 21,41129, 1997. Sensitivity of Ozone Trends to Bromine BryTROP = 8 ppt model accounts for ~94% of observed O3 depletion in the N.H. Enhanced Bromine:  increase in computed ozone depletion  better agreement with observation IPCC 4AR dq/dt: Difference Between Model Forecasts Pressure (hPa) Latitude What Characterizes the Eocene? • Warm deep ocean temperatures: 10 K warmer than at present • Warm polar sea surface temperatures • Northern Hemisphere continental interiors were warm enough throughout year to sustain palm trees and tropical flora/fauna to northern Canada • Continental glaciation absent • Tropical temperatures similar to present Sloan and Pollard [1998] imposed optically thick PSCs in a GCM in combination with increased greenhouse gas concentration. Wintertime warming of 4 K at mid latitudes 20 K at polar latitudes Origin of PSCs? Methane CH 4  O( 1 D)  OH  CH 3  H 2 O Increased swamp and wet lands PROBLEM: Eocene warmth uninterrupted for 10 million years CH  Chem ~ 7 years 4 Evidence for episodic release from isotopes, but not sustained release Feedback Between CO2, Stratospheric Overturning, and Stratospheric H2O 1. When CO2 increases, GCMs predict increasing surface warming in the polar regions from ice/snow albedo feedback 2. This leads to reduced equator-to-pole temperature gradient (Teq  Tp), potentially in concert with ocean/atmos heat flux changes 3. This leads to reduced excitation of gravity and planetary waves (A), Reduced wave breaking in the stratosphere diminishes the delivery of momentum (M) to the stratosphere 4. This decrease in overturning results in an increase in the temperature of the cold-point tropopause (TT) IPCC 4AR dT/dt: Difference Between Model Forecasts Pressure (hPa) Pressure (hPa) Latitude Latitude Global Climate Benchmark Measurements Occultation methods: How they work Signal Source EM Signals Signal Source LEO Sensor Signal Source [Basic figures from D. Feng, Univ. of Arizona, private communications, 2001 (modified)] LEO Transmitted Signals Received Signals Occultation methods • Exploit extinction and/or refraction of electromagnetic signals along limb paths • Providing self-calibrated measurements of transmission and/or Doppler shift profiles • Leading via opt. thickness or column density, bending angle, and (complex) refractivity • To key atmospheric and climate parameters such as temperature, humidity, ozone, and geopotential height (among others) GPS Occultation: The Time Standard • GPS occultation is tied to ground-based atomic clock standards by doubledifferencing technique. NIST F1 measures time with fractional error of 1.7•10-15 (as of 1999). • Radiosondes and GPS Occultation COSMIC • Six satellites in three 72° orbit planes • > 3000 soundings per day • Launch in 2005 • Taiwan, NSF (UCAR) Five days’ worth of COSMIC occultations with GPS orbits as of June 1, 2004. STRAT/TROP EXCHANGE and TRANSPORT PATHWAYS at this MEETING • Convection on Clouds and Water Vapor in the TTL – Pfister • Convection on Summertime Extratropical LS from Aura – Dessler • Transport Pathways into Subtropical LS – Pittman • Accuracy of water vapor and total water via laboratory and intercomparison – Weinstock, Spackman • Isotopic composition of the TTL, lower stratosphere, middleworld – Moyer, Hanisco, Keutsch II. ELEMENTS OF THE FORECAST • Form a Consortium to Develop the Forecast Structure Establishing Priorities for Required Satellite, Airborne, and Modeling Components • Address, in Terms of the Required Objectives, What Level of Sophistication is Required for the Observations that will Result in a Forecast That is Tested and Trusted • Establish a Systematic Analysis of the Intrinsic Quality of the Data That Enters the Analysis – just as we have with laboratory kinetics and photochemistry data • Decide on how the Operational Forecast will be Tested and How it will be Systematically Improved • Build Union with Medical Community to link UV Dosage to Human Health • Assume Responsibility for the Long-Term Forecast