HIRDLS Applications and Development Status: Scientific Insights for Climate Studies

1. HIRDLSSPARC Applications and Development Status John Gille University of Colorado and NCAR John Barnett Oxford University Alyn Lambert, David Edwards, Christopher Palmer Michael Dials, Chris Halvorson, Eric Johnson, Wayne Rudolf Ken Stone, Bob Wells, John Whitney, Douglas Woodard

2. HIRDLS Scientific Goals • The primary goals of the High Resolution Dynamics Limb Sounder (HIRDLS) experiment are to acquire data with which to investigate • 1) the recovery of the ozone layer following the phase-out of some halogen-containing chemicals; • 2) the role of the upper troposphere and lower stratosphere (UT/LS) in climate; and • 3) the chemistry of the upper troposphere.

3. Recovery of the Ozone Layer • Stratospheric chlorine is predicted to decrease as a result of the Montreal Protocol and subsequent agreements • Chlorine abundances are decreasing in the troposphere, and now, in the stratosphere • The recovery of the ozone layer with decreasing Cl will be complicated by the lower temperatures in the lower stratosphere, due to greenhouse effects as well as the reduction in ozone itself • HIRDLS, and the Aura spacecraft, will fly during the unique period near the maximum loading of stratospheric chlorine. It will be important to acquire a record of atmospheric composition and behavior during this singular period. • One of the goals of HIRDLS is to document this period in the atmosphere, and use these data to understand ozone chemistry and radiative effects in this unique period.

4. A3 C H B r ( A ) 3 H C F C s 3.0 H a l o n s ) b C C l 4 p C H C C l p 3 3 ( 2.0 C S E C F C s E 1.0 C H B r ( N ) 3 C H C l 3 1960 1980 2000 2020 2040 2060 Stratospheric Chlorine Growth of stratospheric chlorine according to various scenarios Figure 1

5. The Role of the UT/LS in Climate • The structure and behavior of the atmosphere around the tropopause are now known to be more complex than previously thought. • Exchange of material between the troposphere and the stratosphere takes place not only through ascent through the tropical tropopause, but also through transports along isentropic surfaces that cross the tropopause. These transports include those of radiatively active (e.g. CO2, H2O, CH4, etc.) and chemically active (N2O, CFC11, CFC12, H2O, etc.) gases that directly or indirectly influence the earth’s radiative balance. • Many of these transports are on finer scales than have been observed before. In addition, there are other features which lead to the formation of fine scale filaments. • One of HIRDLS’ goals is to observe these small-scale transports and subsequent mixing, and to clarify their effects in the climate system.

6. Transport Features Observed by HIRDLS Figure 2 (from J. Holton/UGAMP)

7. Stratosphere-troposphere exchange on small scales Passive tracers on the 320 K isentrope. Coloured air is stratospheric, blank is tropospheric Figure 3 [From Appenzeller et al. [1995]]

8. UT/LS Chemistry • HIRDLS measurements will extend down into the lower stratosphere and upper troposphere when clouds are not too optically thick. • Trace species in this region are rapidly transported over long distances. • HIRDLS will obtain measurements of: • O3, H2O, and HNO3, CFC11, CFC12, CH4, N20 and aerosols. • These data will greatly augment knowledge of composition and transports at these levels.

9. Summary of Measurement Requirements Temperature <50 km 0.4 K precision 1 K absolute >50 km 1 K precision 2 K absolute Constituents O3, H2O, CH4, H2O, HNO3, NO2, N2O5, 1-5% precision ClONO2, CF2Cl2, CFCl3, Aerosol 5-10% absolute Geopotential height gradient 20 metres/500 km (vertical/horizontal) (Equivalent 60oN geostrophic wind) (3 m s-1) Coverage: Horizontal - global 90oS to 90oN (must include polar night) Vertical - upper troposphere to mesopause (8-80 km) Temporal - long-term, continuous (5 years unbroken) Resolution: Horizontal - profile spacing of 5o latitude x 5o longitude (approx 500 km) Vertical - 1-1.25 km Temporal - complete field in 12 hours

10. The LIMB Scanning Technique Infrared radiance emitted by the earth’s atmosphere, seen at the limb, is measured as a function of relative altitude

11. Spectral Locations of the HIRDLS Channels Figure 5

12. Examples of Calculated Radiance Profiles

13. Driving Requirements on Accuracy and Precision Retrieval based on N (h). This leads to the most stringent requirements: Radiance Accuracy 1% (temperature channels 0.5%), Random noise1-12 x 10-4 Wm-2 sr-1 (channel dependent) Sample spacing Accuracy 0.25%, random error of 1 arcsec (1 ). Requirements are divided between - encoder on the scan mirror (motion relative to optical bench), and - gyroscope on the optical bench (motion of bench in inertial space).

14. HIRDLS Alternative Global Mode Sub-Tangent Point HIRDLS BoresightTangent Point Latitudes and Longitudes in the Alternative Global Mode Figure 6

15. HIRDLS Instrument Consists of 9 Subsystems SUN-SHIELD SUBSYSTEM (SSH) IN-FLIGHT CALIBRATION SUBSYSTEM (IFC) OPTICAL ITEMS AND ELECTRONICS TO ENABLE RADIOMETRIC CALIBRATION DURING FLIGHT OPERATIONS. TELESCOPE SUBSYSTEM (TSS) INSTRUMENT TELESCOPE AND RELATED ELECTRONICS UNITS POWER SUBSYSTEM (PSS) PROVIDES BASIC POWER CONVERSION AND SWITCHING • UK • US DETECTOR SUBSYSTEM (DSS) MULTI-CHANNEL INFRARED RADIOMETRIC DETECTOR ARRAY AND DEWAR ASSEMBLY INSTRUMENT PROCESSING SUBSYSTEM (IPS) SIGNAL AND DATA PROCESSING TO SUPPORT MISSION SCIENCE OPERATIONS AND HOUSEKEEPING FUNCTIONS GYRO SUBSYSTEM (GSS) PROVIDES PRECISION BASE MOTION DISTURBANCE DATA STRUCTURAL THERMAL SUBSYSTEM (STH) PRIMARY STRUCTURAL SUPPORT AND ENVIRONMENTAL ENCLOSURE FOR ELECTRONIC UNITS AND TELESCOPE COOLER SUBSYSTEM (CSS) PROVIDES ACTIVE CRYO-COOLING FOR THE INSTRUMENT DETECTOR ARRAY Figure 7

16. INSTRUMENT SUBSYSTEMS - EXPLODED VIEW Fixed Sunshield (STH) LEGEND STH SSH TSS DSS GSS CSS IFC PSS IPS Sunshield-Door (SSH) Black Body Assembly (IFC) Optical Bench Assy. with Shroud (TSS) External Connector Bulkhead Encoder Electronics Assy. (TSS) Power Converter Unit (PSS) Telescope Electronics Unit (TSS) Cooler Control Unit (CSS) Space-View Aperture Assembly (SSH) Signal Processing Unit (IPS) Gyro Electronics Unit (GSS) Detector Dewar (DSS) Gyro Mechanical Unit (GSS) Baseplate (STH) Black Body Electronics Unit (IFC) S-Link (CSS) Cooler Radiator Panel with Compressors & Displacer (CSS) Inst. Processor Unit (IPS) Flexible Vacuum Enclosure (CSS) Vibration Isolators (TSS)

17. Optical Schematic Figure 8

18. Figure 9

19. Figure 10

20. Structure Thermal Subsystem Status Dummy MLI on Flight Structure in MMS Clean Room Figure 11

21. HIRDLS Calibration Facility Chamber optical bench Clean room and vacuum chamber Seismic isolator Monochromator turret

25. Verification of 1 KM Resolution True Temperature Wave Retrieved Temperature Wave

26. Figure 12

27. Summary • HIRDLS is a powerful and flexible instrument for the global measurement from the upper troposphere into the mesosphere of Temperature, 10 trace species and aerosols • New features are: • Fine spacing of measured profiles in the longitudinal direction (<500km) • High vertical resolution (<2 km vertical wavelength) • Ability to sound the upper troposphere and low stratosphere (UT/LS) regions • Measurement of many species with a range of chemical lifetimes • 5-6 year instrument life • Standard data will provide long-term detailed data and important insights into: • Evolution of the ozone layer • Climate processes, especially in the tropopause region • Upper troposphere chemistry

28. Additional information on HIRDLS can be found at the HIRDLS website, http://www.eos.ucar.edu/hirdls/home.html.