J. Delamere, E. Mlawer, V. Payne, S. Clough (AER, Inc.) D. Turner (U. Wisconsin), P. Green (Imperial College) E. Westwater (U. Colorado), N. Cimini (U. L’Aquila) Improved Understanding of Far-Infrared Radiative Processes in the Earth's Atmosphere Investigation of Far-Infrared Radiative Processes Using Measurements from the ARM North Slope of Alaska Climate Research Facility J. Delamere, E. Mlawer, V. Payne (AER, Inc.) S. Clough (Clough Associates) D. Turner (U. Wisconsin) R. Gamache (U. Mass. Lowell)

Maximum cooling occurs in the far-IR (10 to 650 cm -1, > 15  m) MLS Atmosphere Why the Far-IR? Cooling Rate Calculation Up to 40% of the OLR occurs in far-IR So important but significantly understudied….. Clough & Iacono (1995)

The SHEBA Experience Collocated far-IR radiance measurements (AERI) and atmospheric profiling instruments deployed in the Arctic in cases from October used to adjust foreign water vapor continuum model (Tobin et al., JGR, 1999) Far-IR Mid-IR Total Post-SHEBA Effect of Change

Post-SHEBA Far-IR Residuals

ARM North Slope of Alaska Facility Daily radiosonde launches Continuous operation of AERI Continuous operation of 2 microwave radiometers: 23.8 & 31.4 GHz (since 1998) and 183 GHz (since 2006)

Radiative Heating in Underexplored Bands Campaign (RHUBC) 1.Collect high-resolution, downwelling radiance measurements in the IR in low precipitable water vapor (PWV) conditions. 2.Collect collocated measurements of the atmospheric state, including radiosondes and 183 GHz radiance measurements from which accurate water vapor fields can be obtained. 3.Using the atmospheric state measurements, calculate the downwelling surface radiance with a line-by-line radiative transfer model (LBLRTM) 4.Compare the measurements to the model calculations. Validate and refine, where necessary, the water vapor continuum model and the water vapor line parameters Evaluate modeled optical properties of ice clouds Incorporate improvements into GCM-appropriate radiative transfer models (e.g. RRTM).

RHUBC - Phase 1 RHUBC-I: North Slope of Alaska Feb-March 2007 Principal Investigators: David Turner and Eli Mlawer

RHUBC - Phase 1 RHUBC-I: North Slope of Alaska Feb-March 2007 Principal Investigators: David Turner and Eli Mlawer

Key RHUBC Instruments Key Far-Infrared Radiance Instruments - AERI-ER ( µm) - TAFTS ( µm) PWV retrievals Key Water Vapor Instruments - Vaisala RS-92 radiosondes - GVR ( GHz) - GSR ( GHz) - MP-183 ( GHz)

Creating the Atmospheric Profile Radiosonde Profile (T,WV) Surface Met Data + Climatology Reduced std. dev. of spectral infrared residuals using “scaled-sonde” approach

183 GHz Study Air-broadened Half-Widths of the 22 GHz and 183 GHz Water Vapor Lines (Accepted IEEE TGRS, 2008) V. Payne, J. Delamere, S. Clough, K. Cady-Pereira, J. Moncet, E. Mlawer (AER, Inc.) R. Gamache (University of Massachusetts - Lowell)

183 GHz Spectroscopic Parameters Line intensity Known to within 0.5% Clough et al., 1973 Width HITRAN value ~5% different from most recent HITRAN update ~3% PWV error at 0.2 cm PWV Temperature dependence of width HITRAN 2000+: 0.64 (unrealistic) HITRAN 2004+: 0.77

Determination of 183 GHz Width Objective: Determine best value of 183 GHz width using ground-based radiometric measurements G-band Vapor Radiometer (GVR): –Manufacturer: ProSensing (ARM SBIR) –Operating continuously at the NSA –4 double sideband channels /- 1, 3, 7, 14 GHz –Measurements averaged for 35 minutes around radiosonde launch Model: MonoRTM –HITRAN line parameters (with some exceptions) –CKD Continuum Model Date range used: January to October 2007 –Includes RHUBC campaign –“Clear-sky” conditions (no liquid cloud)

Retrieval of 183 GHz Half Width Sensitivities to PWV and half width changes are distinct –Crucial for half width retrieval “Pivot point”: +/-2 GHz 183+/-3 channel is least sensitive to the width –can be used to get good first guess at PWV scaling for sondes Width retrieval uses channels on either side of pivot point –Crucial for information on width Frequency [GHz]

Retrieval of 183 GHz Width: Results GVR-based width retrieval: cm -1 /atm(  2.5 %) MonoRTM v3.3 CRB calculations (Gamache): cm -1 /atm (  3 %) Improved and continuous estimates of atmospheric water vapor for dry conditions See poster by Payne et al.

Retrieval of PWV from GVR Response of ±1, ±3 GHz channels: - Non-linear ±14 GHz channel: - anomalous residuals at higher PWV PWV retrieval: Use ±7 GHz channel - Use cases in linear region - Threshold of 120 K - Reduce set from 100 to 39 cases Response of T b to PWV 120 K

Results of NSA PWV retrievals

AERI-ER at NSA Extended Range Atmospheric Emitted Radiance Interferometer: –Operating continuously at the NSA –Range µm with 0.5 cm -1 resolution –Calibrated with two internal reference blackbodies traceable to NIST standards –Accuracy better than 1% ambient radiance –Corrections are applied to data (~ 1 RU)

Case Selection for Far-IR Study Removed cloud (liquid or ice) cases Removed cases with interference from nearby radar in AERI measurements (26 cases remain)

Case Selection for Far-IR Study Removed cloud (liquid or ice) cases Removed cases with interference from nearby radar in AERI measurements (26 cases remain)

Radiative Transfer Model Line intensities HITRAN 2004 with Updates Widths HITRAN 2004 with Updates LBLRTM v11.1 WV Continuum MT_CKD_1.2 Improved CO2 Line-coupling (Niro et al., 2005) Modified CO 2 Continuum CO 2 N2ON2O

Sensitivity of Far-IR

Preliminary Foreign Continuum Adjustment

Initial Half-Width Adjustments Update HITRAN 2004 line parameters - New CRB calculations for air-broadened half-width, temperature dependence of the width, and line shift

Summary of Far-IR Study (to date) Suite of 22 optimal cases established – PWV values from radiosondes scaled to agree with 183 GHz retrievals Initial adjustment to MT_CKD continuum released (MT_CKD_2.1) Improved spectral residuals result from use of newly calculated CRB line widths relative to HITRAN widths – Final analysis pending receipt of consistent set of CRB widths/pressure shifts Improved water vapor continuum fit forthcoming (Clough)

RHUBC-II Cerro Chajnantor, Chile Aug-Oct 2009

RHUBC-II (Expected PWV)

RHUBC-II (The Near-IR)

Additional Slides

Atmospheric State Profiles PWV range: 0.07 to 2.2 cm Vaisala RS-92 sondes + 40 m Meteorological Tower data Sonde RH values “bottom out” at km - Leads to unrealistic H 2 O values in stratosphere - Stratospheric values set to climatological values 100 cases

Retrieval of 22 GHz width MWRP-based width retrieval: cm -1 /atm(  1.6 %) MonoRTM v3.3 CRB calculations: cm -1 /atm(  3.0 %) See poster by Payne et al. MWRP at Southern Great Plains

HITRAN Width Information