1. METR 5970.002 Advanced Atmospheric Radiation Dave Turner Lecture 6

2. Parameterization The representation, in a dynamic model, of physical effects in terms of admittedly oversimplified parameters, rather than realistically requiring such effects to be consequences of the dynamics of the system Why do we parameterize? – Don’t understand the physical process fully, yet the process is needed in the dynamic model, so we use a simplified representation – Physical process is not resolved by the model – “Proper” treatment of the physical process is too computationally expensive for the dynamic model

3. Typical Profiles of Atmospheric Gases From Goody

4. Absorption & Quantum Mechanics Absorption/emission: redistribution of internal energy through Change of rotational kinetic energy of polyatomic molecules Change of vibrational energy of polyatomic molecule Change of electric charge within molecule (including complete separation or reunification) Collisions lead to quick equilibrium distribution of the energy forms  Local Thermodynamic Equilibrium LTE Absorption/emission: must obey quantum-mechanical rules! Absorption dependent purely on characteristics (composition, phase) of absorbing medium

5. Absorptions Lines 5 Hypothetical molecule with permitted energy states E o, E 1 and E 2 3 possible transitions for an incident photon Photon only absorbed if interaction leads to transition into a permitted state A molecule in its base state E o cannot emit a photon Defined temperature T: predictable occupation of energy states Petty Fig. 9.1 NOccupation number k Boltzmann constant T absolute temperature Thermodynamic equilibrium: internal energy states E k occupied according to Boltzmann law For E i, E j with E j > E i, the number occupation ratio leads to

6. Rotational Transitions Mass of a molecule: indicator of resistance w.r.t. a linear acceleration Kinetic energy of molecule (translation)  in gas proportional to temperature Linear momentum aAcceleration [m s -2 ] m Mass [kg] pMomentum [kg m s -1 ] LAngular momentum [kg m 2 s -1 ] TTorque [Nm] v Velocity [m s -1 ] ωAngular velocity [s -1 ] Moment of inertia I [kg m 2 ]: indicates resistance to rotational acceleration  depends on mass distribution about the rotational axis Rotation Molecule has only one mass, but 3 moments of intertia I x, I y and I z

7. Moments of Inertia: Atmospheric Gases Isolated atoms: no rotational transitions Di-atomic and all linear molecules: I 1 =0 and I 2 =I 3 Spherical top I 1 =I 2 =I 3 Symmetric top: I 1 =I 2 and I 1 ≠I 3 Asymmetric top: I 1 ≠I 2 ≠I 3 Petty Fig. 9.2 120° Methane Ammonia Water vapor

8. Dipole Moment Molecule needs an electric dipole moment for an interaction with EM radiation External magnetic or electrical field must exert torque on molecule! Homo-nuclear molecules (i.e O 2 and N 2 ): no permanent dipole moment (symmetrical charge distribution) Hetero-nuclear molecules (i.e. CO) generally exhibit permanent dipole moment Basically all 3- or poly-atomic molecules (exception CO 2 and CH 4 ) have permanent dipole moment (different asymmetries) Argon (single atom): no rotation transitions Molecular N 2 : neither electric nor magnetic dipole moments  no rotation transitions Molecular O 2 : magnetic dipole moment  transitions at 60 & 118 GHz CO 2 and CH 4 : normally no dipole moments, however vibration transitions can overcome symmetry of molecule All other important atmospheric gases exhibit permanent electric dipole moments

9. Poly-atomic Molecules Petty Fig. 9.4 Molecule with N coupled atoms has 3N degrees of freedom (DOF) 3 DOF for translation 3 DOF for rotation 3N-6 DOF for vibration

10. Vibrational Modes for the H 2 O Molecule H 2 O molecule: three atoms (N=3)  3 DOF of vibration and three classical frequencies ν i corresponding to λ 1, λ 2 and λ 3 wavelengths Example harmonic: 2ν 3  λ=1.33 μm Example: combination oscillation: ν 2 + ν 3  1/λ = 1/λ 3 + 1/λ 2 (λ=1.87 μm)

12. Electron Transitions n n Petty Fig. 9.5

13. Q-branch vs. P- and R-branch Spectroscopy

14. Absorption – CO 2 Petty Fig. 9.12 and 9.13

15. Absorption – High Resolution Measurements 15 Petty Fig. 9.10 pure rotation

16. Line Shapes: Broadening Natural broadening: Heisenberg’s uncertainty principle: limited lifetime Δt of energy state  negligible Doppler broadening: random movement of molecules leads to frequency shift  dominant in mesosphere Pressure broadening: collisions interrupt transitions  dominant in troposphere and stratosphere Petty Fig. 9.6 energetic consequences!

17. Line Description Position of line: center frequency ν 0 Line shape: function dependent on distance to ν 0, normalization to 1 Line strength S σAbsorption cross section per molec. α 1/2 Half-power width SLine strength ν 0 Center frequency ν0ν0 S typically: symmetrical line shapes Half-power width determines when amplitude of line is reduced by factor of 2: Petty Fig. 9.6

18. Doppler Broadening Gas molecules in constant movement Temperature is measure for mean kinetic energy Statistical distribution of velocity in direction s according to Maxwell-Boltzmann: Doppler shift mMass of molecule (=M/N a ) vel s Velocity in direction s σ s Standard deviation of vel s with Doppler half-power width Petty Fig. 9.7 same S and same α Note heavier molecules have smaller Doppler broadened widths!

19. Pressure Broadening Frequent collisions of molecules (dense atmosphere) Collision influences current absorption/emission processes  pressure broadening Adequate (but not perfect!): Lorentz line shape α L Lorentz half power width α 0 Reference measurements in laboratory at T 0, p 0 nempirical exponent ν 0 center frequency

20. Line Strength High-resolution transmission database – Larry Rothman, Air Force Geophysics Lab – GEISA from Laboratorie de Meteorogie Dynamique in France is similar 47 molecules, including most isotopologues – E.g.; H 2 16 O, H 2 18 O, H 2 17 O, HD 16 O, HD 18 O, HD 17 O Over 4,000,000 lines Most entries are from theoretical calculations; only a small fraction come from direct observations (primarily from lab work) Used in line-by-line radiative transfer models E’’ i is energy of lower energy state T 0 is 273 K S i0 is measured in lab or computed m ~ 1 HITRAN

22. Simple Picture Tutorial on the Water Vapor Continuum Dr. David Turner NOAA National Severe Storms Laboratory 2011

23. H 2 O and CO 2 Absorption Lines Water Vapor Carbon Dioxide

24. What is the Water Vapor Continuum? Computing the radiative contribution for a given molecule requires that the shape of the absorption line is well-known The H 2 O line shape is not well-known –Assuming a Lorentzian line shape (impact approximation) grossly over-estimates the radiative contribution in the wings Current state-of-art parameterizations treats the contribution from each H 2 O line as two components: –Local contribution –Continuum (everything in gray) H 2 O continuum models are semi-empirical fits to lab and atmospheric data Far-wingBasement

25. Water Vapor Continuum Tutorial (1) 16.720.025.033.350.0100 Wavelength [μm]

26. Water Vapor Continuum Tutorial (2) 16.720.025.033.350.0100 Wavelength [μm]

27. Water Vapor Continuum Tutorial (3) 16.720.025.033.350.0100 Wavelength [μm]

28. Water Vapor Continuum Tutorial (4) 16.720.025.033.350.0100 Wavelength [μm]

29. Water Vapor Continuum Tutorial (5) 16.720.025.033.350.0100 Wavelength [μm]

30. Water Vapor Continuum Tutorial (6) 16.720.025.033.350.0100 Wavelength [μm]

32. From old presentation by Tony Clough

34. Radiance Closure Exercise Let’s evaluate/improve the line-by-line RT models Objective is to get agreement between observed radiance and computed radiance (within uncertainties) Three critical components: –Radiance observations –Model physics and spectroscopy –Input data for model These closure exercises have been heavily utilized by ARM in the infrared Uncertainties in water vapor profiles from radiosondes are significant, and ARM has invested heavily in field experiments to characterize/improve routine water vapor observations

35. Improved Infrared Radiative Transfer Models in the 8-13 µm Window Turner et al., JAS, 2004 AERI observations used to evaluate clear sky IR radiative transfer models Long-term comparisons have improved –Spectral line database parameters –Water vapor continuum absorption models Reduced errors in computation of downwelling radiative IR flux by factor of 3-4; current uncertainty is on the order of 1.5 W/m 2 1 RU = 1 mW / (m 2 sr cm -1 ) AERI - (Pre-ARM Model) AERI - (Model in 2003)

36. Mlawer and Turner, 2016: Spectral Radiation Measurements and Analysis in the ARM Program. The Atmospheric Radiation Measurement (ARM) Program: The First 20 Years. AMS Meteor. Monograph, Chapter 14.

37. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Using Microwave and Submillimeter Radiometer Observations to Improve Climate Models David D. Turner National Severe Storms Laboratory / NOAA Hans Liebe Lecture National Radio Science Meeting 8-11 January 2014 Boulder, Colorado

38. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Motivation to Study the Far-IR Emission from far-IR accounts for ~40% of outgoing longwave radiation (OLR) Accurate radiative transfer parameterizations are needed for computing tropospheric radiative heating rates –Important for atmospheric circulation (e.g., vertical velocity) –Cirrus processes Far-IR is underexplored –Few observational tools to look at this spectral region –Far-IR is opaque from most surface locations –Scattering from ice crystals very important in far-IR –Significant uncertainties in the treatment of this band in GCMs New observational capabilities recently developed –Improved spectral radiometers with sensitivity in the far-IR –Improved methods to measure water vapor when PWV is small

39. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting RHUBC-I Barrow, Alaska Feb-Mar 2007

40. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting RHUBC Details RHUBC-I –ARM North Slope of Alaska Site, Barrow, AK (71ºN, 157ºE, 8 m MSL) –February - March 2007, 70 radiosondes launched –Minimum PWV: 0.95 mm (observed) –2 far-IR / IR interferometers –3 sub-millimeter radiometers for PWV observations –Lidar for cirrus detection Radiative Heating in Underexplored Bands Campaign

41. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting ARM NSA Site Layout Looking WNW User Facility “Great White” AERI C1 MP-183 TAFTS AERI-S01 GVR GSR MWR MWRP

42. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Water Vapor Continuum Circa 1999 Pure line shape formulation After field campaigns This large change was due to SHEBA field campaign in 1998 Cntnm in 1990 Cntnm in 1999

43. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting State-of-Art in Far-IR: Circa 1999 Delamere et al., JGR, 2010 RHUBC-I AERI Data

44. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting State-of-Art in Far-IR: After RHUBC-I Delamere et al., JGR, 2010 Many changes to half-widths of the water vapor absorption lines RHUBC-I AERI Data

45. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Water Vapor Continuum After RHUBC-I

46. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting COPS Black Forest, Germany Apr-Dec 2007

47. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting ARM Mobile Facility in the Black Forest COPS: Convective and Orographic Precipitation Study

48. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Large Differences Among RT Models 6 MONORTM simulations for 2 climatologies, only WV and O 2 considered, 2 overlapping pairs with similar water vapor amount Rosen98 - MonoRTM Liebe87 - MonoRTM Liebe93 - MonoRTM Turner et al., TGRS, 2009

49. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Two 90/150 GHz Radiometers ARM MWRHFUniversity of Munich DPR Built by same manufacturer; similar “insides” Both calibrated with LN 2 ; 90 GHz also used tip curves –Dew on radome & clouds contaminated most tip curves –LN 2 calibration procedure was different for two instruments Turner et al., TGRS, 2009

50. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Comparison of Two Systems at 150 GHz Independently calibrated systems 2122 clear sky cases from 24 different days Bias: -0.12 K RMS: 1.29 K Slope: 0.998 K/K Correlation: 0.998 Turner et al., TGRS, 2009

51. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Absorption Model Evaluation at 150 GHz 71 clear-sky cases with coincident radiosonde and DPR or MWRHF obs Scaled radiosondes to match PWV retrieved from MWR’s 23.8 GHz obs –Needed in order to remove diurnal sonde humidity bias Only able to compare with 150 GHz obs, as 90 GHz obs could not be calibrated Significant differences btwn obs and calc, especially for the MonoRTM and Liebe93 models Turner et al., TGRS, 2009

52. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Water Vapor Continuum Formulation MonoRTM formulation Multipliers derived to make: – abs (slope of residuals at 150 GHz vs. PWV) < 0.1 K/cm – abs (bias of residuals at 150 GHz) < 0.1 K Liebe93 treats WV cntnm as a pseudo-line… Turner et al., TGRS, 2009

53. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting DD Turner, et al., TGRS 2009 Rosen98 - MonoRTM Liebe87 - MonoRTM Spectral Impact of Modification Relative to the MonoRTM Original Model ResultsModified Model Results Liebe93 - MonoRTM Turner et al., TGRS, 2009

54. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting H 2 O Continuum After RHUBC-I & COPS Before RHUBC 150 GHz data from COPS

55. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting H 2 O Continuum After RHUBC-I & COPS Turner et al., TGRS, 2009 Payne et al. TGRS, 2011 Before RHUBC After RHUBC/COPS 150 GHz data from COPS

56. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting

57. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting RHUBC-II Cerro Toco, Chile Aug-Oct 2009

58. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting RHUBC Details RHUBC-I –ARM North Slope of Alaska Site, Barrow, AK (71ºN, 157ºE, 8 m MSL) –February - March 2007, 70 radiosondes launched –Minimum PWV: 0.95 mm (observed) –2 far-IR / IR interferometers –3 sub-millimeter radiometers for PWV observations –Lidar for cirrus detection RHUBC-II –Cerro Toco, Chile (23ºS, 68ºE, 5340 m MSL) –August - October 2009, 144 radiosondes were launched –Minimum PWV: ~0.2 mm –3 far-IR / IR interferometers –1 sub-millimeter radiometer for PWV –1 sub-millimeter FTS –1 near-IR FTS –Lidar for cirrus detection 5x drier! Radiative Heating in Underexplored Bands Campaign

59. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting View from Cerro Toco Location Feb 2008 Instruments were located here Site location DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting

60. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting ALMA Site, 2013 Photo credit: Clem and Adri Bacri-Normier ARM Cerro Toco Site 5300 m MSL (17,500 ft) Atacama Large Millimeter Array

61. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting RHUBC-II Cerro Toco Field Site

62. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Two Key RHUBC-II Instruments ARM 183.3 GHz Microwave Radiometer Cimini et al., TGRS, 2009 Smithsonian Astrophysical Observatory Sub-millimeter FTS (300 GHz - 3 THz) Paine and Turner, TGRS, 2013

63. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Observed Entire Terrestrial Spectrum 0.28 mm PWV Turner et al., GRL, 2012

64. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Zoom on Far-Infrared 0.28 mm PWV Turner et al., GRL, 2012

65. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Looking in a Few Microwindows 0.28 mm PWV Turner et al., GRL, 2012

66. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Same Microwindows, Different Case 0.81 mm PWV New MT_CKD v2.4 fits obs better than CKD v2.4 Still needs to be adjusted slightly, esp in the sub-mm Turner et al., GRL, 2012

67. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Is this Important? How important is this difference? Before RHUBC After RHUBC/COPS

68. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Impact on Net Flux Profiles New minus Old Turner et al., JGR, 2012

69. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Impact on a GCM Simulation? RHUBC-I suggested large change of the strength of modeled H 2 O cntnm –RHUBC-II data supported this change Would this change make a substantial change in a GCM simulation? –If so, how would the modeled climate be impacted? Performed two simulations using CESM v1 –CNTL: CAM5, with the RRTM model (based upon LBLRTM, with CKD v2.4 H 2 O cntnm) –EXPT: CAM5 with RRTM using MT_CKD v2.4 H 2 O cntnm Fixed sea surface temps, 20-yr integration

70. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Zonal LW Heating Rate Diffs Turner et al., JGR, 2012 EXPT – CNTL

71. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Impact on the Tropical Atmosphere 15°S to 15°N Turner et al., JGR, 2012 EXPT – CNTL

72. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Impact on a GCM Simulation Tested using two 20-yr simulations in the CAM5 GCM In summary, the change in the H 2 O continuum absorption: –Changes the LW cloud-free radiative heating rate profile –Which affects the temperature and water vapor profiles, and hence the RH profile –Which impacts the middle- and upper-tropospheric cloud amounts –Which impacts the LW cloud radiative forcing and diabatic heating due to other cloud processes, which partly offsets the change in the clear sky radiative heating rate –Changes were significant in all global regions (indep of latitude) CAM5 had a radiative and dynamic response! Other GCMs have different cloud treatments, and may respond differently Turner et al., JGR, 2012

73. DD Turner, “Improving GCMs” Hans Liebe Lecture, NRS Meeting Summary Microwave and millimeter-wave radiometers are critical instruments used in atmospheric science Absorption models (such as the ones developed by Hans Liebe) are essential for turning the radiometer observations into geophysical variables Carefully constructed field campaigns and closure studies have been used to improve µwave and mm- wave absorption models These have led to improvements in IR radiative transfer parameterizations used in GCMs These improvements in the IR parameterizations have made a big impact on GCM simulations Currently working to improve liquid water absorption models in the µwave and mm-wave region