Shepard A. Clough

Assessing 1D Atmospheric Solar Radiative Transfer Models: Interpretation and Handling of Unresolved Clouds

Abstract The primary purpose of this study is to assess the performance of 1D solar radiative transfer codes that are used currently both for research and in weather and climate models. Emphasis is on interpretation and handling of unresolved clouds. Answers are sought to the following questions: (i) How well do 1D solar codes interpret and handle columns of information pertaining to partly cloudy atmospheres? (ii) Regardless of the adequacy of their assumptions about unresolved clouds, do 1D solar codes perform as intended? One clear-sky and two plane-parallel, homogeneous (PPH) overcast cloud cases serve to elucidate 1D model differences due to varying treatments of gaseous transmittances, cloud optical properties, and basic radiative transfer. The remaining four cases involve 3D distributions of cloud water and water vapor as simulated by cloud-resolving models. Results for 25 1D codes, which included two line-by-line (LBL) models (clear and overcast only) and four 3D Monte Carlo (MC) photon transport ...

Coriolis Interaction in the ν1 and ν3 Fundamentals of Ozone

The v1 and v3 vibration rotation spectrum of 16O3 in the 9.0‐μ region has been analyzed. The two vibrational states are coupled through a Coriolis term, iY13Py, and a second‐order distortion term, −X13(PxPz+PzPx), in the Hamiltonian. The interaction has been treated by numerically diagonalizing the secular determinant for the two states with the coupling included. The effect of the interaction on the intensities has been considered and absorption contours calculated in satisfactory agreement with experiment. With the distortion parameters fixed to the ground‐state values the following constants have been obtained: ν1=1103.157, A1=3.5569, B1=0.44272, C1*=0.39262, ν3=1042.096, A3=3.5004, B3=0.44125, C3*=0.39097, Y13=−0.466, and X13=−0.0098 cm−1. The value of the dipole‐moment ratio, (∂Mz∂Q3|0Q3)⧸(∂Mx∂Q1|0Q1), is 10.0±1.5.

History of one family of atmospheric radiative transfer codes

Beginning in the early 1970s, the then Air Force Cambridge Research Laboratory initiated a program to develop computer-based atmospheric radiative transfer algorithms. The first attempts were translations of graphical procedures described in a 1970 report on The Optical Properties of the Atmosphere, based on empirical transmission functions and effective absorption coefficients derived primarily from controlled laboratory transmittance measurements. The fact that spectrally-averaged atmospheric transmittance (T) does not obey the Beer-Lambert Law (T equals exp(-(sigma) (DOT)(eta) ), where (sigma) is a species absorption cross section, independent of (eta) , the species column amount along the path) at any but the finest spectral resolution was already well known. Band models to describe this gross behavior were developed in the 1950s and 60s. Thus began LOWTRAN, the Low Resolution Transmittance Code, first released in 1972. This limited initial effort has how progressed to a set of codes and related algorithms (including line-of-sight spectral geometry, direct and scattered radiance and irradiance, non-local thermodynamic equilibrium, etc.) that contain thousands of coding lines, hundreds of subroutines, and improved accuracy, efficiency, and, ultimately, accessibility. This review will include LOWTRAN, HITRAN (atlas of high-resolution molecular spectroscopic data), FASCODE (Fast Atmospheric Signature Code), and MODTRAN (Moderate Resolution Transmittance Code), their permutations, validations, and applications, particularly as related to passive remote sensing and energy deposition.

Reviewing atmospheric radiative transfer modeling: new developments in high- and moderate-resolution FASCODE/FASE and MODTRAN

Spectrally uniform treatment of the atmospheric radiative transfer (RI) problem has been approached through two different techniques - very high resolution line-by-line (LBL) algorithms and lower resolution band models (BM). Each has its advantages and specific applications. However, if commonality and validation of a specific pair of RI approaches is to be mutually maintained, then these codes must be continually reevaluated against both measurements and other models.

Complex susceptibility for collisional broadening

A unified approximate expression for the real part of the susceptibility for collisionally broadened transitions, including line coupling, has been developed. The Hilbert transform has been applied to the impact approximation line shape (Kramers-Kronig relationship) to obtain a result that is applicable from the microwave to the infrared. The approximate function has been compared numerically with the exact result using a newly developed algorithm. The results are applicable to spectral computations of the index of refraction and propagation delays.

CONTINUATION OF DATA ANALYSIS SOFTWARE DEVELOPMENT FOR THE ATMOSPHERIC EMITTED RADIANCE INTER- FEROMETER (AERI)

Data from the Atmospheric Emitted Radiance Interferometer (AERI) has been analyzed under the ARM Fourier Transform Data Analysis Tools science team project. A portion of the effort was accomplished through a subcontract to S. A. Clough of Atmospheric Environmental Research (AER), Inc. This section of the proposal highlights a few important accomplishments obtained during the past grant period. Specific accomplishments include: 1) The AERIplus temperature and moisture retrieval algorithm (Feltz et al. 2003, 2005) has now implemented a new fast model based upon LBLRTM. The fast model provides a doubling of vertical resolution within the first 100 hPa of atmosphere (surface to 900 hPa) from 10 hPa spacing to 5 hPa. This algorithm has been implemented at Pacific Northwest National Laboratories to upgrade previous AERI retrieval software. A peer reviewed paper has been published with regard to this work along with Value Added Product (VAP) technical document available through ARM web site. 2) Developed an objective methodology to detect planetary boundary layer (PBL) height using the AERI derived potential temperature field. AERI temperature and moisture data are also used to correlate the perturbation temperature and moisture in time within the planetary boundary layer (PBL) to view the structure of PBLmorexa0» turbulence and convection. 3) The temporal resolution of the DOE ARM AERI systems is now being increased to less than 20 seconds (currently ~ 8 minutes depending on system). The University of Wisconsin mobile AERI system was deployed three times (Texas 2002 at SGP, CRYSTAL-FACE in southern Florida, and AWEX 2003 at SGP) collecting data at 40 second temporal resolution. The DOE ARM science team has requested that all DOE ARM AERI systems be upgraded to run in rapid sampling mode (including the ARM Mobile Facility AERI) to provide improved sampling of changing cloud characteristics using high spectral resolution infrared data. This grant has facilitated in the demonstration of improved science when the AERI systems on operated in this higher temporal resolution mode.«xa0less

Capturing tropospheric ozone time variability : a study using TES Nadir Retrievals

We perform nadir rebievals of ozone using simulated radiances from ozone-sondes over Bermuda from April 14 to May 25, 1993. Using a novel two-step retrieval strategy, we characterize the sensitivity of TES nadir retrievals to time variations of ozone.

Effects of Atmospheric Obscurants on the Propagation of Optical/IR Radiation

Every optical remote sensor, whether looking at the natural atmospheric constituents or other obscurants or pollutants, has to be able to look through the atmosphere. It is therefore important that one understands and can reliably predict the propagation properties of the ambient atmosphere for these remote sensing systems.