Fast-JX code now replaces Fast-J  & Fast-J2

          » rapid, quadrature-based, flexible photolysis codes
          » cross-sections for many species, updated to 2004 (IUPAC & JPL)
          » combined stratosphere & troposphere J-values (0-60 km)
          » pseudo-spherical attenuation of incident sunlight
          » accurate plane-parallel treatment of all aerosol and cloud scattering
          » optimizes addition of extra layers in thick clouds (no limit on OD,  err < 0.5%)
          » fixes on cross-section generating code (avcs.f)
v5.3c » Updated SOLAR FLUX (SUSIM adopted, J(O2) up 5-10%)
          » calculates reflected UV-vis solar energy
v5.5   » cleaned code for generating and solving the block tri-diagonal scattering
v5.6   » corrected problems with thick clouds, solar attenuation into cloud sub-layers
          » new flux budgets at top/bottom of atmosphere
          » corrects typo (JAC,2000) to calculate I reflected from lower boundary, J's unaffected
v5.7r  » current, with typos fixed, old tri-diagonal solver (faster), and spherical flux dep.
v6.1   » scattering data extended to 200 nm (Pinatubo aerosols), heating rates included
          » calculate deposition of solar flux in each CTM layer (spherical, incl. SZA >90)
v6.2   >> spherical ray-tracing now done for mid-point of layers (differences at large SZA)
v6.4   >> major rewrite to speed up the fast-JX code:
                all wavelengths &  full vertical levels passed to deepest part of scattering code
                some loops made explicit since the code is locked to 8-stream scattering (4 angles)
                allows for vectorization / loop unrolling in previously dependent code (e.g., matrix inversion)
          >> SPECIAL OPTION for troposphere-only runs
                setting parameter W_  = 18 in 'parm_MIE.f' = std full wavelength fast-JX (equiv to v6.2)
                set W_ = 12 for Trop-ONLY, drops Xsections for strat-species, trop J-O2 good to 1%
                set W_ = 08 for Trop-QUICK, ditto, but trop J-O2 only good to 10%, all other J's to <0.1%.

          >> includes v 6.3 (= external spec. of cloud OD @600 nm, scales optical properties with wavelength)
          >> can be run (with proper cloud OD & W_ = 18) to be identical to v6.2

         

now available
          >>  program to generate new fast-JX cross-sections for v6 and greater (see link below)

coming soon
          >>  fractional cloud cover algorithm with fast-J (see preprint below)

Fast - JX code version 6.4 (8/2008)
         in a zip-file: UCI_fastJX-64.zip

Fast - JX code version 6.2 (6/2008)
         in a zip-file: UCI_fastJX-62.zip

Fast - JX cross-section generator for ver 6+ (6/2008)
         in a zip-file: UCI_fastJX-newXsect.zip  (link should be ready late June)

Fast - J2

Huisheng Bian and M.J. Prather, Fast-J2: Accurate Simulation of Stratospheric Photolysis in Global Chemical  Models, J. Atmos. Chem., 41, 281-296, 2002.  (Copyright 2002 Kluwer Academic Publishers. Further reproduction or electronic distribution is not permitted.)  Tables I &  II corrected (June 2008).

Abstract. Modeling photochemistry in the stratosphere requires solution of the equation of radiative transfer over an extreme range of wavelengths and atmospheric conditions, from transmission through the Schumann–Runge bands of O2 in the mesosphere, to multiple scattering from tropospheric clouds and aerosols. The complexity and range of conditions makes photolysis calculations in 3-D chemical transport models computationally expensive. This study pesents a fast and accurate numerical method, Fast-J2, for calculating photolysis rates (J-values) and the deposition of solar flux in stratosphere. Fast-J2 develops an optimized, super-wide 11-bin quadrature for wavelengths from 177 to 291 nm that concatenates with the 7-bin quadrature (291–850 nm) already developed for the troposphere as Fast-J. Below 291 nm the effects of Rayleigh scattering are implemented as a pseudoabsorption, and above 291 nm the full multiple-scattering code of Fast-J is used. Fast-J2 calculates the mean ultraviolet-visible radiation field for these 18 wavelength bins throughout the stratosphere, and thus new species and new cross sections can be readily implemented. In comparison with a standard, high-resolution, multiple-scattering photolysis model, worst-case errors in Fast-J2 do not exceed 5% over a wide range of solar zenith angles, altitudes (0–60 km), latitudes, and seasons where the rates are important in photochemistry.

Fast - J

Oliver Wild, Xin, Zhu, and M.J. Prather, Fast-J: Accurate Simulation of In- and Below-Cloud Photolysis in Tropospheric Chemical Models (corrected 3/2007), J. Atmos. Chem., 37, 245-282, 2000.  (Copyright 2000 Kluwer Academic Publishers. Further reproduction or electronic distribution is not permitted.)

Abstract. Photolysis rates in the troposphere are greatly affected by the presence of cloud and aerosol layers. Yet, the spatial variability of these layers along with the difficulty of multiplescattering calculations for large particles makes their inclusion in 3-D chemical transport models computationally very expensive. This study presents a flexible and accurate photolysis scheme, Fast-J, which calculates photolysis rates in the presence of an arbitrary mix of cloud and aerosol layers.  The algorithm is sufficiently fast to allow the scheme to be incorporated into 3-D global chemical transport models and have photolysis rates updated hourly. It enables tropospheric chemistry simulations to include directly the physical properties of the scattering and absorbing particles in the column, including the full, untruncated scattering phase function and the total, uncorrected optical depth. The Fast-J scheme is compared with earlier methods that have been used in 3-D models to parameterize the effects of clouds on photolysis rates. The impact of Fast-J on tropospheric ozone chemistry is demonstrated with the UCI tropospheric CTM.

Corrected page only (p.266)

Cloud Fraction

Jessica L. Neu, M.J. Prather and J.E. Penner, Global Atmospheric Chemistry:  Integrating over Fractional Cloud Cover, J. Geophys. Res. Dxx,  (Copyright 2007 American Geophysical Union. Further reproduction or electronic distribution is not permitted.)

Abstract. A new approach defined here allows for the averaging of photochemistry over complex cloud fields within a grid square and can be readily implemented in current global models.  As diagnosed from observations or meteorological models, fractional cloud cover with many overlying cloud layers can generate hundreds to thousands of different cloud profiles per grid square.  We define a quadrature-based method, applied here to the problem of averaging photolysis rates over this range of cloud patterns, which opens new opportunities for modeling in-cloud chemistry in global models.  We select up to four representative cloud profiles, optimizing the selection and weighting of each to minimize the difference in photolysis rates when compared with the integration over the entire set of cloud distributions.  To implement our algorithm, we adapt the UCI fast-JX photolysis code to the cloud statistics from the ECMWF forecast model at T42L40 resolution.  For the tropics and midlatitudes, grid-square-averaged photolysis rates for O3, NO2, and NO3 using four representative atmospheres differ by at most 3.2% rms from rates averaged over the hundreds or more cloudy atmospheres derived from a maximum-random overlap scheme.  Further, bias errors in both the free troposphere and the boundary layer are less than 1%.  Similar errors are shown to be 10-20% for current approximation methods.  Errors in the quadrature method are less than the uncertainty in the choice of maximum-random overlap schemes.  We apply the method to the averaging of photochemistry over different cloud profiles and outline extensions to heterogeneous cloud chemistry.