Todd K. Schaack

Global Objective Tropopause Analysis

Abstract The European Center for Medium Range Weather Forecasts (ECMWF) level IIIb dataset is used to construct global pressure analyses of the tropopause surface during January 1979. Two methods are employed: a dynamical method based on isentropic potential vorticity (IPV) and a thermal method based on lapse rate criteria. Regional tropopause pressure analyses are extracted from the global analyses and compared against distributions derived from rawinsonde data. The coarse vertical resolution of the ECMWF data compromises the ability to resolve abrupt stability changes between the troposphere and stratosphere and impacts tropopause analyses using both methods. Sensitivity of the derived tropopause pressures to a range of IPV and lapse rate thresholds is examined. For the assimilated dataset employed herein, 3.5 IPV units represent an optimal value for tropopause analysis outside the tropics. Modification of the WMO lapse rate criteria does not significantly improve tropopause analysis globally. Both meth...

A Global Analysis of Stratospheric–Tropospheric Exchange during Northern Winter

Abstract Using a mathematical formulation of stratospheric-tropospheric (ST) exchange, the cross-tropopause mass flux is diagnosed globally for January 1979. Contributions by physical mechanisms including the diabatic transport and the quasi-horizontal adiabatic transport along isentropes that intersect the tropopause surface are evaluated. Both thermal and dynamical definitions of the tropopause are used. Two regions of zonally integrated mass flux into the stratosphere are found, one over tropical latitudes associated with diabatic transports, and a second over subpolar latitudes associated with adiabatic transports. The ingress to the stratosphere in each of the latitude bands 50°–70°N and 40°–70°S is as intense as that occurring over the tropics, a feature of the global budget not previously documented. Compensating mass outflow from the stratosphere occurs mainly over midlatitudes near axes of strong upper-level westerlies. Large zonal asymmetries are found in the regional patterns of ST exchange. Co...

REMOTE SENSING OF TROPOSPHERIC POLLUTION FROM SPACE

We review the progress of tropospheric trace gas observations and address the need for additional measurement capabilities as recommended by the National Research Council. Tropospheric measurements show pollution in the Northern Hemisphere as a result of fossil fuel burning and a strong seasonal dependence with the largest amounts of carbon monoxide and nitrogen dioxide in the winter and spring. In the summer, when photochemistry is most intense, photochemically generated ozone is found in large concentrations over and downwind from where anthropogenic sources are largest, such as the eastern United States and eastern China. In the tropics and the subtropics, where photon flux is strong throughout the year, trace gas concentrations are driven by the abundance of the emissions. The largest single tropical source of pollution is biomass burning, as can be seen readily in carbon monoxide measurements, but lightning and biogenic trace gases may also contribute to trace gas variability. Although substantive pr...

Intercomparison of near-real-time biomass burning emissions estimates constrained by satellite fire data

We compare biomass burning emissions estimates from four different techniques that use satellite based fire products to determine area burned over regional to global domains. Three of the techniques use active fire detections from polar-orbiting MODIS sensors and one uses detections and instantaneous fire size estimates from geostationary GOES sensors. Each technique uses a different approach for estimating trace gas and particulate emissions from active fires. Here we evaluate monthly area burned and CO emission estimates for most of 2006 over the contiguous United States domain common to all four techniques. Two techniques provide global estimates and these are also compared. Overall we find consistency in temporal evolution and spatial patterns but differences in these monthly estimates can be as large as a factor of 10. One set of emission estimates is evaluated by comparing model CO predictions with satellite observations over regions where biomass burning is significant. These emissions are consistent with observations over the US but have a high bias in three out of four regions of large tropical burning. The large-scale evaluations of the magnitudes and characteristics of the differences presented here are a necessary first step toward an ultimate goal of reducing the large uncertainties in biomass burning emission estimates, thereby enhancing environmental monitoring and prediction capabilities.

A Comparison of Inert Trace Constituent Transport between the University of Wisconsin Isentropic–Sigma Model and the NCAR Community Climate Model

Abstract Five- and 10-day inert trace constituent distributions prognostically simulated with the University of Wisconsin (UW) hybrid isentropic–sigma (θ–σ) model, the nominally identical UW sigma (σ) model, and the National Center for Atmospheric Research Community Climate Model 2 (CCM2) are analyzed and compared in this study. The UW θ–σ and σ gridpoint models utilize the flux form of the primitive equations, while CCM2 is based on the spectral representation and uses semi-Lagrangian transport (SLT) for trace constituents. Results are also compared against a version of the CCM that uses spectral transport for the trace constituent. These comparisons 1) contrast the spatial and temporal evolution of the filamentary transport of inert trace constituents simulated with the UW θ–σ and σ models against a “state of the art” GCM under both isentropic and nonisentropic conditions and 2) examine the ability of the models to conserve the initial trace constituent maximum value during 10-day integrations. Results ...

Numerical Uncertainties in the Simulation of Reversible Isentropic Processes and Entropy Conservation

Abstract A challenge common to weather, climate, and seasonal numerical prediction is the need to simulate accurately reversible isentropic processes in combination with appropriate determination of sources/sinks of energy and entropy. Ultimately, this task includes the distribution and transport of internal, gravitational, and kinetic energies, the energies of water substances in all forms, and the related thermodynamic processes of phase changes involved with clouds, including condensation, evaporation, and precipitation processes. All of the processes noted above involve the entropies of matter, radiation, and chemical substances, conservation during transport, and/or changes in entropies by physical processes internal to the atmosphere. With respect to the entropy of matter, a means to study a model’s accuracy in simulating internal hydrologic processes is to determine its capability to simulate the appropriate conservation of potential and equivalent potential temperature as surrogates of dry and moi...

Global Climate Simulation with the University of Wisconsin Global Hybrid Isentropic Coordinate Model

Abstract The purpose of this study is to briefly describe the global atmospheric University of Wisconsin (UW) hybrid isentropic–eta coordinate (UW θ–η) model and document results from a 14-yr climate simulation. The model, developed through modification of the UW hybrid isentropic–sigma (θ–σ) coordinate model, employs a vertical coordinate that smoothly varies from terrain following at the earths surface to isentropic coordinates in the middle to upper troposphere. The UW θ–η model eliminates the discrete interface in the UW θ–σ model between the PBL expressed in sigma coordinates and the free atmosphere expressed in isentropic coordinates. The smooth transition of the modified model retains the excellent transport characteristics of the UW θ–σ model while providing for straightforward application of data assimilation techniques, use of higher-order finite-difference schemes, and implementation on massively parallel computing platforms. This study sets forth the governing equations and describes the vert...

Real-Time Simulation of the GOES-R ABI for User Readiness and Product Evaluation

AbstractIn support of the Geostationary Operational Environmental Satellite R series (GOES-R) program, the Cooperative Institute for Meteorological Satellite Studies (CIMSS) at the University of Wisconsin–Madison is generating high quality simulated Advanced Baseline Imager (ABI) radiances and derived products in real time over the continental United States. These data are mainly used for testing data-handling systems, evaluating ABI-derived products, and providing training material for forecasters participating in GOES-R Proving Ground test bed activities. The modeling system used to generate these datasets consists of advanced regional and global numerical weather prediction models in addition to state-of-the-art radiative transfer models, retrieval algorithms, and land surface datasets. The system and its generated products are evaluated for the 2014 Pacific Northwest wildfires; the 2013 Moore, Oklahoma, tornado; and Hurricane Sandy. Simulated aerosol optical depth over the Front Range of Colorado duri...

Numerical Uncertainties in Simulation of Reversible Isentropic Processes and Entropy Conservation: Part II

Abstract The objectives of this study are 1) to provide the framework for an in-depth statistical analysis of the numerical uncertainties in the simulation of conservation of entropy, potential vorticity, and like properties under appropriate modeling constraints, and 2) to illustrate the discriminating nature of the analysis in an application that isolates internal numerical inaccuracies in the simulation of reversible atmospheric processes. In an earlier study the authors studied the pure error sum of squares function as a quadratic measure of uncertainties by summing the squared differences between equivalent potential temperature as simulated by the nonlinear governing equations for mass, energy, water vapor, and cloud water and its counterpart simulated as a trace constituent. Within the experimental design to examine a models capabilities to conserve the moist entropy, the continuum equations demand that the differences between equivalent potential temperature θe and proxy equivalent potential temp...

January and July Global Distributions of Atmospheric Heating for 1986, 1987, and 1988

Abstract Three-dimensional global distributions of atmospheric heating are estimated for January and July of the 3-year period 1986–88 from the ECMWF/TOGA assimilated datasets. Emphasis is placed on the interseasonal and interannual variability of heating both locally and regionally. Large fluctuations in the magnitude of heating and the disposition of maxima/minima in the Tropics occur over the 3-year period. This variability, which is largely in accord with anomalous precipitation expected during the ENSO cycle, appears realistic. In both January and July, interannual differences of 1.07−1.5 K day−1 in the vertically averaged heating occur over the tropical Pacific. These interannual regional differences are substantial in comparison with maximum monthly averaged Heating rates of 2.0−2.5 K day−1. In the extratropics, the most prominent interannual variability occurs along the wintertime North Atlantic cyclone track. Vertical profiles of heating from selected regions also reveal large interannual variabi...