Allen J. Lenzen

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...

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...

Joint distributions of potential vorticity and inert trace constituent in CCM2 and UW θ‐σ model simulations

This letter describes an experiment that examines the ability of the University of Wisconsin (UW) hybrid isentropic-sigma (θ-σ) and sigma (σ) coordinate models and the NCAR Community Climate Model 2 (CCM2) to transport and conserve the joint distributions of isentropic potential vorticity (P θ ) and a source-free inert trace constituent related to the initial distribution of P θ , called proxy ozone (O 3 ), during 10-day isentropic integrations. Under the idealized conditions of this experiment, the governing equations for the atmospheric continuum require that the initial joint distribution of P θ and O 3 be conserved, thereby establishing a test of model accuracy from statistical comparisons of paired values of O 3 and P θ . Any decrease in the initial correlation of unity of P θ and O 3 after integration is an objective measure of a models skill. Results show that correlation coefficients for the UW θ-σ model remain higher than those from CCM2 and the UW σ model, demonstrating an inherent advantage in the simulation of trace constituent transport relative to dynamical processes in isentropic versus sigma coordinate models.

Simulations of tropospheric joint distributions in the UW θ‐σ model and CCM2

Results are presented for experiments which examine the ability of the University of Wisconsin (UW) hybrid isentropic-sigma (θ-σ) and sigma (σ) coordinate models and the NCAR Community Climate Model 2 (CCM2) to transport and conserve the joint distributions of potential temperature (θ) or equivalent potential temperature (θe) and a source-free inert trace constituent identical to the respective initial distribution (tθ or tθe). Under the idealized isentropic conditions of these experiments, the governing equations for the atmospheric continuum require that the joint distributions (θ, tθ or θe, tθe) be conserved throughout the integration. Deviation in the paired values is an objective measure of a models skill to conserve the joint distributions. Results show that conservation remains higher in the UW θ-σ model than in the other models, even near the interface between isentropic and sigma model domains.

Analysis of the Impact of Seasat Scatterometer Data and Horizontal Resolution on GLA Model Simulations of the QE II Storm

Abstract Quasi-Lagrangian diagnostics of mass, angular momentum, water vapor, and kinetic energy are evaluated for four different Goddard Laboratory for Atmospheres model simulations of the Queen Elizabeth II storm of 9–11 September 1978 to study the impact of Seasat-A satellite Scatterometer (SASS) winds and horizontal resolution in numerical prediction. In a four-way comparison, the diagnostics investigate the impact of including dealiased SASS winds in the initial conditions of the model and doubling the horizontal resolution on 36 h simulations of the QE II storm. The largest impact on the simulation stemmed from doubling the models horizontal resolution from 4° × 5° to 2° × 2.5°. The increased resolution resulted in a storm track much closer to that observed, a much deeper surface development, a stronger mass circulation, stronger heating, and stronger increase of angular momentum. The inclusion of SASS data resulted in an approximately 2–3-mb-deeper surface cyclone for both the 2° × 2.5° and 4° × 5...