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Malcolm K. W. Ko, Nien Dak Sze, Mikhail Livshits, Michael B. McElroy, and John A. Pyle

Abstract

A two-dimensional zonal-mean model with parameterized dynamics and an advanced photochemical scheme is used to simulate the stratospheric distributions of atmospheric trace gases including ozone. The model calculates the distributions of 37 species that are photochemically coupled via 140 reactions with rate data from WMO/NASA. A full diurnal treatment is used to calculate the diurnal variations of the short-lived species and the diurnal mean of the production/loss rates for the long-lived species. The calculated concentrations are compared with a wide range of observations with emphasis on the seasonal and latitudinal features. In this work, no post hoc adjustment of the dynamical parameters has been attempted to improve agreement with observations.

In general, the model results are in good agreement with observations, although several discrepancies are noted. Rather than focusing on any individual species, we look for systematic agreements and discrepancies between model and observations for a wide range of species. The model appears to successfully simulate the major features of the mixing ratio surfaces for the long-lived species. However, at the equatorial region, the model tends to underestimate the concentrations of upward diffusing species (e.g., CFCs, CH4, N2O) and overestimate the column abundances of the downward diffusing species (HNO3, HCl, O3). These discrepancies are systematically examined and their implications for transport parameterization assessed.

The model successfully simulates the general latitudinal and seasonal behavior of the local concentration and column abundance of O3. Apart from the overestimation of the column abundances at the equator, the model also underestimates its seasonal contrast at high latitudes. There are difficulties in explaining the observed low concentrations of NO2 in winter at high latitudes. It is shown that errors in the simulation of NO2 concentration in these regions can significantly affect the calculated seasonal and latitudinal behavior of the column abundance of ozone in the middle and high latitudes.

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Charles Chemel, Maria R. Russo, John A. Pyle, Ranjeet S. Sokhi, and Cornelius Schiller

Abstract

The development of a severe Hector thunderstorm that formed over the Tiwi Islands, north of Australia, during the Aerosol and Chemical Transport in Tropical Convection/Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere (ACTIVE/SCOUT-O3) field campaign in late 2005, is simulated by the Advanced Research Weather Research and Forecasting (ARW) model and the Met Office Unified Model (UM). The general aim of this paper is to investigate the role of isolated deep convection over the tropics in regulating the water content in the upper troposphere/lower stratosphere (UT/LS). Using a horizontal resolution as fine as 1 km, the numerical simulations reproduce the timing, structure, and strength of Hector fairly well when compared with field campaign observations. The sensitivity of results from ARW to horizontal resolution is investigated by running the model in a large-eddy simulation mode with a horizontal resolution of 250 m. While refining the horizontal resolution to 250 m leads to a better representation of convection with respect to rainfall, the characteristics of the Hector thunderstorm are basically similar in space and time to those obtained in the 1-km-horizontal-resolution simulations. Several overshooting updrafts penetrating the tropopause are produced in the simulations during the mature stage of Hector. The penetration of rising towering cumulus clouds into the LS maintains the entrainment of air at the interface between the UT and the LS. Vertical exchanges resulting from this entrainment process have a significant impact on the redistribution of atmospheric constituents within the UT/LS region at the scale of the islands. In particular, a large amount of water is injected in the LS. The fate of the ice particles as Hector develops drives the water vapor mixing ratio to saturation by sublimation of the injected ice particles, moistening the air in the LS. The moistening was found to be fairly significant above 380 K and averaged about 0.06 ppmv in the range 380–420 K for ARW. As for UM, the moistening was found to be much larger (about 2.24 ppmv in the range of 380–420 K) than for ARW. This result confirms that convective transport can play an important role in regulating the water vapor mixing ratio in the LS.

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Jiankai Zhang, Wenshou Tian, Fei Xie, John A. Pyle, James Keeble, and Tao Wang

Abstract

Recent studies have found a shift of the Arctic stratospheric polar vortex toward Siberia during late winter since 1980, intensifying the zonally asymmetric ozone (ZAO) depletion in the northern middle and high latitudes with a stronger total column ozone decline over Siberia compared with that above other regions at the same latitudes. Using observations and a climate model, this study shows that zonally asymmetric stratospheric ozone depletion gives a significant feedback on the position of the polar vortex and further favors the stratospheric polar vortex shift toward Siberia in February for the period 1980–99. The polar vortex shift is not significant in the experiment forced by zonal mean ozone fields. The February ZAO trend with a stronger ozone decline over Siberia causes a lower temperature over this region than over the other regions at the same latitudes, due to shortwave radiative cooling and dynamical cooling. The combined cooling effects induce an anomalous cyclonic flow over Siberia, corresponding to the polar vortex shift toward Siberia. In addition, the ZAO depletion also increases the meridional gradient of potential vorticity over Siberia, which is favorable for the upward propagation of planetary wave fluxes from the troposphere over this region. Increased horizontal divergence of planetary waves fluxes over the region 60°–75°N, 60°–90°E associated with ZAO changes accelerates the high-latitude zonal westerlies in the middle stratosphere, further enhancing the shift of the stratospheric polar vortex toward Siberia. After 2000, the ZAO trend in February is weaker and induces a smaller polar vortex shift than that in the period 1980–99.

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Adam J. Clark, Israel L. Jirak, Scott R. Dembek, Gerry J. Creager, Fanyou Kong, Kevin W. Thomas, Kent H. Knopfmeier, Burkely T. Gallo, Christopher J. Melick, Ming Xue, Keith A. Brewster, Youngsun Jung, Aaron Kennedy, Xiquan Dong, Joshua Markel, Matthew Gilmore, Glen S. Romine, Kathryn R. Fossell, Ryan A. Sobash, Jacob R. Carley, Brad S. Ferrier, Matthew Pyle, Curtis R. Alexander, Steven J. Weiss, John S. Kain, Louis J. Wicker, Gregory Thompson, Rebecca D. Adams-Selin, and David A. Imy

Abstract

One primary goal of annual Spring Forecasting Experiments (SFEs), which are coorganized by NOAA’s National Severe Storms Laboratory and Storm Prediction Center and conducted in the National Oceanic and Atmospheric Administration’s (NOAA) Hazardous Weather Testbed, is documenting performance characteristics of experimental, convection-allowing modeling systems (CAMs). Since 2007, the number of CAMs (including CAM ensembles) examined in the SFEs has increased dramatically, peaking at six different CAM ensembles in 2015. Meanwhile, major advances have been made in creating, importing, processing, verifying, and developing tools for analyzing and visualizing these large and complex datasets. However, progress toward identifying optimal CAM ensemble configurations has been inhibited because the different CAM systems have been independently designed, making it difficult to attribute differences in performance characteristics. Thus, for the 2016 SFE, a much more coordinated effort among many collaborators was made by agreeing on a set of model specifications (e.g., model version, grid spacing, domain size, and physics) so that the simulations contributed by each collaborator could be combined to form one large, carefully designed ensemble known as the Community Leveraged Unified Ensemble (CLUE). The 2016 CLUE was composed of 65 members contributed by five research institutions and represents an unprecedented effort to enable an evidence-driven decision process to help guide NOAA’s operational modeling efforts. Eight unique experiments were designed within the CLUE framework to examine issues directly relevant to the design of NOAA’s future operational CAM-based ensembles. This article will highlight the CLUE design and present results from one of the experiments examining the impact of single versus multicore CAM ensemble configurations.

Open access