Valery A. Yudin

A two-dimensional model with input parameters from a general circulation model : Ozone sensitivity to different formulations for the longitudinal temperature variation

Net heating and temperature derived from the middle atmospheric version of the National Center for Atmospheric Researchs Community Climate Model (MA CCM2) history tapes are used to evaluate three different approaches to account for zonal temperature asymmetries in the calculation of gas phase and heterogeneous chemical reaction rate constants and polar stratospheric cloud (PSC) surface area in a two-dimensional chemistry transport model (2-D CTM). The first method uses the daily (and monthly) averaged three-dimensional (3-D) temperature distribution derived from the MA CCM2 to calculate chemical and heterogeneous reaction rates at each 3-D grid point, followed by zonal averaging (pseudo-3-D method). The second method uses 3-D daily temperature statistics from the MA CCM2 to calculate the monthly averaged probability function (stochastic approach). The third method is based on a planetary wave superposition on the zonally averaged temperature (wave approach). The sensitivity of the gas phase reactions to the longitudinal temperature asymmetry is small, while the sensitivity of the heterogeneous reaction rates is comparable to the ozone response to aircraft emissions. All three methods of accounting for longitude temperature asymmetry give similar PSC morphologies in the southern hemisphere, in good agreement with climatological data and independent model calculations. In the northern hemisphere, where the CCM2 winter temperatures at high latitudes are known to be warmer than those observed, the PSCs predicted by the pseudo-3-D and wave methods are much scarcer than those observed or calculated by other authors using climatological temperatures. For the same reason, all other methods employed in the present study failed to predict any PSCs in the northern hemisphere.

Nitrate ion spikes in ice cores not suitable as proxies for solar proton events

Nitrate ion spikes in polar ice cores are contentiously used to estimate the intensity, frequency, and probability of historical solar proton events, quantities that are needed to prepare for potentially society-crippling space weather events. We use the Whole Atmosphere Community Climate Model to calculate how large an event would have to be to produce enough odd nitrogen throughout the atmosphere to be discernible as nitrate peaks at the Earths surface. These hypothetically large events are compared with probability of occurrence estimates derived from measured events, sunspot records, and cosmogenic radionuclides archives. We conclude that the fluence and spectrum of solar proton events necessary to produce odd nitrogen enhancements equivalent to the spikes of nitrate ions in Greenland ice cores are unlikely to have occurred throughout the Holocene, confirming that nitrate ions in ice cores are not suitable proxies for historical individual solar proton events.

Sensitivity of model assessments of high-speed civil transport effects on stratospheric ozone resulting from uncertainties in the NOxproduction from lightning

Lightning NOx production is one of the most important and most uncertain sources of reactive nitrogen in the atmosphere. To examine the role of NOx lightning production uncertainties in supersonic aircraft assessment studies, we have done a number of numerical calculations with the State University of New York at Stony Brook-Russian State Hydrometeorological Institute of Saint-Petersburg two-dimensional model. The amount of nitrogen oxides produced by lightning discharges was varied within its quoted uncertainty from 2 to 12 Tg N/yr. Different latitudinal, altitudinal, and seasonal distributions of lightning NOx production were considered. Results of these model calculations show that the assessment of supersonic aircraft impacts on the ozone layer is very sensitive to the strength of NOx production from lightning. The high-speed civil transport produced NOx leads to positive column ozone changes for lightning NOx production less than 4 Tg N/yr, and to total ozone decrease for lightning NOx production more than 5 Tg N/yr for the same NOx emission scenario. For large lightning production the ozone response is mostly decreasing with increasing emission index, while for low lightning production the ozone response is mostly increasing with increasing emission index. Uncertainties in the global lightning NOx production strength may lead to uncertainties in column ozone up to 4%. The uncertainties due to neglecting the seasonal variations of the lightning NOx production and its simplified latitude distribution are about 2 times less (1.5–2%). The type of altitude distribution for the lightning NOx production does not significally impact the column ozone, but is very important for the assessment studies of aircraft perturbations of atmospheric ozone. Increased global lightning NOx production causes increased total ozone, but for assessment of the column ozone response to supersonic aircraft emissions, the increase of lightning NOx production leads to column ozone decreases in response to aircraft emissions.

Energy considerations in the Community Atmosphere Model (CAM)

An error in the energy formulation in the Community Atmosphere Model (CAM) is identified and corrected. Ten year AMIP simulations are compared using the correct and incorrect energy formulations. Statistics of selected primary variables all indicate physically insignificant differences between the simulations, comparable to differences with simulations initialized with rounding sized perturbations. The two simulations are so similar mainly because of an inconsistency in the application of the incorrect energy formulation in the original CAM. CAM used the erroneous energy form to determine the states passed between the parameterizations, but used a form related to the correct formulation for the state passed from the parameterizations to the dynamical core. If the incorrect form is also used to determine the state passed to the dynamical core the simulations are significantly different. In addition, CAM uses the incorrect form for the global energy fixer, but that seems to be less important. The difference of the magnitude of the fixers using the correct and incorrect energy definitions is very small.

Observations and simulations of midlatitude ionospheric and thermospheric response to the January 2013 stratospheric sudden warming event

Using observations from mid latitudes, we examine the ionospheric and thermospheric responses to the 2013 stratospheric sudden warming event by comparing data with four simulations performed by the WACCM-X, TIMEGCM, and TIEGCM. The WACCM-X simulation was nudged by the GEOS-5 data. The two TIMEGCM simulations were nudged by the MERRA data and by the aforementioned WACCM-X outputs, respectively. The standard TIEGCM simulation was also performed. These four simulations were compared with Millstone Hill (42.6°N, 71.4°W) incoherent scatter radar data, Millstone Hill and Boulder (40.1°N, 105.2°W) upper and lower thermospheric wind data. The meteor radar data from Collm (51.3°N, 13°E) were also used to examine the zonal wavenumber of the semidiurnal tide (SD). We evaluate the model simulations of the mesospheric and thermospheric responses to the 2013 SSW. The TIMEGCM simulation nudged with the WACCM-X output has suitable stratospheric input and ionospheric dynamics and can reproduce a sharp rise of hmf2 on January 12 observed by the Millstone Hill radar. The comparison of different models with the lower thermospheric SD tide yielded mixed results. The SD tide maintained mostly as a migrating tide for most of the time and matched the TIEGCM simulation very well. The WACCM-X appeared to perform better when the observed SD tide displays the large phase shift. It also has larger and more variable SD tide amplitude. The two TIMEGCM simulations have smaller SD amplitudes in general. Observations showed complex SD tide patterns after January 20, which was difficult to characterize as a migrating tidal mode.