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  • 1
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    Trends and Variability in Surface Ozone over the United States (2015)
    Wiley
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    Publikationsdatum: 2015-08-15
    Beschreibung: We investigate the observed trends and interannual variability in surface ozone over the United States using the Global Modeling Initiative chemical transport model. We discuss the roles of meteorology, emissions, and transport from the stratosphere in driving the interannual variability in different regions and seasons. We demonstrate that a hindcast simulation for 1991–2010 can reproduce much of the observed variability and the trends in summertime ozone, with correlation coefficients for seasonally and regionally averaged median ozone ranging from 0.46 to 0.89. Reproducing the interannual variability in winter and spring in the western United States may require higher resolution models to adequately represent stratosphere-troposphere exchange. Hindcast simulations with fixed versus variable emissions show that changes in anthropogenic emissions drive the observed negative trends in monthly median ozone concentrations in the eastern United States during summer, as well as the observed reduction in the amplitude of the seasonal cycle. The simulation underestimates positive trends in the western United States during spring, but excluding the first four years of data removes many of the statistically significant trends in this region. The reduction in the slope of the ozone versus temperature relationship before and after major emission reductions is also well represented by the model. Our results indicate that a global model can reproduce many of the important features of the meteorologically induced ozone variability as well as the emission-driven trends, lending confidence to model projections of future changes in regional surface ozone.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 2
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    Wet Scavenging of Soluble Gases in DC3 Deep Convective Storms Using WRF-Chem Simulations and Aircraft Observations (2016)
    Wiley
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    Publikationsdatum: 2016-04-03
    Beschreibung: We examine wet scavenging of soluble trace gases in storms observed during the Deep Convective Clouds and Chemistry (DC3) field campaign. We conduct high-resolution simulations with the Weather Research and Forecasting model with Chemistry (WRF-Chem) of a severe storm in Oklahoma. The model represents well the storm location, size, and structure as compared with NEXRAD reflectivity, and simulated CO transport is consistent with aircraft observations. Scavenging efficiencies (SEs) between inflow and outflow of soluble species are calculated from aircraft measurements and model simulations. Using a simple wet scavenging scheme, we simulate the SE of each soluble species within the error bars of the observations. The simulated SEs of all species except nitric acid (HNO 3 ) are highly sensitive to the values specified for the fractions retained in ice when cloud water freezes. To reproduce the observations, we must assume zero ice retention for formaldehyde (CH 2 O) and hydrogen peroxide (H 2 O 2 ) and complete retention for methyl hydrogen peroxide (CH 3 OOH) and sulfur dioxide (SO 2 ), likely to compensate for the lack of aqueous chemistry in the model. We then compare scavenging efficiencies among storms that formed in Alabama and northeast Colorado and the Oklahoma storm. Significant differences in SEs are seen among storms and species. More scavenging of HNO 3 and less removal of CH 3 OOH are seen in storms with higher maximum flash rates, an indication of more graupel mass. Graupel is associated with mixed phase scavenging and lightning production of nitrogen oxides (NO x ), processes that may explain the observed differences in HNO 3 and CH 3 OOH scavenging.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 3
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    Planning, implementation and scientific goals of the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) field mission (2016)
    Wiley
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    Publikationsdatum: 2016-04-07
    Beschreibung: The Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC 4 RS) field mission based at Ellington Field, Texas, during August and September 2013 employed the most comprehensive airborne payload to date to investigate atmospheric composition over North America. The NASA ER-2, DC-8, and SPEC Inc. Learjet flew 57 science flights from the surface to 20 km. The ER-2 employed 7 remote sensing instruments as a satellite surrogate, and 8 in situ instruments. The DC-8 employed 23 in situ and 5 remote sensing instruments for radiation, chemistry and microphysics. The Learjet used 11 instruments to explore cloud microphysics. SEAC 4 RS launched numerous balloons, augmented AERONET, and collaborated with many existing ground measurement sites. Flights investigating convection included close coordination of all 3 aircraft. Coordinated DC-8 and ER-2 flights investigated the optical properties of aerosols, the influence of aerosols on clouds, and the performance of new instruments for satellite measurements of clouds and aerosols. ER-2 sorties sampled stratospheric injections of water vapor and other chemicals by local and distant convection. DC-8 flights studied seasonally evolving chemistry in the Southeastern U.S., atmospheric chemistry with lower emissions of NO x and SO 2 than in previous decades, isoprene chemistry under high and low NO x conditions at different locations, organic aerosols, air pollution near Houston and in petroleum fields, smoke from wildfires in western forests and from agricultural fires in the Mississippi Valley, and the ways in which the chemistry in the boundary layer and the upper troposphere were influenced by vertical transport in convective clouds.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 4
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    Surface Dimming by the 2013 Rim Fire Simulated by a Sectional Aerosol Model (2016)
    Wiley
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    Publikationsdatum: 2016-06-05
    Beschreibung: The Rim Fire of 2013, the third largest area burned by fire recorded in California history, is simulated by a climate model coupled with a size-resolved aerosol model. Modeled aerosol mass, number and particle size distribution are within variability of data obtained from multiple airborne in-situ measurements. Simulations suggest Rim Fire smoke may block 4-6% of sunlight energy reaching the surface, with a dimming efficiency around 120-150 W m -2 per unit aerosol optical depth in the mid-visible at 13:00-15:00 local time. Underestimation of simulated smoke single scattering albedo at mid-visible by 0.04 suggests the model overestimates either the particle size or the absorption due to black carbon. This study shows that exceptional events like the 2013 Rim Fire can be simulated by a climate model with one-degree resolution with overall good skill, though that resolution is still not sufficient to resolve the smoke peak near the source region.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 5
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    Microphysical Simulations of Large Volcanic Eruptions: Pinatubo and Toba (2013)
    Wiley
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    Publikationsdatum: 2013-02-16
    Beschreibung: [1]  Simulations of stratospheric clouds from eruptions ranging in size from the 1991 eruption of Mount Pinatubo to that of Toba 74,000 years ago have been completed using a 3D microphysical sectional aerosol model advectively coupled to a general circulation model with prognostic chemistry (WACCM/CARMA). For Pinatubo, properties of the aerosol cloud peak within the ranges derived from observations in the Northern Hemisphere, but reduce faster than observed and a general low-bias is found in the Southern Hemisphere. These biases could be reduced by adding aerosol radiative coupling, a QBO, and the Cerro Hudson eruption to the model. Simulations of eruptions 10 times and 100 times larger than Pinatubo suggest burdens and AOD increase less than linearly (a 100-fold injection increase produces a 20-fold AOD increase) due to particle growth and sedimentation, consistent with previous work that also found the radiative forcings from large eruptions to be self-limiting. Global-averaged AOD remains elevated for 1, 2, and 4 years, respectively, for the three simulated eruptions. The inclusion of van der Waals forces in our coagulation scheme increases peak effective radius and reduces peak AOD by about 10-20%, with bigger effects for larger eruptions. Our simulations find peak mode size to vary by up to an order of magnitude and mode width to vary by up to 50%, suggesting that two-moment modal models may not accurately capture the evolving size distribution. These simulations suggest the value of including van der Waals forces in the coagulation scheme and sectional size distributions in climate models.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 6
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    Effect of emissions inventory versus climate model resolution on radiative forcing and precipitation over the continental United States (2012)
    Wiley
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    Publikationsdatum: 2012-03-01
    Beschreibung: We evaluate the impact of anthropogenic emission inventory and climate model grid resolution on aerosol concentrations and black direct aerosol top of atmosphere forcing. Anthropogenic aerosol concentrations of sulfate, black carbon (BC), and organic carbon (OC) are simulated using a high-resolution (25 km) regional climate model (RegCM) with (1) the 2000 1° × 1° EDGAR inventory and (2) the 1999 4 km U.S. Environmental Protection Agency (EPA) National Emissions Inventory. A third 60 km EPA simulation tests the effect of climate model resolution. Simulated SO2 and SO42− concentrations from the 25 km simulations agree with observations in DJF, but JJA modeled SO2 is high and SO42− is low by a factor of 2–3 suggesting incomplete sulfate conversion in the model. Simulated BC and OC concentrations are lower than observations, and sensitivity tests suggest the inventories are missing carbonaceous sources. Total aerosol optical depth (AOD) is greater than observations in DJF and lower in JJA, confirming an underestimation of aerosols during summertime. Derived top of atmosphere radiative forcing has a maximum JJA decrease of 7, 8, and 10 W/m2 in the EDGAR, EPA 25 km, and EPA 60 km simulations, respectively. Generally, the 60 km simulations improve measured-modeled aerosol agreement due to reduced precipitation and wet deposition in the 60 km simulation. Comparisons with observations indicate that total precipitation in the 60 km simulation is closer to observations. Thus, aerosol forcings from a regional model may be equally sensitive to resolution and emissions inventory due to the parameterization of large-scale precipitation and wet removal processes.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 7
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    How much tropical cyclone intensification can result from the energy released inside of a convective burst? (2011)
    Wiley
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    Publikationsdatum: 2011-10-25
    Beschreibung: This study proposes a framework for estimating how much tropical cyclone intensification could result from the amount of energy released inside of a convective burst. A convective burst is a sequence of vigorous convective cells occupying one portion of a tropical cyclone's eyewall for approximately 9 to 24 h. On the basis of Tropical Rainfall Measuring Mission (TRMM) satellite radar observations and previous modeling studies, a typical convective burst may release in 12 h an extra 6 × 1017 J of latent heat. TRMM observations suggest that this extra energy represents an increase of 25% or more in the rate that the eyewall releases latent heat prior to the convective burst. Previous studies suggest that 4.5% to 11% of this extra latent heat may be transformed, after a lag of several hours, into an increase in the kinetic energy of the tropical cyclone's inner-core tangential wind. On the basis of the H*wind analysis of aircraft and dropsonde observations, an increase in kinetic energy of this magnitude may be associated with an intensification of 9–16 m s−1 (17–31 kt) in a tropical cyclone's maximum surface wind. This conservative estimate takes into account the increase in ocean surface friction during the period of intensification and assumes that the associated increase in ocean surface enthalpy flux does not counteract any of the frictional loss. Despite sources of uncertainty, it still appears that significant intensification is possible from the amount of energy released inside of a typical convective burst.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 8
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    An evaluation of the representation of Tropical Tropopause cirrus in the CESM/CARMA model using satellite and aircraft observations (2019)
    Wiley
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    Publikationsdatum: 2019
    Beschreibung: Abstract Observations from the third campaign of the NASA Airborne Tropical Tropopause Experiment (ATTREX 3) field mission and CALIPSO satellite mission are used to evaluate simulations of tropical tropopause layer (TTL) cirrus clouds in the Community Earth System Model's (CESM) atmosphere model, CAM5. In this study, CAM5 is coupled with a sectional ice cloud model, the Community Aerosol and Radiation Model for Atmospheres (CARMA). We find that both model variants underrepresent cloud frequency along the ATTREX 3 flight path and both poorly represent relative humidity in the TTL. Furthermore, simulated in‐cloud ice size distributions contained erroneous amounts of ice crystals throughout the distribution. In response, we present a modified ice cloud fraction scheme which boosts the cloud fraction within the TTL. Due to coarse vertical model resolution in the TTL, we also prescribe a 2 K decrease in cold point tropopause temperatures to better align with observed temperatures. Our modifications improve both CAM5 and CAM5/CARMA's in‐cloud ice size and mass distributions. However only CAM5/CARMA has a significant improvement in cloud frequency and relative humidity. An investigation of cloud extinction in the ATTREX 3 region found that each model variant struggles to reproduce observed extinctions. As a first order approximation, we introduce randomly generated temperature perturbations to simulate the effect of gravity waves into the CAM5/CARMA simulation. These gravity waves significantly increase the incidence of low extinction (〈 0.02 km‐1) values, ice cloud fraction between 16‐18km, and ice crystal smaller than 100μm concentrations, but provided only small changes to high extinction values.
    Print ISSN: 2169-897X
    Digitale ISSN: 2169-8996
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 9
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    Modeled optical thickness of sea-salt aerosol (2011)
    Wiley
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    Publikationsdatum: 2011-04-26
    Beschreibung: We simulate the generation and microphysical evolution of sea-salt aerosol using a climatologically driven 3-D microphysical model for the year 2006. We then apply Mie theory to calculate the extinction and scattering efficiencies of our transported, size-resolved sea-salt aerosol, accounting for hygroscopic growth due to changes in ambient relative humidity. We calculate the column optical thickness of our modeled sea-salt aerosol for comparison to three previously published wind speed–dependent clean marine air optical thickness formulations. Variously derived from optical thickness measurements and retrievals taken from the Midway Island AERONET site, the satellite-based MODIS instruments, and the Global Atmospheric Watch (GAW) site at Mace Head, Ireland, the three formulations report similar background levels of clean marine AOT at zero wind speed but significantly different functional dependencies for nonzero wind speeds. We find that our modeled sea-salt aerosol optical thickness very closely depends on the square of surface wind speed under steady state conditions. This relationship is consistent across all latitudes. However, due to the fact that steady state winds are seldom maintained, the 24 h mean wind is more frequently applicable to calculations of sea-salt AOT, with only slightly diminished accuracy.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 10
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    Transport of Asian ozone pollution into surface air over the western United States in spring (2012)
    Wiley
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    Publikationsdatum: 2012-02-18
    Beschreibung: Many prior studies clearly document episodic Asian pollution in the western U.S. free troposphere. Here, we examine the mechanisms involved in the transport of Asian pollution plumes into western U.S. surface air through an integrated analysis of in situ and satellite measurements in May–June 2010 with a new global high-resolution (∼50 × 50 km2) chemistry-climate model (GFDL AM3). We find that AM3 with full stratosphere-troposphere chemistry nudged to reanalysis winds successfully reproduces observed sharp ozone gradients above California, including the interleaving and mixing of Asian pollution and stratospheric air associated with complex interactions of midlatitude cyclone air streams. Asian pollution descends isentropically behind cold fronts; at ∼800 hPa a maximum enhancement to ozone occurs over the southwestern U.S., including the densely populated Los Angeles Basin. During strong episodes, Asian emissions can contribute 8–15 ppbv ozone in the model on days when observed daily maximum 8-h average ozone (MDA8 O3) exceeds 60 ppbv. We find that in the absence of Asian anthropogenic emissions, 20% of MDA8 O3 exceedances of 60 ppbv in the model would not have occurred in the southwestern USA. For a 75 ppbv threshold, that statistic increases to 53%. Our analysis indicates the potential for Asian emissions to contribute to high-O3 episodes over the high-elevation western USA, with implications for attaining more stringent ozone standards in this region. We further demonstrate a proof-of-concept approach using satellite CO column measurements as a qualitative early warning indicator to forecast Asian ozone pollution events in the western U.S. with lead times of 1–3 days.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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