bluuebunny/crossref_metadata_2025 huggingface dataset:
Arctic climate sensitivity to local black carbon
Authors: Flanner Mark G.
Published: April 2013

Recent attention has focused on the impact of black carbon (BC) on Arctic climate. Here, idealized equilibrium climate experiments are conducted to explore the dependence of Arctic temperature change on the altitude and season of local BC forcing. BC residing in the lowest atmospheric layer produces very strong Arctic warming per unit mass and forcing [ 2.8 ± 0.5 K (Wm − 2) − 1] because of low cloud and sea‐ice feedbacks that amplify both summer and winter warming. BC operating only within Arctic snow and sea‐ice also effectively warms the surface, but forcings at 400–750mbar and 210–250mbar cause weak surface warming and cooling, respectively, despite increasing atmospheric moist static energy. This is a consequence of stable atmospheric conditions in the Arctic limiting vertical mixing, and of higher‐altitude BC reducing surface insolation, increasing stability and summer low‐cloud cover, and decreasing poleward energy transport. The current simulated distribution of Arctic atmospheric BC slightly cools the surface, supporting an earlier study, while local atmospheric and cryosphere‐deposited BC warms the Arctic with a sensitivity of + 0.5 ± 0.4 K  (Wm − 2) − 1. By season, April–May tropospheric BC induces the greatest mass‐normalized Arctic warming [0.18 K (Gg yr)  − 1] because high insolation and surface albedo facilitate large specific forcing during this season. Forcing efficacy, however, increases with summer progression because of decreasing atmospheric stability, leading to a narrow range of mass‐normalized response with season. Although limited by exclusion of aerosol indirect effects, changes in ocean heat transport and forcing by co‐emitted species, these experiments show that Arctic climate response is sensitive to the vertical distribution and deposition efficiency of BC reaching the Arctic.
Transport effects on the vertical distribution of tropospheric ozone over the tropical marine regions surrounding India
Authors: Lal S. , Venkataramani S. , Srivastava S. , Gupta S. , Mallik C. , Naja M. , Sarangi T. , Acharya Y. B. , Liu X.
Published: April 2013

The measurements of vertical distribution of ozone have been made over the Bay of Bengal and the Arabian Sea in spring 2006 during a cruise campaign, namely, the Integrated Campaign for Aerosol, Gases and Radiation Budget. The average tropospheric columnar ozone (TCO) values are found to be 36.1 ± 6.9 Dobson unit (DU) and 41.7 ± 5.0 DU over the Bay of Bengal and the Arabian Sea, respectively. In contrast to TCO, ozone mixing ratios are higher by about 10 ppbv in the lower 3 km over the Bay of Bengal due to Indo Gangetic outflow above the marine atmospheric boundary layer. Major contribution in the higher TCO value over the Arabian Sea is, possibly, by stratospheric intrusion when ozone in the upper troposphere is higher by about 20 ppbv. The lowest columnar ozone content of 22.4 DU was observed on 30 March in the central Bay of Bengal due to convective activity resulting into lower ozone throughout the troposphere, except between 6 and 10 km altitude. These near simultaneous ozone observations over the Bay of Bengal and the Arabian Sea in spring season have revealed the role of regional and long‐range transport and local dynamics on the vertical distribution of ozone over these tropical marine regions.
Effect of soluble surfactant on bubble persistence and bubble‐produced aerosol particles
Authors: Modini R. L. , Russell L. M. , Deane G. B. , Stokes M. D.
Published: April 2013

The effect of soluble surfactant on the persistence of salt‐water bubbles and their ability to produce aerosol particles upon bursting was investigated. Ensembles of individual, millimetric bubbles were produced in NaCl solutions of varying surfactant concentration. Aerosol production efficiency—a fundamental property of single bubbles defined as the number of particles produced per bubble film cap area—decreased by 79% to 98% following the addition of surfactant and increase in solution film pressure from 1–2 to 7–27 mN m−1. The generated particle size distributions (0.01–10 µm dry diameter) contained up to three modes and did not change much for film pressures up to 13.8 mN m−1. The persistence of the bubbles at the water surface and the thickness of their film caps were investigated with high‐speed videography. Addition of soluble surfactant increased average bubble persistence providing more time for the bubbles to drain and thin out with the aid of marginal regeneration flows. Bubble film cap thicknesses ranged from around 1 µm for relatively clean, short‐lived bubbles to less than 0.1 µm for surfactant‐stabilized, persistent bubbles. The suppression of aerosol production from the surfactant‐stabilized bubbles may have resulted from the dramatic thinning of their caps or reduced surface forces at high film pressure. Previously reported Sea Spray Aerosol source functions were compared to measured aerosol production efficiencies and found to be significantly greater in magnitude, suggesting that there is a source of particles from whitecaps that was not captured in these single‐bubble experiments.
Source apportionment of formaldehyde during TexAQS 2006 using a source‐oriented chemical transport model
Authors: Zhang Hongliang , Li Jingyi , Ying Qi , Guven Birnur Buzcu , Olaguer Eduardo P.
Published: April 2013

In this study, a source‐oriented version of the Community Multiscale Air Quality (CMAQ) model was developed and used to quantify the contributions of five major local emission source types in Southeast Texas (vehicles, industry, natural gas combustion, wildfires, biogenic sources), as well as upwind sources, to regional primary and secondary formaldehyde (HCHO) concentrations. Predicted HCHO concentrations agree well with observations at two urban sites (the Moody Tower [MT] site at the University of Houston and the Haden Road #3 [HRM‐3] site operated by Texas Commission on Environmental Quality). However, the model underestimates concentrations at an industrial site (Lynchburg Ferry). Throughout most of Southeast Texas, primary HCHO accounts for approximately 20–30% of total HCHO, while the remaining portion is due to secondary HCHO (30–50%) and upwind sources (20–50%). Biogenic sources, natural gas combustion, and vehicles are important sources of primary HCHO in the urban Houston area, respectively, accounting for 10–20%, 10–30%, and 20–60% of total primary HCHO. Biogenic sources, industry, and vehicles are the top three sources of secondary HCHO, respectively, accounting for 30–50%, 10–30%, and 5–15% of overall secondary HCHO. It was also found that over 70% of PAN in the Houston area is due to upwind sources, and only 30% is formed locally. The model‐predicted source contributions to HCHO at the MT generally agree with source apportionment results obtained from the Positive Matrix Factorization (PMF) technique.
Constraints on the major sources of dissolved organic carbon in Alpine ice cores from radiocarbon analysis over the bomb‐peak period
Authors: May B. , Wagenbach D. , Hoffmann H. , Legrand M. , Preunkert S. , Steier P.
Published: April 2013

Radiocarbon (14C) has proven to be a powerful tool in distinguishing modern and fossil fuel sources contributing to organic aerosols. By applying this concept to ice core records of the dissolved organic carbon (DOC) fraction, we developed a setup dedicated to the extraction of DOC from Alpine ice core samples for 14C microanalysis. With respect to the difficulties and limitations of this analytical method, it is shown that a total process blank mass of (6 ± 3) μgC with a 14C signature of (0.71 ± 0.17) can be obtained, corresponding to a minimum sample size between 200 g for industrial and 800 g for pre‐industrial ice. Radiocarbon analyses of eight DOC ice core samples from the high accumulation glacier Col du Dôme (European Alps) were mainly performed over the bomb‐peak period. These data, being associated with snow deposition over the summer half‐years, show an overall mean fossil contribution of (25 ± 9) %. Adaptation of the DO14C values to the atmospheric 14CO2 record revealed that the biogenic input to ice core DOC is associated with a fast recycling biospheric component, likely linked to a turnover time of less than 3 years.
Major 20th century changes of water‐soluble humic‐like substances (HULISWS) aerosol over Europe inferred from Alpine ice cores
Authors: Guilhermet J. , Preunkert S. , Voisin D. , Baduel C. , Legrand M.
Published: April 2013

Using a newly developed method dedicated to measurements of water‐soluble humic‐like substances (HULISWS) in atmospheric aerosol samples, the carbon mass quantification of HULISWS in an Alpine ice core is achieved for the first time. The method is based on the extraction of HULISWS with a weak anion‐exchanger resin and the subsequent quantification of the extracted carbon fraction with a total organic carbon (TOC) analyzer. Measurements were performed along a Col du Dôme (4250 m above sea level, French Alps) ice core covering the 1920–2004 time period. The HULISWS concentrations exhibit a well‐marked seasonal cycle with winter minima close to 7 ppbC and summer maxima ranging between 10 and 50 ppbC. Whereas the winter HULISWS concentrations remained unchanged over the twentieth century, the summer concentrations increased from 20 ppbC prior to the Second World War to 35 ppbC in the 1970–1990s. These different trends reflect the different types of HULISWS sources in winter and summer. HULISWS are mainly primarily emitted by domestic wood burning in winter and secondary in summer being produced from biogenic precursors. For unknown reason, the HULISWS signal is found to be unusual in ice samples corresponding to World War II.
Trends in ISCCP, MISR, and MODIS cloud‐top‐height and optical‐depth histograms
Authors: Marchand Roger
Published: April 2013

In this article, temporal changes in the Multiangle Imaging Spectro Radiometer (MISR) and Moderate Resolution Imaging Spectrometer (MODIS) joint histograms of cloud‐top height (CTH) and optical depth (OD) over the period 2001 to 2011 are examined. The analysis shows no significant trend in total cloud cover averaged over all oceans between 60°N and 60°S from 2001 to 2011. There are, however, significant trends in the amount of some CTH‐OD histogram components or cloud types. In particular, there was an increase in the amount of cloud with intermediate optical thickness (23 > OD > 3.6) and a decrease in the amount of the most optically thick cloud (OD > 23) over this period. The total cloud amount shows no trend because the increase in the amount of intermediate optically thick clouds is nearly balanced by the decrease in the amount of the most optically thick clouds. This balance is not due to a simple shift toward optically thinner clouds in all regions but has a complex spatial pattern both regionally and vertically. An examination of the geographic distribution of the change shows that the decrease in the amount of the most optically thick cloud occurred primarily in the extratropics. International Satellite Cloud Climatology Project (ISCCP) observations are briefly compared with those from MODIS and MISR. The comparison shows that ISCCP‐retrieved total‐cloud fraction is reasonably robust, but changes in the ISCCP component cloud fractions sometimes show large deviations from those of MISR and MODIS.
Global precipitation trends in 1900–2005 from a reconstruction and coupled model simulations
Authors: Ren Li , Arkin Phillip , Smith Thomas M. , Shen Samuel S.P.
Published: April 2013

The trends of global precipitation in 1900–2005 are evaluated using a historical precipitation reconstruction and coupled model simulations, Coupled Model Intercomparison Project 5 (CMIP5) and Coupled Model Intercomparison Project Phase 3. A significant increasing trend in the global oceanic precipitation is identified in both the reconstruction and models. The trend from the reconstructed ocean precipitation is 0.04 mm day−1 over 100a (100 years) and is about twice that of the mean of all models. Over land, the spatial patterns of the trends from both the reconstruction and the models are similar to those shown in the Intergovernmental Panel on Climate Change Fourth Assessment Report. Over the ocean, both reconstruction and models show positive trends in the equatorial and subpolar regions and negative trends over the subtropics. However, the trend magnitude and the locations of the trend peaks are different near the equator (10°S to 10°N) between the reconstruction and the models. CMIP5 future simulations for the global mean project a continuing and stronger precipitation trend in the 21st century than the 20th century.
Production rate and climate influences on the variability of 10Be deposition simulated by ECHAM5‐HAM: Globally, in Greenland, and in Antarctica
Authors: Heikkilä U. , Smith A. M.
Published: April 2013

Ice core concentrations of 10Be are used as a proxy for solar activity, but they might be affected by atmospheric transport and deposition and their changes. During the Holocene, the influence is likely to be small, but during glacials it has to be accounted for. First, the climate influence has to be understood during the present climate. This study uses an ECHAM5‐HAM 30‐year climatological simulation of 10Be to investigate the production and climate‐related influences on 10Be deposition with focus on Greenland and Antarctica. We examine the climate modes driving snow accumulation and hence potentially 10Be deposition over a climatologically relevant period. The North Atlantic Oscillation (NAO) is found to be the main driver of changes in precipitation and 10Be deposition in Greenland, in agreement with previous studies. In Antarctica, the picture is more complex as precipitation and 10Be deposition are only weakly correlated with the Southern Annular Mode (SAM), El Niño‐Southern Oscillation (ENSO), or Zonal Wave 3 pattern (ZW3). The results suggest that on seasonal scale, 10Be deposition is linked with both precipitation rate and tropopause height, mainly due to the similar seasonal cycle. However, the correlation with tropopause height persists on the annual time scale. All in all, 10Be variability in Antarctica is an interplay of several processes whose contribution varies in time and space. When interpreting 10Be ice core records for solar activity, the time scale is essentially important. On seasonal scale, the 10Be signal is dominated by weather influences, but on multiannual scales, the production rate is the main driver. On multidecadal scale, large long‐term trends in climatic factors have the potential to distort the signal again as is seen in 10Be records during glacials. This study shows how climate modes connect to 10Be variability and how this connection could be used to correct for the climate impact. The established connections during present climatic conditions can be used as a basis to investigate these connections during glacial climate in a glacial model simulation.
The structure of the mesosphere during sudden stratospheric warmings in a global circulation model
Authors: Zülicke Christoph , Becker Erich
Published: April 2013

Mesospheric coolings and wind reversals during sudden stratospheric warmings are studied in a 570 day permanent January simulation with the Kühlungsborn Mechanistic Circulation Model (KMCM). The model is run at a high resolution in combination with an advanced parameterization of turbulence, allowing for an explicit description of gravity‐wave effects. Self‐generated major sudden stratospheric warmings are quantified with benchmark tests of Charlton and Polvani (2007) and are found to be nearly realistic. Extension of the tests into the mesosphere gives rise to a benchmark diagram for the entire middle atmosphere, showing that the mesospheric cooling is robust while the mesospheric wind response is variable. The same features appear in a composite constructed from five stratospheric warming events. The zonal‐mean structures indicate an old stratopause descending with about 6 km per day during about 5 days before the central date. About 10 days after the central date, an elevated new stratopause develops in the upper mesosphere and subsequently progresses downward, which is driven by westward gravity waves. Temporal characteristics are deduced from 7 day smoothed daily time series from representative stratospheric and mesospheric zonal‐mean quantities. A correlation analysis shows that the temperature signals are anticorrelated, while the wind signals are uncorrelated. The begin, peak, and end times of the events are diagnosed with two objective methods. Both methods reveal nearly equal‐time appearance of stratospheric warming and wind deceleration (within 2 days), followed by mesospheric cooling with a delay of less than 5 days. This rules out mesospheric precursors of sudden stratospheric warmings in our simulation.
Antarctic ice sheet mass loss estimates using Modified Antarctic Mapping Mission surface flow observations
Authors: Ren Diandong , Leslie Lance M. , Lynch Mervyn J.
Published: April 2013

The long residence time of ice and the relatively gentle slopes of the Antarctica Ice Sheet make basal sliding a unique positive feedback mechanism in enhancing ice discharge along preferred routes. The highly organized ice stream channels extending to the interior from the lower reach of the outlets are a manifestation of the role of basal granular material in enhancing the ice flow. In this study, constraining the model‐simulated year 2000 ice flow fields with surface velocities obtained from InSAR measurements permits retrieval of the basal sliding parameters. Forward integrations of the ice model driven by atmospheric and oceanic parameters from coupled general circulation models under different emission scenarios provide a range of estimates of total ice mass loss during the 21st century. The total mass loss rate has a small intermodel and interscenario spread, rising from approximately −160 km3/yr at present to approximately −220 km3/yr by 2100. The accelerated mass loss rate of the Antarctica Ice Sheet in a warming climate is due primarily to a dynamic response in the form of an increase in ice flow speed. Ice shelves contribute to this feedback through a reduced buttressing effect due to more frequent systematic, tabular calving events. For example, by 2100 the Ross Ice Shelf is projected to shed ~40 km3 during each systematic tabular calving. After the frontal section's attrition, the remaining shelf will rebound. Consequently, the submerged cross‐sectional area will reduce, as will the buttressing stress. Longitudinal differential warming of ocean temperature contributes to tabular calving. Because of the prevalence of fringe ice shelves, oceanic effects likely will play a very important role in the future mass balance of the Antarctica Ice Sheet, under a possible future warming climate.
Multimodel attribution of the Southern Hemisphere Hadley cell widening: Major role of ozone depletion
Authors: Min Seung‐Ki , Son Seok‐Woo
Published: April 2013

It has been suggested that the Hadley cell has been widening during the past three decades in both hemispheres, but attribution of its cause(s) remains challenging. By applying an optimal fingerprinting technique to 7 modern reanalyses and 49 coupled climate models participating in the CMIP3 and CMIP5, here we detect an influence of human‐induced stratospheric ozone depletion on the observed expansion of the Hadley cell in the Southern Hemisphere (SH) summer. The detected signal is found to be separable from other external forcings that include greenhouse gases (GHGs), confirming a dominant role of stratospheric ozone in the SH summer climate change. Our results are largely insensitive to observational and model uncertainties, providing additional evidence for a human contribution to the atmospheric circulation changes.
Processes driving thunderstorms over the Agulhas Current
Authors: de Boer Agatha M. , Collier Andrew B. , Caballero Rodrigo
Published: April 2013

Lightning occurs predominantly over land and is not common over the open ocean. We study here one oceanic region in which thunderstorms are frequently found, namely the warm Agulhas Current off the southeast coast of South Africa. The seasonal and interannual lightning variability is derived from satellite and terrestrial data sets. Favorable climatic conditions for lightning are investigated using both ERA‐Interim and NCEP/NCAR reanalysis data. We find peak lightning in austral autumn over the Agulhas Current but with low seasonality (i.e., there is considerable lightning throughout the year). While the climatological wind direction varies strongly with latitude and season, the wind direction is predominantly northerly throughout the region during thunderstorms. A composite of sea level pressure during thunderstorm days indicates that thunderstorms are related to eastward‐propagating synoptic‐scale wave trains passing through the Agulhas Current region. The strong convective activity during thunderstorms occur in the warm sector of a cyclone and is associated with horizontal convergence and lifting of warm, moist surface air originating over the warm Agulhas Current.
Attribution of observed historical near‒surface temperature variations to anthropogenic and natural causes using CMIP5 simulations
Authors: Jones Gareth S. , Stott Peter A. , Christidis Nikolaos
Published: April 2013

We have carried out an investigation into the causes of changes in near‒surface temperatures from 1860 to 2010. We analyze the HadCRUT4 observational data set which has the most comprehensive set of adjustments available to date for systematic biases in sea surface temperatures and the CMIP5 ensemble of coupled models which represents the most sophisticated multi‒model climate modeling exercise yet carried out. Simulations that incorporate both anthropogenic and natural factors span changes in observed temperatures between 1860 and 2010, while simulations of natural factors do not warm as much as observed. As a result of sampling a much wider range of structural modeling uncertainty, we find a wider spread of historic temperature changes in CMIP5 than was simulated by the previous multi‒model ensemble, CMIP3. However, calculations of attributable temperature trends based on optimal detection support previous conclusions that human‒induced greenhouse gases dominate observed global warming since the mid‒20th century. With a much wider exploration of model uncertainty than previously carried out, we find that individually the models give a wide range of possible counteracting cooling from the direct and indirect effects of aerosols and other non‒greenhouse gas anthropogenic forcings. Analyzing the multi‒model mean over 1951–2010 (focusing on the most robust result), we estimate a range of possible contributions to the observed warming of approximately 0.6 K from greenhouse gases of between 0.6 and 1.2 K, balanced by a counteracting cooling from other anthropogenic forcings of between 0 and −0.5 K.
Energy budget change in the tropics according to the SRES A1B scenario in the IPCC AR4 models
Authors: Kim Kwang‐Yul , Na Hanna , Lee Hun‐Gyu
Published: April 2013

The IPCC AR4 model data sets were investigated in order to address how the energy balance will change in the tropics (30°S–30°N) under the SRES A1B scenario. A climate change signal with a well‐defined trend was extracted using cyclostationary empirical orthogonal function analysis; this signal depicts near‐linear warming in the tropics. This “warming” signal, together with the seasonal cycle, explains most of the variance (91.32–94.86%) in the AR4 model datasets. In addition to the warming of the atmospheric column and the surface, the cloud fraction decreased over most of the tropics, except over the equatorial Pacific. Specific humidity generally increased over the entire troposphere. The decreased cloud fraction and the increased specific humidity resulted in a net increase in shortwave radiation (by ~3.58 (±1.92) W m–2) in the atmospheric column. Simultaneously, the increased atmospheric and surface temperatures (resulting from positive water vapor feedback) caused enhanced longwave radiation exchange between the surface and the atmospheric column; net downward longwave radiation increased by ~19.22 (±3.85) W m–2, and net upward longwave radiation increased by ~14.50 (±3.04) W m–2 over 100 years. The second largest change was found in the heat flux leaving the surface, which amounted to ~4.55 (±1.72) W m–2. As a result of the radiation budget change associated with warming and meridional energy transport by the atmosphere and the ocean, net energy gains were found for both the tropical atmosphere (~5.82 (±3.23) W m–2) and the tropical surface (~0.48 (±0.30) W m–2).
Baffin Island snow extent sensitivity: Insights from a regional climate model
Authors: Berdahl Mira , Robock Alan
Published: April 2013

Recent modeling efforts suggest that the Little Ice Age (LIA) onset could be explained by a series of four large decadally‐spaced volcanic eruptions. At that time, glaciers on Baffin Island advanced and did not retreat until the past century, perhaps due to Arctic and North Atlantic Ocean sea ice feedbacks. To try to determine what parameters sustain snow cover, we investigate the relative impacts of changes in radiation and advection on minimum summer snow extent over Baffin Island. We used the Weather Research and Forecasting (WRF) model to run eight 6 month long (April‐September), 10 km resolution simulations, in which we varied boundary condition temperatures, solar radiation, and sea ice cover. Although the Control Run underestimated cloud cover and thus produced an exaggerated diurnal 2 m temperature cycle, the relative changes of snow extent show that WRF accurately simulates snow expansion into the same regions as during the LIA. With an average temperature decrease from current temperatures by −3.9 ± 1.1 K, it only requires one season for the model to lower the snowline by comparable elevation changes seen during the descent into the LIA. WRF's maximum snow line sensitivity is 7 K/km, within the range of the typically assumed lapse rate of 5–7 K/km in the Canadian Arctic. Thus, if a shift in the Arctic climate greatly expanded sea ice coverage following large volcanic eruptions, this would have been enough to perpetuate an ice sheet on Baffin Island throughout the LIA.
Final warming of the Southern Hemisphere polar vortex in high‐ and low‐top CMIP5 models
Authors: Wilcox L. J. , Charlton‐Perez A. J.
Published: April 2013

The final warming date of the polar vortex is a key component of Southern Hemisphere stratospheric and tropospheric variability in spring and summer. We examine the effect of external forcings on Southern Hemisphere final warming date and the sensitivity of any projected changes to model representation of the stratosphere. Final warming date is calculated using a temperature‐based diagnostic for ensembles of high‐ and low‐top models from the fifth Coupled Model Intercomparison Project (CMIP5), under the historical, Representative Concentration Pathway (RCP4.5) and RCP8.5 forcing scenarios. The final warming date in the models is generally too late in comparison with those from reanalyses: around 2 weeks too late in the low‐top ensemble, and around 1 week too late in the high‐top ensemble. Ensemble Empirical Mode Decomposition (EEMD) is used to analyze past and future change in final warming date. Both the low‐ and high‐top ensemble show characteristic behavior expected in response to changes in greenhouse gas and stratospheric ozone concentrations. In both ensembles, under both scenarios, an increase in final warming date is seen between 1850 and 2100, with the latest dates occurring in the early twenty‐first century, associated with the minimum in stratospheric ozone concentrations in this period. However, this response is more pronounced in the high‐top ensemble. The high‐top models show a delay in final warming date in the late 21st century in RCP8.5 that is not produced by the low‐top models, which are shown to be less responsive to greenhouse gas forcing. This suggests that it may be necessary to use stratosphere resolving models to accurately predict Southern Hemisphere surface climate change.
Future projections of heat waves around Japan simulated by CMIP3 and high‐resolution Meteorological Research Institute atmospheric climate models
Authors: Nakano Masuo , Matsueda Mio , Sugi Masato
Published: April 2013

Future changes in heat wave characteristics around Japan are investigated using Coupled Model Intercomparison Project Phase 3 (CMIP3) model outputs, and high‐resolution present‐day (1979–2003) and future (2075–2099) climate simulations under the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A1B emission scenario. The high‐resolution simulations are conducted using 20, 60, and 180 km mesh atmospheric general circulation models (AGCMs), as well as a 5 km mesh regional climate model (RCM) nested within the 20 km mesh AGCM. The CMIP3 models project that the frequency of heat wave days (HWF) will increase 22.8, 22.3, and 26.5 d yr–1 in northern, eastern, and western Japan, respectively. The multimodel ensemble spread of future changes in HWF averaged around Japan is large (4–58 d yr–1). The spread is affected by the climate sensitivity of the models and the simulated magnitude of the interannual variation of the daily maximum temperature in present‐day climate. In the atmospheric model simulations, the 5 and 20 km mesh models can qualitatively simulate observed HWF distributions, which are affected by steep backbone mountain ranges in Japan. The 5 and 20 km mesh models project large (>30 d yr–1) increases in HWF in the coastal areas of Japan. The duration of heat wave days is projected to increase in areas with increasing HWF.
Development and evaluation of an ammonia bidirectional flux parameterization for air quality models
Authors: Pleim Jonathan E. , Bash Jesse O. , Walker John T. , Cooter Ellen J.
Published: April 2013

Ammonia is an important contributor to particulate matter in the atmosphere and can significantly impact terrestrial and aquatic ecosystems. Surface exchange between the atmosphere and biosphere is a key part of the ammonia cycle. New modeling techniques are being developed for use in air quality models that replace current ammonia emissions from fertilized crops and ammonia dry deposition with a bidirectional surface flux model including linkage to a detailed biogeochemical and farm management model. Recent field studies involving surface flux measurements over crops that predominate in North America have been crucial for extending earlier bidirectional flux models toward more realistic treatment of NH3 fluxes for croplands. Comparisons of the ammonia bidirection flux algorithm to both lightly fertilized soybeans and heavily fertilized corn demonstrate that the model can capture the magnitude and dynamics of observed ammonia fluxes, both net deposition and evasion, over a range of conditions with overall biases on the order of the uncertainty of the measurements. However, successful application to the field experiment in heavily fertilized corn required substantial modification of the model to include new parameterizations for in‐soil diffusion resistance, ground quasi‐laminar boundary layer resistance, and revised cuticular resistance that is dependent on in‐canopy NH3 concentration and RH at the leaf surface. This new bidirectional flux algorithm has been incorporated in an air quality modeling system, which also includes an implementation of a soil nitrification model.
Impacts of climate change on surface ozone and intercontinental ozone pollution: A multi‐model study
Authors: Doherty R. M. , Wild O. , Shindell D. T. , Zeng G. , MacKenzie I. A. , Collins W. J. , Fiore A. M. , Stevenson D. S. , Dentener F. J. , Schultz M. G. , Hess P. , Derwent R. G. , Keating T. J.
Published: April 2013

The impact of climate change between 2000 and 2095 SRES A2 climates on surface ozone (O)3 and on O3 source‐receptor (S‐R) relationships is quantified using three coupled climate‐chemistry models (CCMs). The CCMs exhibit considerable variability in the spatial extent and location of surface O3 increases that occur within parts of high NOx emission source regions (up to 6 ppbv in the annual average and up to 14 ppbv in the season of maximum O3). In these source regions, all three CCMs show a positive relationship between surface O3 change and temperature change. Sensitivity simulations show that a combination of three individual chemical processes—(i) enhanced PAN decomposition, (ii) higher water vapor concentrations, and (iii) enhanced isoprene emission—largely reproduces the global spatial pattern of annual‐mean surface O3 response due to climate change (R2 = 0.52). Changes in climate are found to exert a stronger control on the annual‐mean surface O3 response through changes in climate‐sensitive O3 chemistry than through changes in transport as evaluated from idealized CO‐like tracer concentrations. All three CCMs exhibit a similar spatial pattern of annual‐mean surface O3 change to 20% regional O3 precursor emission reductions under future climate compared to the same emission reductions applied under present‐day climate. The surface O3 response to emission reductions is larger over the source region and smaller downwind in the future than under present‐day conditions. All three CCMs show areas within Europe where regional emission reductions larger than 20% are required to compensate climate change impacts on annual‐mean surface O3.
Aerosol characteristics observed in southeast Queensland and implications for cloud microphysics
Authors: Tessendorf Sarah A. , Weeks Courtney E. , Axisa Duncan , Bruintjes Roelof T.
Published: April 2013

Regular cloud base aerosol measurements were collected by a research aircraft over a 4 month period during the wet season in southeast Queensland, near Brisbane, Australia. In situ cloud microphysical measurements were also collected in many of these clouds. Brisbane is situated on the east coast of Australia and, depending on the synoptic weather conditions, can experience influences from inland or from the adjacent ocean. In situ aerosol measurements were used to compile a climatology of the aerosol conditions in the region and a back trajectory model was run for 120 h from each measurement to determine the possible air mass influences on each measurement. The most influential factor on the measured aerosol concentrations was the time the trajectory spent over land beneath 2 km (a proxy for the boundary layer). Using this criterion, the measurements were divided into two regimes: maritime for those with minimal time histories over land and continental for the remainder. Other influential factors on the aerosol concentration were also diagnosed and quantified with a regression model, including the proximity of the trajectory to the city of Brisbane and the number of fires along the trajectory. Thermodynamic, aerosol, and cloud microphysical characteristics are presented for each regime. The maritime regime tended to have more coarse mode (larger) aerosol particles and a tail of larger drops in the cloud base droplet spectra, which could be due to nucleation on the larger aerosol particles. The city influence on maritime regime trajectories yielded enhanced nucleation (fine) particle concentrations.
A global survey of the effect of cloud contamination on the aerosol optical thickness and its long‐term trend derived from operational AVHRR satellite observations
Authors: Zhao Tom X.‐P. , Chan Pui K. , Heidinger Andrew K.
Published: April 2013

Subpixel cloud contamination is one of the major issues plaguing passive satellite aerosol remote sensing. Its impact on the aerosol optical thickness (AOT) retrieval has been analyzed/evaluated by many studies. However, the question of how it influences the AOT trend remains to be answered. In this paper, four long‐term advanced very high resolution radiometer (AVHRR) AOT data sets from 1981 to 2009 over global oceans for four different definitions of clear sky, respectively, are produced by applying a two‐channel aerosol retrieval algorithm to the AVHRR clear‐sky reflectances derived by combining NOAA Pathfinder Atmosphere's Extended AVHRR climate data record level‐2b all‐sky reflectances with the cloud probability parameter determined from the Bayesian probabilistic cloud detection technique. A global analysis of the effect of cloud contamination on the AVHRR AOT retrieval as well as on its long‐term trend is then performed by comparing the results from the four data sets. It was found that cloud contamination imposes not only a positive bias on AOT values but also a positive bias on its long‐term trend such that negative trends become less negative and positive trends become more positive. A cloud probability value of ≤1% has been identified as an optimal criterion for clear‐sky definition to minimize the cloud contamination in the AVHRR aerosol retrieval while still retaining strong aerosol signals. In order for a satellite aerosol product to be useful and reliable in aerosol trend detection, the cloud contamination effect on aerosol trends needs to be studied/evaluated carefully along with the effects of calibration error, surface disturbance, and aerosol model assumptions.
Reply to “Reply to ‘Comment on “Hydrocarbon emissions characterization in the Colorado Front Range – A Pilot Study”’ by Michael A. Levi” by Gabrielle Pétron et al.
Authors: Levi Michael A.
Published: April 2013

The reply by Pétron et al. (2012a) to my comment, Levi (2012), on their paper, Pétron et al. (2012a), defends their original conclusion: fugitive emissions in an area that they observed in 2008 were likely larger than those indicated by previous estimates. The reply also claims to have now better characterized the uncertainties in their and my approaches. In particular, they question the representative nature of a data set that Pétron et al. (2012) relied on, and that Levi retained, although they do not recalculate their estimates. Pétron et al. (2012) also claim to show that the analysis in Levi (2012) is flawed because, they argue, it implies the physically unrealistic conclusion that fugitive emissions from the natural gas operations that Pétron et al. (2012) studied may be negative. Pétron et al. (2012a) are reasonable to be skeptical of the data set that they highlight. I show in this reply that if that data set is indeed not representative of condensate tank flashing in the area under study, it is impossible to produce the results in Pétron et al. (2012a) that the authors now defend. I also show that the other critique of Levi (2012) offered by Pétron et al. (2012a), i.e., that Levi's analysis has physically unrealistic implications, relies on an incorrect interpretation of the formulas in that comment. Only one of two conclusions is possible: the results in Levi (2012) are correct, or the conclusions in both Levi (2012a) and Pétron et al. (2012a) are unjustified.
Radar and lightning analyses of gigantic jet‐producing storms
Authors: Meyer Tiffany C. , Lang Timothy J. , Rutledge Steven A. , Lyons Walter A. , Cummer Steven A. , Lu Gaopeng , Lindsey Daniel T.
Published: April 2013

An analysis of thunderstorm environment, structure, and evolution associated with six gigantic jets (five negative polarity, one positive) was conducted. Three of these gigantic jets were observed within detection range of very high frequency lightning mapping networks. All six were within range of operational radars and two‐dimensional lightning network coverage: five within the National Lightning Detection Network and one within the Global Lightning Detection (GLD360) network. Most of the storms producing the jets formed in moist tropical or tropical‐like environments (precipitable water ranged from 37 to 62 kg m−2, and 0–6 km shear from 3.5 to 24.8 m s−1), featuring high convective available potential energy (1200–3500 J kg−1) and low lifted indices (−2.8 to −6.4). The storms had maximum radar reflectivity factors of 54 to 62 dBZ, and 10 dBZ echo contours reached 14–17 km. Storms covered by three‐dimensional lightning mappers were near peak altitude of lightning activity (modes of the vertical distributions of radio sources were at altitudes colder than −50°C) and vertical reflectivity intensity, with overshooting echo tops around the times of their jets. Two of the other three jet‐producing storms produced their jet around the time of a convective surge as indicated by radar data and likely featured overshooting tops. The observations suggest a link between convective surges, overshooting tops, and the occurrence of gigantic jets, similar to prior modeling studies.
On the relation between large‐scale circulation pattern and heavy rain events over the Hawaiian Islands: Recent trends and future changes
Authors: Elison Timm Oliver , Takahashi Mami , Giambelluca Thomas W. , Diaz Henry F.
Published: April 2013

The aim of this paper is to present a statistical downscaling method in which the relationships between present‐day daily weather patterns and local rainfall data are derived and used to project future shifts in the frequency of heavy rainfall events under changing global climate conditions. National Centers for Environmental Prediction and the National Center for Atmospheric Research (NCEP/NCAR) reanalysis data from wet season months (November to April) 1958–2010 are composited for heavy rain days at 12 rainfall stations in the Hawaiian Islands. The occurrence of heavy rain events (days with amounts above the 90th percentile estimated from all wet season rain days 1958–2010) was found to be strongly correlated with upper level cyclonic circulation anomalies centered northwest of Hawai‘i and south‐to‐north transport of water vapor in the middle troposphere. The statistical downscaling model (SD) developed in this study was able to reproduce the observed interannual variations in the number of heavy rain events based on cross‐validation resampling during the more recent interval 1978–2010. However, multidecadal changes associated with the mid‐1970s' climate shift were not well reproduced by the SD using NCEP/NCAR reanalysis data, likely due to inhomogenities in the presatellite period of the NCEP/NCAR reanalysis. Application of the SD to two model scenarios from the CMIP3 database indicates a reduction of heavy rain events in the mid‐ to late 21st century. Based on these models, the likelihood of a widespread increase in synoptic heavy rain events in Hawai‘i as a result of anthropogenic climate change is low over the remainder of the century.
Characterization of fresh and aged biomass burning events using multiwavelength Raman lidar and mass spectrometry
Authors: Nicolae D. , Nemuc A. , Müller D. , Talianu C. , Vasilescu J. , Belegante L. , Kolgotin A.
Published: April 2013

This paper focuses on optical and microphysical properties of long‐range transported biomass burning (BB) aerosols and their variation with atmospheric evolution (ageing), as observed by a multiwavelength Raman lidar, part of EARLINET (European Aerosol LIdar NETwork). Chemical analysis of the atmospheric aerosol was done using a colocated aerosol mass spectrometer (AMS). One relevant optical parameter for the ageing process is the Ångström exponent. In our study, we find that it decreases from 2 for fresh to 1.4–0.5 for aged smoke particles. The ratio of lidar (extinction‐to‐backscatter) ratios (LR532/LR355) changes rapidly from values <1 for fresh to >1 for aged particles. The imaginary part of the refractive index is the most sensitive microphysical parameter. It decreases sharply from 0.05 to less than 0.01 for fresh and aged smoke particles, respectively. Single‐scattering albedo (SSA) varies from 0.74 to 0.98 depending on aerosol age and source. The AMS was used to measure the marker ions of wood‐burning particles during 2 days of measurements when the meteorological conditions favored the downward mixing of aerosols from lofted layers. Particle size distribution and particle effective radius from both AMS and lidar are similar, i.e., particle effective radii were approximately 0.27 µm for fresh BB aerosol particles. Microphysical aerosol properties from inversion of the lidar data agree with similar studies carried out in different regions on the globe. Our study shows that the Ångström exponent LR532/LR355 and the imaginary part of the refractive index can be used to clearly distinguish between fresh and aged smoke particles.
Development, importance, and effect of a ground truth correction for the Moon Mineralogy Mapper reflectance data set
Authors: Isaacson Peter J. , Petro Noah E. , Pieters Carle M. , Besse Sebastien , Boardman Joseph W. , Clark Roger N. , Green Robert O. , Lundeen Sarah , Malaret Erick , McLaughlin Stephanie , Sunshine Jessica M. , Taylor Lawrence A.
Published: April 2013

We evaluate the effect and importance of a ground truth correction for the Moon Mineralogy Mapper (M3) level 2 (reflectance) data set. This correction is derived from extensive laboratory characterizations of mature feldspathic lunar soils and is designed to improve the accuracy of 1 µm absorption features in M3 reflectance data. To evaluate the correction, the band strength across a subset of the feldspathic highlands terrane (FHT) is analyzed with M3 imaging spectroscopy data. Using M3 reflectance data and derived products, we find significant differences in band strength and shape between M3 observations collected over identical terrain but under different observational and operational conditions. The ground truth correction minimizes these differences in 1 µm band strengths and also brings the 1 µm band strengths measured with M3 data into closer agreement with laboratory measurements of lunar soil samples. Although the FHT region studied was found to have very low band strengths, the M3 ground truth correction results in overall stronger absorption features for all mature soils relative to uncorrected level 2 (reflectance) data for the same region. These differences between M3 data collected under different operational conditions and the effects of the ground truth correction, while minor in appearance, can have significant implications for interpretations of any regional soil analyses with M3 data that rely on absolute 1 µm absorption feature strength. The M3 ground truth correction corrects only wavelengths below ~1500 nm, and comparisons between corrected and uncorrected wavelengths must be done with caution.
Cross‐sector emergency planning for water supply utilities and healthcare facilities
Authors: Welter Gregory , Socher Myra , Needham Patricia , Bieber Steve , Bonnaffon Heidi
Published: April 2013

The purpose of this article is to outline the criticality of water supply in sustained operations of healthcare facilities, particularly during community emergencies, and to advocate for enhanced cross‐sector support from the water utilities in meeting this need. Information and ideas presented here were developed in the course of a regional project sponsored by the Metropolitan Washington Council of Governments (MWCOG) for development of emergency water supply operations plans for critical water uses in the Washington, DC, area.
Safety and underwater birth—what every risk manager should know
Authors: Veltman Larry , Doherty Diane
Published: April 2013

Underwater birthing has become a popular birth practice in some areas of the country. Although many of these deliveries occur in a home birth setting, the practice has also been implemented in hospitals and birthing centers. There is continued controversy about the risks and benefits of underwater birthing (as opposed to hydrotherapy during labor), and many risk managers are unaware of these potential risks and benefits. The purpose of this article is to review the significant risks and benefits of underwater birthing, to review relevant literature and several Professional Organizations' Position Statements regarding underwater birthing, and to provide a safety checklist for hospital risk managers who wish to consider adding underwater birthing to their current scope of perinatal care.