bluuebunny/crossref_metadata_2025 huggingface dataset:
The roles of aerosol direct and indirect effects in past and future climate change
Authors: Levy Hiram , Horowitz Larry W. , Schwarzkopf M. Daniel , Ming Yi , Golaz Jean‐Christophe , Naik Vaishali , Ramaswamy V.
Published: April 2013

Using the Geophysical Fluid Dynamics Laboratory's (GFDL's) fully coupled chemistry‐climate (ocean/atmosphere/land/sea ice) model (CM3) with an explicit physical representation of aerosol indirect effects (cloud‐water droplet activation), we find that the dramatic emission reductions (35%–80%) in anthropogenic aerosols and their precursors projected by Representative Concentration Pathway (RCP) 4.5 result in ~1 °C of additional warming and ~0.1 mm day−1of additional precipitation, both globally averaged, by the end of the 21st century. The impact of these reductions in aerosol emissions on simulated global mean surface temperature and precipitation becomes apparent by mid‐21st century. Furthermore, we find that the aerosol emission reductions cause precipitation to increase in East and South Asia by ~1.0 mm day−1through the second half of the 21st century. Both the temperature and the precipitation responses simulated by CM3 are significantly stronger than the responses previously simulated by our earlier climate model (CM2.1) that only considered direct radiative forcing by aerosols. We conclude that the indirect effects of sulfate aerosol greatly enhance the impacts of aerosols on surface temperature in CM3; both direct and indirect effects from sulfate aerosols dominate the strong precipitation response, possibly with a small contribution from carbonaceous aerosols. Just as we found with the previous GFDL model, CM3 produces surface warming patterns that are uncorrelated with the spatial distribution of 21st century changes in aerosol loading. However, the largest precipitation increases in CM3 are colocated with the region of greatest aerosol decrease, in and downwind of Asia.
Correction to “Rain on small tropical islands”
Authors: Sobel A. H. , Burleyson C. D. , Yuter S. E. , Biasutti M.
Published: April 2013

Key Points

Observations of pitch‐angle distributions with repeated probe configurations

Electron flux variations depend on probe relative to the flow

type of electron PAD depends on position relative to the neutral sheet
Forced Sahel rainfall trends in the CMIP5 archive
Authors: Biasutti M.
Published: April 2013

The simulations of the fifth Coupled Models Intercomparison Project (CMIP5) strengthen previous assessments of a substantial role of anthropogenic emissions in driving precipitation changes in the Sahel, the semiarid region at the southern edge of the Sahara. Historical simulations can capture the magnitude of the centennial Sahel drying over the span of the 20th century and confirm that anthropogenic forcings have contributed substantially to it. Yet, the models do not reproduce the amplitude of observed oscillations at multidecadal timescales, suggesting that either oscillations in the forcing or the strength of natural variability are underestimated. Projections for Sahel rainfall are less robust than the 20th century hindcast and outlier projections persist, but overall the CMIP5 models confirm the CMIP3 results in many details and reaffirm the prediction of a rainy season that is more feeble at its start, especially in West Africa, and more abundant at its core across the entire Sahel. Out of 20 models, four buck this consensus. Idealized simulations from a subset of the CMIP5 ensemble—simulations designed to separate the fast land‐atmosphere response to increased greenhouse gases (GHGs) from the slow response mediated through changes in sea surface temperature (SST)—confirm that the direct effect of CO2 is to enhance the monsoon, while warmer SST induce drying over the Sahel. At the same time, these simulations suggest that the seasonal evolution of the rainfall trends in the scenario simulations, spring drying and fall wetting, is an inherently coupled response, not captured by the linear superposition of the fast and slow response to CO2.
Emission estimates of HCFCs and HFCs in California from the 2010 CalNex study
Authors: Barletta Barbara , Carreras‐Sospedra Marc , Cohan Alex , Nissenson Paul , Dabdub Donald , Meinardi Simone , Atlas Elliot , Lueb Rich , Holloway John S. , Ryerson Thomas B. , Pederson James , VanCuren Richard A. , Blake Donald R.
Published: April 2013

The CalNex 2010 (California Research at the Nexus of Air Quality and Climate Change) study was designed to evaluate the chemical composition of air masses over key source regions in California. During May to June 2010, air samples were collected on board a National Oceanic and Atmospheric Administration (NOAA) WP‐3D aircraft over the South Coast Air Basin of California (SoCAB) and the Central Valley (CV). This paper analyzes six effective greenhouse gases—chlorodifluoromethane (HCFC‐22), 1,1‐dichloro‐1‐fluoroethane (HCFC‐141b), 1‐chloro‐1,1‐difluoroethane (HCFC‐142b), 2‐chloro‐1,1,1,2‐tetrafluoroethane (HCFC‐124), 1,1,1,2‐tetrafluoroethane (HFC‐134a), and 1,1‐difluoroethane (HFC‐152a)—providing the most comprehensive characterization of chlorofluorocarbon (CFC) replacement compound emissions in California. Concentrations of measured HCFCs and HFCs are enhanced greatly throughout the SoCAB and CV, with highest levels observed in the SoCAB: 310 ± 92 pptv for HCFC‐22, 30.7 ± 18.6 pptv for HCFC‐141b, 22.9 ± 2.0 pptv for HCFC‐142b, 4.86 ± 2.56 pptv for HCFC‐124, 109 ± 46.4 pptv for HFC‐134a, and 91.2 ± 63.9 pptv for HFC‐152a. Annual emission rates are estimated for all six compounds in the SoCAB using the measured halocarbon to carbon monoxide (CO) mixing ratios and CO emissions inventories. Emission rates of 3.05 ± 0.70 Gg for HCFC‐22, 0.27 ± 0.07 Gg for HCFC‐141b, 0.06 ± 0.01 Gg for HCFC‐142b, 0.11 ± 0.03 Gg for HCFC‐124, 1.89 ± 0.43 Gg for HFC‐134a, and 1.94 ± 0.45 Gg for HFC‐152b for the year 2010 are calculated for the SoCAB. These emissions are extrapolated from the SoCAB region to the state of California using population data. Results from this study provide a baseline emission rate that will help future studies determine if HCFC and HFC mitigation strategies are successful.
A high‐frequency response relaxed eddy accumulation flux measurement system for sampling short‐lived biogenic volatile organic compounds
Authors: Arnts Robert R. , Mowry Fred L. , Hampton Gary A.
Published: April 2013

A second‐generation relaxed eddy accumulation system was built and tested with the capability to measure vertical biogenic volatile organic compound (VOC) fluxes at levels as low as 10 µg C m−2 hr−1. The system features a continuous, integrated gas‐phase ozone removal procedure to allow for the measurement of highly reactive species such as β‐caryophyllene and polar terpenoids such as linalool. A two‐component internal standard continuously added to the accumulators was used to correct for switching‐induced volumetric errors and as a check on VOC losses exceeding accumulator tube adsorption limits. In addition, the internal standards were used to demonstrate that accumulators quickly return to target flow rates at segregation valve switching frequencies up to at least 0.8 Hz. The system was able to measure daytime hourly fluxes of individual biogenic VOC including oxygenated terpenoids, monoterpenes, and sesquiterpenes.
Impact of model errors in convective transport on CO source estimates inferred from MOPITT CO retrievals
Authors: Jiang Zhe , Jones Dylan B. A. , Worden Helen M. , Deeter Merritt N. , Henze Daven K. , Worden John , Bowman Kevin W. , Brenninkmeijer C. A. M. , Schuck T. J.
Published: April 2013

Estimates of surface fluxes of carbon monoxide (CO) inferred from remote sensing observations or free tropospheric trace gas measurements using global chemical transport models can have significant uncertainties because of discrepancies in the vertical transport in the models, which make it challenging to unequivocally relate the observations back to the surface fluxes in the models. The new Measurement of Pollution in the Troposphere (MOPITT) version 5 retrievals provide greater sensitivity to lower tropospheric CO over land relative to the previous versions and are, therefore, useful for evaluating vertical transport in models. We have assimilated the new MOPITT CO retrievals, using the Goddard Earth Observing System (GEOS)‐Chem model, to study the influence of vertical transport errors on inferred CO sources. We compared the source estimates obtained by assimilating the CO profiles, the column amounts, and the surface level retrievals for June–August 2006. The three different inversions produced large differences in the source estimates in regions of convection and strong CO emissions. The inversion using the CO profiles suggested an 85% increase in emissions in India/Southeast Asia, which exacerbated the model bias in the lower and middle troposphere, whereas using the surface level retrievals produced a 37% decrease in Indian/Southeast Asian emissions, which exacerbated the underestimate of CO in the upper troposphere. Globally, the inversion with the surface retrievals suggested a 22% reduction in emissions from the a priori estimate of 161 Tg CO/month (from combustion and the oxidation of biogenic volatile organic compounds), averaged in June–August 2006. The analysis results were validated with independent surface CO measurements from NOAA Global Monitoring Division (GMD) network and upper troposphere CO measurements from the Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrumented Container (CARIBIC). We found that the inversion with the surface retrievals agreed best with surface CO data but produced the largest discrepancy with the CARIBIC aircraft data in the upper troposphere, suggesting the influence of vertical transport errors in the model. Our results show that the comparison of the a posteriori CO distributions obtained from the inversions using the surface and profile retrievals provides a means of characterizing the potential impact of the vertical transport biases on the source estimates and the CO distribution.
A climatology of the stratopause in WACCM and the zonally asymmetric elevated stratopause
Authors: France J. A. , Harvey V. L.
Published: April 2013

A climatology of the stratopause is produced using a 40 year simulation of the Whole Atmosphere Community Climate Model (WACCM). Anomalies in polar winter stratopause temperature and height are interpreted with respect to the location of the polar vortices and anticyclones. The WACCM climatology is compared to an 8 year climatology based on Microwave Limb Sounder (MLS) observations and data from the Goddard Earth Observing System (GEOS) version 5 from August 2004 to July 2012. The WACCM climatology is in excellent agreement with observations, except in the Antarctic vortex where the WACCM stratopause is ~10K warmer and ~5 km higher than observations. WACCM diabatic heating rates support the hypothesis that ageostrophic vertical motions associated with baroclinic planetary waves are responsible for producing Arctic winter temperature anomalies. The area of the winter polar vortices in WACCM at the stratopause is 30% smaller in the NH and 45% smaller in the SH compared to GEOS. The long WACCM record allows us to explore the geographical distribution and temporal evolution of a composite of 15 elevated stratopause (ES) events. This composite is in good agreement with the 2012 ES event observed by MLS, though December ES events in WACCM are not observed by MLS. This is the first work to show that ES events are not zonally symmetric. In the 30 days following ES events, the ES composite shows that the stratopause altitude is highest over the Canadian Arctic, and the highest stratopause temperatures occur 90° to the east over the Norwegian Sea.
Observations of the Madden Julian Oscillation during Indian Ocean Dipole events
Authors: Wilson Earle A. , Gordon Arnold L. , Kim Daehyun
Published: April 2013

The characteristics of Madden Julian Oscillation (MJO) development and propagation during Indian Ocean Dipole (IOD) events are presented in this study. We find that MJO activity over the Indian Ocean and Maritime Continent is enhanced during negative IOD and subdued during positive IOD. MJO events occurring during positive IOD have weaker convection and less organized wind anomalies than those occurring during neutral or negative IOD. These differences are starkest over the eastern Indian Ocean where the IOD has the greatest effect on low‐level humidity. Based on these observations and current MJO theories, we posit that the IOD primarily influences the MJO through its modulation of local low‐level moisture.
Modeled rapid adjustments in diurnal temperature range response to CO2 and solar forcings
Authors: Jackson Lawrence S. , Forster Piers M.
Published: April 2013

We used the National Center for Atmospheric Research single column climate model to determine if rapid adjustments to surface heat fluxes contribute to a change in skin surface or surface air diurnal temperature range (DTR) under 2 × CO2 and −2% solar forcings. An ensemble of model runs was employed with locations selected to represent a range of different climatic conditions and with forcing implemented hourly throughout the diurnal cycle. The change in skin surface DTR and surface energy fluxes during the 3 days after forcing were used to quantify the rapid adjustment response and temperature related feedback. Averaged over all locations, skin surface DTR reduced by 0.01°C after CO2 forcing and included a rapid adjustment to skin surface DTR of −0.12°C. Skin surface DTR reduced by 0.17°C after solar forcing and included a rapid adjustment of −0.01°C. The rapid adjustments in skin surface DTR were associated with rapid adjustments in surface sensible and latent heat fluxes necessary to balance the energy budget immediately after forcing. We find that the sensitivity of skin surface DTR to mean temperature related feedback is the same for CO2 and solar forcings when skin surface DTR rapid adjustments are allowed for. Rapid adjustments played a key role in the geographic variation of the skin surface DTR response to forcing. Our results suggest that diurnal variations in trends of downwelling longwave radiation and rapid reductions in DTR associated with CO2 forcing potentially contributed to the observed global trend in surface air DTR.
A new statistical approach to downscale wind speed distributions at a site in northern Europe
Authors: Devis Annemarie , van Lipzig Nicole P. M. , Demuzere Matthias
Published: April 2013

This paper explores a statistical regression approach to downscale large‐scale global circulation model output to the wind speed distribution at the hub‐height of tall wind turbines. The methodology is developed for Cabauw, using observational, ERA‐Interim and ECHAM5 data. The regression analysis is based on the parameters of the probability distribution functions (pdfs) and includes a variable evaluation prior to the development of the statistical models. During winter ECHAM5 performs very well in representing the ERA‐Interim wind speed pdf at hub‐height. However, during summer, the hub‐height wind speed pdf is not well represented by ECHAM5. A regression analysis shows that during summer‐day the hub‐height wind speed is strongly linked to the wind speed at higher, skillfully represented levels. The summer‐day hub‐height wind speed can therefore be skillfully predicted using wind speed pdf parameters of higher levels (R2 of the model using 500 m wind speed scale parameter as a predictor is 0.84). During the summer‐night, the stable boundary layer is much shallower and the statistical model shows that solely the higher level wind speed is not able to skillfully predict the hub‐height wind speed pdf (R2 of 0.59). Including temperature information in the downscaling model substantially improves the prediction of the summer‐night hub‐height wind speed pdf (R2 adjusted of 0.68).
Long‐term measurement of daytime atmospheric mixing layer height over Hong Kong
Authors: Yang Dongwei , Li Chengcai , Lau Alexis Kai‐Hon , Li Ying
Published: April 2013

Lidar has unique advantages in temporal and spatial resolution to measure the atmospheric mixing layer height (MLH), which is important for analyzing atmospheric phenomena. However, long‐term MLH information over several years, which has important significance in air quality and climate studies, is seldom obtained from lidar data due to the scarcity of long‐running lidar observations. In this paper, we retrieve and analyze daytime MLH from a data set of a lidar that operated continuously over 6.5 years at Yuen Long, Hong Kong. A new algorithm has been developed for consistently retrieving MLH from this large data set, handling all possible weather conditions and aerosol layer structures. We analyze the diurnal, seasonal and inter‐annual variation of MLH over Hong Kong and find a unique phenomenon that the afternoon MLH is higher in autumn than in summer, which is verified by radiosonde results and explained by thermal stability and humidity effect. Moreover, we find a slightly decreasing trend of the daily maximum of MLH, which implies a continually compressed air volume into which pollutants and their precursors are emitted, which is one of the possible factors leading to deteriorated air quality over Hong Kong region.
Third‐order resonant interaction of atmospheric gravity waves
Authors: Huang Kai Ming , Zhang Shao Dong , Yi Fan , Huang Chun Ming , Gan Quan , Gong Yun , Zhang Ye Hui
Published: April 2013

Relative to the extensive studies of third‐order nonlinearity for oceanic gravity waves, third‐order interaction of atmospheric gravity waves has drawn little attention. By numerical experiments with a two‐dimensional, fully nonlinear model, third‐order resonant excitation of atmospheric gravity waves is clearly exhibited. The numerical results indicate that third‐order interaction can take place in the atmosphere, and significant energy exchange occurs in interaction. Wave energy mainly transfers from the high frequency primary wave to the excited wave, and an intense secondary wave can strengthen this energy transfer, which is consistent with the results in second‐order interaction. In the whole process of interaction, both the wave numbers and frequencies of the interacting waves are in good agreement with the third‐order resonant conditions. Third‐order resonance arises through direct interaction of waves that satisfy the corresponding resonant conditions, and there is not a second‐order harmonic or an intermediate forced mode involved in nonlinear interaction. Because gravity waves in the middle and upper atmosphere generally have rather large amplitudes, strong third‐order interaction may frequently occur. Thus, this nonlinearity may be regarded as a significant local source for high frequency gravity waves in the middle and upper atmosphere.
Models versus radiosondes in the free atmosphere: A new detection and attribution analysis of temperature
Authors: Lott F. C. , Stott P. A. , Mitchell D. M. , Christidis N. , Gillett N. P. , Haimberger L. , Perlwitz J. , Thorne P. W.
Published: April 2013

This analysis revisits detection and attribution of free atmosphere temperatures from radiosondes, almost a decade after previous studies. Since that time, data sets have not only become longer, but understanding of observational uncertainty has vastly improved. In addition, a coordinated set of experiments exploring the effects of human and natural forcings on past climate change has been made with a new generation of climate models. These advances allow a much more thorough analysis of the effects of modeling and observational uncertainty on attribution results than previously possible. Observational uncertainty is explored using multiple radiosonde reconstructions including those with ensembles of realizations exploring the effects of processing choices. Modeling uncertainty is explored by calculating multiple fingerprints of natural influence (from changes in solar irradiance and volcanic aerosols) and of human influence (due to greenhouse gases and due to the effects of combined anthropogenic forcings including stratospheric ozone depletion). With increased confidence over previous studies, human influences (both greenhouse gas and other anthropogenic forcings) have been detected in spatiotemporal changes in free atmosphere temperature from 1961 to 2010, irrespective of whether the full atmospheric column (30–850 hPa) is examined or purely the troposphere, with stratospheric ozone depletion dominating the cooling that has been observed in the lower stratosphere. Thus the advances of the last decade yield increased confidence that anthropogenic influences have made a substantial contribution to the evolution of free atmosphere temperatures.
The large‐scale frozen‐in anticyclone in the 2011 Arctic summer stratosphere
Authors: Allen Douglas R. , Douglass Anne R. , Strahan Susan E.
Published: April 2013

The 2011 Arctic stratospheric final warming was characterized by a large‐scale frozen‐in anticyclone (FrIAC) that rapidly displaced the winter polar vortex, establishing unusually strong polar easterlies. A comprehensive overview of the 2011 FrIAC is provided using meteorological analyses, Microwave Limb Sounder (MLS) N2O observations, and N2O simulations from the Global Modeling Initiative (GMI) 3‐D chemistry and transport model and the Van Leer Icosahedral Triangular Advection (VITA) 2‐D (latitude × longitude) isentropic transport model. A vortex edge diagnostic is used to determine the FrIAC boundary, allowing quantification of several FrIAC properties. The 2011 FrIAC originated over North Africa in late March and traveled eastward and poleward over 2 weeks, forming a strong anticyclone that extended from ~580–2100 K potential temperature (~25–50 km). Low potential vorticity (PV) was transported to the pole with the FrIAC in early April; during May, most of the PV signature decayed due to diabatic processes. A small remnant negative PV anomaly persisted near the pole until mid‐June. Tracer equivalent latitude was low initially and remained low throughout the summer. GMI, VITA, and MLS showed elevated N2O in the FrIAC, although the peak value was smaller in GMI due to a subtropical low bias. The high‐resolution (~20 km) VITA filamentary structure quantitatively matched most of the features observed by MLS when smoothed to match the MLS resolution. The high‐N2O anomaly persisted in the middle stratosphere over 4 months until late August, when it was destroyed by horizontal and vertical shearing, combined with photochemical processes.
An “anomalous” triggered lightning flash in Florida
Authors: Gamerota W. R. , Uman M. A. , Hill J. D. , Pilkey J. , Ngin T. , Jordan D. M. , Mata C. T.
Published: April 2013

An “anomalous” rocket‐and‐wire triggered lightning flash, a flash whose leaders do not follow the triggering wire remnants to ground, is characterized via high‐speed video images at 10 and 300 kilo‐frames per second, still camera images, 66–72 MHz source locations from a Lightning Mapping Array, channel‐base current, and electric field and electric field derivative (dE/dt) measurements. This is the first anomalous flash of about 410 classically triggered flashes in north‐central Florida. The flash began with an upward positively charged leader (UPL) initiating from the tip of the upward‐moving triggering wire about 280 m above ground level. All but the bottom 17 m of wire exploded (became luminous) 37.6 ms after UPL initiation. A stepped leader initiated, likely from the top of the wire remnants, 282 m above ground level about 1.3 ms after the wire explosion and propagated downward for 2.1 ms, attaching to the top of a grounded utility pole 117 m southwest of the launching facility. The line charge density on the stepped leader is estimated to be of the order of 10−3 C m−1. Contrary to previously reported “anomalous” flashes in France and New Mexico (roughly 16% and 31%, respectively, of their triggered flashes), in our event, there was not a tens of milliseconds current‐zero period preceding the stepped leader, there was no observed downward dart leader in the UPL channel prior to the stepped leader to ground, and there was a failed attempt to reestablish current in the exploded‐wire channel between the UPL and ground.
Changes in mesospheric dynamics at 78°N, 16°E and 70°N, 19°E: 2001–2012
Authors: Hall C. M. , Tsutsumi M.
Published: April 2013

Mesospheric wind data from meteor wind radars situated on Svalbard (78°N, 16°E) and the Norwegian mainland (70°N, 19°E) are examined for evidence of systematic change during the interval 2001–2012. For both locations, we find changes that suggest a strengthening of the summer westward jet, a weakening of the local winter eastward flow and, yet at the same time, weak evidence for any significant corresponding trend in the winter poleward flow. There is also a suggestion of an increase in the altitude of the summer polar jet, but more data will be required to confirm this. The main finding of a strengthening zonal flow is consistent with earlier studies and also with a contemporary scenario of progressive strengthening of the Brewer‐Dobson circulation. We show that inclusion of sudden stratospheric warmings strongly influences trends. There is no obvious causality between the changes detected over the 2001–2012 time interval and the solar cycle parameterized by total solar irradiance.
Characterization and applications of VLF/LF source locations from lightning using the Huntsville Alabama Marx Meter Array
Authors: Bitzer Phillip M. , Christian Hugh J. , Stewart Mike , Burchfield Jeff , Podgorny Scott , Corredor David , Hall John , Kuznetsov Evgeny , Franklin Veronica
Published: April 2013

Arrays that detect and locate the four‐dimensional spacetime positions of radiation sources from lightning have largely utilized sensors sensitive to the very high frequency (VHF) regime with ∼ 15 km baselines or very low frequency/low frequency (VLF/LF) regime with ∼ 100 km baselines. This paper details initial results from the newly developed Huntsville Alabama Marx Meter Array (HAMMA), consisting of Marx meters (electric field change meters) sensitive to a frequency band ∼ 1 Hz to 400 kHz. The arrival time of HAMMA waveforms due to radiation sources from lightning are used to determine the spacetime position of these sources. The locations are compared with two well‐documented and operational arrays, the National Lightning Detection Network (NLDN) and the North Alabama Lightning Mapping Array (NALMA). The standard deviation of the difference between HAMMA and NLDN locations of return strokes is 305 and 266 m in x and y, respectively, while the standard deviation of the difference between HAMMA and NALMA sources is 237, 226, and 688 m in x, y and z, respectively. We further show that NLDN intracloud locations differ in horizontal distance from the corresponding HAMMA locations by a median value of 479 m. In addition, we use HAMMA source locations to map several lightning flashes in the VLF/LF and show HAMMA sources largely map out the same electrical extent as VHF sources and provide unique insights to the properties of the discharges occurring. Finally, we show that VLF/LF sources can determine the leader polarity in several example flashes but not necessarily whether a flash comes to ground. Copyright © 2013 American Geophysical Union. All rights reserved.
Validation of MOPITT Version 5 thermal‐infrared, near‐infrared, and multispectral carbon monoxide profile retrievals for 2000–2011
Authors: Deeter M. N. , Martínez‐Alonso S. , Edwards D. P. , Emmons L. K. , Gille J. C. , Worden H. M. , Pittman J. V. , Daube B. C. , Wofsy S. C.
Published: April 2013

Validation results are reported for the MOPITT (Measurements of Pollution in the Troposphere) “Version 5” (V5) product for tropospheric carbon monoxide (CO) and are compared to results for the “Version 4” product. The V5 retrieval algorithm introduces (1) a method for reducing retrieval bias drift associated with long‐term instrumental degradation, (2) a more exact representation of the effects of random errors in the radiances and, for the first time, (3) the use of MOPITT's near‐infrared (NIR) radiances to complement the thermal‐infrared (TIR) radiances. Exploiting TIR and NIR radiances together facilitates retrievals of CO in the lowermost troposphere. V5 retrieval products based (1) solely on TIR measurements, (2) solely on NIR measurements and (3) on both TIR and NIR measurements are separately validated and analyzed. Actual retrieved CO profiles and total columns are compared with equivalent retrievals based on in situ measurements from (1) routine NOAA aircraft sampling mainly over North America and (2) the “HIAPER Pole to Pole Observations” (HIPPO) field campaign. Particular attention is focused on the long‐term stability and geographical uniformity of the retrieval errors. Results for the retrieved total column clearly indicate reduced temporal bias drift in the V5 products compared to the V4 product, and do not exhibit a positive bias in the Southern Hemisphere, which is evident in the V4 product.
North‐south cross sections of the vertical aerosol distribution over the Atlantic Ocean from multiwavelength Raman/polarization lidar during Polarstern cruises
Authors: Kanitz T. , Ansmann A. , Engelmann R. , Althausen D.
Published: April 2013

Shipborne aerosol lidar observations were performed aboard the research vessel Polarstern in 2009 and 2010 during three north‐south cruises from about 50°N to 50°S. The aerosol data set provides an excellent opportunity to characterize and contrast the vertical aerosol distribution over the Atlantic Ocean in the polluted northern and relatively clean southern hemisphere. Three case studies, an observed pure Saharan dust plume, a Patagonian dust plume east of South America, and a case of a mixed dust/smoke plume west of Central Africa are exemplarily shown and discussed by means of their optical properties. The meridional transatlantic cruises were used to determine the latitudinal cross section of the aerosol optical thickness (AOT). Profiles of particle backscatter and extinction coefficients are presented as mean profiles for latitudinal belts to contrast northern‐ and southern‐hemispheric aerosol loads and optical effects. Results of lidar observations at Punta Arenas (53°S), Chile, and Stellenbosch (34°S), South Africa, are shown and confirm the lower frequency of occurrence of free‐tropospheric aerosol in the southern hemisphere than in the northern hemisphere. The maximum latitudinal mean AOT of 0.27 was found in the northern tropics (0– 15°N) in the Saharan outflow region. Marine AOT is typically 0.05 ± 0.03. Particle optical properties are presented separately for the marine boundary layer and the free troposphere. Concerning the contrast between the anthropogenically influenced midlatitudinal aerosol conditions in the 30– 60°N belt and the respective belt in the southern hemisphere over the remote Atlantic, it is found that the AOT and extinction coefficients for the vertical column from 0–5km (total aerosol column) and 1–5km height (lofted aerosol above the marine boundary layer) are a factor of 1.6 and 2 higher at northern midlatitudes than at respective southern midlatitudes, and a factor of 2.5 higher than at the clean marine southern‐hemispheric site of Punta Arenas. The strong contrast is confined to the lowermost 3km of the atmosphere.
Numerical simulations of dust fluxes to the eastern Qinghai‐Tibetan Plateau: Comparison of model results with a Holocene peat record of dust deposition
Authors: Ferrat Marion , Langmann Baerbel , Cui Xuefeng , Gomes Jefferson , Weiss Dominik J.
Published: April 2013

Numerical model simulations provide a useful platform for investigating the interactions between the atmospheric dust cycle and environmental change in Asia. However, model validation is still limited by the scarcity of ground observations of past terrestrial dust deposition fluxes. Here we apply a regional atmosphere‐chemistry/aerosol climate model to simulate Asian dust emissions, transport, and deposition over East Asia during the years 1996–1998 and compare the present‐day deposition fluxes and dominant dust sources obtained from the numerical simulations to those measured in a high‐resolution Holocene palaeodust peat record on the eastern Qinghai‐Tibetan Plateau. The model was found to produce reasonable dust emission fluxes from the Chinese dust sources, with average annual emissions of 179 Mt y−1, and successfully reproduced both the dominant dust sources and average deposition fluxes to the peat core, with modeled and observed fluxes of 6.1 g m−2 y−1. Sensitivity tests show that modeled dust fluxes are sensitive to the parameterization of erodible surfaces, and future development of the regional model to simulate dust emissions in Asia should include an improved scheme for the soil surface properties. The results presented here suggest that the regional model holds the potential to study past and present dust cycles in Asia but evidence the need for both further refinement of the model's dust parameterizations in this region and more high‐resolution terrestrial validation data sets such as peat archives. This study demonstrates how present‐day simulations, for which reanalysis data is available as boundary conditions, are useful tools to explore the relationship between the dust cycle and environmental change during the Holocene.
Influence of ENSO on precipitation in the East River basin, south China
Authors: Zhang Qiang , Li Jianfeng , Singh Vijay P. , Xu Chong‐Yu , Deng Jingyun
Published: April 2013

A majority of the literature analyzing the role of El Niño–Southern Oscillation (ENSO) and other teleconnections has focused on summer precipitation and on global and regional scales. Seasonal precipitation, occurring at local scale (<50,000 km2; i.e., a size of one grid cell of a typical global climate model), is of considerable importance for flood mitigation, water supply, and water resources management. In view of the relative absence of studies exploring the forces driving local precipitation, the present study examines this precipitation regime (represented by monthly precipitation data for a period of 1956–2005 from 21 gauge stations in the East River basin) as a response to well‐known determining factors, i.e., Southern Oscillation Index (SOI), El Niño Modoki index (EMI), and sea surface temperature anomalies (SSTA) of Niño 1 + 2, Niño 3, Niño 4, and Niño 3.4. To achieve the goal of the study, three types of ENSO events were defined: eastern Pacific warming (EPW), central Pacific warming (CPW), and eastern Pacific cooling (EPC). Mann–Whitney U test was applied to assess whether the probabilistic behavior of precipitation in the ENSO period was different from that in the normal period. The Pearson correlation coefficient was calculated to investigate the relations between areal precipitation in the East River basin and the above‐mentioned ENSO indices. Results indicated that (1) EPW caused more precipitation in autumn and winter, but less precipitation in summer. EPW even brought about extremely heavy precipitation in summer and winter. (2) CPW caused less precipitation in spring, autumn, and the annual totals. Sometimes, CPW might bring about heavy precipitation. The precipitation pattern in summer in CPW was different from the normal years. (3) EPC caused more precipitation in autumn and less precipitation in spring and winter. The middle East River basin is the region where precipitation has decreased most severely due to EPC. (4) SSTA, SOI, and EMI had significant relations with areal precipitation from January to March. EMI is the only index having significant correlation with precipitation in April.
Study of atmospheric CH4 mole fractions at three WMO/GAW stations in China
Authors: Fang Shuang‐Xi , Zhou Ling‐Xi , Masarie Kenneth A. , Xu Lin , Rella Chris W.
Published: April 2013

Atmospheric CH4 mole fractions were continuously measured from 2009 to 2011 at three WMO/GAW stations in China (Lin'an, LAN; Longfengshan, LFS; and Waliguan, WLG) using three Cavity Ring Down Spectroscopy instruments. LAN and LFS are GAW regional measurement stations. LAN is located in China's most economically developed region, and LFS is in a rice production area (planting area > 40,000 km2). WLG is a global measurement station in remote northwest China. At LAN, high methane mole fractions are observed in all seasons. Surface winds from the northeast enhance CH4 values, with a maximum increase of 32 ± 15 ppb in summer. The peak to peak amplitude of the seasonal cycle is 77 ± 35 ppb. At LFS, the diurnal cycle amplitude is approximately constant throughout the year except summer, when a value of 196 ± 65 ppb is observed. CH4 values at LFS reach their peak in July, which is different from seasonal variations typically observed in the northern hemisphere. CH4 mole fractions at WLG show both the smallest values and the lowest variability. Maximum values occur during summer, which is different from other northern hemisphere WMO/GAW global stations. The seasonal cycle amplitude is 17 ± 11 ppb. The linear growth rates at LAN, LFS, and WLG are 8.0 ± 1.2, 7.9 ± 0.9, and 9.4 ± 0.2 ppb yr−1, respectively, which are all larger than the global mean over the same 3 year period. Results from this study attempt to improve our basic understanding of observed atmospheric CH4 in China.
Mid‐Holocene Asian summer climate and its responses to cold ocean surface simulated in the PMIP2 OAGCMs experiments
Authors: Wang Tao , Wang Huijun
Published: April 2013

In this study, the outputs from four Ocean‐Atmosphere Coupled General Circulation Model experiments within the Paleoclimate Modelling Intercomparison Project phase 2 and four sets of Atmospheric General Circulation Model experiments were used to analyze the Asian summer climate during the mid‐Holocene (6 ka, about 6000 years ago). Additionally, the role of the orbital forcings and the effects of a cold ocean surface for the 6 ka were investigated by comparing the Atmospheric General Circulation Model simulations forced by different combinations of forcing parameters. The results indicated that in the 6 ka summer, the orbital forcings were the prime drivers of the increased temperature and precipitation and the strengthened summer monsoon over the Asian continent. On the other hand, these different orbital forcings also resulted in a colder Indian Ocean‐northwestern Pacific during this period. Our results suggested that this cold ocean surface could reduce the warming amplitude and precipitation enhancement over the Asian monsoon area in the 6 ka summer. The changes caused by the different ocean surface conditions were comparable with simulated 6 ka climate changes. The cold ocean surface also suppressed the Asian summer monsoon circulations. Therefore, the influences from anomalous ocean surface conditions played an important role on regulating the Asian summer climate during the 6 ka. In addition, it was found that the summer climate in the South Asian monsoon area was more sensitive to the changes in the orbital forcings and ocean surface conditions than that in the East Asian monsoon area.
The representation of the TTL in a tropical channel version of the WRF model
Authors: Evan Stephanie , Rosenlof K. H. , Dudhia J. , Hassler B. , Davis S. M.
Published: April 2013

In this study, the Weather Research Forecast (WRF) model is used to investigate key physical processes controlling the Tropical Tropopause Layer (TTL) temperature and water vapor distributions in December 2005 to January–February 2006. The model domain is configured as a tropical channel with a horizontal grid spacing of 36 km, a vertical grid spacing of 500 m, and a top at 0.1 hPa. Initial and boundary conditions are set using the ERA‐Interim reanalysis data set. An ozone distribution computed from satellite and ozonesonde measurements is used for radiative forcing calculations. The model's ability to replicate observed TTL temperatures is evaluated via comparisons with radiosonde data and reanalyses (MERRA and ERA‐Interim). The Microwave Limb Sounder (MLS) water vapor measurements are used to evaluate WRF‐simulated water vapor in the TTL. Results of the simulations show that the model reproduces the mean temperature and its variability above 50 hPa as well as the tropical tropopause height. However, the model cold point tropopause temperature is colder than the reanalyses by ~1.2 K. The model captures the location of TTL water vapor minimum in the Western Pacific but is drier than the MLS observations in the TTL. To assess possible reasons for the tropopause temperature discrepancy, an additional WRF experiment was conducted using analysis nudging for water vapor. This experiment produces more tropical cirrus clouds in the upper troposphere and a warming of ~1.5 K of the cold point tropopause. This suggests that the radiative effects of cirrus clouds and water vapor must be considered for accurate temperature simulations in the TTL.
Chemical discontinuity at the extratropical tropopause and isentropic stratosphere‐troposphere exchange pathways diagnosed using Aura MLS data
Authors: Jin J. J. , Livesey N. J. , Manney G. L. , Jiang J. H. , Schwartz M. J. , Daffer W. H.
Published: April 2013

The chemical discontinuity at the extratropical tropopause (ExTP) and stratosphere‐troposphere exchange (STE) pathways are investigated using the long‐lived chemical species carbon monoxide (CO) and ozone (O3) measured by the Aura Microwave Limb Sounder (MLS). A relative coordinate, tropopause latitude (TpLat), is developed based on potential vorticity (PV) from the Goddard Earth Observing System version 5 (GEOS‐5) data assimilation system. TpLat is defined as the shortest geographic distance along an isentropic surface from the extratropical tropopause (ExTP) to an observation location. Our results show that this coordinate highlights the sharp chemical discontinuities at the ExTP more clearly than the widely‐used equivalent latitude coordinate. Geographical distributions of STE pathways and barriers are investigated based on meridional gradients in O3 abundances in the new TpLat coordinate in conjunction with analysis of Rossby wave breaking between 330 K and 360 K. In northern hemispheric (NH) winter (Dec–Jan–Feb), NH STE pathways are seen mainly above the northeast Pacific. In NH summer (Jun–Jul–Aug), the NH pathway covers all longitudes at 330 K. However, it is mainly located above Asia at 340 K and above the Atlantic and the North Pacific at 350 K and 360 K. In the southern hemisphere (SH), there is a weaker STE region above the Eastern Indian Ocean and the southwestern Pacific, at and above 350 K in SH winter, and a stronger STE region over the Southeastern Pacific at these levels during SH summer. In addition, this study shows NH PV gradients are slightly stronger near the ExTP in summer than in winter even though the subtropical jet is weaker and Rossby wave breaking is stronger in summer than in winter.
Drivers of projected change in arctic moist static energy transport
Authors: Skific Natasa , Francis Jennifer A.
Published: April 2013

We explore annual and seasonal changes in moist static energy transport (MSE) into the Arctic over the 21st century as projected by the National Center for Atmospheric Research Community Climate System Model, version 3. Self‐organizing maps are used to assess changes in MSE and its components—the latent heat flux and dry static energy flux (DSE)—across 70°N. These are computed from multilevel fields of specific humidity, meridional wind, geopotential, and temperature spanning periods in the 20th century (1960 to 1999) and the 21st century (2070 to 2089). The 21st century simulation incorporates the Special Report on Emission Scenarios A2 scenario. A strong decrease in tropospheric DSE of about 9% by the end of 21st century offsets an increase in latent heat flux of about 20% relative to its 20th century average. The combined changes result in a total annual decrease in tropospheric MSE of about 3% by the late 21st century. The difference, while statistically not significant, represents a weak negative feedback on Arctic amplification. Self‐organizing maps also allow an attribution of changes in MSE to factors related to varying atmospheric dynamics and/or thermodynamics. A positive contribution to the MSE related to more frequent low pressure systems in high latitudes (dynamic factor) occurs in all seasons, particularly in the summer. The decrease in DSE is mainly due to a weakened poleward temperature gradient (thermodynamic factor) during all seasons except summer, which in turn is caused by amplified warming at high latitudes as a result of increased greenhouse gases.
Ozone distribution in the lower troposphere over complex terrain in Central Chile
Authors: Seguel Rodrigo J. , Mancilla Carlos A. , Rondanelli Roberto , Leiva Manuel A. , Morales Raúl G. E.
Published: April 2013

Observations were performed in 12 communities of Central Chile in order to determine the horizontal gradients of ozone in the Santiago Basin and surrounding valleys. Higher ozone mixing ratios were found northeast of the Santiago Basin and included east of the Aconcagua Valley (~70 km from Santiago) suggesting that photochemical pollution produced in Santiago is capable of passing through the Chacabuco mountain chain (~1.3 km) and have impact downwind from the regions with the largest NOx and VOC emissions. To complement existing surface observations, ozonesonde and tethersonde campaigns were performed in the Santiago Basin and the Aconcagua Valley. The results suggest ozone can accumulate in layers aloft (e.g., >102 ppb at 2 km) similarly to layers observed in complex topography coastal regions like Southern California. Layers of significant ozone concentrations having a near surface origin were observed above the mixed layer and below the subsidence inversion base. We propose that the ozone in this residual layer can be transported large distances (at least to 70 km) to further penetrate into the local environment under conditions of a well‐mixed boundary layer.
PV‐based diagnostic quantities of heavy precipitation: Solenoidal vorticity and potential solenoidal vorticity
Authors: Ran Lingkun , Li Na , Gao Shouting
Published: April 2013

Two new diagnostic quantities called solenoidal vorticity (SV) and potential solenoidal vorticity (PSV) are defined in this paper for a moist atmosphere based on the generalized moist potential vorticity (GMPV). SV and PSV are introduced to incorporate vorticity information along the isentropic surfaces that GMPV (or PV) has lost. SV is the scalar product of vorticity and the moist solenoidal term ∇ p × ∇ α*, while PSV is the scalar product of vorticity and (∇ p × ∇ α*) × ∇ θ* (a new vector). Application of GMPV, SV, and PSV to a diagnostic study of a heavy rainfall case shows that SV reflects the coupling of vertical wind shear and the baroclinity of the moist atmosphere weighted by the vertical gradient of pressure, while PSV reflects the coupling of vertical wind shear and baroclinity, the static stability, and the vertical gradient of pressure. Although all three quantities exhibit strong signals over the observed precipitation region, SV and PSV are more capable of distinguishing between precipitation and non‐precipitation areas. The following three main factors are concluded to contribute to the very different distribution patterns of GMPV, SV, and PSV: static stability,the vertical gradient of pressure, and different ways of coupling vertical wind shear and baroclinity. These factors are responsible for the good performance of SV and PSV in tracing and predicting heavy rainfall, as demonstrated by the correlation coefficient between SV (PSV) and the rainfall amount obtained from long time series analyses. The results of this study suggest that SV and PSV are good detectors of heavy rainfall and may be used as precipitation prediction parameters.