Journal of Geophysical Research: Atmospheres

Stone, Kane A.; Solomon, Susan; Kinnison, Doug E.; Pitts, Michael C.; Poole, Lamont R.; Mills, Michael J.; Schmidt, Anja; Neely, Ryan R.; Ivy, Diane; Schwartz, Michael J.; Vernier, Jean‐Paul; Johnson, Bryan J.; Tully, Matthew B.; Klekociuk, Andrew R.; König‐Langlo, Gert; Hagiya, Satoshi

doi: 10.1002/2017JD026987pmid: N/A

The Southern Hemisphere Antarctic stratosphere experienced two noteworthy events in 2015: a significant injection of sulfur from the Calbuco volcanic eruption in Chile in April and a record‐large Antarctic ozone hole in October and November. Here we quantify Calbuco's influence on stratospheric ozone depletion in austral spring 2015 using observations and an Earth system model. We analyze ozonesondes, as well as data from the Microwave Limb Sounder. We employ the Community Earth System Model, version 1, with the Whole Atmosphere Community Climate Model (WACCM) in a specified dynamics setup, which includes calculations of volcanic effects. The Cloud‐Aerosol Lidar with Orthogonal Polarization data indicate enhanced volcanic liquid sulfate 532 nm backscatter values as far poleward as 68°S during October and November (in broad agreement with WACCM). Comparison of the location of the enhanced aerosols to ozone data supports the view that aerosols played a major role in increasing the ozone hole size, especially at pressure levels between 150 and 100 hPa. Ozonesonde vertical ozone profiles from the sites of Syowa, South Pole, and Neumayer display the lowest individual October or November measurements at 150 hPa since the 1991 Mount Pinatubo eruption period, with Davis showing similarly low values, but no available 1990 data. The analysis suggests that under the cold conditions ideal for ozone depletion, stratospheric volcanic aerosol particles from the moderate‐magnitude eruption of Calbuco in 2015 greatly enhanced austral ozone depletion, particularly at 55–68°S, where liquid binary sulfate aerosols have a large influence on ozone concentrations.

Xiao, Wei; Lee, Xuhui; Hu, Yongbo; Liu, Shoudong; Wang, Wei; Wen, Xuefa; Werner, Martin; Xie, Chengyu

doi: 10.1002/2017JD026774pmid: N/A

The oxygen isotopes of water (H218O and H216O) are tracers widely used for the investigation of Earth science problems. The tracer applications are based on the premise that the 18O/16O ratio of open‐water evaporation (δ18OE) can be calculated from environmental conditions. A long‐standing issue concerns the role of kinetic fractionation, or diffusion transport, in the evaporation process. Here we deployed an optical instrument at a large lake (area 2,400 km2) to make in situ measurement of δ18O and δD of atmospheric vapor, then determined δ18O and δD of open‐water evaporation using the gradient‐diffusion method. Our results show a much weaker kinetic effect than suggested by the kinetic factor εk adopted in some previous studies of lake hydrology (14.2‰). By incorporating into the H218O isotopic mass balance of the lake a lower εk value (about 6.2‰) used for ocean evaporation in global climate models, we obtain an annual lake evaporation rate that agrees with an independent eddy‐covariance observation, but the rate is 72% higher than if the commonly used lake εk value of 14.2‰ is applied. The applicability of this results to small lakes is uncertain and in need of field‐based assessment.

Li, Dongshuai; Rubinstein, Marcos; Rachidi, Farhad; Diendorfer, Gerhard; Schulz, Wolfgang; Lu, Gaopeng

doi: 10.1002/2017JD027520pmid: N/A

In this paper, we analyze the location error of time of arrival (ToA)‐based lightning location systems (LLSs) caused by propagation effects over mountainous terrain around the Säntis tower located in the Swiss Alps. The study is based on a full‐wave three‐dimensional (3‐D) finite difference time domain approach using the topographic map including the Säntis tower and the nearby sensors belonging to LLSs. It is found that the vertical electric fields are strongly affected by the presence of the mountainous terrain and the finite ground conductivity and that the location error associated with the ToA technique depends strongly on the used onset time estimation technique. The evaluated location errors associated with amplitude thresholds of 10% and 20% and the time of the linear extrapolation of the tangent at maximum field derivative are found to be smallest (about 300 m or less). Finally, we assess the accuracy of two simplified methods (terrain envelope method and tight‐terrain‐fit method) to account for the location error due to propagation over mountainous terrain. These two methods might represent an efficient alternative to estimate the additional time delay due to propagation over a nonflat terrain by using available topographic data. In addition, a possible real‐time location error compensation algorithm using the elongated propagation path method to improve the location error of the LLSs in mountainous regions is presented and discussed.

Mekhaldi, F.; McConnell, J. R.; Adolphi, F.; Arienzo, M. M.; Chellman, N. J.; Maselli, O. J.; Moy, A. D.; Plummer, C. T.; Sigl, M.; Muscheler, R.

doi: 10.1002/2017JD027325pmid: N/A

Knowledge on the occurrence rate of extreme solar storms is strongly limited by the relatively recent advent of satellite monitoring of the Sun. To extend our perspective of solar storms prior to the satellite era and because atmospheric ionization induced by solar energetic particles (SEPs) can lead to the production of odd nitrogen, nitrate spikes in ice cores have been tentatively used to document both the occurrence and intensity of past SEP events. However, the reliability of the use of nitrate in ice records as a proxy for SEP events is strongly debated. This is partly due to equivocal detection of nitrate spikes in single ice cores and possible alternative sources, such as biomass burning plumes. Here we present new continuous high‐resolution measurements of nitrate and of the biomass burning species ammonium and black carbon, from several Antarctic and Greenland ice cores. We investigate periods covering the two largest known SEP events of 775 and 994 Common Era as well as the Carrington event and the hard SEP event of February 1956. We report no coincident nitrate spikes associated with any of these benchmark events. We also demonstrate the low reproducibility of the nitrate signal in multiple ice cores and confirm the significant relationship between biomass burning plumes and nitrate spikes in individual ice cores. In the light of these new data, there is no line of evidence that supports the hypothesis that ice cores preserve or document detectable amounts of nitrate produced by SEPs, even for the most extreme events known to date.

Wang, Xinke; Hayeck, Nathalie; Brüggemann, Martin; Yao, Lei; Chen, Hangfei; Zhang, Ci; Emmelin, Corinne; Chen, Jianmin; George, Christian; Wang, Lin

doi: 10.1002/2017JD026930pmid: N/A

Particulate matter 2.5 (PM2.5) filter samples were collected in July and October 2014 and January and April 2015 in urban Shanghai and analyzed using ultrahigh‐performance liquid chromatography coupled to Orbitrap mass spectrometry. The measured chromatogram‐mass spectra were processed by a nontarget screening approach to identify significant signals. In total, 810–1,510 chemical formulas of organic compounds in the negative polarity (negative electrospray ionization (ESI−)) and 860–1,790 in the positive polarity (ESI+), respectively, were determined. The chemical characteristics of organic aerosols (OAs) in Shanghai varied among different months and between daytime and nighttime. In the January samples, organics were generally richer in terms of both number and abundance, whereas those in the July samples were far lower. More CHO− (compounds containing only carbon, hydrogen, and oxygen and detected in ESI−) and CHOS− (sulfur‐containing organics) were found in the daytime samples, suggesting a photochemical source, whereas CHONS− (nitrogen‐ and sulfur‐containing organics) were more abundant in the nighttime samples, due to nocturnal nitrate radical chemistry. A significant number of monocyclic and polycyclic aromatic compounds, and nitrogen‐ and sulfur‐containing heterocyclic compounds, were detected in all samples, indicating that biomass burning and fossil fuel combustion made important contributions to the OAs in urban Shanghai. Additionally, precursor‐product pair analysis indicates that the epoxide pathway is an important formation route for organosulfates observed in Shanghai. Moreover, a similar analysis suggests that 35–57% of nitrogen‐containing compounds detected in ESI+ could be formed through reactions between ammonia and carbonyls. Our study presents a comprehensive overview of OAs in urban Shanghai, which helps to understand their characteristics and sources.

Phillips, Thomas J.; Klein, Stephen A.; Ma, Hsi‐Yen; Tang, Qi; Xie, Shaocheng; Williams, Ian N.; Santanello, Joseph A.; Cook, David R.; Torn, Margaret S.

doi: 10.1002/2017JD027141pmid: N/A

Several independent measurements of warm‐season soil moisture and surface atmospheric variables recorded at the ARM Southern Great Plains (SGP) research facility are used to estimate the terrestrial component of land‐atmosphere coupling (LAC) strength and its regional uncertainty. The observations reveal substantial variation in coupling strength, as estimated from three soil moisture measurements at a single site, as well as across six other sites having varied soil and land cover types. The observational estimates then serve as references for evaluating SGP terrestrial coupling strength in the Community Atmospheric Model coupled to the Community Land Model. These coupled model components are operated in both a free‐running mode and in a controlled configuration, where the atmospheric and land states are reinitialized daily, so that they do not drift very far from observations. Although the controlled simulation deviates less from the observed surface climate than its free‐running counterpart, the terrestrial LAC in both configurations is much stronger and displays less spatial variability than the SGP observational estimates. Preliminary investigation of vegetation leaf area index (LAI) substituted for soil moisture suggests that the overly strong coupling between model soil moisture and surface atmospheric variables is associated with too much evaporation from bare ground and too little from the vegetation cover. These results imply that model surface characteristics such as LAI, as well as the physical parameterizations involved in the coupling of the land and atmospheric components, are likely to be important sources of the problematical LAC behaviors.

Zhou, Botao; Wang, Zunya; Shi, Ying

doi: 10.1002/2017JD027574pmid: N/A

This article revealed that strengthening of winter Hadley circulation in the context of climate change may partially contribute to interdecadal increasing of snowfall intensity over northeastern China in recent decades. This hypothesis is well supported by the process‐based linkage between Hadley circulation and atmospheric circulations over the Asian‐Pacific region on the interdecadal time scale. The strengthening of winter Hadley circulation corresponds to a weakening of the Siberian high, an eastward shifting of the Aleutian low, a reduction of the East Asian trough, and anomalous southwesterly prevailing over northeastern China. These atmospheric situations weaken the East Asian winter monsoon and lead to an increase of air temperature over northeastern China. Increased local evaporation due to the increase of air temperature, concurrent with more water vapor transported from the Pacific Ocean, can significantly enhance atmospheric water vapor content in the target region. Meanwhile, the ascending of airflows is also strengthened over northeastern China. All of these provide favorable interdecadal backgrounds for the occurrence of intense snowfalls, and thus, snowfall intensity is intensified over northeastern China after the 1980s. Further analysis suggests that the circum‐Pacific‐like teleconnection pattern may play an important role in connecting Hadley circulation strengthening signal and atmospheric circulation anomalies favoring interdecadal intensification of snowfalls over northeastern China.

Seela, Balaji Kumar; Janapati, Jayalakshmi; Lin, Pay‐Liam; Reddy, K. Krishna; Shirooka, Ryuichi; Wang, Pao K.

doi: 10.1002/2017JD026816pmid: N/A

Raindrop size distribution (RSD) characteristics in summer season rainfall of two observational sites (Taiwan (24°58′N, 121°10′E) and Palau (7°20′N, 134°28′E)) in western Pacific are studied by using five years of impact type disdrometer data. In addition to disdrometer data, Tropical Rainfall Measuring Mission, Moderate Resolution Imaging Spectroradiometer, and ERA‐Interim data sets are used to illustrate the dynamical and microphysical characteristics associated with summer season rainfall of Taiwan and Palau. Taiwan and Palau's raindrop spectra showed a significant difference, with a higher concentration of middle and large drops in Taiwan than Palau rainfall. RSD stratified on the basis of rain rate showed a higher mass‐weighted mean diameter (Dm) and a lower normalized intercept parameter (log10Nw) in Taiwan than Palau rainfall. Precipitation classification into stratiform and convective regimes showed higher Dm values in Taiwan than Palau. Furthermore, for both the locations, the convective precipitation has a higher Dm value than stratiform precipitation. The radar reflectivity‐rain rate relations (Z = A*Rb) of Taiwan and Palau showed a clear variation in the coefficient and a less variation in exponent values. Terrain‐influenced clouds extended to higher altitudes over Taiwan resulted with higher Dm and lower log10Nw values as compared to Palau.

McCoy, Isabel L.; Wood, Robert; Fletcher, Jennifer K.

doi: 10.1002/2017JD027031pmid: N/A

Mesoscale cellular convective (MCC) clouds occur in large‐scale patterns over the ocean and have important radiative effects on the climate system. An examination of time‐varying meteorological conditions associated with satellite‐observed open and closed MCC clouds is conducted to illustrate the influence of large‐scale meteorological conditions. Marine cold air outbreaks (MCAO) influence the development of open MCC clouds and the transition from closed to open MCC clouds. MCC neural network classifications on Moderate Resolution Imaging Spectroradiometer (MODIS) data for 2008 are collocated with Clouds and the Earth's Radiant Energy System (CERES) data and ERA‐Interim reanalysis to determine the radiative effects of MCC clouds and their thermodynamic environments. Closed MCC clouds are found to have much higher albedo on average than open MCC clouds for the same cloud fraction. Three meteorological control metrics are tested: sea‐air temperature difference (ΔT), estimated inversion strength (EIS), and a MCAO index (M). These predictive metrics illustrate the importance of atmospheric surface forcing and static stability for open and closed MCC cloud formation. Predictive sigmoidal relations are found between M and MCC cloud frequency globally and regionally: negative for closed MCC cloud and positive for open MCC cloud. The open MCC cloud seasonal cycle is well correlated with M, while the seasonality of closed MCC clouds is well correlated with M in the midlatitudes and EIS in the tropics and subtropics. M is found to best distinguish open and closed MCC clouds on average over shorter time scales. The possibility of a MCC cloud feedback is discussed.

Ooi, M. C. G.; Chan, A.; Subramaniam, K.; Morris, K. I.; Oozeer, M. Y.

doi: 10.1002/2017JD026690pmid: N/A

Rapid urbanization of cities has greatly modified the thermal and dynamic profile in the urban boundary layer. This paper attempts to study the interaction of urban heating and the local topographic‐induced flow circulation for a tropical coastal city, Greater Kuala Lumpur, in Malaysia. The role of sea‐and‐valley‐breeze‐orientated synoptic flow (SBOS) on the interaction is determined by comparing two intermonsoon periods. A state‐of‐the‐art numerical model, Advanced Research Weather Research and Forecasting model, is used to identify the influence of urbanization through modification of urban surfaces. The model reasonably reproduces the vertical sounding data and near‐surface weather parameters. The diurnal urban heating pattern is attributed to three predominant factors: (i) weak under calm and clear‐sky condition (morning heating), (ii) weak under larger atmospheric moisture content (late afternoon convection), and (iii) largest (1.4°C) due to differential cooling rate of urban and rural surface at night. The interaction of urban thermals and upper level SBOS affects the effect of urbanization on local circulation during the day. The urban thermals reduce the weak opposing SBOS (<2 m s−1) and enhance the inflow of moisture‐rich sea breeze passage. This increases the intensity of downwind convective precipitation during late afternoon. On contrary, the strong opposing SBOS (>2 m s−1) suppresses the vertical lifting of urban thermals and decelerates the sea breeze front. It is discovered that the interaction of urban heating and topographic‐induced flow is interdependent while the synoptic flow plays a critical role in modifying both factors, respectively.