The multispecies analysis of daily air samples collected at the NOAA Boulder Atmospheric Observatory (BAO) in Weld County in northeastern Colorado since 2007 shows highly correlated alkane enhancements caused by a regionally distributed mix of sources in the Denver‐Julesburg Basin. To further characterize the emissions of methane and non‐methane hydrocarbons (propane, n‐butane, i‐pentane, n‐pentane and benzene) around BAO, a pilot study involving automobile‐based surveys was carried out during the summer of 2008. A mix of venting emissions (leaks) of raw natural gas and flashing emissions from condensate storage tanks can explain the alkane ratios we observe in air masses impacted by oil and gas operations in northeastern Colorado. Using the WRAP Phase III inventory of total volatile organic compound (VOC) emissions from oil and gas exploration, production and processing, together with flashing and venting emission speciation profiles provided by State agencies or the oil and gas industry, we derive a range of bottom‐up speciated emissions for Weld County in 2008. We use the observed ambient molar ratios and flashing and venting emissions data to calculate top‐down scenarios for the amount of natural gas leaked to the atmosphere and the associated methane and non‐methane emissions. Our analysis suggests that the emissions of the species we measured are most likely underestimated in current inventories and that the uncertainties attached to these estimates can be as high as a factor of two.

Recent, heavy snow accumulation events over Dronning Maud Land (DML), East Antarctica, contributed significantly to the Antarctic ice sheet surface mass balance (SMB). Here we combine in situ accumulation measurements and radar‐derived snowfall rates from Princess Elisabeth station (PE), located in the DML escarpment zone, along with the European Centre for Medium‐range Weather Forecasts Interim reanalysis to investigate moisture transport patterns responsible for these events. In particular, two high‐accumulation events in May 2009 and February 2011 showed an atmospheric river (AR) signature with enhanced integrated water vapor (IWV), concentrated in narrow long bands stretching from subtropical latitudes to the East Antarctic coast. Adapting IWV‐based AR threshold criteria for Antarctica (by accounting for the much colder and drier environment), we find that it was four and five ARs reaching the coastal DML that contributed 74–80% of the outstanding SMB during 2009 and 2011 at PE. Therefore, accounting for ARs is crucial for understanding East Antarctic SMB.

Model experiments have revealed that stratospheric polar ozone depletion and anthropogenic increase of greenhouse gases (GHG) have both contributed to the observed increase of summertime tropospheric westerlies in the Southern Hemisphere (SH) with the ozone influence dominating. As the stratospheric halogen loading decreases in the future, ozone is expected to return to higher values, with the disappearance of the Antarctic ozone hole. The impact of this ozone recovery on SH climate is investigated using 21st century simulations with a chemistry climate model (CCM). The model response to the ozone recovery by 2100 shows that tropospheric circulation changes during austral summer caused by ozone depletion between 1970 and 2000 almost reverse, despite increasing GHG concentrations. Comparison of the CCM results with multi‐model scenario experiments from the Fourth Assessment Report (AR4) by the Intergovernmental Panel on Climate Change (IPCC) emphasize the importance of stratospheric ozone recovery for Antarctic climate.

Cloud and atmospheric properties strongly influence the mass and energy budgets of the Greenland Ice Sheet (GIS). To address critical gaps in the understanding of these systems, a new suite of cloud- and atmosphere-observing instruments has been installed on the central GIS as part of the Integrated Characterization of Energy, Clouds, Atmospheric State, and Precipitation at Summit (ICECAPS) project. During the first 20 months in operation, this complementary suite of active and passive ground-based sensors and radiosondes has provided new and unique perspectives on important cloud?atmosphere properties. High atop the GIS, the atmosphere is extremely dry and cold with strong near-surface static stability predominating throughout the year, particularly in winter. This low-level thermodynamic structure, coupled with frequent moisture inversions, conveys the importance of advection for local cloud and precipitation formation. Cloud liquid water is observed in all months of the year, even the particularly cold and dry winter, while annual cycle observations indicate that the largest atmospheric moisture amounts, cloud water contents, and snowfall occur in summer and under southwesterly flow. Many of the basic structural properties of clouds observed at Summit, Greenland, particularly for low-level stratiform clouds, are similar to their counterparts in other Arctic regions. The ICECAPS observations and accompanying analyses will be used to improve the understanding of key cloud?atmosphere processes and the manner in which they interact with the GIS. Furthermore, they will facilitate model evaluation and development in this data-sparse but environmentally unique region

Abstract. A sulfur field study (SCATE) at Palmer Station Antarctica (January 18 to February 25) has revealed several major new findings concerning (dimethyl sulfide) DMS oxidation chemistry and the cycling of sulfur within the Antarctic environment. Significant evidence was found supporting the notion that the OH/DMS addition reaction is a major source of dimethyl sulfoxide (DMSO). Methane sulfonic acid (MSA(g)) levels were also found to be consistent with an OH/DMS addition mechanism involving the sequential oxidation of the products DMSO and methane sulfinic acid (MSIA). Evidence supporting the hypothesis that the OH/DMS addition reaction, as well as follow-on reactions involving OH/DMSO, are a major source of SO2 was significant, but not conclusive. No evidence could be found supporting the notion that reactive intermediates (i.e., SO3) other than SO2 were an important source of H2SO 4. Quite clearly, one of the major findings of SCATE was the recognition that a large fraction of the Antarctic oxidative cycle for DMS (near Palmer Station) took place above the boundary layer (BL) in what we have labeled here as the atmospheric buffer layer (BuL). Although still speculative in places, the overall picture emerging from the SCATE field/modeling results is one involving major coupling between chemistry and dynamics in the Antarctic. At Palmer the evidence points to frequent episodes of rapid vertical transport from a very shallow marine BL into the overlying BuL. Due to the combination of a long photochemical lifetime for DMS and the frequency of shallow convective events, a large fraction of ocean released DMS is transported into the BuL while still in its unoxidized state. There, in the presence of elevated OH and low aerosol scavenging, high levels of oxidized sulfur accumulate. Parcels of this BuL air are then episodically entrained back into the BL, thereby providing a controlling influence on BL SO2, DMSO, and DMSO2. Additionally, because SO2 and DMSO are major precursors to H2SO 4 and MSA, BuL chemistry, in conjunction with vertical transport, also act to control BL levels of the latter species. Although many uncertainties remain in our understanding of Antarctic DMS chemistry, the above picture already suggests that previous chemical interpretations of Antarctic field data may need to be altered.

Recent decades have seen increased melting of the Greenland ice sheet. On 11 July 2012, nearly the entire surface of the ice sheet melted; such rare events last occurred in 1889 and, prior to that, during the Medieval Climate Anomaly. Studies of the 2012 event associated the presence of a thin, warm elevated liquid cloud layer with surface temperatures rising above the melting point at Summit Station, some 3212 m above sea level. Here we explore other potential factors in July 2012 associated with this unusual melting. These include (1) warm air originating from a record North American heat wave, (2) transitions in the Arctic Oscillation, (3) transport of water vapor via an Atmospheric River over the Atlantic to Greenland, and (4) the presence of warm ocean waters south of Greenland. For the 1889 episode, the Twentieth Century Reanalysis and historical records showed similar factors at work. However, markers of biomass burning were evident in ice cores from 1889 which may reflect another possible factor in these rare events. We suggest that extreme Greenland summer melt episodes, such as those recorded recently and in the late Holocene, could have involved a similar combination of slow climate processes, including prolonged North American droughts/heat waves and North Atlantic warm oceanic temperature anomalies, together with fast processes, such as excursions of the Arctic Oscillation, and transport of warm, humid air in Atmospheric Rivers to Greenland. It is the fast processes that underlie the rarity of such events and influence their predictability.

The first airborne measurements of nitric oxide (NO) on the Antarctic plateau have demonstrated that the previously reported elevated levels of this species extend well beyond the immediate vicinity of South Pole. Although the current database is still relatively weak and critical laboratory experiments are still needed, the findings here suggest that the chemical uniqueness of the plateau may be substantially greater than first reported. For example, South Pole ground-based findings have provided new evidence showing that the dominant process driving the release of nitrogen from the snowpack during the spring/summer season (post-depositional loss) is photochemical in nature with evaporative processes playing a lesser role. There is also new evidence suggesting that nitrogen, in the form of nitrate, may undergo multiple recycling within a given photochemical season. Speculation here is that this may be a unique property of the plateau and much related to its having persistent cold temperatures even during summer. These conditions promote the efficient adsorption of molecules like HNO 3 (and very likely HO 2 NO 2) onto snow-pack surface ice where we have hypothesized enhanced photochemical processing can occur, leading to the efficient release of NO x to the atmosphere. In addition, to these process-oriented tentative conclusions, the findings from the airborne studies, in conjunction with modeling exercises suggest a new paradigm for the plateau atmosphere. The near-surface atmosphere over this massive region can be viewed as serving as much more than a temporary reservoir or holding tank for imported chemical species. It defines an immense atmospheric chemical reactor which is capable of modifying the chemical characteristics of select atmospheric constituents. This reactor has most likely been in place over geological time, and may have led to the chemical modulation of some trace

Flow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods. Understanding turbulence intermittency and wave-turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans. The stable atmospheric boundary layer (SABL) commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces, or even daytime over snow and ice surfaces, and when warm air is advected over cold surfaces. Intermittent turbulence intensification in the SABL impacts human activities and weather variability, yet it cannot be generated in state-of-the-art numerical forecast models. This failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow, in which wave-turbulence interaction is a potential mechanism for turbulence intermittency. A workshop on wave-turbulence interactions in the SABL addressed the current understanding and challenges of wave-turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory, observations, and numerical parameterization. There have been a number of reviews on waves, and a few on turbulence in stably stratified flows, but not much on wave-turbulence interactions. This review focuses on the nocturnal SABL; however, the discussions here on intermittent turbulence and wave-turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general.