Abstract: We present a 650-year Antarctic ice core record of concentration and isotopic ratios ((13)C and (18)O) of atmospheric carbon monoxide. Concentrations decreased by ~25% (14 ppbv) from mid-1300s to the 1600s, then recovered completely by the late 1800s. (13)C and (18)O decreased by about 2 and 4 respectively from mid-1300s to the 1600s, then increase by about 2.5 and 4 by the late 1800s. These observations and isotope mass balance model results imply that large variations in the degree of biomass burning in the Southern Hemisphere occurred during the last 650 years, with a decrease by about 50% in the 1600s, an increase of about 100% by the late 1800s, and another decrease by about 70% from the late 1800s to present day.

Abstract: We measured light absorption in 42 marine snow, sea ice, seawater, brine, and frost flower samples collected during the OASIS field campaign between February 27 and April 15, 2009. Samples represented multiple sites between landfast ice and open pack ice in coastal areas approximately 5 km west of Barrow, Alaska. The chromophores that are most commonly measured in snow, H2O2, NO3-, and NO2-, on average account for less than 1% of sunlight absorption in our samples. Instead, light absorption is dominated by unidentified “residual” species, likely organic compounds. Light absorption coefficients for the frost flowers on first-year sea ice are, on average, 40 times larger than values for terrestrial snow samples at Barrow, suggesting very large rates of photochemical reactions in frost flowers. For our marine samples the calculated rates of sunlight absorption and OH production from known chromophores are (0.1–1.4) 1014 (photons cm-3 s-1) and (5–70) 10-12 (mol L-1 s-1), respectively. Our residual spectra are similar to spectra of marine chromophoric dissolved organic matter (CDOM), suggesting that CDOM is the dominant chromophore in our samples. Based on our light absorption measurements we estimate dissolved organic carbon (DOC) concentrations in Barrow seawater and frost flowers as approximately 130 and 360 μM C, respectively. We expect that CDOM is a major source of OH in our marine samples, and it is likely to have other significant photochemistry as well.

Abstract: We Measured Aerosol Size Distributions And Conducted Bulk And Size-segregated Aerosol Sampling During Two Summer Campaigns In January 2015 And January 2016 At The Continental Antarctic Station Kohnen (Dronning Maud Land). Physical And Chemical Aerosol Properties Differ Conspicuously During The Episodic Impact Of A Distinctive Low-pressure System In 2015 (Lps15) Compared To The Prevailing Clear Sky Conditions. The Approximately 3-day Lps15 Located In The Eastern Weddell Sea Was Associated With The Following: Marine Boundary Layer Air Mass Intrusion; Enhanced Condensation Particle Concentrations (1400±700cm−3 Compared To 250±120cm−3 Under Clear Sky Conditions; Mean±sd); The Occurrence Of A New Particle Formation Event Exhibiting A Continuous Growth Of Particle Diameters (Dp) From 12 To 43nm Over 44h (Growth Rate 0.6nmh−1); Peaking Methane Sulfonate (Ms−), Non-sea-salt Sulfate (Nss–so42-), And Na+ Concentrations (190ngm−3ms−, 137ngm−3 Nss–so42-, And 53ngm−3na+ Compared To 24±15, 107±20, And 4.1±2.2ngm−3, Respectively, During Clear Sky Conditions); And Finally An Increased Ms−∕nss–so42- Mass Ratio βMs Of 0.4 Up To 2.3 (0.21±0.1 Under Clear Sky Conditions) Comparable To Typical Values Found At Coastal Antarctic Sites. Throughout The Observation Period A Larger Part Of Ms− Could Be Found In Super-micron Aerosol Compared To Nss–so42-, I.e., (10±2) % By Mass Compared To (3.2±2) %, Respectively. On The Whole, Under Clear Sky Conditions Aged Aerosol Characterized By Usually Mono-modal Size Distributions Around Dp=60nm Was Observed. Although Our Observations Indicate That The Sporadic Impacts Of Coastal Cyclones Were Associated With Enhanced Marine Aerosol Entry, Aerosol Deposition On-site During Austral Summer Should Be Largely Dominated By Typical Steady Clear Sky Conditions.

Abstract: We investigated the agreement between real seismograms and those predicted by long wavelength mantle models by looking at phase and amplitude differences. We computed full synthetic seismograms using a spectral element method together with 3-D mantle models and the appropriate crustal model on top. We selected differently damped mantle models to see the effect of regularization on the computed seismograms. To check the phase agreement, we measured time-shifts between the real and synthetic surface waves and body wave phases such as P, S and SS using a cross-correlation technique. We also compared the amplitudes of the real and synthetic seismograms to understand how well the models explain not only the phases, but the whole waveforms. 3-D mantle models improve the phase agreement of surface waves in particular. The remaining misfit, however, is still so large that we cannot distinguish between different tomographic models. We suggest that this is mainly due to an imperfect modelling of the crust, and/or source location if body waves are included, which have to be addressed in future inversions. Amplitude mismatches are large, regardless which 3-D mantle model is used. We observe that 3-D scattering or focusing/defocusing effects can only explain half of the surface wave amplitudes whereas body wave amplitudes are dominated by scattering effects. 1-D Q models, particularly in the crust and upper-mantle, strongly affect surface wave amplitudes and have to be modelled properly.

Abstract: We investigate the performance of cloud convection and tracer transport in a global off-line 3-D chemical transport model. Various model simulations are performed using different meteorological (re)analyses (ERA-40, ECMWF operational and ECMWF Interim) to diagnose the updraft mass flux, convective precipitation and cloud top height.
The diagnosed upward mass flux distribution from TOMCAT agrees quite well with the ECMWF reanalysis data (ERA-40 and ERA-Interim) below 200 hPa. Inclusion of midlevel convection improves the agreement at mid-high latitudes. However, the reanalyses show strong convective transport up to 100 hPa, well into the tropical tropopause layer (TTL), which is not captured by TOMCAT. Similarly, the model captures the spatial and seasonal variation of convective cloud top height although the mean modelled value is about 2 km lower than observed.
The ERA-Interim reanalyses have smaller archived upward convective mass fluxes than ERA-40, and smaller convective precipitation, which is in better agreement with satellite-based data. TOMCAT captures these relative differences when diagnosing convection from the large-scale fields. The model also shows differences in diagnosed convection with the version of the operational analyses used, which cautions against using results of the model from one specific time period as a general evaluation.
We have tested the effect of resolution on the diagnosed modelled convection with simulations ranging from 5.6° × 5.6° to 1° × 1°. Overall, in the off-line model, the higher model resolution does not make a large change to the diagnosed convective tracer transport. Similarly, the resolution of the forcing winds in the higher resolution CTM does not make a large improvement compared to the archived mass fluxes.
Including a radon tracer in the model confirms the importance of convection for reproducing observed midlatitude profiles. The model run using archived mass fluxes transports significantly more radon to the upper troposphere but the available data does not strongly discriminate between the different model versions.