Atmospheric Sciences

Biomass burning represents an important source of atmospheric aerosols and greenhouse gases, yet little is known about its interannual variability or the underlying mechanisms regulating this variability at continental to global scales. Here we investigated fire emissions during the 8 year period from 1997 to 2004 using satellite data and 5 20 savanna fires that responded to different environmental and human factors. Biomass burning emissions showed large interannual variability with a range of more than 1 Pg

We report on total gaseous mercury (TGM) measurements made in Pudong, Shanghai in August/September 2009. The average TGM was 2.7±1.7 ng m −3 . This represents about 90% of the total atmospheric mercury. This is an underestimate for an annualmean concentration because the meteorology in September favored predominantly 5 easterly oceanic air, replaced in other seasons by airflow from industrial areas. The observed TGM follows a pattern seen in other cities around the world: a background elevated over mean hemispheric background (1.5 ng m −3 ), and pollution plumes of different magnitude and duration, interspersed with very sharp spikes of high concentration (60 ng m −3 ). The September 2009 Shanghai measurements are lower than those 10 reported for most other Chinese cities and Mexico City, and similar to concentrations found in some Asian and in North American cities. Such comparisons are tenuous because of differences in season and year of the respective measurements. We find that the observed TGM are most likely coming from coal fired power plants, smelters and industrial sources, based on its high correlation with NO x , SO 2 , CO and wind di-15 rections. 20 the atmosphere (Pirrone et al., 2010)

This chapter represents a new addition to the UNEP global mercury budget: the mercury emissions from biomass burning, here defined as emissions from wildfires and prescribed burns, and excluding contributions from bio-fuel consumption and charcoal production and use. The results cover the 1997-2006 timeframe. The average annual global mercury emission estimate from biomass burning for 1997-2006 is 675 ± 240 Mg yr -1 . This accounts for 8% of all current anthropogenic and natural emissions. The largest Hg emissions are from tropical and boreal Asia, followed by Africa and South America. They do not coincide with the largest carbon biomass burning emissions, which originate from Africa. Our methodology for budget estimation is based on a satellite-constrained bottom-up global carbon fire emission database (GFED version 2), which divides the globe into regions with similar ecosystems and burn behaviour. To estimate mercury emissions, the carbon model output is paired with regional emission factors for Hg, EF(Hg). There are large uncertainties in the budget estimation associated with burned area, fuel mass, and combustion completeness. The discrepancy between the model and traditional ground based assessments (e.g. FRA, 2000) is unacceptably large at this time. Of great urgency is the development and validation of a model for mercury cycling in forests, accounting for the biogeochemistry for each region. This would provide an understanding of the source/sink relationship and thus mercury accumulation or loss in ecosystems. Limiting the burning of tropical and boreal forests would have two beneficial effects: reducing the source of mercury releases to the atmosphere from burning, and maintaining a sink for atmospheric mercury. Restricting the global release mercury would reduce the vegetation/soil pools, and the potential Hg release in case of fire.

The influence of the Madden-Julian oscillation (MJO) on synoptic-scale waves, important precursors to tropical cyclones and tropical cyclogenesis, is investigated using a regional model of the eastern North Pacific basin. Cyclogenesis frequency is evaluated with respect to the MJO using a combination of the regional model and the archive best-track data. The statistics of the regional model compare well to the data and suggest that the MJO predominantly deters cyclogenesis during the suppressed phase rather than enhances it during the active phase when compared to neutral conditions. Synoptic-scale variability of cloudiness and eddy kinetic energy and analysis of vortex track statistics show a consistent enhancement of wave strength during the active phases of the MJO supported by both barotropic energetics and tropospheric moisture availability. Vertical wind shear, of critical importance to cyclone development, also exhibits strong variability associated with the phase of the MJO but, contrary to synoptic activity and moisture, results in unfavorable conditions for cyclogenesis during the active phase of the MJO in the region. The result is for the MJO to enhance cyclogenesis frequency relative to neutral conditions during the early active phase but otherwise to result in suppressed activity. In addition to the basinwide longitudinal structure, the local MJO exhibits a distinct north-south structure not apparent in the global pattern but in agreement with recent studies of tropical eastern North Pacific subseasonal variability.

Atmospheric O3 mixing ratios measured by ILAS and HALOE are compared for periods from March 25-31, 1997 in the NH and from November 20-24, 1996 and December 13-14, 1996 in the SH. Both instruments observe consistent vertical and horizontal structure in the highly variable polar vortex regions. In the ozone peak region, ILAS ozone values are smaller compared to HALOE values in both hemispheres, but the differences are less than 13% and 20% in 40-20 km altitude range, respectively, for the NH and the SH, which are both close to the sum of uncertainties of the two instruments. When validation is complete, ILAS data will be useful for the study of the chemistry and dynamics at high latitudes.

For the first time a mesoscale-resolving whole atmosphere general circu-3 lation model (GCM) has been developed, using the NCAR Whole Atmosphere 4 Community Climate Model (WACCM) with ∼0.25 • horizontal resolution and 5 0.1 scale height vertical resolution above the middle stratosphere (higher res-6 olution below). This is made possible by the high accuracy and high scal-7 ability of the spectral element dynamical core from the High-Order Method 8 Modeling Environment (HOMME). For the simulated January-February pe-9 riod, the latitude-height structure and the magnitudes of the temperature 10 variance compare well with those deduced from SABER observations. The 11 simulation reveals the increasing dominance of gravity waves (GWs) at higher 12 altitudes through both the height dependence of the kinetic energy spectra, 13 which display a steeper slope (∼-3) in the stratosphere and an increasingly 14 shallower slope above, and the increasing spatial extent of GWs (including 15 a planetary-scale extent of a concentric GW excited by a tropical cyclone) 16 at higher altitudes. GW impacts on the large-scale flow is evaluated in terms 17 of zonal mean zonal wind and tides: with no GW drag parameterized in the 18 simulations, forcing by resolved GWs does reverse the summer mesospheric 19 wind, albeit at an altitude higher than climatology, and only slows down the 20 winter mesospheric wind without closing it. The hemispheric structures and 21 magnitudes of diurnal and semidiurnal migrating tides compare favorably 22 with observations.

The High Resolution Dynamics Limb Sounder (HIRDLS) experiment was designed to provide global temperature and composition data on the region from the upper troposphere to the mesopause with vertical and horizontal resolution not previously available. The science objectives are the study of small-scale dynamics and transports, including stratosphere-troposphere exchange, upper troposphere/lower stratosphere chemistry, aerosol, cirrus and PSC distributions, and gravity