n fŻÈwêU n ÈwçtÁÊuï ú: 2011N311ú(à) 13:00`16:00 ê: sċww1Ù5K563ş yPz uPèĵF Long-term changes in the observing system and their stratospheric impacts in the MERRA reanalysis uÒPF Steven Pawson(GSFC/NASA) uPv|F Long-term meteorological analyses of the atmosphere conducted with a fixed configuration of the data assimilation system (DAS) are known as reanalyses. The Modern-Era Retrospective analysis for Research and Applications (MERRA) reanalysis was conduced with a fixed version of the GEOS-5 DAS. The configuration was a half-degree resolution with 72 layers, extending from the surface to the mesosphere, with operational nadir-sounding satellite observations providing data constraints up to about 50km altitude (near the stratopause). MERRA spans the period 1979-2011. This work examines the long-term behavior of the stratosphere in MERRA, showing examples of how changes in the observations available to assimilate can impact the performance of GEOS-5. Changes in available satellite information, such as different Stratospheric Sounding Units (SSU) and Advanced Microwave Sounding Units (AMSU) instruments on different satellites, impact the time series in the middle and upper stratosphere, where these are the only data available to assimilate. In the low stratosphere, there are impacts of in-situ observations (sondes and aircraft measurements) and satellite observations. Near the tropopause the direct influences of local data insertion are complicated by remote affects: tropsopheric satellite information leads to changes in the hydrological cycle in the 2000s compared to earlier decades; there is a dynamical response to this change that impacts forecast skill near the tropical tropopause, but which is compensated for by radiosonde observations - this has a large impact on the "observation minus forecast" statistics in MERRA. yQz uQèĵF Polar Chemical Ozone Loss using SD-WACCM uÒQF Douglas Kinnison (UCAR) uQv|F It is well know that halogen chemistry affects polar stratospheric ozone abundance. In this work we will examine how one 3D chemistry climate models represent the fundamental processes that control ozone loss. The method we will used to quantify chemical ozone loss is the pseudo-passive subtraction technique. This method subtracts simulated inert ozone from observed or predicted ozone. The work here uses the Specified Dynamics version of the Whole Atmosphere Community Climate Model (SD-WACCM) to simulate the pseudo-passive ozone; observations are from the Earth Observing System Microwave Limb Sounder (MLS). Data from MLS is also used to initialize and evaluate SD-WACCM. Results achieved thus far show that Arctic ozone loss during winter 2004/05 is in good agreement with previous work. yRz uRèĵF Halogen oxide observations in the Southern Hemisphere uÒRF Karin Kreher (NIWA Lauder) uRv|F Enhanced concentrations of reactive halogen species, including bromine monoxide (BrO) and iodine monoxide (IO) radicals, in the lowermost troposphere are responsible for very efficient photocatalytic ozone destruction, as well as oxidation of gaseous elemental mercury and dimethyl sulphide (DMS), but many key processes involving these halogen species remain poorly understood. Although enhanced BrO concentrations (so called bromine explosion events) in the polar boundary layer are naturally occurring phenomena, areas covered by elevated BrO columns, as measured by the Global Ozone Monitoring Experiment (GOME) satellite instrument, have been expanding, possibly due to anthropogenic influences on climate. Bromine availability in turn affects the deposition of mercury, a bio-toxin, from the atmosphere to the surface. Therefore, climate-induced changes in sea ice are likely to affect mercury levels in Antarctic ecosystems. I will be discussing the measurements and findings from 2 Antarctic field campaigns supporting this theory. These halogen oxide measurements made on Ross Island (78S) in the Antarctic will also be put in context with observations made in the Tropics and Southern Hemisphere mid-latitudes. â˘íıĉF JëlEàĦzq