EAS Graduate Student Symposium

Submitted Abstracts

Oral Presentations Coral Records of 20th Century Warming and Freshening in the Central Tropical Pacific Intan Suci Nurhati Advisor: Kim Cobb intan@gatech.edu Tropical Pacific climate variability strongly influences the global climate. How tropical Pacific climate might evolve under continued anthropogenic greenhouse warming is unclear; observation and modeling studies suggest both strengthening and weakening of the zonal sea-surface temperature (SST) gradient $^{1,4}$ . Modern corals from the central tropical Pacific (CTP) have provided high monthly resolved climate proxy records that contain trends toward depleted coral $\delta^{18}$ O values, suggesting that warming and/or freshening has occurred in this region over the late 20th century $^{3,2}$ . It is important to understand the physical mechanism that underlie these trends in order to better predict low-frequency changes in tropical Pacific climate over the next decades. One mechanism involves a weakening in the zonal SST gradient, which would warm the CTP by reducing upwelling while increasing rainfall in the CTP. On the other hand, warming might have occurred absent any change in upwelling, and the lower salinities may signal decadal-scale changes in the location and/or intensity of the Inter-Tropical Convergence Zone (ITCZ). Here we apply $\delta^{18}$ O and Sr/Ca proxies to modern corals from Palmyra, Fanning and Christmas Islands (2 $^{\circ}$ N-6 $^{\circ}$ N, 157 $^{\circ}$ W-162 $^{\circ}$ W) in order to reconstruct SST and sea-surface salinity (SSS) over the last several decades. The three islands span strong gradients in temperature and salinity. The islands are aligned in a NW-SE fashion, with Christmas bathed by the South Equatorial Current (SEC) and dominated by upwelling variability at the southern end; while Palmyra as the northern-most island, lies in the core of the North Equatorial Counter Current (NECC) and is heavily influenced by ITCZ variability. We measure Sr/Ca ratio as a proxy for SST with an analytical error of less than $\pm$ 0.3%(1 $\sigma$ ) or $\sim$ $\pm$ 0.4 $^{\circ}$ C(1 $\sigma$ ). We measure coral $\delta^{18}$ O with an analytical error of $\pm$ 0.05%(1 $\sigma$ ), and derive $\delta^{18}$ O of seawater ( $\delta^{18}$ O $_{sw}$ - a proxy for SSS) by removing the Sr/Ca-derived SST contribution from coral $\delta^{18}$ O. Sr/Ca-based SST reconstructions show that Palmyra and Christmas have warmed by 0.6 $^{\circ}$ C and 1.5 $^{\circ}$ C over the period 1970-1998, respectively. A stronger warming trend in Christmas may suggest slowing down of the equatorial upwelling. Over the same period, Palmyra and Christmas have experienced freshening of seawater by 0.94psu and 0.36psu, respectively. A stronger freshening trend in Palmyra may suggest enhanced and/or southward migration of the ITCZ as well as changes in the salinity of waters advected from the Western Pacific Warm Pool by the NECC. Preliminary SST and SSS reconstructions from Fanning, which lies between Palmyra and Christmas, confirm these late 20th century warming and freshening trends. Hence, the simultaneous warming and freshening evident in CTP corals may indicate the weakening of the zonal SST gradient in the late 20th century tropical Pacific climate. $^{1}$ Cane et al. (1997). Science, 275(5302): 957-960. $^{2}$ Cobb et al. (2001). Geophys. Res. Lett., 28(11): 2209-2212. $^{3}$ Urban et al. (2000). Nature, 407(6807): 989-993. $^{4}$ Vecchi et al. (2006), Nature, 441: 73-76. Modeling the impacts of convective transport and lightning NOx production over North America: Dependence on cumulus parameterizations Chun Zhao Advisor: Yuhang Wang chun.zhao@eas.gatech.edu A 3-D regional chemical transport model (REAM) is applied to examine the uncertainties in modeling the effects of convective transport and lightning NO $_{x}$ production on upper tropospheric O $_{3}$ and its precursors. To assess the model uncertainties, two different cumulus convective parameterizations, KF-eta and Grell, are adopted in REAM from the respective meteorological models, WRF and MM5. The model simulations are evaluated using INTEX-NA aircraft measurements. A major improvement of the KF-eta scheme (in WRF) is its inclusion of entrainment and detrainment processes. It simulates larger convective updraft mass fluxes below 300 hpa than the Grell scheme (in MM5), resulting in better simulations of vertical profiles of the concentrations of CO, C $_{3}$ H $_{8}$ , and C $_{4}$ H $_{10}$ in the middle and upper troposphere. More efficient scavenging from entrainment and detrainment also results in better simulations of highly soluble pollutant HNO $_{3}$ in the free troposphere in WRF-REAM. The inclusion of entrainment and detrainment processes in the KF-eta scheme also leads to lower cloud top heights (10-12 km in WRF) than the Grell scheme (13-16 km in MM5) and hence smaller amounts of estimated intra-cloud lightning flashes. WRF simulated cloud top heights are in better agreement with GOES satellites measurements over the southeastern United States and the Atlantic Ocean. The WRF-REAM model better simulates lightning NO $_{x}$ distributions than the MM5-REAM, especially over the Atlantic Ocean. Lightning NO $_{x}$ production enhances the concentration of upper tropospheric NO $_{2}$ by a factor of 2 ( 50 pptv) and increases O $_{3}$ by up to 20 ppbv. Temporal Changes of Shear Wave Velocity and Anisotropy in the Shallow Crust Induced by the 10/22/1999 M6.4, and M6.0, Chia-Yi, Taiwan Earthquake Kevin Chao Advisor: Zhigang Peng kevinchao@gatech.edu We analyze temporal changes of seismic velocity and anisotropy in the shallow crust from similar earthquake clusters that are recorded at a 200-m-deep borehole station CHY of the Taiwan Central Weather Bureau Seismic Network. This station is located directly above the hypocenter of the 10/22/1999, M6.4 and M6.0, Chia-Yi, Taiwan earthquakes, and is immediately south of the rupture zone of the 09/20/1999 Mw7.6 Chi-Chi earthquake. We perform waveform cross correlation on three-component seismograms generated by 2571 local earthquakes with straight-line incident angle to station CHY less than 45 degrees. The similar earthquake clusters are identified with inter-hypocentral distance less than 5 km and the medium correlation coefficient (CC) greater than 0.90. The three-component seismograms show clear shear wave splitting ( $\sim$ 0.16 s time delay and a near E-W fast polarization direction), and surface-reflected downgoing shear waves $\sim$ 1 s after the direct upgoing waves [Liu et al. 2004, 2005]. We apply a 1-Hz high-pass filter, and compute the autocorrelation function for each horizontal component in a time window 2 s before and 3 s after the handpicked S arrival. The secondary peak in the autocorrelation function is used as a measure of the time delay between the upgoing and downgoing shear waves for the horizontal components of each event. The time delays for both E-W and N-S components measured from similar earthquake clusters increase by 3 percent at the time of the Chia-Yi mainshock, and followed by a logarithmic recovery. However, the difference of time delay between the N-S and E-W components, which represents the shear-wave anisotropy in the top 200 m of the crust, remains essentially unchanged. We propose that opening of microcracks in the shallow crust with no preferred orientation due to the strong shaking of the Chia-Yi mainshock, followed by gradual closure, would explain the temoral changes of the seismic velocity for both horizontal components, but virtually no observable changes in shear wave anisotropy. We also use different median CC values to identify similar clusters, and separate earthquakes into different groups based on their hypocentral locations. The obtained results are esentially the same, suggesting that the observed temporal changes are not sensitive to the raypath between station CHY and the epicenter of each event, but are mostly controlled by variation in material property in the top 200 m of the crust. The Impact of Surface Ocean Organics on Surface Tension, CCN Activity and Droplet Growth Kinetics of Marine Aerosol Richard Moore Advisor: Athanasios Nenes richard.moore@chbe.gatech.edu Oceanic surface waters contain substantial amounts of organic surfactants that are transferred to the aerosol phase during the process of sea spray generation. It is known that these organics depress surface tension, and such a depression could significantly alter the ability of marine aerosol to act as cloud condensation nuclei (CCN). While the CCN properties of the inorganic marine aerosol fraction have been studied extensively, the contribution of the organic fraction is less well-understood. It would be advantageous, then, to be able to isolate the organic species present in marine aerosol in order to characterize their aggregate thermodynamic properties (e.g., molar volume, surface tension, and water uptake coefficient) and better understand the role of organics in marine CCN. A recently-developed technique using electrodialysis and reverse osmosis to remove the electrolyte salts and concentrate the dissolved organic matter present in seawater provides the means to accomplish this goal. Samples were taken in July 2006 in the Atlantic Ocean surface waters offshore of Georgia. Organics present in the concentrated sample likely include surface-active species such as short-chain fatty acids, proteinaceous material, and humic substances among others. Because marine aerosol are formed from sea spray, which involves the generation of droplets from wave breaking, the chemical species found in surface waters are expected to be the same as those in marine aerosol. In the present study, we examine, using Köhler Theory Analysis $^{2,3}$ , the surface tension, CCN activity, and droplet growth kinetics of laboratory-generated particles containing mixtures of these concentrated organics and inorganic salts. Previous studies have observed size-dependent enrichment of organic surfactants in marine aerosol $^{4,5}$ , and we simulate this enrichment by varying the ratio of organics to salts in the laboratory-generated particles. The implications of organic enrichment on droplet activation and growth will be discussed. Vetter, T.A. et al., in review. Asa-Awuku, A. et al., Atmos. Chem. Phys. Discuss., in review. Padro, C. et al., Atmos. Chem. Phys., 7, 2007. Oppo, C. et al., Mar. Chem., 63, 1999. O'Dowd, C. et al., Nature, 431, 2004. In Search of Water Vapor on Jupiter: Simulated Microwave Radiometer Sensitivity to Water Vapor Abundance and a New High Pressure System for Laboratory Measurements under Jovian Conditions Bryan M. Karpowicz Advisor: Paul G. Steffes karpob@eas.gatech.edu A wealth of data regarding the early formation of our solar system is locked within the atmospheres of the outer planets. The atmosphere of Jupiter is particularly intriguing for planetary scientists since it holds the keys to understanding its formation process. Understanding the composition of Jupiter via ground based radio astronomy has provided insight with regard to atmospheric composition, but does not offer a complete picture of its composition due to interference from Jupiter's synchrotron radiation belts. Orbiting spacecraft equipped with microwave instruments can offer a more in-depth picture of atmospheric composition by avoiding these synchrotron belts. However, retrievals using such instruments rely heavily upon both laboratory measurements of microwave absorption, and detailed forward modeling. A framework is presented using sensitivity analysis from a developed forward model to simulate microwave brightness as viewed from an orbiting spacecraft, along with a system capable of measuring microwave absorption under the high-pressure and temperature conditions deep within the Jovian atmosphere. We will show the effects of HO vapor, and HO-NH clouds upon brightness temperature, along with plans for our laboratory measurement system. Boundary layer models of Martian hydrothermal systems Kathleen Craft Advisor: Bob Lowell with: Erin Kraal Department of Geosciences, Virginia Tech, Blacksburg, VA kcraft@gatech.edu Many geomorphic features on the surface of Mars, such as gullies, fans, paleolakes, outflow channels, and deltas, were likely caused by flowing water; however, the source of that water is disputed. One possible water source is a hydrothermal system driven by a magma intrusion. We investigated such hydrothermal systems by first developing analytical, steady state, two-dimensional, thermal boundary layer models in order to determine the mass and heat fluxes near the quasi-vertical boundaries of magma intrusions with heights ranging from 1 to 10 km. We analyzed the effects of various permeabilities and intrusion dimensions on the heat and mass fluxes generated by hydrothermal flow. Results showed, for example, that a 100 km long dike with a depth of $\sim$ 5 km injected into a highly permeable rock would produce $\sim$ 1019 J/yr of heat and transport $\sim$ 10 km $^{3}$ /yr of fluid. This and additional mass flux results were compared with hydrographs estimating the volumes of fluid outflow and durations of flow needed to form various observed geomorphic features. The hydrograph comparisons indicate that flow from such hydrothermal systems could be responsible for some fluvial features on Mars including gullies and stepped fans. The relatively small flow volumes suggest it is unlikely that the larger features were formed directly by out flowing hydrothermal fluids. However, additional fluid may result from the melting of subsurface ice as a result of hydrothermal heat transport. Towards Parameterization of Cloud Drop Size Distribution For Large-Scale Models Wei-chun Hsieh Advisor: Athanasios Nenes wei-chun.hsieh@eas.gatech.edu A parameterization framework that links cloud activation and microphysical evolution is developed for usage in aerosol-cloud interaction studies with large scale models. The framework computes vertical evolution of droplet population beyond activation; this is then used to directly compute height-dependant properties, such as autoconversion rates. The framework also computes the ratio between effective radius and volumetric radius, which is used for computing cloud optical depth and indirect forcing. In this work, we present results using an adiabatic framework. The framework is evaluated by comparison with a detailed numerical parcel model and in-situ data. Good agreement of relative dispersion between parameterization and a detailed numerical parcel model indicates the framework capture the physics of droplet formation and growth. Evaluation with in-situ measurements were done for clouds sampled aboard the CIRPAS Twin Otter during the CRYSTAL-FACE and CSTRIPE campaigns. On average, the predicted relative dispersion from homogeneous updraft simulation is lower than measurement for clouds sampled during CRYSTAL-FACE and CSTRIPE missions. Using PDF updrafts has the effect to broaden the width of spectra but the predicted relative dispersion is still lower by a factor of 5 as compared to the measured values. This underestimation of the predicted relative dispersion cause relatively larger uncertainty in predicting autoconversion rates: 41.1% (CRYSTAL-FACE) and 58.4% (CSTRIPE). The autoconversion uncertainty associated with the predicted cloud drop number is 3.4% (CRYSTAL-FACE) and 5.6% (CSTRIPE). This underestimation of the relative dispersion is largely due to the assumption of adiabaticity which can be relaxed using an entraining parcel framework. The Global Seismic Energy to Moment Ratio: A Tool for Basic Research and Real-Time Identification of ``Tsunami Earthquakes'' Jaime Andres Convers Advisor: Andrew Newman jconvers@gatech.edu Using the methodology developed by Newman & Okal [1998], we develop an improved global earthquake catalog, including the last ten years of earthquake activity of M6.6. This global dataset contains calculated radiated earthquake energies using broadband data from IRIS, taking seismograms azimuthally distributed and in the range of 30 $^{\circ}$ to 80 $^{\circ}$ . For each of the events, the radiated seismic energy, is calculated and compared to the seismic moment, to determine average values and variations in earthquake strong shaking. We extend the original dataset upward by a unit of magnitude due to the inclusion of very large, recent events. Likewise, with 10 additional years of activity and improved global coverage, the new catalog has 5x the number of earthquakes and 20x the waveforms of the original study. For most events greater than M7.3 we additionally determine rapid rupture duration estimates, , a tool to aid in rapid identification of very large and tsunami earthquakes. Because tsunami earthquakes rupture more slowly than regular ``strong'' earthquakes, they are identifiable by an ratio reduction of at least 1 unit magnitude (Newman & Okal, 1998). We additionally examine the relationship between and to determine a more robust discriminant for tsunami earthquakes. Along with improving the global characterization of and an initial characterization of rapid , we explore regional effects along the middle America Subduction zone, the site of an energy deficient tsunami earthquake in 1992. Initial results suggest that this region shows a broad-scale deficiency in energy suggesting generally slower ruptures and increased tsunami earthquake potential. Spatio-temporal Distribution of Latent Heating in the Southeast Asian Monsoon Region Manuel Zuluaga Advisor: Peter Webster mzuluaga3@mail.gatech.edu The Latent Heat (LH), released as a result of deep convection, plays an important role in the vertical distribution of the diabatic energy budget from the surface to the atmosphere: the motor which drives the global atmospheric circulation, including the Southeast Asian Monsoon. In particular, knowing the spatio-temporal structure of the LH during the wet monsoon season could be a key factor to understand the interaction between seasonal features of the monsoon with the summer manifestation of the intra-seasonal oscillation in the Indian Ocean basin, and hence the distribution of the precipitation. Several studies have investigated how the structure of heating in the tropics has a direct influence in the dynamical response of the atmosphere to the large-scale dynamical forcing associated with tropical precipitating systems. However, these studies assume a uniform geographically distribution of the vertical diabatic heating profiles across the Tropics. The major objective of this study is to produce and to examine three-dimensional latent heating structures over the Indian Monsoon region for the three summer seasons of 1998-2000 period using TRMM-2A12 (GPROF algorithm) and TRMM-CSH (CSH algorithm) data. A specific goal in this work is to explore the differences in the distribution of the latent heating throughout the intraseasonal cycle. This intra-seasonal cycle not only generates wet and dry spells over the South-East Asian continent but also determines the spatial distribution of the climatological JJAS rainfall in the Indian Monsoon Region. Results show spatial distribution differences between the LH profiles during the suppressed and active phases of the oscillation as well as differences in the vertical. During an active phase of the oscillation over the Indian Ocean, the released latent heat is concentrated predominantly near the equator while during the suppressed phased the heating is concentrated in the Bay of Bengal and the continental South East Asia. In the vertical, a deep warm blob aloft over the Bay of Bengal contrast with lower heating peaks over equatorial regions, related with the characteristics of the cloud systems in these regions. These differences in profiles can be used as key inputs in the forcing of general circulation models and cloud resolving models to understand the main differences in the atmospheric response to the geographic location of the heating. Rapid Temporal Changes of Fault Zone Site Response Associated With Strong Ground Motion Chunquan Wu Advisor: Zhigang Peng chunquanwu@gatech.edu We systematically analyze temporal changes in fault zone (FZ) site response along the Karadere-Düzce branch of the North Anatolian fault that ruptured during the 1999 Izmit and Düzce earthquake sequences. The study involves primarily comparisons of strong motion seismic data recorded by station VO inside the Karadere fault and station FP $\sim$ 300 m away from the fault starting 8 days before and ending 72 days after the Düzce mainshock. The spectral ratio between stations VO and FP is computed from the averaged spectra for the two horizontal components, and is used as a measure for FZ site response. The peak spectral ratio increases 80-150% and the peak frequency drops 20-40% at the time of the Düzce mainshock, and is followed by near-complete recovery with time scale of $\sim$ 1 day. The observed temporal changes of FZ site response can be explained as reduction of seismic velocities by opening of pre-existing cracks inside the FZ due to strong groun d motion, followed by logarithmic recovery. Our observations suggest nonlinear behavior of the fault zone material under strong ground motion of nearby major earthquakes. We also apply this method to all the weak motion records including those generated by the 36 repeating earthquake clusters identified by Peng and Ben-Zion (2006) during the same period, but no clear temporal changes of peak spectral ratio or peak frequency is observed. This is likely because the first post-Düzce events in the repeating clusters occurred at least a few hours after the Düzce mainshock, when most of the rapid coseismic changes have been recovered. Examining the Effects of Seasonal and Salinity Variations on Satilla River Sediments (Georgia, U.S.A.) Using In Situ Voltammetric Depth Profile Measurements Deidre Meiggs Advisor: Martial Taillefert deidre.meiggs@eas.gatech.edu Estuarine and continental shelf sediments are areas where rates of natural organic matter respiration are shown to be extreme, yet very few studies have thoroughly investigated variations in biogeochemical processes and elemental fluxes in such environments. The Satilla River in the South Atlantic Bight, (Georgia, USA) is an example of a relatively pristine estuary that experiences pronounced seasonal variations. To study these sediments, an autonomous benthic lander was constructed and equipped with a micromanipulator for voltammetric profiling of the main redox species in sediment porewaters (O $_{2}$ , Mn $^{+2}$ , Fe $^{+2}$ , & $\Sigma$ H $_{2}$ S, and other iron and sulfur complexes). The lander was deployed seasonally for more than two years at multiple stations along the river and the nearby shelf. Based on the in situ profiles garnered, a seasonal variability between iron reduction and sulfate reduction is clearly apparent. Additionally, due to extreme drought conditions experienced throughout 2006 & 2007, conclusions can be drawn regarding the dynamic effects of changing river discharge and salinity on these sediments. Comparing the Volatility of Newly Formed Organic Aerosol to Secondary Nitrate in Mexico City Chris Hennigan Advisor: Rodney Weber chennigan@eas.gatech.edu Measurements of atmospheric gases and particulate components were made in the Mexico City Metropolitan Area (MCMA) as part of the Megacity Initiative: Local and Global Research Objectives (MILAGRO) field campaign. Ammonium nitrate dominated the inorganic aerosol fraction and showed a distinct diurnal signature characterized by rapid morning production and an equally rapid concentration decrease before noon. The concentration increase was due to secondary formation and agreed with the predicted photochemical production rate, while the concentration decrease was shown by the ISORROPIA aerosol equilibrium model to be caused by a thermodynamic shift from the particle to the gas phase. Water-soluble organic carbon (WSOC) in fine particles was also produced in the early morning and appeared to be secondary since it tracked the increase in nitrate. However, in contrast to the morning increase, after accounting for dilution by normalizing concentrations to a conservative tracer, WSOC did not follow the mid-day nitrate loss. The findings suggest that, compared to ammonium nitrate, the secondary organic aerosol observed in the MCMA was not semi-volatile in the $\sim$ 2-3 hours following formation. Study of the bio-reduction of Mn oxides by Shewanella putrefaciens Hui Lin Advisor: Martial Taillefert hlin30@gatech.edu Several species of bacteria are known to grow with Mn as terminal electron acceptor, Shewanella putrefaciens is one of the most studies species. Dissimilatory Mn reduction is an anaerobic respiration process, important in aquatic environment, and may affect the biogeochemical cycle of other important metals, due to the high absorption capacity of Mn oxides. While, knowledge gap still exists in the mechanism of the bio-reduction of Mn oxides, especially for the electron transfer pathway during the reduction process. In this study, experimental incubations with wide type Shewanella putrefaciens and different type of Mn oxides (colloidal Mn oxides and amorphous Mn oxides) were applied to simulate the time evolution of Mn bio-reduction process. Voltammetry, UV spectra and furnace atomic absorption spectrometry are employed to identify and quantify three oxidation states of Mn: Mn (IV), Mn (III) and Mn (II). Evidence of Mn (III) production during the reduction from Mn (IV) to Mn (II) had been observe, suggesting two steps of one-electron-transfer pathway may preferred in the Mn bio-reduction process. Meanwhile, bio-reduction rate for colloidal Mn oxides was much higher than for amorphous Mn oxides. Variations of velocity contrast along the rupture zone of the 2004 M6 Parkfield earthquake on the San Andreas Fault Peng Zhao Advisor: Zhigang Peng pzhao@gatech.edu We systematically investigate the velocity contrast along the Parkfield section of the San Andreas Fault (SAF) that ruptured during the 2004 M6 Parkfield earthquake, using fault zone head waves (FZHW) that refract along the bimaterial interface. The analysis employs a total of 322 repeating earthquakes clusters identified from 8993 earthquakes in the relocated catalog of Thurber et al. (2006). The seismic data are recorded by 13 borehole stations in the High Resolution Seismic Network (HRSN) since 1987 and 23 surface stations in the Northern California Seismic Network (NCSN) since 1984,with normal distances to the fault less than 6 km. The study is part of a larger project on imaging bimaterial interfaces in the Parkfield region with multiple seismic networks. We stack waveforms of each repeating earthquake cluster, and align the peaks or troughs of the direct P waves assuming right-lateral strike-slip focal mechanisms. Clear FZHW are observed at 18 stations that are within 2.5 km on the NE side (slow) of the SAF. The obtained velocity contrast is about 8% north of Middle Mountain, and decreases rapidly toward Gold Hill near the epicenter of the 2004 event. This implies an abrupt change of velocity contrast along the Parkfield section of SAF near Gold Hill. The observed variation of velocity contrast is consistent with 3-D tomography models of the Parkfield section, which include a high velocity body near Gold Hill on the NE side that produces a local reversal of the velocity contrast, and geological observations of a sliver of high-velocity rock immediately to the NE of the SAF associated with the GH fault. Development of an Online System to Measure Water-Soluble Trace Metals in Aerosols Michelle Oakes Advisor: Rodney Weber michelle.oakes@eas.gatech.edu Water-soluble trace metals in the atmosphere, such as Cr(VI), Cu(I+II), Fe(II), and Mn(II) influence public health, ocean biogeochemistry, and climate. Filter-based measurements with a 24-hr integration time are predominately used to quantify trace metals. Although this method provides an adequate measurement of daily contributions of trace metals, it does not provide insight into acute exposures that could be higher than daily averages, nor sources with high temporal variability. An enhanced time-resolved data set may help identify sources and lead to more effective control strategies to improve public health. A Particle-Into-Liquid Sampler (PILS) has been used to collect atmospheric particulate matter into purified water for online measurements. In previous studies, the PILS has been coupled to a dual channel ion chromatograph and total organic carbon analyzer to measure specific atmospheric ions and water-soluble organic carbon, respectively $^{1,2}$ . Both s ystems have produced robust measurements comparable to existing measurements from offline techniques. Our research has been focused on the development of a method to quantify water-soluble trace metals in aerosols with a 10-minute integration time using a PILS and a Liquid Waveguide Capillary Cell (LWCC). Spectrophotometry is a powerful tool for real-time detection of light absorbing species. Ligands interact with specific metals to form colored complexes with high absorptivities at specific wavelengths. When coupled to a 1 m path-length liquid waveguide capillary cell (LWCC), the spectrophotometric technique is capable of detecting trace metals at concentrations that are typical in the atmosphere (parts-per-billion). Majestic et al. demonstrated that an LWCC can be used to measure soluble Fe(II) in ambient particulate matter from filter-based collections with concentrations ranging from 0.50 and 20 ng Fe(II) m air. This poster presents preliminary results of our research on the development of an online method to measure water-soluble Cr(VI), Cu(I+II), Fe(II), and Mn(II) and ambient Fe(II) data from Atlanta. Orsini et al., Atm. Env. 37, 2003. Sullivan et al., Geophys. Res. Lett., 31, 2004. Majestic et al., Env. Sci. & Tech. 40, 2006. Reconstructing Tropical Sea Surface Temperatures Using Precipitation Proxy Records: Methods and Uncertainties Jason Furtado Advisor: Emanuele Di Lorenzo jason.furtado@eas.gatech.edu Reconstruction of past tropical sea surface temperatures (SSTs) over the last millennia and beyond is an active venture in current paleoclimate research. This study explores the potential of using tropical precipitation data from paleoclimate proxy locations to reconstruct tropical ocean SSTs. The goal is to quantify the range of uncertainties in the SST reconstruction and their dependence on both errors in the proxy data and distribution of the proxy network. Two reconstruction methods are presented and applied to observational and modeled datasets over the period 1950-2000. The first reconstruction method exploits the high correlation between the leading mode of variability of precipitation and SST, which corresponds to ENSO and accounts for more than 50% of the total covariance. The second method uses a multiple regression technique to exploit additional modes of covariability between precipitation and SSTs. We find that in addition to the ENSO mode, the second mode of covariability ( $\sim$ 15% of the total covariance) captures variations in the spatial expression of ENSO. This second mode has a large-scale spatial signature and is robust in all the precipitation datasets used in this study. Inclusion of this mode in the linear model leads to an approximate 30% improvement in the overall reconstruction skill. Uncertainty estimates computed from the regression model are consistent with those obtained using Monte Carlo simulations. Given the few degrees of freedom in the covariability modes, we find that a relatively sparse network of individual precipitation time series captures the phase of the modes and leads to high SST reconstruction skills in the tropical Pacific and Indian Ocean. Poster Presentations Using Remotely Sensed Data to Characterize the Okefenokee Swamp WildfireÕs Effects upon Air Quality in Atlanta, GA Erica Alston Advisors: Irina Sokolik and Judith Curry erica.alston@gatech.edu The wildfires that swept through southeastern GA are the largest wildfire events to devastate GA in recorded history. The fires raged for over two months and consumed hundreds of thousands of acres. Wildfires are a source of fine particulate matter i.e. PM 2.5 (measured in micrograms per cubic meter) that can contain breathable irritant particles. It is this combination that causes wildfires to have significant impacts upon air quality in the surrounding areas. This work seeks to characterize the air quality impacts felt in metropolitan Atlanta, GA through the use of ground based and remotely sensed data. The ground based data is provided through a network of ambient air monitoring stations that provide real-time measurements for locations across Georgia. The remotely sensed data will be a multi-instrument view of the event through CALIPSO, MODIS Aqua, and MODIS Terra. During active burning period, Atlanta experienced seven PM2.5 exceedances, with most occur ring during May. High exceedance days show well correlated values cross the metropolitan area. Correctly predicting air quality during a wildfire can be difficult, as shown by the missed AQI forecasts for those exceedance days. Using CALIPSO Space Lidar Data in Conjunction with Passive Remote Sensing for Characterization of Spatiotemporal Distribution of Asian Dust Outbreaks Hyung-Jin Choi Advisor: Irina Sokolik hyung-jin.choi@eas.gatech.edu A better understanding of the properties and spatiotemporal distribution of atmospheric dust is needed for improved predictions of aerosol radiative forcing on climate. We use CALIPSO data in conjunction with A-Train satellite multi-sensor observations (Ozone Monitoring Instrument, OMI, Moderate-Resolution Imaging Spectroradiometer, MODIS, and CloudSat) as well as ground-based data to investigate the dynamics of East Asian dust plumes during March-April of 2007, considering dust sources and mid- and long-range transport. In addition, using recent data on the composition of Asian dust, we compute the dust optical properties (lidar ratio, particle depolarization ratio and color ratio) to aid in interpretation of CALIPSO data. Marine Polyphosphate: A Key Player in Geologic Phosphorus Sequestration Julia Diaz Advisor: Ellery Ingall julia.diaz@gatech.edu Excess nutrient phosphorus is removed from wastewater by driving the bacterial synthesis of polyphosphate. Here, we describe a similar mechanism by which dissolved phosphate in marine surface waters is sequestered by polyphosphate forming diatoms and then transported to sediments as these polyphosphate-rich organisms sink. Cultured marine algae grown under phosphorus replete conditions have previously been shown to store significant phosphorus as inorganic polyphosphate. But our findings show that natural communities of common marine diatoms synthesize polyphosphate under sub-micromolar dissolved phosphate concentrations. Our findings further demonstrate that polyphosphate may nucleate the authigenic formation of calcium phosphate minerals in marine sediments. Thus, the transport of polyphosphate from its planktonic origin in surface waters to the underlying sediment, followed by subsequent mineral transformation provides a critical ``biological pump'' mechanism for the long-term sequestration of water column derived phosphorus in marine sediments. This phosphorus removal mechanism is the first to explain the puzzlingly disperse distribution of fine-grained apatites observed in marine sediments worldwide. Characterization of Santorini Caldera and the Socoro Magma Body Grant Farmer Advisor: Andrew Newman grant.farmer@gatech.edu Santorini Caldera, in the southern Aegean, is part of a well developed, and very active volcanic system fueled by subduction along the Hellenic arc. The system had its most recent caldera-forming event around 1650 B.C. in a massive series of Plinean eruptions that expelled some 60 km of volcanic material. Currently, the caldera is partially submerged, with only pieces of caldera wall, flanks, and central post-caldera lavas exposed above the sea level, comprising a grouping of five small islands. In late-spring 2006, with UNAVCO field support and support form the Santorini Volcano Observatory, a network of two continuous GPS monuments spanning the caldera was established, and completion of a third monument is planned for this coming year. Additionally, 18 existing and new geodetic markers were first occupied with GPS across the 5-island group in 2006. Preliminary data from the two continuous GPS sites suggest that deformation across the caldera is currently minimal, and below the detection threshold for the 1.5 year continuous network. Given that the system is currently active (last erupting in 1957), and the threat of eruption and tsunami endangers local populations, numerous tourists, and much of coastal Turkey, Greece and North Africa, we will continue to observe it for signs of increasing unrests. The Socoro Magma Body in New Mexico lies within the central Rio Grande Rift Valley and is one of the largest known magma bodies in the Earth's continental crust. Studies of local microseismicity and deep seismic soundings revealed an unusually strong reflector approximately 70 km wide at 19 km depth and identified it as a large active sill-like crustal magma intrusion. Using continuous and campaign GPS, a smaller body has been identified as the source of inflation between 5-10 km depth between 2002 and 2003. More recent observations using both InSAR and GPS indicate that this inflation may be marked by transient rapid uplift events rather than continuous and slow ones. Geodetic and Modeling Constraints From Ongoing Uplift at Long Valley Caldera: Continued Episodic Dome Growth Observed in 2002-2003 Lujia Feng Advisor: Andrew V. Newman lfeng@gatech.edu Long Valley Caldera (LVC), a 17 $\times$ 32 km collapse crater in eastern California, sits on the eastern edge of the Sierra Nevada Mountains. It was created by a catastrophic eruption 760,000 yrs ago. Within 100,000 yrs or less after caldera formation, a 10-km-wide and 0.5-km-high resurgent dome was formed in the centre of caldera from uplift induced by magmatic intrusion. Beginning around 1978, signs of renewed unrest were first observed in LVC. This and subsequent periods of episodic uplift in 1978-1982, 1989-1991, 1997-1998 and 2002-2003 were interrupted by periods of relative inactivity. While an understanding of the dynamics of this complicated time-history remains elusive, we focus here on the previously undescribed episode which occurred between 2002 and 2003. We use the continuous regionally filtered 3-component GPS data processed by the USGS, from which we remove the motion of the Sierra Nevada Block relative to North American plate (defined by Dixon et al., [2000]). The maximum uplift during the 2002-2003 episode is $\sim$ 3.5 cm, about 1/3 the size but with a similar exponential shapes as the 1997-1998 episode, while the overall uplift from late 1970s is estimated to be $\sim$ 80cm. The uplift pattern is mostly radial, like deformation from the previous episodic uplift and interim periods, and can mostly be explained by a single magma source located just west of the central resurgent dome. To locate this most recent inflation source, we use a grid-search to find the best-fit solutions for both a finite spherical and a vertically dipping prolate spheroidal (axis ratio=1:2) source models. Both models are found to accommodate $\sim$ 95% of the surface deformation. The best-fit locations are well constrained at 118.925 $^{\circ}$ W, 37.679 $^{\circ}$ N (spherical) and 118.928 $^{\circ}$ W, 37.679 $^{\circ}$ N (prolate), however, a trade-off between source depth and volume change is observed. The data reveals relatively large deviations from the two analytical models for GPS stations (KNOL, CASA/CA99, MWTP, TILC) in south moat. Using available seismic data we outline a recently active South Moat fault and examine possible dislocation and rheological effects of this boundary on the overall and observed deformation fields. 1-D Air-snowpack Modeling of Atmospheric Nitrous Acid (HONO) during ANTCI 2003 Wei Liao Advisor: David Tan lliaowei@gatech.edu HONO measurements in ambient air during ANTCI (Antarctic troposphere chemistry investigation) 2003 exceed the pure gas phase model predictions by a factor of 1.92 $\pm$ 0.67, which implies snow emission of HONO. A 1D air-snowpack model of HONO was developed and constrained by observed chemistry and meteorology data. The 1D model includes pure gas phase chemical mechanisms, molecular diffusion and mechanical dispersion, windpumping in snow, gas phase to quasi-liquid layer phase HONO transfer and quasi-liquid layer (QLL) nitrate photolysis. Dominant snowpack HONO sources include QLL nitrite in equilibrium with firn air deep below the snow surface and snowpack nitrate photolysis. The high concentration of HONO in the firn air is subsequently transported above the snowpack by diffusion and windpumping. The primary model uncertainties include the pH and volume of the QLL and snowpack nitrite concentration profiles. Hydrothermal Heat Output from a Convecting, Crystallizing, Replenished Sub-Axial Magma Chamber Lei Liu Advisor: Robert Lowell lei@gatech.edu Models of high-temperature seafloor hydrothermal systems require that heat is transferred from an underlying magma body across a conducting boundary layer to the hydrothermal system. Because magma is typically at or near its liquidus, heat transfer will result in crystallization and cooling of the magma itself. In previous models of magma cooling and crystallization, solidification was assumed to occur from the top downwards. Consequently, the conducting thermal boundary layer between the hydrothermal system and the magma body rapidly thickened, resulting in a concomitant decay in the hydrothermal heat output and vent temperature. We present a simple time-dependent model of heat transfer between a turbulently convecting crystallizing thin basaltic magma lens and the overlying hydrothermal circulation. Two different crystallization scenarios are considered-crystals in suspension and crystals settling. In either case, we assume that large-scale convection within the magma chamber is homogenous and can be parameterized by its Rayleigh and Nusselt numbers. Also, the effect of crystallinity-dependent magmatic viscosity is considered. The simulation results show that without magma replenishment, the heat output and the hydrothermal temperature decay markedly on a decadal time scale, though decay occurs more slowly for the crystal settling model. The rapid decay of heat transfer from a crystallizing magma lens leads us to consider the effects of magma replenishment. To investigate the heat output from a growing magma chamber, we consider replenishment at both a constant rate at an exponentially declining rate, respectively. Simulation results show that magma heat flux approaches a steady state on decadal time scales, provided the magma volume doubles during a replenishment episode of approximately 20 years duration. Relating Remote Sensing Data Products to Soil Texture and Dust Emission Modeling Drex Waggoner Advisor: Irina Sokolik gtg403d@mail.gatech.edu The aeolian erosion of soils in arid and semi-arid regions is the main natural source of mineral dust and this process of wind driven erosion has proven difficult to model on a large scale. Satellite based remote sensing is an important tool as it gives the potential for access to 100% of the EarthÕs surface and provides surface parameters important to dust emission modeling. Dust emission has been successfully modeled with surface roughness, smooth roughness and clay fraction. The fundamental property observed by remote sensing is top of the atmosphere radiance, from which surface reflectance, albedo, vegetation indices and a variety of other parameters are derived. Correlation of wind-driven erosion to surface features such as albedo has been demonstrated in a number of papers, as has correlation to soil types. The MODIS sensor, one of the suite of sensors on the Terra and Aqua satellites of the NASA sponsored Earth Observing System satellites, provides 32 bands of data from 0.4 $\mu$ m to 12 $\mu$ m. This study will use MODIS albedo data in Bands 1-7 covering 0.4 $\mu$ m to 2.2 $\mu$ m, the Normalized Difference Vegetation Index product, and a surface roughness parameter based on the bidirectional reflectance coefficients product. This poster will look at the correlation of albedo, NDVI, and surface roughness to soil textures and a number of indices derived from soil texture relating to sand, silt and clay fractions. It will present highlights from selected band data, and relate the correlations presented back to previous works with the objective of illustrating relationships of soil components, or derived indices, to albedo band products. Examples of correlation to other RS parameters of NDVI and a surface roughness coefficient will be also presented. The goal of the presentation is to illustrate the relationship of surface characteristics observable through remote sensing to physical characteristics of the soil and to dust emission modeling. Temporal and Spatial Variations of Primary Organic Carbon Sources and SOA Impacts Bo Yan Advisors: Armistead G. Russell, and Mei Zheng byan@eas.gatech.edu Fine particulate matter (PM2.5) ambient samples were collected with Hi-Vol samplers in summer 2005 and winter 2006 in Atlanta, GA. Three sampling sites were utilized: a roadside highway site (directly beside the I-75/85 connector in the midtown Atlanta); a more typical urban site in the Georgia Tech campus (approximately 450 meters away from the highway) and a rural site in Yorkville, GA (impacted primarily by biogenic emissions and regional transport). At the urban and rural sites, 12-hr sampling and 24-hr sampling were performed, respectively. Solvent-extractable compounds in carbonaceous aerosols were identified and quantified by gas chromatograph/mass spectrometry (GC/MS), including alkanes, hopanes, steranes, polycyclic aromatic hydrocarbons (PAHs), fatty acids, and resin acids. A few important organic tracers of biogenic secondary organic aerosols (SOA) were also measured here such as 2-methyltetrol (2-methylthreitol and 2-methylerythritol), pinonic acid and pinic acid. Temporal and spatial variations of primary emission source contributions to organic carbon (OC) were apportioned using molecular marker-based chemical mass balance (CMB-MM) modeling. Contributions of biogenic SOA to carbonaceous aerosols were investigated, and the correlation with unidentified OC in CMB-MM modeling was examined. Preliminary results indicated that seasonal variations exist for 2-methyltetrol, a photochemical oxidation product of isoprene, and levoglucosan, a typical tracer of wood burning. In summer, the average ambient 2-methyltetrol and levoglucosan concentrations are 167.6 and 26.8 $\frac{\mathrm{ng}}{\mathrm{m}^{3}}$ at the rural site and 208.9 and 61.1 $\frac{\mathrm{ng}}{\mathrm{m}^{3}}$ at the urban site. 2-methyltetrol accounts for 2.6% and 2.0% of OC at the rural and urban sites, respectively, while levoglucosan only contributes 0.4% and 0.7% of OC. In winter, the average ambient 2-methyltetrol is 0.77 $\frac{\mathrm{ng}}{\mathrm{m}^{3}}$ at the rural site, but close to the detection limit in urban samples. However, levoglucosan concentrations were very high with an average value of 217.6 $\frac{\mathrm{ng}}{\mathrm{m}^{3}}$ at the rural site and 249.9 $\frac{\mathrm{ng}}{\mathrm{m}^{3}}$ at the urban site in winter. Much higher 2-methyltetrol concentrations in summer imply strong photochemical activities and higher isoprene emission, which lead to accumulated secondary organic aerosol (SOA) in PM2.5. Higher levoglucosan concentrations in winter indicate that wood burning is a seasonally significant source to OC. Both pinonic acid and pinic acid, condensable oxidation products of monoterpenes, were detected in most samples from summer and winter. However, no clear seasonal trend was found since high pinonic acid concentrations can be measured in some samples in winter. This might be due to the continued emission of terpenes by pine forests throughout the year. The study of tropospheric ozone column enhancements over North America using a regional model and satellite data Qing Yang Advisor: Derek Cunnold gtg422j@mail.gatech.edu We examine the variability of tropospheric ozone columns (TCOs) using a 3-D Regional chEmical trAnsport Model (REAM), the Aura derived tropospheric ozone residuals (TORs) and the Tropospheric Emission Spectrometer (TES) measurements for spring and summer 2005. PV/Geopotential height mapping and 2-D interpolation techniques have been applied to Microwave Limb Sounder (MLS) profiles to derive the Ozone Monitoring Instrument (OMI)/MLS tropospheric ozone columns. Comparisons of monthly mean distributions show good agreements between OMI/MLS tropospheric ozone column, REAM column, and TES column. Two six-day periods in March have been selected to study the periodic TCO enhancements in two regions, around the Baja peninsula (Mexico) and on the west coast of California. Thirteen day back trajectories and daily maps of carbon monoxide (CO) and ozone from GEOS-CHEM and OMI/MLS have been integrated to investigate the influence of cross-Pacific transport. The high ozone concentration in mid- and lower- troposphere over the west coast of California is concluded to have been under the influence of cross-Pacific transport. Meteorological fields indicate that the high ozone concentration in the upper troposphere over the west coast of California and the high TCOs over the Baja peninsula are associated with a stratospheric intrusion through a deep Rossby wave breaking event. The correlation between REAM TCOs and the surface ozone from Environmental Protection Agency ground network measurements suggest that the TCO enhancement over the west coast is associated with an increase of surface ozone. The correlations with geopotential height, wind fields, and tropopause height suggest that TCO enhancement is best characterized in spring time by geopotential height decreases on the 500 mb surface.