B43D-01 13:40h
The NH$_{4}$$^{-}$-NO$_{3}$$^{-}$-Cl$^{-}$-SO$_{4}$$^{2-}$-H$_{2}$O Aerosol System and its Gas Phase Precursors at a Rural Site in the Amazon Basin: How Relevant are Mineral Cations and Soluble Organic Acids?
We performed real-time measurements of ammonia (NH$_{3}$), nitric acid (HNO$_{3}$), hydrochloric acid (HCl), sulfur dioxide (SO$_{2}$) and the water-soluble inorganic aerosol species, ammonium (NH$_{4}$$^{+}$), nitrate (NO$_{3}$$^{-}$), chloride (Cl$^{-}$), and sulfate (SO$_{4}$$^{2-}$) at a pasture site in the Amazon Basin (Rondonia, Brazil). The measurements were made during the closing of the dry season (biomass burning), the transition period, and the onset of the wet season (clean conditions) (12 Sep. to 14 Nov. 2002, LBA-SMOCC*), using a wet-annular denuder (WAD) in combination with a Steam-Jet Aerosol Collector (SJAC). Real-time data were combined with measurements of mineral cations (K$^{+}$ , Ca$^{2+}$ , Mg$^{2+}$) and low-molecular weight (LMW) polar organic acids on 12-, 24- and 48-hours integrated filter samples. The contribution of inorganic species to the fine particulate mass (D$_{p}$ $<$ 2.5 um)was frequently below 20 % by mass, indicating the preponderance of organic matter. The high abundance of NH$_{3}$ at the sampling site substantially influenced gas/aerosol partitioning processes, being responsible for complete acid neutralization through the aerosol phase forming aerosol NH$_{4}$$^{+}$. Balances of aerosol fine mode inorganic ionic charges indicated the role of dissociated low-molecular weight (LMW) polar organic acids, which were apparently neutralized by excess NH$_{3}$. The measured concentration products of NH$_{3}$ x HNO$_{3}$ and NH$_{3}$ x HCl persistently remained below the theoretical equilibrium dissociation constants of the NH$_{3}$/HNO$_{3}$/NH$_{4}$NO$_{3}$ and NH$_{3}$/HCl/NH$_{4}$Cl systems during daytime (RH $<$ 90 %). The application of thermodynamic equilibrium models (EQMs), namely EQSAM, ISORROPIA, GEFMN and SCAPE2 indicated that balancing of aerosol NO$_{3}$$^{-}$, Cl$^{-}$ and SO$_{4}$$^{2-}$ preferentially proceeded via mineral cations (particularly pyrogenic K$^{+}$) during daytime. At nighttime (RH $<$ 90 %) NH$_{4}$NO$_{3}$ and NH$_{4}$Cl were predicted to be formed in the aqueous aerosol phase. Cl$^{-}$ was largely driven out of the aerosol phase by reaction of KCl with HNO$_{3}$ and H$_{2}$SO$_{4}$. As shown by an updated version of EQSAM, which incorporates mineral aerosol species and lumped LMW polar organic acids, daytime aerosol NH$_{4}$$^{+}$ was mainly balanced by organic compounds. *Large Scale Biosphere Atmosphere Experiment in Amazonia Smoke Aerosols, Clouds, Rainfall and Climate: Aerosols from Biomass Burning Perturb Global and Regional Climate).
B43D-02 13:55h
Strong Correlation Between Isoprene Emission and Gross Photosynthetic Capacity During Leaf Phenology of the Tropical Tree Species Hymenaea courbaril
Composition and amount of volatile organic compound (VOC) emission of the tropical tree species Hymenaea courbaril was studied under different developmental stages at a remote Amazonian rainforest site. The different stages covered young leaves (= grown full in size, but not fully turgescent) in the end of the dry season, mature leaves in the end of dry and wet season, and senescent leaves in the end of dry season. Though the diel isoprene emissions pattern could adequately be modelled by a current isoprene algorithm, the basal emission capacity of isoprene changed considerably over the course of leaf development. The inadequacy of using one single standard emission factor to represent the VOC emission capacity of tropical vegetation for an entire seasonal cycle is obvious. A strong linear correlation between the isoprene emission capacity and the gross photosynthetic capacity (GPmax) covering all developmental stages and seasons was observed. Hence, basic leaf photosynthetic activity may offer a valuable basis to model the seasonal variation of isoprene emission, especially in tropical regions where the environmental conditions vary less than in temperate regions. Of special interest was the light dependent monoterpene emission found exclusively in the period between bud break and leave maturity. The finding of this temporary emergence of monoterpene emission may be of general interest in understanding both the ecological functions of isoprenoid production and the regulatory processes involved.
B43D-03 14:10h
Radiation Budgets in Support of LBA Hydrological Modeling
To improve the understanding of the hydrological cycle in the Amazon region, information on radiative fluxes is needed for improving parameterization of surface processes and for modeling and predicting the surface hydrological and energy budgets. This on time scales from diurnal to interannual, and on spatial scales as required by climate, meso-scale, and local scale models. In response to such needs, the following steps were taken: 1. About twenty years of historical satellite observations from PATHFINDER data were used to infer radiative fluxes at 2.5-degree resolution on global scale. The PATHFINDER data sets merge observations from both geostationary and polar orbiting satellites. 2. About ten years of GOES and METEOSAT observations sampled at 30 km were used to infer radiative fluxes at 0.5 degree resolution over North and South America, using optimal interpolation techniques to merge the observations. 3. Three years of GOES pixel level data spanning the intensive observational period of LBA were used to obtain radiative fluxes for the Amazon Basin at a 1/8-degree resolution. New methodologies were developed for implementing the inference schemes at this scale and for incorporating updated information on aerosols. All of the above products provide information on the total shortwave radiative fluxes, Photosynthetically Active Radiation (PAR), Near-Infra-Red (NIR) radiation (upwelling and downwelling), at both boundaries of the atmosphere. The time scale for the first two products is 3 hourly instantaneous and hourly, daily and monthly averaged; the high spatial resolution product is available at hourly time scale. In the presentation, described will be methodologies used to infer such fluxes; available products; and their evaluation against independent satellite estimates as well as against ground observations. Examples will be given how this information is being used to address scientific issues.
B43D-04 14:25h
Measuring Vegetation Aerodynamic Roughness Over the Amazon Basin
The aerodynamic roughness length (Z0) is an important parameter to determine the vertical gradients of mean wind speed and the conditions for momentum transfer over a vegetated or bare rough surface. Over vegetated surfaces, the aerodynamic roughness length has a simple one-to-one relationship with the rms height of the vegetation at the top of the canopy. Once this roughness length is determined for a surface, it does not change with wind speed, stability or stress. During the LBA experiment the Regional Atmospheric Modeling System (RAMS) with flexible horizontal and vertical resolution will be used in conjunction with other models to simulate the atmospheric circulation and trace gas concentration and transport at various scales. This model is suitable to determine the effect of surface roughness parameter at trace gas transport both at local level for LBA study areas and on at the regional level for the entire Amazon basin. In this paper, we present the estimation of this parameter from two sources: 1) From a sample SRTM (Shuttle Radar Topography Mission) data over one of the LBA study areas. The cross correlation between two interferometric SRTM images will be used to estimate the rms height of the vegetation at 90 m resolution and relate that to aerodynamic roughness. This methodology will be applied to the entire SRTM data (when it becomes available) to estimate the roughness length over the basin. 2) Various statistical moments of the JERS-1 image mosaic in fusion with other regional data sets will be used in a semi-empirical model to estimate the vegetation roughness length over the entire basin at 1 km resolution. Both parameters will be integrated into the RAMS model to demonstrate the effect of spatially explicit roughness length on trace gas transport simulations and to test the impact of errors associated with the estimation process.
http://www-radar.jpl.nasa.gov/carbon
B43D-05 14:40h
Sources of Variation of Albedo of Amazonian Tropical Vegetation
We investigate the main sources of variation of surface albedo of Amazonian tropical vegetation, at both the hourly and seasonal time scales. In particular, we investigate the role of canopy wetness and cloud cover, in addition to the traditional sources of variation (land cover and zenithal angle), as well as the interactions among the sources of variation. Field data used in this analysis were collected at eight micrometeorological sites during ABRACOS (Anglo Brazilian Amazonian Climate Observation Study) and LBA projects (Large-Scale Biosphere-Atmosphere Experiment in Amazonia). At the hourly-scale, land cover variation (forest x pasture), atmospheric transmissivity, canopy wetness (wet x dry) and zenithal angle explains 43.99, 6.77, 3.42 and 0.06 percent of the variance observed in the data, respectively. We also find out that, when calculating the land surface albedo, neither the role of atmospheric transmissivity nor the role of canopy wetness is well represented in land surface models today. Future work will incorporate the results of this study in land surface models to improve the accuracy of land surface albedo simulations.
B43D-06 14:55h
Parcel Model Simulations of Aerosol-Cloud Microphysics Interactions over the Amazon
Over tropical regions, such as the Amazon, biomass burning is a major source of aerosols that serve as cloud condensation nuclei (CCN). Changes in the cloud microphysics in association with smoke aerosols were first assessed as a possibility via modeling studies or satellite retrievals, and later verified by means of in-situ measurements. In particular, changes in the CCN field influence precipitation development in Amazon clouds, with significant suppression of warm rain processes, in agreement with previous satellite and radar studies. Nevertheless, there are still many questions regarding the formation of precipitation in the Amazon clouds that cannot be answered from the in-situ data alone: What is the role of the giant cloud condensation nuclei (GCCN) found in the different environments? How different updraft velocities influence precipitation development? How changes in the environmental humidity may influence the cloud life cycle? In this paper, we use a parcel model to simulate the development of warm rain in different aerosol regimes, from very clean to extremely polluted, as well as to explore sensitivities regarding the presence of giant CCN, the strength of the updraft velocities, and the availability of moisture at the sub-cloud layer. We found that the presence of GCCN and the control exerted by the low-level moisture over the warm rain height appear to be of comparable importance to CCN concentrationimportant to the change in rain characteristics in the transition from the dry to wet seasons over the Amazon.
B43D-07 15:10h
What Controls Evapotranspiration in the Amazon Basin
Evapotranspiration (ET) is an important meteorological variable and a key element in assessing the water cycle over a region, though not yet well known over the Amazon river basin. Previous studies have mainly used radiation observations to estimate ET, which generally assumes that there is no soil water limitation for plant transpiration. As part of the LBA experiment, several towers were equipped to perform eddy-covariance measurements of carbon and energy fluxes. We use these different measurements of water fluxes to compare ET across sites over the Amazon and understand latitudinal variations in ET. Results are also compared to radiation-estimated ET to test the soil water availability assumption. Finally, measured ET are compared to simulated climate models output to understand how well and where the models are able to reproduce the measured ET and why.
B43D-08 15:25h
Hydroclimate Scenarios of Amazon Deforestation
The regional and global implications of the replacement of natural forest by degraded vegetation in the Amazon on the regional and global hydroclimate have yet to be fully understood and quantified. In this study, regional and global climate models are used in conjunction with scenarios of land-cover change resulting from socio-economic and ecological analyses for the coming decades, to estimate potential hydroclimate changes in and outside of the Amazon basin. Four ensembles of six realizations, twelve years each, are produced with the NASA-GISS GCM II: (1) a "control" ensemble that simulates the land cover in the Amazon basin before massive deforestation started; (2) a "current land cover" ensemble; (3) a "scenario for 2030" ensemble; and (4) a "scenario for 2050" ensemble. In addition, The Regional Atmospheric Modeling System (RAMS) is used at a high resolution (20 km grid size) over the Amazon Basin and using the same four land-cover scenarios but with the NCEP reanalysis for three different years (wet, dry, and typical) forcing its lateral boundaries. The combination of these different simulations reveals significant impact of deforestation on the regional and global hydroclimate.