FORM A: GACP ACCOMPLISHMENT REPORT FOR 1st YEAR (9/l/98-8/31/99)
Name: Peter V. Hobbs
Institution: Cloud and Aerosol Research Group (CARG)
Department of Atmospheric Sciences
University of Washington
Seattle, WA 98195
TITLE: "Utilization of the University of Washington's Airborne Measurements for Studies of the Radiative Effects of Aerosols on the Earth's Climate"
ORIGINAL ABSTRACT OF PROPOSAL:
Over the past six years the Cloud and Aerosol Research Group (CARG) at the University of Washington (UW) has participated in seven cooperative field research projects (ASTEX, MAST, ARMCAS, SCAR-A, -B, and -C, and TARFOX). In these projects the UW research aircraft was used to obtain extensive in situ and remote sensing measurements on aerosols and clouds under conditions ranging from pristine (the Arctic), through light and moderately polluted (the US West and East Coast), to highly polluted by smoke (SCAR-B and -C). Many of the flights were carried out beneath the NASA ER-2 aircraft (which carried remote sensing instrument, including the MODIS Airborne simulator, AVIRIS and LASE), beneath a variety of satellites, and above ground-based remote-sensing instruments (e.g., sun photometers, Raman lidar). These combined data sets provide a unique resource for evaluating and improving the utility of current and future remote sensing techniques for quantifying atmospheric aerosol and their effects on the radiative balance of the earth. This will be one of the main goals of the work proposed here.
The extensive data collected aboard the UW aircraft in the field research projects listed above are also ideally suited for providing many of the parameters needed as inputs to numerical models used to quantify aerosol radiative forcing on regional and global scale. These parameters include emission factors of aerosols from various sources, aerosol size distributions and compositions, aerosol optical properties, humidification factors for various aerosols, and the evolution of these parameters as aerosols age. Data is also available on the effects of various aerosols on cloud structures and radiative properties. The second main goal of this proposal will be to fully utilize these data sets to quantify the effects of various types of aerosols on direct and indirect radiative forcing.
The CARG, with its new Convair-580 research aircraft, will continue to participate in field projects designed to improve understanding of radiative forcing by aerosols from a variety of sources. Although funds to participate in these field projects are not requested in this proposal, analysis of the data acquired from them should help fulfill the main goals of the proposal.
GOALS AND OBJECTIVES: To reduce current uncertainties in estimates of aerosol radiative forcing of the Earth's climate.
APPROACH: To use measurements obtained aboard the University of Washington's research aircraft in a variety of airsheds to derive aerosol optical properties needed to calculate aerosol radiative forcing, and to improve the derivation of aerosol properties from remote sensing measurements.
TASKS COMPLETED: Analysis of airborne data on aerosols collected in smoke-dominated air masses in Brazil (SCAR-B) and on the United States East Coast (TARFOX). Publications of 22 papers describing the airborne measurements, their comparisons with remote sensing measurements, and their application to deriving values for regional and global aerosol radiative forcing.
FUTURE PLANS:
1) Several manuscripts are being prepared for a second Special Issue of the Journal of Geophysical Research devoted to TARFOX (see Form B for details).
2) To compare our derivations of aerosol optical depths obtained from in situ measurements aboard the UW-CARG research aircraft in TARFOX with those derived from simultaneous satellite measurements.
3) To use the in situ measurements obtained aboard the UW-CARG research aircraft in TARFOX to derive aerosol phase functions and asymmetry factors.
4) To analyze the nature of the aerosols measured aboard the UW-CAR research aircraft in the Arctic in FIRE-ACE.
5) To analyze the radiative effects of aerosols in some well-documented cases in FIRE-ACE in which an absorbing aerosol layer overlay a stratus cloud layer.
6) To analyze a new set of extensive aerosol data, and aerosol-cloud interaction data, that we expect to collect in Southern Africa as part of SAFARI-2000.
RESULTS:
A very brief summary of some of our main scientific results are listed below. (See Section B for more details.)
1) For smoke-laden air over the tropical forests of Brazil, the change in the daily average net shortwave flux per unit optical depth (at a wavelength of 550 nm) is -20±7 W m-2, and over cerrado it is -8±9 W m-2. Over a desert it is +25±12 W m-2 per unit optical depth.
2) Total light scattering for smoke particles from biomass burning in Brazil is, on average, 15% less than for biomass smoke particles in North America. The average single-scattering albedo of smoke particles in Brazil is 0.05 to 0.1 less than those in North America.
3) The average value for the mass absorption efficiencies of black carbon in smoke particles in Brazil is 12.1±4.0 m2 g-1.
4) As smoke particles in Brazil age, their masses increase by 20-40%, which has a large effect on their optical properties.
5) During the aging of smoke particles in Brazil over 1-4 days, the physical and optical properties of the smoke aerosol are well correlated.
6) After biomass smoke particles in Brazil have aged for ~1 hr, Mie theory can be used to estimate their optical properties.
7) The average value of the humidification factor for biomass-burning aerosols in Brazil is 1.26.
8) The globally-averaged direct radiative forcing by biomass-burning aerosols is ~0.25 W m-2.
9) Increases in the concentration of accumulation-mode particles from biomass burning above about 3000-4000 cm-3 do not change the concentration of droplets in clouds over Brazil.
10) The average value of the humidification factor for aerosol off the mid-Atlantic Coast of the USA, measured in TARFOX, was 2.30±0.24 in westerly airflows, and 1.81±O.37 in northerly and southerly airflows.
FORM B: GACP SIGNIFICANT HIGHLIGHTS FOR 1ST YEAR (9/l/98-8/31/99)
Name:
Peter V. Hobbs
Institution: Cloud and Aerosol Research Group (CARG)
Department of Atmospheric Sciences
University of Washington
Seattle, WA 98195
SIGNIFICANT HIGHLIGHT:
(a) SCAR-B Special Issue
During the period covered by this report a Special Issue of the Journal of Geophysical Research devoted to SCAR-B was published. This issue contained ten papers co-authored by members of the UW Cloud and Aerosol Research Group (CARG). Summaries are given below of some of the results that are of particular importance for the NASA Aerosol Program. (CARG co-authors and contractors are underlined.)
(i) "Radiative Characteristics of Regional Haze Dominated by Smoke from Biomass Burning in Brazil: Closure Tests and Direct Radiative Forcing" by J. L. Ross, P. V. Hobbs and B. Holben (J. Geophys. Res., 103, 31,925-31,941, 1998).
In this paper data collected during several flights of the UW's aircraft over ground-based sun photometers in Brazil are used for aerosol radiative vertical column and local radiative closure tests. Optical depths (up to 2.5) at mid-visible wavelengths measured directly by the sun photometers and derived from the airborne measurements agreed, on average, to within -20%. Local aerosol closure tests, using airborne in situ measurements of particle size distributions as input to an aerosol model for the (smoke-dominated) region, yielded aerosol masses, absorption, and scattering within ~25% of measured values. The same model was used to derive regional values of direct aerosol radiation forcing produced by smoke aerosol in the cerrado and primary forest areas of Brazil. The results show that the net direct radiative forcing can be either cooling or heating depending on the underlying surface albedo.; Over a typical tropical forest the change in the daily average net shortwave flux per unit optical depth (at 550 nm) is -20±7 W m-2; over the cerrado it is -8±9 W m-2; over a dark surface, such as the ocean, it is -26±6 W m-2; and over a reflecting surface, such as a desert, it is +25±12 W m-2.
(ii) "Physical and Optical Properties of Young Smoke from Individual Biomass Fires in Brazil" by J. S. Reid and P. V. Hobbs (J. Geophys. Res., 103, 32,013-32,030, 1998)
Measurements obtained from the UW's research aircraft on 19 biomass fires in Brazil are used to derive the physical and optical properties of the smoke. These properties are related to fuel type, fire intensity, combustion efficiency, and particle composition. The measured particle radiative properties correlate well with the particle sizes and composition, and relationship between these parameters are described fairly well by Mie theory. The optical properties of smoke from individual biomass fires in Brazil differ significantly from those of smoke from biomass burning in North America. In particular, total light scattering for smoke particles in Brazil is, on average, 15% less than for smoke particles in North America. Also, the average value of the single-scattering albedo of smoke particles in Brazil is 0.05 to 0.1 less than those in North America.
(iii) "Comparison of Techniques for Measuring Shortwave Absorption and Black Carbon Content of Aerosols from biomass Burning in Brazil" by J. S. Reid, P. V. Hobbs, C. Liousse, J. V. Martins, R. E. Weiss, and T. E. Eck (J. Geophys. Res., 103, 32,031-32,040, 1998).
With sufficient sample size, the values of absorption coefficient of aerosols from biomass burning in Brazil determined from several optical methods converged to within 20% of each other. This led to a systematic difference of ±0.02 in the values of the single-scattering albedo derived from the different techniques.
(iv) "Effects of Black Carbon Content, Particle Size, and Mixing on Light Absorption by Aerosols from Biomass Burnhig in Brazil" by J. V. Martins, P. Artaxo, C. Liousse, J. S. Reid, P. V. Hobbs, and Y. J. Kaufman (J. Geophys. Res., 103, 32,043-32,050, 1998).
Black carbon mass absorption efficiencies of smoke particles measured for various types of biomass fires in Brazil ranged from 1.2-19.3 m2 g-1, with an average value of 12.1±4.0 m2 g-1. Mie theory was used to model the optical properties of the particles assuming both internal and external mixtures. The modeled results for layered spheres and packed clusters explain black carbon mass absorption coefficients up to 25 m2 g-1, but the measurements show even higher values.
(v) "Sphericity and Morphology or Smoke Particles from Biomass Burning in Brazil" by J. V. Martins, P. V. Hobbs, R, E. Weiss and P. Artaxo (J. Geophys. Res., 103, 32,051-32,047, 1998).
Measurements aboard the UW's research aircraft in Brazil showed that the maximum value of the nonsphericity of smoke particles was 13%, with the degree of nonsphericity being related to combustion efficiency, the mass absorption efficiency, and the fraction of black carbon to total particle mass. After biomass smoke particles have aged for about 1 hr, Mie theory is reasonably good for estimating their optical properties.
(vi) "Physical, Chemical and Optical Properties of Regional Hazes Dominated by Smoke in Brazil" by J. S. Reid, P. V. Hobbs, R. J. Ferek, D. R. Blake, J. V. Martins, M. R. Dunlap and C. Liousse (J. Geophys. Res., 103, 32,059-32,080).
The properties of aged particles (and gases), in regional hazes dominated by smoke from biomass fires in Brazil, are significantly different from those of young smoke (<4 min old). As the smoke particles aged, their masses Increased by -20-40% due to coagulation and gas-to-particle conversion. This increase in Mass had a large effect on the optical properties of the particles. Over a 2-4 day period, the fire particle mass-scattering efficiency and single-scattering albedo increased by 1 m2 g-1 and -0.06, respectively. Conversely, the Angstrom coefficient, backscatter ratio, and mass absorption efficiency decreased with age.
(vii) "Humidification Factors of Aerosols from Biomass Burning in Brazil" by R. A. Kotchenruther and P. V. Hobbs (J. Geophys. Res., 103, 32,081-32,089, 1998)
At a wavelength of 550 nm, the ratio of the light-scattering coefficient at a relative humidity (RH) of 80% to that at 30% for aerosol from biomass burning in Brazil ranged from 1.01 to 1.51, with an average value of 1.16. The aerosol backscatter ratio decreased by 10-20% as the RH was increased from 30 to 80%. Application of these humidity factors yields an estimate for the globally-averaged direct radiative forcing by biomass-burning aerosol of -0.25 W m-2.
(viii) "Emission Factors of Hydrocarbons, Halocarbons, Trace Gases and Particles from Biomass Burning in Brazil" by R. J. Ferek, J. S. Reid, P. V. Hobbs, D.B.Blake and C. Liousse (J. Geophys. Res., 103, 32,107-32, 118, 1998).
Provides emission factors from biomass fires in Brazil for 43 gaseous and aerosol species, including aerosol mass and particulate carbon. Particle emission factors from biomass fires in Brazil are 20-40% lower than those from North American boreal forest fires.
(b) Additional SCAR-B Publications
The following papers, describing SCAR-B studies, were prepared following the SCAR-B Special Issue.
(i) "Relationships Between Cloud Droplet Effective Radius, Liquid Water Content, and Droplet Concentration for Warm Clouds in Brazil Embedded in Biomass Smoke" by J. S. Reid, P. V. Hobbs, A. L. Rangno and D. A. Hegg (J. Geophys. Res., 104, 6145-6153, 1999).
In SCAR-B the UW-CARG obtained airborne measurements of the structures of over 1000 non-precipitating clouds embedded in continental-scale, smoky haze in Brazil. For the entire data set, the best parameterization of the cloud droplet effective radius (reff) is as a function of cloud LWC to droplet concentration (essentially the volume mean radius, rv). Comparisons of SCAR-B data with those from the US East Coast and clean oceanic areas show that the reff-rv relationship is similar in all three cases. Beyond an ambient concentration of accumulation-mode particles of 3000-4000 cm-3, cloud drop number concentrations for cumulus clouds in Brazil did not change; in this case, reff correlates well with LWC alone. Our measured values of reff were 3-8 m m, compared to 9-14 um inferred from satellite measurements of cloud reflectivity at 3.7 um.
(ii) "Use of the Angstrom Exponent to Estimate the Variability of Optical and Physical Properties of Aging Smoke Particles in Brazil" by J. S. Reid, T. F. Eck, S. A. Christopher, P. V. Hobbs, and B. Holben (J. Geophys. Res., submitted).
The UW-CARG airborne measurements in SCAR-B show that during the aging of smoke-dominated aerosol over 1-4 days the physical and optical properties of the aerosol are well correlated. Therefore, if one optical or physical property is determined, others can be derived. For example, the Angstrom exponent determined from sunphotometers for the wavelength intervals 339-437 nm and 437-669 nm are well correlated with particle size, single-scattering albedo, and the backscatter ratio (r2 > 0.8). Therefore, when almucantar sky radiance data are not available, and for remote sensing applications, uncertainties in some of the derived values of the properties of smoke can be reduced by using the empirical relationships given in this paper.
(iii) "Estimation of Surface and Top-of-Atmosphere Shortwave Irradiance in Biomass Burning Regions During SCAR-B" by S. A. Christopher, X. Li, R. M. Welch, J. S. Reid, P. V. Hobbs, T. F. Eck and B. Holben (J. Appl. Meteor. - submitted).
Using in situ measurements of aerosol optical properties from the UW-CARG research aircraft and ground-based measurements of AOT obtained in SCAR-B, a four-stream broadband radiative transfer model was used to estimate the downward surface (DSWI) and top-of-atmosphere (TOA) shortwave irradiance in regions of Brazil dominated by smoke from biomass burning. The calculated DSWI values are compared with broadband pyranometer measurements at the surface. The results show that for two days when near-coincident measurements of the single-scattering albedo (w0) and AOT were available, the rms errors between the measured and calculated DSWI are within 30 W m-2. However, for five days, when assumptions about w0 had to be made, the difference is as large as 100 W m-2! At the TOA, the shortwave aerosol radiative forcing (SWARF) per unit AOD ranges from -20 to -80 W m-2 over four major ecosystems in Brazil. The value of w0 must be known to within 0.05, and the AOT (at 550 nm) to within 0.1, to estimate DSWI to within 20 W m-2. If global retrievals of DSWI and SWARF are to be obtained from satellites in the presence of biomass-burning aerosols, a concerted effort will be needed to develop methodologies for routinely determining w0 and AOT.
(c) TARFOX 1st Special Issue
During the period covered by this Annual Report, a Special Issue of the Journal of Geophysical Research devoted to TARFOX results was published. This issue contains six papers co-authored by CARG researchers. Summaries of the main results presented in these papers are given below.
(i) "Aerosol Properties and Radiative Effects in the United States East Coast Haze Plume: An Overview of the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX)" by P. B. Russell, P. V. Hobbs and L. S. Stowe (J. Geophys. Res., 104, 2213-2222, 1999).
The TARFOX field study was conducted July 10-31, 1996. It included coordinated measurements from four satellites, four aircraft (including the UW-CARG research aircraft), land sites and ships. A variety of aerosol conditions were sampled, ranging from relatively clean to moderately polluted (AOD=0.5 at 550 nm). Results from TARFOX showed the unexpected importance of carbonaceous compounds (vis-a-vis sulfates) and water condensed on aerosol in determining AOD and direct aerosol radiative forcing on the US East Coast.
(ii) "An Overview of the University of Washington Airborne Measurements and Results from the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX)" by P. V. Hobbs (J. Geophys. Res., 104, 2233-2238, 1999).
In TARFOX, the UW-CARG research aircraft was used to obtain comprehensive in situ and remote sensing measurements of the physical and chemical nature of the aerosol and its effects on direct radiative forcing. This paper describes the airborne instrumentation used, the sampling strategy, the times and locations of the 18 research flights, and a summary of the major results revealed by this unique data set.
(iii) "Humidification Factors for Atmospheric Aerosols off the Mid-Atlantic Coast of the United States" by R. A. Kotchenruther, P. V. Hobbs and D. A. Hegg (J. Geophys. Res., 104, 2239-2251, 1999)
At a wavelength of 550 nm the mean value of the ratio of the total light scattering at a relative humidity (RH) of 80% to that at 30% in westerly airflows in TARFOX was 2.30±0.24; in northerly and southerly airflows was 1.81±0.37. The ratio decreased with increasing altitude and with increasing mass ratio of aerosol carbon to sulfate, and it increased with increasing wavelength. The aerosol hemispherical backscatter ratio decreased by 30 to 40% as the RH increased from 30 to 80%. Direct radiative forcing by aerosols on the US East Coast is strongly dependent on RH. At a RH of 8O%, direct radiative forcing by the aerosol is about twice that of the dry aerosol.
(iv) "Aerosol Optical Depth Retrieval Using ATSR-2 and AVHRR Data During TARFOX" by J. P. Veefkind, G. de Leeuw, P. D. Durkee, P. B. Russell, P. V. Hobbs and J. M. Livingston (J. Geophys. Res., 104, 2253-2260, 1999).
Aerosol optical properties retrieved from satellite measurements are compared to UW-CARG airborne sunphotometer measurements obtained in TARFOX. The AOD derived from ATSR-2 satellite data agree within 0.03 with collocated sunphotometer measurements. Good correlation is found between the AOD for AVHRR channel 1 (640 nm) and sunphotometer values, but the satellite values are 0.05-0.15 lower.
(v) "Retrieval of Aerosol Optical Thickness and Size Distribution Over Ocean from the MODIS Airborne Simulator During TARFOX" by D. Tanre, L. A. Remer, Y. J. Kaufman, S. Mattoo, P. V. Hobbs, J. M. Livingston, P. B. Russell, and A. Smirnov (J. Geophys. Res., 104, 2261-2278).
The algorithm to be used for retrieving AOD from MODIS was tested by comparing results with sunphotometer measurements obtained aboard the UW-CARG research aircraft in TARFOX. The AOD (at 550 nm), as well as its spectral dependence, from these two data sets compared well.
(vi) "Aerosol-Induced Radiative Flux Changes off the United States mid-Atlantic Coast: Comparison of Values Calculated from Sunphotometer and In Situ Data with those Measured by Pyranometer" by P. B. Russell, J. M. Livingston, P. Hignett, S. Kinne, J. Wong, A. Chien, R. Bergstrom, P. Durkee and P. V. Hobbs (J. Geophys. Res., 104, 2289-2307,1999).
Aerosol and surface properties measured in TARFOX are used to compute shortwave radiative flux changes for various aerosol situations, with mid-visible AOD ranging from 0.06 to 0.55. Calculations using several approaches yield downward and upward flux changes that agree with measurements. The agreement is best when the aerosols are modeled as moderately absorbing (mid-visible single-scattering albedos from 0.89 to.93). The calculated values for instantaneous daytime upwelling flux changes are 14 to 48 W m-2 for mid-visible AOD between 0.2 and 0.55. These value are 10 to 100 times the globally-average direct forcing expected for the global-average sulfate AOD of 0.04. The reasons for the larger flux changes in TARFOX are the large AOD and the focus on cloud-free daytime conditions over the dark ocean surface.
(d) TARFOX 2nd Special Issue
The following papers have been submitted to Journal of Geophysical Research for the 2nd TARFOX Special Issue.
(i) "Properties of Aerosol Aloft Relevant to Direct Radiative Forcing off the Mid-Atlantic Coast of the United States" by W. S. Hartley, P. V. Hobbs, J. L. Ross, P. B. Russell, and J. M. Livingston. J. Geophys. Res., TARFOX 2nd Special Issue (submitted).
Comparisons are made of AOD derived from in situ and sunphotometer measurements obtained aboard the UW-CARG aircraft in TARFOX. At 450 nm the sunphotometer measurements were greater than the in situ by, on average, 12±5%. Single-scattering albedos and Angstrom coefficients are also compared.
(ii) "Comparison of Aerosol Optical Properties and Water Vapor Among Ground and Airborne Lidars and Sun Photometers During TARFOX" by R. Ferrare et al. (P. V. Hobbs is a co-author), I. Geophys. Res., TARFOX 2nd Special Issue (submitted).
AOT and precipitable water vapor (PWV) measurements derived from ground and airborne lidars and sunphotometers in TARFOX are compared. The lidar measurements of AOT are within 10-15% of the sunphotometer measurements. PWV derived by LASE are within 8-15% of sunphotometer values.
(iii) "Comparison of LASE, Aircraft and Satellite Measurements of Aerosol Optical Properties and Water Vapor During TARFOX" by R. Ferrare et al.. (P. V. Hobbs is a co-author), J. Geophys. Res., TARFOX 2nd Special Issue (submitted).
LASE profiles of aerosol extinction and AOD in TARFOX are generally within 20% of those derived from airborne and in situ measurements. The LASE profiles of AOD are 10% higher than those derived from the AOD are 10% higher than those derived from the airborne sunphotometer, which in turn are about 10% higher than those derived from the airborne in situ measurements. LASE measurements of AOD generally agree with those derived from the ATSR-2 aboard the ERS-2 satellite and from the MODIS airborne simulator on the ER-2.
(iv) "Retrieving the Vertical Structure of the Effective Aerosol Complex Index of Refraction from a Combination of Aerosol In Situ and Remote Sensing Measurements During TARFOX (Part 1)" by J. Redemann et al. (P. V. Hobbs is a co-author), J. Geophys. Res., TARFOX 2nd Special Issue (submitted).
Aerosol backscatter measurements from the LASE and in situ airborne measurements of aerosol size spectra from the UW-CARG aircraft are used to derive vertical profiles of the effective aerosol complex index of refraction at 815 nm. Absolute errors are less than 0.04 for the real part and 0.042 for the imaginary part in the case of a 30% error in the lidar-derived aerosol backscatter. In TARFOX, values of the derived complex aerosol refractive index ranged from 1.34 to 1.45 for the real part and 0.001 to 0.008 for the imaginary part.
(v) "Case Studies of the Vertical Structure of the Shortwave Direct Aerosol Radiative Forcing During TARFOX" by J. Redemann, B. P. Turco, K.-N. Liou, R. W. Bergstrom, P. V. Hobbs, E. V. Browell and P. B. Russell, J. Geophys. Res., TARFOX 2nd Special Issue (submitted).
This paper presents the first estimates of the vertical structure of aerosol radiative forcing based on two TARFOX case studies. Aerosol properties used in the Fu-Liou radiative transfer model were derived from estimates of the vertically-resolved complex aerosol index of refraction and profiles of in situ particle size spectra from UW-CARG research aircraft. Aerosol single-scattering albedos at 450 nm thus determined range from 0.9 to 0.985, and the asymmetry factor from 0.6 to 0.8. The instantaneous shortwave aerosol radiative forcings are ~36 W m-2 at the TOA and ~56 W m-2 at the surface.
FORM C: FUTURE PLANS (FOR 2nd YEAR)
Name: Peter V. Hobbs
Institution: Cloud and Aerosol Research Group (CARG)
Department of Atmospheric Sciences
University of Washington
Seattle, WA 98195
FUTURE PLANS:
1) Several manuscripts are being prepared for a second Special Issue of the Journal of Geophysical Research devoted to TARFOX (see Form B for details).
2) To compare our derivations of aerosol optical depths obtained from in situ measurements aboard the UW-CARG research aircraft in TARFOX with those derived from simultaneous satellite measurements.
3) To use the in situ measurements obtained aboard the UW-CARG research aircraft in TARFOX to derive aerosol phase functions and asymmetry factors.
4) To analyze the nature of the aerosols measured aboard the UW-CARG research aircraft in the Arctic in FIRE-ACE.
5) To analyze the radiative effects of aerosols in some well-documented cases in FIRE-ACE in which an absorbing aerosol layer overlay a stratus cloud layer.
6) To analyze a new set of extensive aerosol data, and aerosol-cloud interaction data, that we expect to collect in Southern Africa as part of SAFARI-2000.
FORM D: GACP BIBLIOGRAPHY FOR 1st YEAR (9/l/98-8/31/99)
Name: Peter V. Hobbs
Institution: Cloud and Aerosol Research Group (CARG)
Department of Atmospheric Sciences
University of Washington
Seattle, WA 98195
BIBLIOGRAPHY:
(a) Publications
(i) "Radiative Characteristics of Regional Haze Dominated by Smoke from Biomass Burning in Brazil: Closure Tests and Direct Radiative Forcing" by J. L. Ross, P. V. Hobbs and B. Holben (J. Geophys. Res., 103, 31,925-31,941, 1998).
(ii) "Physical and Optical Properties of Young Smoke from Individual Biomass Fires in Brazil" by J. S. Reid and P. V. Hobbs (J. Geophys. Res., 103, 32,013-32,030, 1998).
(iii) "Comparison of Techniques for Measuring Shortwave Absorption and Black Carbon Content of Aerosols from Biomass Burning in Brazil" by J. S. Reid, P. V. Hobbs, C. Liousse, J. V. Martins, R. E. Weiss, and T. E. Eck (J. Geophys. Res., 103, 32,031-32,040, 1998).
(iv) "Effects Of Black Carbon Content, Particle Size, and Mixing on Light Absorption by Aerosols from Biomass Burning in Brazil" by J. V. Martins, P. Artaxo, C. Liousse, J. S. Reid, P. V. Hobbs, and Y. J. Kaufman (J. Geophys. Res., 103, 32,043-32,050, 1998).
(v) "Sphericity and Morphology of Smoke Particles from Biomass Burning in Brazil" by J. V. Martins. P. V. Hobbs, R. E. Weiss and P. Artaxo (J. Geophys. Res., 103, 32,051-32,047, 1998).
(vi) "Physical, Chemical and Optical Properties of Regional Hazes Dominated by Smoke in Brazil" by J. S. Reid, P. V. Hobbs, R. J. Ferek, D. R. Blake, J. V. Martins, M. R. Dunlap and C. Liousse (J. Geophys. Res., 103, 32,059-32,080).
(vii) "Humidification Factors of Aerosols from Biomass Burning in Brazil" by R. A. Kotchenruther and P. V. Hobbs (J. Geophys. Res., 103, 32,081-32,089, 1998).
(viii) "Emission Factors of Hydrocarbons, Halocarbons, Trace Gases and Particles from Biomass Burning in Brazil" by R. J. Ferek, J. S. Reid, P. V. Hobbs, D. B. Blake and C. Liousse (J. Geophys. Res., 103, 32,107-32,118, 1998).
(ix) "Relationships Between Cloud Droplet Effective Radius, Liquid Water Content, and Droplet Concentration for Warm Clouds in Brazil Embedded in Biomass Smoke" by J. S. Reid, P. V. Hobbs, A. L. Rangno and D. A. Hegg (J. Geophys. Res., 104, 6115-6153, 1999).
(x) "Use of the Angstrom Exponent to Estimate the Variability of Optical and Physical Properties of Aging Smoke Particles in Brazil" by J. S. Reid, T. F. Eck, S. A. Christopher, P. V. Hobbs, and B. Holben (J. Geophys. Res., submitted).
(xi) "Estimation of Surface and Top-of-Atmosphere Shortwave Irradiance in Biomass Burning Regions During SCAR-B" by S. A. Christopher, X. Lit, R. M. Welch, J. S. Reid, P. V. Hobbs, T. F. Eck and B. Holben (J. Appl. Meteor.-submitted).
(xii) " Aerosol Properties and Radiative Effects in the United States East Coast Haze Plume: An Overview of the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX)" by P. B. Russell, P. V. Hobbs and L. S. Stowe (J. Geophys. Res., 104, 2213-2222, 1999).
(xiii) "An Overview of the University of Washington Airborne Measurements and Results from the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX)" by P. V. Hobbs (J. Geophys. Res., 104, 2233-2238, 1999).
(xiv) "Humidification Factors for Atmospheric Aerosols off the Mid-Atlantic Coast of the United States" by R. A. Kotchenruther, P. V. Hobbs and D. A. Hegg (J. Geophys. Res., 104, 2239-2251, 1999).
(xv) "Aerosol Optical Depth Retrieval Using ATSR-2 and AVHRR Data During TARFOX" by J. P. Veefkind, G. de Leeuw, P. D. Durkee, P. B. Russell, P. V. Hobbs and J. M. Livingston (J. Geophys. Res., 104, 2253-2260,1999).
(xvi) "Retrieval of Aerosol Optical Thickness and Size Distribution Over Ocean from the MODIS Airborne Simulator During TARFOX" by D. Tanre, L. A. Remer, Y. J. Kaufman, S. Mattoo, P. V. Hobbs, J. M. Livingston, P. B. Russell, and A. Smirnov (J. Geophys. Res., 104, 2261-2278).
(xvii) "Aerosol-Induced Radiative Flux Changes off the United States Mid-Atlantic Coast: Comparison of Values Calculated from Sunphotometer and In Situ Data with those Measured by Pyranometer" by P. B. Russell, J. M. Livingston, P. Hignett, S. Kinne, J. Wong, A. Chien, R. Bergstrom, P. Durkee and P. V. Hobbs (J. Geophys. Res., 104, 2289-2307, 1999).
(xviii) "Properties of Aerosols Aloft Relevant to Direct Radiative Forcing off the Mid-Atlantic Coast of the United States" by W. S. Hartley. P. V. Hobbs, J. L. Ross, P. B. Russell, and J. M. Livingston. (J. Geophys. Res., TARFOX 2nd Special Issue, submitted).
(xix) "Comparison of Aerosol Optical Properties and Water Vapor Among Ground and Airborne Lidars and Sun Photometers During TARFOX" by R. Ferrare et al. (P. V. Hobbs is a co-author), J. Geophys. Res., TARFOX 2nd Special Issue (submitted).
(xx) "Comparison of LASE, Aircraft and Satellite Measurements of Aerosol Optical Properties and Water Vapor During TARFOX" by R. Ferrare et al. (P. V. Hobbs is a co-author), J. Geophys. Res., TARFOX 2nd Special Issue (submitted).
(xxi) "Retrieving the Vertical Structure of the Effective Aerosol Complex Index of Refraction From a Combination of Aerosol In Situ and Remote Sensing Measurements During TARFOX (Part 1)" by J. Redemann et al. (P. V. Hobbs is a co-author), J. Geophys. Res., TARFOX 2nd Special Issue (submitted).
(xxii) "Case Studies of the Vertical Structure of the Shortwave Direct Aerosol Radiative Forcing During TARFOX" by J. Redemann, B. P. Turco, K.-N. Liou, R. W. Bergstrom, P. V. Hobbs, E. V. Browell and P. B. Russell, J. Geophys. Res., TARFOX 2nd Special Issue (submitted).
(b) Oral Presentations
(i) "Relative Contributions of Atmospheric Aerosol Constituents to Optical Depths and Direct Radiative Forcing on the US East Coast." Talk given by P. V. Hobbs at the 5th Int. Aerosol Conf., Edinburg, Scotland, 18 Sept. 1998.
(ii) "Aerosol Emissions from Biomass Burning in Brazil and their Effects on Regional and Global Climate." Talk given by P. V. Hobbs at the Wenger Workshop on Biomass Burning and its Interrelationships with the Climate System, Wengen, Switzerland, 28 Sept.-2 Oct. 1998.
(iii) "Some Comments and Some New Data on Indirect Aerosol Forcing." Talk given by P. V. Hobbs at the Meeting of NASA Aerosol Radiative Forcing Science Team, GISS, New York, NY, 18-20 Nov. 1998.
(iv) "Outline of University of Washington's Proposed Studies." Talk given by P. V. Hobbs at the Meeting of NASA Aerosol Radiative Forcing Science Team, GISS, New York, NY, 18-20 Nov. 1998.
(v) "Overview of FIRE-ACE/SHEBA Observations Obtained Aboard the University of Washington's Convair-580 Research Aircraft." Talk given by P. V. Hobbs at the FIRE-ACE/SHEBA Workshop, Tucson, Arizona, 25-28 January 1999.
(vi) "Aerosols on the East Coast of the United States and their Radiative Effects." Colloquitim to Atmospheric Science Dept., Univ. of Wash., Seattle, 21 January 1999.
