bluuebunny/crossref_metadata_2025 huggingface dataset:
A dynamic water vapor correction method for the retrieval of land surface temperatures from the advanced very high resolution radiometer
Authors: Steyn‐Ross Moira L. , Steyn‐Ross D. Alistair , Emery W. J.
Published: February 2004

We present a method which permits retrievals of land surface temperatures (LSTs) from AVHRR (advanced very high resolution radiometer) radiances sensed through atmospheres which may contain a large and strongly varying water vapor content. This new method is an extension of the dynamic water vapor (DWV) algorithm which was designed to retrieve sea surface temperatures. The generalization to LST retrievals recognizes that in general, land emissivities are unknown, may be spectrally dependent, and are less than unity. Because the LST retrieval problem is inherently underconstrained (there are more unknowns than radiative transfer equations), some knowledge of surface emissivity is required in order to establish upper and lower bounds on surface temperature. We demonstrate our method by comparing DWV‐LST retrievals with point surface measurements made by a cluster of eight infrared thermometers (IRTs) deployed over a grasslands prairie site in eastern Kansas in July and August 1989; this deployment was part of the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE). We find that several of the AVHRR images supplied on FIFE CD‐ROM contain navigation errors of ∼30 km, consistent with a misidentification of the Tuttle Reservoir ground control point. After correcting the navigation, we identified the IRT pixels and computed the bias and rms errors for a DWV‐IRT comparison. For night passes we obtained agreement to.+0.39±1.11 K, while for day passes the comparison yielded +4.09±3.10 K. The large daytime bias is probably the result of the IRT readings not being representative of the ∼1 km2‐scale areas sensed by AVHRR (the IRT views vegetation; the AVHRR field of view includes warmer, less well vegetated surfaces). Our results show that while a fixed‐coefficient, global split‐window algorithm does not perform well in the relatively moist FIFE atmosphere, it is quite feasible to use the DWV‐LST to derive a local split‐window algorithm whose coefficient is tuned on a per‐pass basis.
Measurement technique for the determination of photolyzable chlorine and bromine in the atmosphere
Authors: Impey G. A. , Shepson P. B. , Hastie D. R. , Barrie L. A.
Published: February 2004

A technique has been developed to enable measurement of photolyzable chlorine and bromine at trace levels in the troposphere. In this method, ambient air is drawn through a cylindrical flow cell, which is irradiated with a Xe arc lamp. In the reaction vessel of the photoactive halogen detector (PHD), photolytically active molecules Clp (including Cl2, HOCl, ClNO, ClNO2, and ClONO2) and Brp (including Br2, HOBr, BrNO, BrNO2, and BrONO2) are photolyzed, and the halogen atoms produced react with propene to form stable halogenated products. These products are then sampled and subsequently separated and detected by gas chromatography. The system is calibrated using low concentration mixtures of Cl2 and Br2 in air from commercially available permeation sources. We obtained detection limits of 4 pptv and 9 pptv as Br2 and Cl2, respectively, for 36 L samples.
Measurements of photolyzable chlorine and bromine during the Polar Sunrise Experiment 1995
Authors: Impey G. A. , Shepson P. B. , Hastie D. R. , Barrie L. A. , Anlauf K. G.
Published: February 2004

We report measurements of rapidly photolyzable chlorine (Clp; e.g., Cl2 And HOCl) and bromine (Brp; e.g., Br2 and HOBr) in the high Arctic using a newly developed photoactive halogen detector (PHD). Ground level ambient air was sampled daily from mid‐February through mid‐April in the Canadian Arctic at Alert, Northwest Territories (82.5°N, 62.3°W), as part of the Polar Sunrise Experiment (PSE) 1995. Concentrations of “total photolyzable chlorine” varied from <9 to 100 pptv as Cl2 and that of “total photolyzable bromine” from <4 to 38 pptv as Br2. High concentration episodes of chlorine were observed only prior to sunrise (March 21), while high concentration episodes of bromine were measured throughout the study. The high concentrations of photolyzable chlorine and bromine prior to sunrise suggest a “dark” production mechanism that we assume yields Cl2 and Br2. An inverse correlation of bromine with ozone is clearly present in one major ozone depletion episode at the end of March. A trajectory analysis, taken with the differences in measured levels of photolyzable chlorine and bromine after sunrise, imply different production mechanisms for these two types of species. A steady state analysis of the data for one ozone depletion episode suggests a [Br]/[Cl] ratio in the range 100–300. The high concentrations of photolyzable bromine after sunrise imply the existence of a precursor other than aerosol bromide.
Modeling quasi‐biennial variability in the semiannual double peak
Authors: Kennaugh Richard , Ruth Sarah , Gray Lesley J.
Published: February 2004

The interannual variability of the stratopause semiannual double peak as seen in methane measurements made by the Halogen Occultation Experiment (HALOE) is investigated using a two‐dimensional isentropic model. It is found that the observed variability is reproduced when the quasi‐biennial oscillation (QBO) of the tropical lower stratosphere is introduced into the model and that there are two distinct means by which the QBO affects stratopause tracer values. First, the QBO modulates the westerly phase of the stratopause semiannual oscillation (SAO) by the selective damping of the parameterized waves responsible for producing this phase of the SAO in the model. This results in a modulation of the strength and duration of the SAO circulation, with it being stronger when the QBO is easterly than when it is westerly. However, when the QBO is easterly, the effect of stronger downwelling in the tropics is negated by subsequent upwelling; the overall effect is to reduce or eliminate the trough of the double peak. For a westerly QBO phase the downwelling, although weaker, is also more persistent, giving a deeper trough. Second, the tropical QBO influences the propagation of planetary waves in the winter hemisphere, thereby producing an extratropical QBO in the winter stratosphere and mesosphere. This alters the circulation in this region, giving more upwelling in the winter extratropics above 0.5 hPa when the QBO (defined at 15 hPa) is westerly. This causes the winter lobe of the double peak to form only when the QBO is westerly. The combined result of the two processes is to produce a double peak when the QBO winds are westerly but a single peak in the summer hemisphere when the QBO winds are easterly. This modeled result agrees well with the interannual variability displayed by the HALOE methane observations.
Halogen‐catalyzed methane oxidation
Authors: Lary D. J. , Toumi R.
Published: February 2004

This paper highlights the importance of halogen‐catalyzed methane oxidation in the upper troposphere and lower stratosphere. The calculated rate of methane oxidation is increased by at least 20% in the upper troposphere when halogen catalysis is included. In the lower stratosphere, approximately 25% of methane oxidation can be initiated by chlorine; the precise fraction is very temperature dependent. Including halogen‐catalyzed methane oxidation increases the HOx and ClOx concentrations and decreases the NOx concentration. The calculated enhancement in the HOx concentration due to halogen‐catalyzed methane oxidation is around 10–15% in the lower stratosphere; and around 20% in the upper troposphere. The decrease in the NOx concentration is around 10% in the upper troposphere. The enhancement in the ClOx concentration is around 7–10% in the lower stratosphere. The increase in the calculated HOx and ClOx concentrations and the decrease in the NOx concentration lead to a enhancement in the calculated O3 loss. The additional O3 loss calculated is most significant in the upper troposphere where over a 7‐day simulation it was of the order of 0.1–1% for midlatitudes at equinox. As the atmospheric loading of chlorine drops the gross odd‐oxygen production by NO + HO2 will increase, so there will be an accelerated ozone recovery. On a per molecule basis, bromine‐catalyzed methane oxidation is approximately 2 orders of magnitude faster than chlorine catalyzed methane oxidation. In the upper troposphere bromine‐catalyzed methane oxidation destroys ozone at a rate which is approximately one third of that at which nitrogen‐catalyzed methane oxidation is producing ozone. Therefore, with the increasing atmospheric bromine loading, bromine‐catalyzed methane oxidation is set to become more important. It would be valuable to have kinetic studies of the reaction BrO with CH3O2 so that the role of bromine‐catalyzed methane oxidation can be quantified more precisely.
Detection of volcanic ash clouds from Nimbus 7/total ozone mapping spectrometer
Authors: Seftor C. J. , Hsu N. C. , Herman J. R. , Bhartia P. K. , Torres O. , Rose W. I. , Schneider D. J. , Krotkov N.
Published: February 2004

Measured radiances from the Version 7 reprocessing of the Nimbus 7/total ozone mapping spectrometer (TOMS) 340‐ and 380‐nm channels are used to detect absorbing particulates injected into the atmosphere after the El Chichon eruption on April 4, 1982. It is shown that while the single‐channel reflectivity determined from the 380‐nm channel is able to detect clouds and haze composed of nonabsorbing aerosols, the spectral contrast between the 340‐ and 380‐nm channels is sensitive to absorbing particulates such as volcanic ash, desert dust, or smoke from biomass burning. In this paper the spectral contrast between these two channels is used to detect the volcanic ash injection into the atmosphere and to track its evolution for several days. The movement of the ash clouds is shown to be consistent with the motions expected from the National Centers for Environmental Prediction (NCEP)‐derived balanced wind fields in the troposphere and lower stratosphere. The movement of the volcanic SO2 cloud detected from TOMS data was also in agreement with the NCEP wind at higher altitudes of up to 100–10 mbar. The vertical wind shear in the neighborhood of the eruption site resulted in a clear separation of the ash and SO2 clouds. The location and movement of the ash cloud are consistent with information obtained by the advanced very high resolution radiometer (AVHRR) instrument on board the NOAA 7 satellite and to ground reports of ash fall.
Aerosol climatology at the high‐alpine site Jungfraujoch, Switzerland
Authors: Baltensperger U. , Gäggeler H. W. , Jost D. T. , Lugauer M. , Schwikowski M. , Weingartner E. , Seibert P.
Published: February 2004

Continuous aerosol measurements have been performed at the high‐alpine site Jungfraujoch (3450 m above sea level) since 1988 by means of an epiphaniometer. The instrument, which determines the Fuchs surface area of the aerosol particles, was operated with a time resolution of 30 min. High correlation coefficients (r>0.8) were found between the epiphaniometer signal and other aerosol parameters, which could be attributed to a rather constant size distribution of the Jungfraujoch aerosol in the accumulation range (0.1<d<1 μm). Well‐defined diurnal variations with a peak in the late afternoon were observed on many days during summer, which was not the case during winter. Comparison with black carbon and radon daughter measurements revealed that these diurnal variations are due to vertical transport processes. A statistical analysis showed that the fraction of days with a well‐defined diurnal pattern increased with decreasing stability of the atmosphere; however, late afternoon peaks also occurred during days when the potential temperature profile indicated a stable atmosphere. First simulations with ALPTHERM, a new convection model which takes topography into account, were able to explain the observed aerosol patterns. This indicates that slope winds over a certain catchment area are responsible for the transport to this high‐elevation site. The distinct seasonal variation with summer values, which are about a factor of 10 higher than winter values, could therefore be attributed to seasonally varying transport processes, due to the seasonal variation of radiation. The data show that even sites at very high elevation cannot be assumed to be in the free troposphere all the time.
Infrared radiative forcing of CFC substitutes and their atmospheric reaction products
Authors: Papasavva Stella , Tai Stephanie , Illinger Karl H. , Kenny Jonathan E.
Published: February 2004

We have employed the radiative forcing function recently computed by Pinnock et al. [1995], in conjunction with infrared cross sections and vibrational frequencies calculated with ab initio quantum‐mechanical methods, to estimate the instantaneous infrared radiative forcing terms ℱtot of a number of CFC substitutes and their atmospheric reaction products. The computed quantities ℱtot are compared with those obtained by Pinnock et al. [1995] employing experimental infrared spectra. In particular, Gaussian‐92TM software has been utilized, at the MP2/6–31G** level of theory, to provide computational estimates of these quantities. Our results agree with the former, with a mean and a standard deviation of the difference of +3% and 15%, respectively. An error analysis is provided to assess the utility of the method. The capability of quantum‐mechanical computational methods to explore structural trends in radiative and physicochemical properties is exploited for the molecular systems examined here.
Mass fluxes of O3, CH4, N2O and CF2Cl2 in the lower stratosphere calculated from observational data
Authors: Gettelman Andrew , Holton James R. , Rosenlof Karen H.
Published: February 2004

Trace gas mixing ratio data from the Upper Atmosphere Research Satellite (UARS) are combined with a radiatively derived transformed Eulerian mean (TEM) stream function to estimate the net ozone (O3) mass flux from the stratosphere to the troposphere and to investigate the net fluxes of methane (CH4), nitrous oxide (N2O), and CFC‐12 (CF2Cl2) into the lower stratosphere. The mass fluxes of ozone and long‐lived tracers such as nitrous oxide, methane, and CFC‐12 in the lower stratosphere can be estimated from data obtained by the cryogenic limb array etalon spectrometer (CLAES), the microwave limb sounder (MLS) for ozone, and the Halogen Occultation Experiment (HALOE) for ozone and methane. The flux of ozone from the stratosphere to the troposphere is estimated to be 510 Tg of ozone per year with a range of 450 to 590 Tg O3/yr. Net fluxes into the stratosphere are estimated as 27 Tg of methane per year, 8 Tg/yr of N in nitrous oxide, and 0.08 Tg/yr of CF2Cl2. There is good agreement with previous estimates within the range of uncertainty of these calculations.
Halogen Occultation Experiment observations of the quasi‐biennial oscillation and the effects of Pinatubo aerosols in the tropical stratosphere
Authors: Luo M. , Russell J. M. , Huang T. Y. W.
Published: February 2004

The time series of Halogen Occultation Experiment (HALOE) observed mixing ratios of chemical tracers in the tropical stratosphere (O3, HCl, HF, CH4, NO2, NO, and H2O) exhibit obvious quasi‐biennial oscillatory (QBO) characteristics. The pressure‐time cross sections for the QBO signals in the mixing ratios of HCl, HF, CH4, NO, and H2O are presented for the first time. The QBO in O3 and NO2 exibits similar amplitudes and patterns as observed and analyzed previously. An apparent in‐phase relationship between O3 and NO2 above 4 mbar is noted, which implies that ozone QBO may not be caused by NO2 chemical destruction in the upper stratosphere. During the early time period of the UARS mission (late 1991 to early 1992), the QBOs in most HALOE species are seen to be strongly affected by Pinatubo aerosols. In order to quantitatively define the different aerosol effects (heating versus chemical) from HALOE data, we calculate the vertical displacements of constant volume mixing ratio surfaces of HALOE‐measured species in the tropical lower stratosphere. The time evolutions of the vertical displacements of HCl and NOx (HALOE NO2 + NO) isopleths are seen to approximately follow that of HF. This indicates that the enhanced vertical velocity that acts to uplift the tracer profiles due to aerosol radiative heating is a significant effect. However, because of the uncertainty in the vertical displacement analyses of these tracers from HALOE data, it can only be concluded that changes in HCl and NOx from chemical effects are less than 30% and 80%, respectively.
Intercomparison of multiplatform stratospheric aerosol and ozone observations
Authors: Lu Jianjun , Mohnen Volker A. , Yue Glenn K. , Jäger Horst
Published: February 2004

Stratospheric aerosol extinction profiles from the satellite‐borne Stratospheric Aerosol and Gas Experiment (SAGE II, data version 5.93) and Halogen Occultation Experiment (HALOE, data version 17) instruments are intercompared with the aerosol lidar data at Garmisch‐Partenkirchen, Germany (47.5°N, 11.1°E) during January and April 1993. Both the HALOE 5.26 μm aerosol extinction and aerosol lidar 0.532 μm backscattering profiles are converted to extinction profiles at the SAGE II 0.525 μm wavelength channel using aerosol size distributions measured by ER‐2 in northern midlatitudes. Within the altitude range of 18–22 km, where most of the stratospheric aerosol resides, the differences between the SAGE II and the HALOE extinction coefficients with respect to HALOE are in general within 30%. The SAGE II‐lidar and HALOE‐lidar differences (with respect to lidar) are generally within 50% in 15–25 km altitudes. The HALOE extinction values are systematically larger than the SAGE II and aerosol lidar values above 25 km altitude. Stratospheric ozone mixing ratio profiles measured by the SAGE II and HALOE sensors are also intercompared during the same period. The percent differences between the SAGE II and HALOE ozone mixing ratios with respect to HALOE are within 20% in 20–60 km altitudes, in general, within the separation between the compared profiles.
Interdecadal variability of summer climate over East Asia and its association with 500 hPa height and global sea surface temperature
Authors: Hu Zeng‐Zhen
Published: February 2004

Interdecadal variability of summer climate (rainfall and temperature) in East Asia (China and Japan) and its association with the anomalies of geopotential heights at 500 hPa over the Northern Hemisphere (NH), global sea surface temperature (SSTA), and outgoing longwave radiation (OLR) were examined. An abrupt change was found in the middle and by the end of the 1970s in the variations of time coefficients of the second mode of singular value decomposition (SVD2) for the summer rainfall and temperature in China. The rainfall anomaly around 1977–1979 changes from above normal to below normal, and the temperature changes from below normal to above normal in the southern and southwestern parts of China. A similar interdecadal variability was also found in the summer climate variations in the Southwest Islands of Japan. The 500 hPa height anomalies related to the spatial pattern of SVD2 shows a clear dipole pattern: the negative center is located in Mongolia and northeastern China, and the positive center is located in middle and southern China. The abrupt change of summer climate in the middle and by the end of the 1970s over the subtropical regions of East Asia is characterized with the intensification and westward and southward extension of the western Pacific subtropical high (WPSH). It is also observed in geopotential height variations over Eurasia around 1977–1978. An abrupt change of SST over the tropical Indian Ocean and tropical western Pacific was also found around 1976–1977. It is indicated that interdecadal variability of summer rainfall and temperature over East Asia is largely influenced by the change of SSTA and convective activity in the tropical Indian Ocean and tropical western Pacific. The convective activity over the tropical Indian Ocean and tropical western Pacific is usually enhanced when the SST is warmer than normal, so the subtropical high anomalies over the subtropical regions of East Asia are intensified through the enhancement of a Hadley cell. As a result the subtropical regions of East Asia, including southern and southwestern China and the Southwest Islands of Japan, are covered by a positive height anomaly at 500 hPa, where the temperature is above normal and the rainfall is below normal.
Distribution of Antarctic polar stratospheric clouds as seen by the CLAES experiment
Authors: Mergenthaler John L. , Kumer John B. , Roche Aidan E. , Massie Steven T.
Published: February 2004

The distribution and optical characteristics of Antarctic polar stratospheric clouds (PSCs) during the winter of 1992 as seen from the cryogenic limb array etalon spectrometer (CLAES) on the NASA Upper Atmosphere Research Satellite (UARS) are presented. The CLAES measurements are the first extensive stratospheric aerosol observations through much of the Antarctic polar night. An analysis of the vertical and areal distribution using the aerosol absorption coefficient measured at 780 cm−1 is presented, including a polar map showing the frequency of PSC occurrence during the two CLAES Antarctic viewing periods June 11 to July 10 and August 16 to September 18. The PSC seasonal evolution from CLAES is compared with a climatology based on the Stratospheric Aerosol Measurements II (SAM II) system. The frequency of PSC occurrence in the CLAES data sampled at latitudes similar to those observed with SAM II shows general agreement with the climatology. Some obvious differences between details of the PSC evolution seen by CLAES and the climatology are investigated with 1992 SAM II aerosol extinction data and shown to be due to intra‐annual variations specific to 1992, which appear in both data sets.
Impact of the Doppler spread parameterization on the simulation of the middle atmosphere circulation using the MA/ECHAM4 general circulation model
Authors: Manzini E. , McFarlane N. A. , McLandress C.
Published: February 2004

The zonal mean circulation of the middle atmosphere simulated by a general circulation model that includes the Doppler spread parameterization of gravity‐wave momentum deposition is presented. To illustrate the impact of the parameterization, this simulation is compared to another obtained by using Rayleigh friction instead. It is found that the Doppler spread parameterization improves the extratropical zonal mean circulation in the mesosphere by reducing the strength of the zonal winds above the jet maximum. The parameterization also improves the simulation of the equatorial semiannual oscillation in the zonal mean zonal wind at the stratopause by enhancing the eastward phase and its downward propagation.
Analysis of flux maps versus surface characteristics from Twin Otter grid flights in BOREAS 1994
Authors: Ogunjemiyo S. , Schuepp P. H. , MacPherson J. I. , Desjardins R. L.
Published: February 2004

In BOREAS 1994 the Canadian Twin Otter research aircraft was flown at a fixed altitude of about 30 m above ground level (agl) over two 16×16 km heterogeneous grid sites, in an attempt to document the spatial distributions of fluxes of sensible heat, latent heat, and CO2 over typical boreal systems and to relate them to spatial distributions of surface characteristics. The acquired data were used to construct maps of surface temperature excess over air temperature (Ts‐Ta) and greenness index (GI) as well as flux maps of sensible heat, latent heat, and CO2. Fluxes were estimated by the eddy correlation method and the scalar and vertical wind variables detrended by a method that takes into account the physical nature of transport during convective daytime conditions. The (Ts‐Ta) maps showed that surface temperatures were relatively cooler over the forests than over the disturbed, regenerating, and burn areas. However, their juxtaposition with sensible heat flux maps showed highest heat flux predominantly over the forest areas. Close correspondence was observed between maps of CO2 flux and greenness. Quantitative comparison of the flux maps for the three intensive field campaigns (IFCs) showed that the CO2 flux was the most conservative of the three fluxes, while latent heat flux showed the highest variations. Areas with persistent patterns of flux distribution across the IFCs were also identified.
Physiological responses of a black spruce forest to weather
Authors: Goulden Michael L. , Daube Bruce C. , Fan Song‐Miao , Sutton Douglas J. , Bazzaz Ammar , Munger J. William , Wofsy Steven C.
Published: February 2004

We used eddy covariance to measure the net exchange of CO2 between the atmosphere and a black spruce (Picea mariana) forest in Manitoba for 16,500 hours from March 16, 1994 to October 31, 1996. We then partitioned net exchange into gross photosynthesis and respiration by estimating daytime respiration as a function of temperature, and used these data to define the physiological responses of the forest to weather. The annual rates of gross production and respiration by the forest were both around 8 t C ha−1 yr−1. Both photosynthetic and respiratory response were reduced in winter, recovered with warming in spring, and varied little in summer. Respiration in mid summer increased with air temperature (Tair) at a Q10 of around 2 to a rate of 2–8 μmol m−2 s−1 at 15°C. Gross photosynthesis at high light (photon flux density (PPFD) greater than 600 μmol m−2 s−1) was negligible at Tair < 0°C, increased linearly with Tair from 0° to 14°C, and was relatively insensitive to Tair > 14°C. Gross CO2 uptake at Tair > 14°C increased with increasing light at an ecosystem‐level quantum yield of 0.05 mol CO2 mol−1 photons before saturating at an uptake rate of 8–18 μmol m−2 s−1 at PPFDs greater than 500–700 μmol m−2 s−1. Photosynthesis in summer did not appear limited by high evaporative demand or soil water depletion.
Formulation of surface heat flux: Application to BOREAS
Authors: Mahrt L. , Sun Jielun , MacPherson J. I. , Jensen N. O. , Desjardins R. L.
Published: February 2004

The aerodynamic temperature is required for prediction of the surface heat flux using Monin‐Obukhov similarity. This “fictitious” temperature is not systematically equal to the actual air temperature near the surface and is not directly available from observations or in numerical models. The aerodynamic temperature is normally replaced with either the canopy air temperature or the surface radiation temperature, sometimes accompanied by adjustment of the thermal roughness length or specification of an excess resistance. In this study, the relationship between the aerodynamic temperature and the surface radiation temperature is examined in terms of the surface energy budget and simple representation of canopy structure. Previous inconsistencies are discussed. The observed behavior of the aerodynamic temperature is studied using Canadian Twin Otter aircraft data from BOREAS over nine different forested and nonforested sites. Variation of the behavior of the aerodynamic temperature between different parts of the boreal forest is found to be strongly correlated with the red reflectance.
Tracer‐tracer correlations: Three‐dimensional model simulations and comparisons to observations
Authors: Avallone Linnea M. , Prather Michael J.
Published: February 2004

Calculations of the stratospheric distributions of 12 trace species (N2O, CH4, CFCl3, CF2Cl2, CFCl2CF2Cl, CHF2Cl, CH3Cl, CH3CCl3, CCl4, CH3Br, CF2ClBr, and CF3Br) are performed by using the Goddard Institute for Space Studies/University of California at Irvine (GISS/UCI) three‐dimensional chemistry transport model (CTM). Because each of these gases is either an important precursor of ozone‐depleting radicals or a significant greenhouse molecule, it is critical that we understand their source strengths and atmospheric lifetimes. In this study, lifetimes against stratospheric loss are determined from the CTM calculations and compared with the currently accepted values. Calculated distributions of these species are compared with observations taken from aircraft platforms at midlatitudes via their correlation with N2O. The sensitivity of the calculated correlations to rate parameters, photolysis cross sections, and lower boundary conditions is explored for several key species. For most of the compounds examined the correlations can be simulated, within the uncertainty of the observations, by using current photochemistry. Finally, the use of correlation diagrams (i.e., scatterplots of one species versus another) as a tool for determining the lifetimes of trace gases on the basis of atmospheric observations is examined in the framework of the theory proposed by Plumb and Ko [1992].
Comparing nocturnal eddy covariance measurements to estimates of ecosystem respiration made by scaling chamber measurements at six coniferous boreal sites
Authors: Lavigne M. B. , Ryan M. G. , Anderson D. E. , Baldocchi D. D. , Crill P. M. , Fitzjarrald D. R. , Goulden M. L. , Gower S. T. , Massheder J. M. , McCaughey J. H. , Rayment M. , Striegl R. G.
Published: February 2004

During the growing season, nighttime ecosystem respiration emits 30–100% of the daytime net photosynthetic uptake of carbon, and therefore measurements of rates and understanding of its control by the environment are important for understanding net ecosystem exchange. Ecosystem respiration can be measured at night by eddy covariance methods, but the data may not be reliable because of low turbulence or other methodological problems. We used relationships between woody tissue, foliage, and soil respiration rates and temperature, with temperature records collected on site to estimate ecosystem respiration rates at six coniferous BOREAS sites at half‐hour or 1‐hour intervals, and then compared these estimates to nocturnal measurements of CO2 exchange by eddy covariance. Soil surface respiration was the largest source of CO2 at all sites (48–71%), and foliar respiration made a large contribution to ecosystem respiration at all sites (25–43%). Woody tissue respiration contributed only 5–15% to ecosystem respiration. We estimated error for the scaled chamber predictions of ecosystem respiration by using the uncertainty associated with each respiration parameter and respiring biomass value. There was substantial uncertainty in estimates of foliar and soil respiration because of the spatial variability of specific respiration rates. In addition, more attention needs to be paid to estimating foliar respiration during the early part of the growing season, when new foliage is growing, and to determining seasonal trends of soil surface respiration. Nocturnal eddy covariance measurements were poorly correlated to scaled chamber estimates of ecosystem respiration (r2=0.06–0.27) and were consistently lower than scaled chamber predictions (by 27% on average for the six sites). The bias in eddy covariance estimates of ecosystem respiration will alter estimates of gross assimilation in the light and of net ecosystem exchange rates over extended periods.
Intercomparison among four flux aircraft at BOREAS in 1994
Authors: Dobosy R. J. , Crawford T. L. , MacPherson J. I. , Desjardins R. L. , Kelly R. D. , Oncley S. P. , Lenschow D. H.
Published: February 2004

Four airplanes measured fluxes of momentum, heat, water vapor, and carbon dioxide in 1994, during the intensive field campaigns of the Boreal Ecosystem‐Atmosphere Study (BOREAS): the NOAA/ATDD Long‐EZ, the NRC Twin Otter, the University of Wyoming King Air, and the NCAR Electra. This paper presents the results of wing‐to‐wing formation flights comparing the flux measurements from these airplanes. Comparisons of the spectra of wind components, air temperature, water vapor concentration, and carbon dioxide concentration along with the cospectra of these quantities with vertical velocity showed numerous instructive differences. However, among the three airplanes using established techniques, the fluxes and variances of these quantities generally did not differ by more than one would expect, given the separation of the airplanes. Statistics computed from the Long‐EZ data, based on a still evolving application of the Global Positioning System, often differed more strongly.
Seasonal variation of carbon dioxide, water vapor, and energy exchanges of a boreal black spruce forest
Authors: Jarvis P. G. , Massheder J. M. , Hale S. E. , Moncrieff J. B. , Rayment M. , Scott S. L.
Published: February 2004

Measurements of the fluxes of latent heat λE, sensible heat H, and CO2 were made by eddy covariance in a boreal black spruce forest as part of the Boreal Ecosystem‐Atmosphere Study (BOREAS) for 120 days through the growing season in 1994. BOREAS is a multiscale study in which satellite, airborne, stand‐scale, and leaf‐scale observations were made in relation to the major vegetation types [Sellers et al., 1995]. The eddy covariance system comprised a sonic anemometer mounted 27 m above the forest, a system for transferring air rapidly and coherently to a closed path, infrared gas analyzer and a computer with the Edinburgh EdiSol software. Over the measurement period, closure of the energy balance on a 24 hour basis was good: (H + λE)/(Rn ‐ G ‐ B ‐ S) = 0.97. The midday Bowen ratio was typically in the range 1.0–2.5, with an average value of ∼1.9 in the first Intensive Field Campaign (IFCl) and 1.3–1.4 in IFC2 and IFC3. Daily ecosystem evapotranspiration from moss, understory, and trees followed daily net radiation. Mean half‐hourly net ecosystem flux followed photosynthetic photon flux density (PPFD) closely, reaching −9 μmol m−2 s−1 in June and August. The mean respiratory efflux on nights during which the atmosphere was well mixed (u*>0.4 m s−1) reached 6 μmol m−2s−1. The PPFD‐saturated biotic CO2 assimilation reached 20 μmol; m−2 s−1 and showed little response to air temperature or vapor pressure deficit (VPD). Storage of CO2 in the air column at night did not account adequately for respiration on stable nights, so nighttime efflux was modeled for periods when u*<0.4 m s−1. There was a net gain of CO2 on most of the 120 days, but on 31 days of high temperature or low PPFD there was a net carbon loss. High PPFD promoted influx of CO2 by the foliage, whereas high temperatures reduced net CO2 influx through high respiration rates by the roots and soil microorganisms, leading to lower net uptake at high PPFD. Over the 120 day period, 95 g m−2 of C were stored (an average of 0.8 g m−2 d−1), and 237 mm of water evaporated (an average of 2 mm d−1).
Seasonal AVHRR multichannel data sets and products for studies of surface‐atmosphere interactions
Authors: Cihlar J. , Chen J. , Li Z.
Published: February 2004

A basic methodological premise in the design of the Boreal Ecosystem‐Atmosphere Study (BOREAS) is that the findings and models obtained at the stand level can be applied at the landscape, regional and global levels by using spatially comprehensive data sets, in particular satellite observations and meteorological measurements. Since many of the processes of interest are strongly influenced by solar radiation, satellite measurements at optical wavelengths are of fundamental importance. We describe a satellite data set and derived products prepared for the studies of the ecosystem‐atmosphere interactions, including the scaling up of site and landscape measurements, model development and validation, and many other applications. It is derived from daily measurements by the advanced very high resolution radiometer (AVHRR) onboard the NOAA 11 satellite. The data set was obtained through a compositing process to minimize the contamination by clouds. Subsequently, the ABC3 procedure [Cihlar et al., 1997] was applied to remove atmospheric attenutation effects, identify residual clouds or snow‐covered pixels and remove the effect of this contamination, remove bidirectional reflectance effects, and correct for surface emissivity effects. The paper briefly reviews the correction procedures, discusses the characteristics of the corrected data set, and presents several derived products of biophysical parameters, including leaf area index and the fraction of photosynthetically active radiation, vegetation index accumulated over the growing season, and the daily total absorbed photosynthetically active radiation.
Estimating spectral albedo and nadir reflectance through inversion of simple BRDF models with AVHRR/MODIS‐like data
Authors: Privette Jeffrey L. , Eck Thomas F. , Deering Donald W.
Published: February 2004

In recent years, many computationally efficient bidirectional reflectance models have been developed to account for angular effects in land remote sensing data, particularly those from the NOAA advanced very high resolution radiometer (AVHRR), polarization and directionality of the Earth's reflectances (POLDER), and the planned EOS moderate‐resolution imaging spectrometer (MODIS) and multi‐angle imaging spectroradiometer (MISR) sensors. In this study, we assessed the relative ability of 10 such models to predict commonly used remote sensing products (nadir reflectance and albedo). Specifically, we inverted each model with ground‐based data from the portable apparatus for rapid acquisition of bidirectional observations of the land and atmosphere (PARABOLA) arranged in subsets representative of satellite sampling geometries. We used data from nine land cover types, ranging from soil to grassland (First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE)) to forest (Boreal Ecosystem‐Atmosphere Study (BOREAS)). Retrieved parameters were used in forward model runs to estimate nadir reflectance and spectral albedo over a wide range of solar angles. We rank the models by the accuracy of the estimated products and find results to be strongly dependent on the view azimuth angle range of the inversion data, and less dependent on the spectral band and land cover type. Overall, the nonlinear model of Rahman et al. [993] and the linear kernel‐driven RossThickLiSparse model [Wanner et al., 1995] were most accurate. The latter was at least 25 times faster to invert than the former. Interestingly, we found these two models were not able to match the various bidirectional reflectance distribution function (BRDF) shapes as well as other models, suggesting their superior performance lies in their ability to be more reliably inverted with sparse data sets. These results should be useful to those interested in the computationally fast normalization of bidirectional reflectance data and the estimation of radiation flux parameters (albedo, absorbed radiation) over diverse land covers.
Multialtitude airborne observations of insolation effects of forest fire smoke aerosols at BOREAS: Estimates of aerosol optical parameters
Authors: Miller John R. , O'Neill Norman T.
Published: February 2004

Forest fire disturbance, as part of the natural cycle of the boreal ecosystem renewal, proved a significant factor in the acquisition scheduling of optical remote imagery at the northern study site of the Boreal Ecosystem‐Atmosphere Study (BOREAS), conducted in northern/central Canada during the July/August months of 1994. One such episode, between July 28 and 31, was due entirely to smoke transported over the study site from nearby and distant downwind fires. Noon insolation was reduced from 800 W/m2 on July 28 to 680 W/m2 on July 31 and incident PAR radiation from 320 to 250 W/m2. During the July 31 smoke episode the compact airborne spectrographic imager (CASI) was flown at 150, 300, 900, 1500, and 3200 m agl over a forested site, while measuring the scene‐reflected radiance as well as upwelling and downwelling irradiances in the spectral range 403 and 916 nm (2.5 nm resolution). These multialtitude observations of upwelling and downwelling irradiance and the hemispherical reflectance are used to estimate at two wavelengths, 550 and 672 nm, the vertical profiles of aerosol optical depth, attenuation coefficient, and single‐scattering albedo representative of the smoke aerosols encountered at BOREAS. For smoke aerosols from distant fires (high altitude) the single‐scattering albedo was 0.9 and the attenuation coefficient was 0.32 km−1 at 672 nm, whereas for smoke aerosols from nearby fires, values of 0.6 and 0.60 km−1 were found. This is qualitatively consistent with differences expected for distant primarily sulfate aerosols and higher soot aerosols for nearby flaming fires.
Signal strength and climate relationships in 13C/12C ratios of tree ring cellulose from oak in east England
Authors: Robertson I. , Switsur V. R. , Carter A. H. C. , Barker A. C. , Waterhouse J. S. , Briffa K. R. , Jones P. D.
Published: February 2004

Annual oak (Quercus robur L.) latewood δ13C values are presented for the period 1895–1994 from two sites with different hydrological characteristics. Both ring width and δ13C indices record high‐frequency common forcing better than lower‐frequency forcing. At both sites the high‐frequency variance in the δ13C indices of latewood cellulose is highly correlated with combined July and August environmental variables. The association between the high‐frequency variance in annual ring width indices and climate is not as strong. Higher correlations with environmental variables were found for the high‐frequency δ13C indices at the dry site (Sandringham) than at the wet site (Babingley), but the differences are not statistically significant. These results illustrate the need for routine signal quantification in isotope records and hence a requirement for between‐tree replication of isotope series in future studies. High‐frequency (year‐to‐year) interseries correlation is shown to be relatively strong, indicating that only small numbers of replicate series are needed to represent interannual isotope variability accurately. However, common signal variance is diminished at lower (decadal and longer period) frequencies. This implies a need for increased sample replication in order to achieve chronology confidence equivalent to that routinely produced for simple ring width data. This work demonstrates that significant high‐frequency climate signals are contained in isotopic measurements of trees whose ring widths contain little or no such information.
Diel variability of soluble Fe(II) and soluble total Fe in North African dust in the trade winds at Barbados
Authors: Zhu X. R. , Prospero J. M. , Millero F. J.
Published: February 2004

There is increased interest in the deposition of wind‐transported mineral dust to the oceans because of the possible role that iron might play as a limiting nutrient in primary productivity. It has been suggested that photochemical processes taking place on mineral particles suspended in the atmosphere could reduce large fractions of the Fe(III) to Fe(II) and thereby increase the soluble fraction of iron; when the particle is deposited in the ocean, the soluble iron would be more readily available to chemical and biological processes. In this study we collected mineral aerosol (carried by the trade winds from North African sources) at Barbados over a diel cycle; we immediately measured Fe(II) and total soluble Fe in filter extracts using as the extractant an acidic saline solution comparable to that expected to be present on mineral aerosols in the marine atmospheric boundary layer. The concentration of mineral dust was quite variable during the experiment, ranging from 1.99 to 18.4 μg/m3 (mean, 6.59 μg/ m3); Fe constituted on average 3.4% of the mineral dust mass. On average, 6.2% of the Fe in the dust was extracted in our process. The concentration of total dissolved Fe varied within a relatively narrow range, closely tracking the variations in dust concentration with no apparent day/night pattern. In contrast, there was a clear day/night pattern in the concentration of soluble Fe(II), with day values (mean 3.7 ng m−3) about twice night values (1.5 ng m m−3); expressed as a fraction of total dissolved Fe, Fe(II) ranged from 5.1% to 55% in the entire (day and night) data set (mean, 25%). Thus soluble Fe(II) constitutes only a small fraction (mean 1.6%) of the total Fe in the mineral aerosol. Furthermore, the Fe(II) concentration varied independently of the concentration of soluble Fe. The well‐defined diel cycle that we observed demonstrates that photochemical processing of Fe does take place; the relatively small dissolved Fe fractions and the absence of a relationship between Fe(II) and total dissolved Fe suggest, however, that the photochemical processes in mineral aerosols do not have a substantial effect on the total Fe solubility.
Mass and energy exchanges over a black spruce forest during key periods of BOREAS 1994
Authors: Pattey E. , Desjardins R. L. , St‐Amour G.
Published: February 2004

Surface fluxes were measured over an old black spruce forest in the southern study area in 1994 between May 24 and June 4 and between July 19–29 and September 8–17 during three of the intensive field campaigns (IFCs) of the Boreal Ecosystem‐Atmosphere Study (BOREAS). Eddy covariance measurements of latent and sensible heat, CO2, and momentum were carried out from a tower at 20 m above the ground. The evaporative fraction, defined as the ratio of latent heat flux over available energy, ranged from 41% (IFC 1) to 47% (IFC 2) and was relatively constant within each IFC (coefficients of variation <23%). During rapidly changing radiation conditions, the sensible heat flux varied with net radiation, while the latent heat flux was relatively constant. The mean evaporation at the old black spruce stand ranged from 1.44 mm d−1 during IFC 3 to 3.32 mm d−1 during IFC 2. Net CO2 fluxes were similar during IFC 1 and 2, with a maximum gain of 12.7 g CO2 m−2 d−1, but it was 20% lower during IFC 3. Increased respiration of the forest stand during IFC 2, which is associated with higher air and soil temperature, seems to account for the lack of increase in net CO2 influx between IFC 1 and 2. Nighttime CO2 fluxes measured by eddy covariance were often underestimated because of the light wind conditions.
Concentrations and seasonal cycle of black carbon in aerosol at a coastal Antarctic station
Authors: Wolff Eric W. , Cachier Hélène
Published: February 2004

Aerosol black carbon concentrations have been measured between 1992 and 1995 at Halley station using an aethalometer. The complete record is dominated by a number of events of high concentration that are clearly due to contamination from the station generators. However, using detailed meteorological data, it is possible rather satisfactorily to remove these events from the record. The events can be used to show that local contamination has no significant effect on sulfate or other major ion data, The remaining data then show a clear seasonal cycle, with monthly mean values of 0.3–2 ng m−3, slightly higher than those recorded at south pole. The cycle peaks in summer, with a possible doublet, and an overall maximum in October. This pattern is similar to that of south pole and of mineral dust at the coastal Neumayer station. The pattern seems to be controlled by the timing of biomass burning in the tropics, strongly modulated by the efficiency of transport to Antarctica. This transport seems to be poorly represented in model simulations. The concentrations are too low to have any significant effect on snow albedo. The similarity of the Halley and south pole data suggest that ice cores should give a historical record of black carbon that is rather representative of the Antarctic as a whole and therefore indicative of trends in biomass burning throughout the southern hemisphere.