Bruce B. Hicks

A canopy stomatal resistance model for gaseous deposition to vegetated surfaces

Abstract A gaseous deposition model, based on a realistic canopy stomatal resistance submodel, is described, analyzed and tested. This model is designed as one of a hierarchy of simulations, leading up to a “big-leaf” model of the processes contributing to the exchange of trace gases between the atmosphere and vegetated surfaces. Computations show that differences in plant species and environmental and physiological conditions can affect the canopy stomatal resistance by a factor of four. Canopy stomatal resistances to water vapor transfer computed with the present model are compared against values measured with a porometer and computed with the Penman-Monteith equation. Computed stomatal resistances from a soybean canopy in both well-watered and water-stressed conditions yield good agreement with test data. The stomatal resistance submodel responds well to changing environmental and physiological conditions. Model predictions of deposition velocities are evaluated for the case of ozone, transferred to maize. Calculated deposition velocities of O 3 overestimate measured values on the average by about 30%, probably largely as a consequence of uncertainties in leaf area index, soil and cuticle resistances, and other modeling parameters, but also partially due to imperfect measurement of O 3 deposition velocities.

Land–Atmosphere Interaction Research, Early Results, and Opportunities in the Walnut River Watershed in Southeast Kansas: CASES and ABLE

Abstract This paper describes the development of the Cooperative Atmosphere Surface Exchange Study (CASES), its synergism with the development of the Atmosphere Boundary Layer Experiments (ABLE) and related efforts, CASES field programs, some early results, and future plans and opportunities. CASES is a grassroots multidisciplinary effort to study the interaction of the lower atmosphere with the land surface, the subsurface, and vegetation over timescales ranging from nearly instantaneous to years. CASES scientists developed a consensus that observations should be taken in a watershed between 50 and 100 km across; practical considerations led to an approach combining long—term data collection with episodic intensive field campaigns addressing specific objectives that should always include improvement of the design of the long—term instrumentation. In 1997, long—term measurements were initiated in the Walnut River Watershed east of Wichita, Kansas. Argonne National Laboratory started setting up the ABLE ar...

Dry deposition inferential measurement techniques—I. Design and tests of a prototype meteorological and chemical system for determining dry deposition

A simple filterpack system and a supporting meteorological and surface-condition monitoring system have been deployed in a trial network to test methods by which dry deposition rates can be estimated on a routine basis, using average air concentration data and site-specific deposition velocities. The filterpack used in this dry deposition inferential measurement (DDIM) sampler differs from standard filterpacks by the use of a heated horizontal settling tube at the inlet. This modification is intended to protect the SO2 sampling system from adverse effects associated with filter liquefaction at high humidities, while at the same time providing a simple means for eliminating large particles from the sampled air. Tests indicate that the sampler works well for SO2 and for particulate species, and that HNO3 concentrations are underestimated by about 25%. The DDIM approach differs from previous network measurement programs in that the data sets are designed to permit extension from observations at a subset of research sites to less intensive routine measurement sites. Hence a major goal is the definition of a suitable set of supporting data from which dry deposition rates can be inferred using air concentration data. Local vegetation characteristics are noted. At present, the additional variables that are monitored are solar radiation, wind speed, wind direction standard deviation, temperature, humidity, surface wetness, and precipitation. Observers report changes in the surrounding surface, such as the presence of snow or unusual drought.

Dry deposition inferential measurement techniques. II, Seasonal and annual deposition rates of sulfur and nitrate

Abstract Since the autumn of 1984, a dry deposition research network has been operated to develop and refine methods to make defensible estimates of dry deposition rates of SO 2 , sulfate and nitrate (particulate and gaseous) on a routine basis. Ten of the sites are located in the eastern part of the U.S. while two are located in the western half. Annual dry deposition rates of sulfur (SO 2 +SO 4 2−2 ) are estimated to range from 2.5 kg ha −1 at Whiteface Mountain, NY to 14 kg ha −1 at Argonne, IL. The majority of deposited sulfur was delivered in the form of SO 2 . Deposition rates were highest during the summer season even though SO 2 concentrations peaked during the winter months because the estimated deposition velocities ( V d ) were much greater in the summer. Nearly all of the dry deposited nitrogen (HNO 3 +NO 3 − ) was in the form of HNO 3 . An annual cycle was not evident in the time series of nitrogen deposition rates. For both sulfur and nitrogen, dry deposition was estimated to provide between 30% and 50% of the total input from the atmosphere (wet+dry) for all sites in the eastern U.S.

On the measurement of dry deposition using imperfect sensors and in non-ideal terrain

Important questions concerning the turbulent exchange of atmospheric pollutants between the air and natural surfaces urgently require answers, but sensors for many important species are not yet sufficiently well developed for use with standard micrometeorological methods. There is need, therefore, to develop methods by which deficient sensors can be used in micrometeorological applications. There is also need to extend micrometeorological methods to circumstances which do not satisfy the conventional perfect-site constraints. Here, methods based upon the assumption of cospectral similarity are explored. Initial tests indicate that it is possible to estimate daytime turbulent fluxes with sensors giving response times considerably greater than the values normally quoted for eddy correlation (e.g., 5 s instead of 1 s), and to compute first-order corrections for the error resulting from the lack of detection of high-frequency turbulence. It is suggested that a similar method might be used to derive flux data in terrain more complex than can be handled by conventional micrometeorology. The techniques outlined here should be applied only with caution, but appear adequate to permit the use of deficient sensors in some circumstances, and good sensors over some micrometeorologically deficient terrain.

A strategy for integrated monitoring

Administrative machinery has been set up to regulate and control most of the emissions that are known to have severe local consequences, such as the discharge of raw sewage into rivers and lakes and the smokestack emission of air pollutants. Now, the nature of environmental degradation is usually different. We are faced with pollutants and effects with more subtle cause-effect relationships, often characterized by larger geographic areas of interest and longer term potential damage; the potential risk is now more chronic than acute. Acid rain and climate change are good examples, in that they are associated with a variety of pollutants from a number of sources and damage to ecosystems occurs over many years. It is argued that monitoring programs should evolve to reflect the changing nature of the environmental problems they are addressing. It is now necessary to consider interactions among many pollutants, mixing among the various media, and potentially affecting many components of the ecosystem in both indirect and direct ways. Here, integrated monitoring and analysis is presented as a unifying strategy to bring together different measurement methodologies in different disciplines, addressing environmental questions of complexity beyond the scope of many existing activites that have a classical narrower focus. The underlying concept is of nested networks, each tier being composed of sites selected for specific purposes but arranged to maximize the number of common sites where more multidisciplinary questions can be addressed.

A national critical loads framework for atmospheric deposition effects assessment: III. Deposition characterization

Methods are discussed for describing patterns of current wet and dry deposition under various scenarios. It is proposed that total deposition data across an area of interest are the most relevant in the context of critical loads of acidic deposition, and that the total (i.e., wet plus dry) deposition will vary greatly with the location, the season, and the characteristics of individual subregions. Wet and dry deposition are proposed to differ in such fundamental ways that they must be considered separately. Both wet and dry deposition rates are controlled by the presence of the chemical species in question in the air (at altitudes of typically several kilometers in the case of wet deposition, and in air near the surface for dry). The great differences in the processes involved lead to the conclusion that it is better to measure wet and dry deposition separately and combine these quantifications to produce “total deposition” estimates than to attempt to derive total deposition directly. A number of options for making estimates of total deposition to be used in critical loads assessment scenarios are discussed for wet deposition (buckets and source receptor models) and for dry deposition (throughfall, micrometeorology, surrogate surfaces and collection vessels, inference from concentrations, dry-wet ratios, and source-receptor models).

Jim Angell's contributions to meteorology

MARCH 2005 AMERICAN METEOROLOGICAL SOCIETY | O ver the past half century, Jim Angell has made pioneering contributions to meteorology, especially to our understanding of climate variability, stratospheric processes, and the ozone layer. On 4 November 2003, many colleagues and friends gathered at the National Oceanic and Atmospheric Administration (NOAA) Science Center in Silver Spring, Maryland, for a 1-day symposium reviewing and honoring Jim’s career achievements and celebrating his 80th birthday (which was 2 November). This article highlights some of Jim’s contributions, both as reviewed during the symposium, and as captured in poems composed in his honor and recited at a birthday dinner celebration.1 Jim’s memories are interspersed in italics. More information about Jim Angell and the Angell Symposium, including photos, some presentations, his publications list, and more poems, can be found on the Angell Symposium Web site (www.arl.noaa.gov/ss/climate/AngellSymposium.html).