Intensive Measurement Periods Research Articles

An evaluation of the water balance technique for the estimation of evapotranspiration for a mixed forest

In the summer of 1987 a detailed field experiment was conducted at the Petawawa National Forestry Institute at Chalk River, Ontario, to evaluate the performance of the water balance technique for the estimation of evapotranspiration. Bowen ratio – energy balance estimates of evapotranspiration, available over a portion of an intensive measurement period, provided an independent check on the water balance estimates. The daily totals of evapotranspiration were on average 1% less than the Bowen ratio – energy balance estimate. The length of time required to maintain the evapotranspiration estimates below a 10% level of uncertainty using the water balance technique is 13 days. The lowest average daily percent probable error is obtained for an integration period with (i) a minimum number of precipitation events, (ii) a large number of days, and (iii) a high evapotranspiration rate.

Medium‐ to large‐scale atmospheric variability during the Frontal Air‐Sea Interaction Experiment

Shipboard, aircraft, and satellite atmospheric data are examined to determine the representativeness of the Frontal Air‐Sea Interaction Experiment (FASINEX) intensive measurement period, Phase II, in terms of climatology, atmospheric forcing, the general structure of the marine atmospheric boundary layer (MABL), and variability in boundary layer properties affecting air‐ocean dynamics and thermodynamics. With regard to climatology, conditions observed during the intensive period were typical in terms of air‐sea temperature differences, surface pressure patterns, cloud cover, and storm tracks. Storm system variabilities, such as the air temperature behind cold fronts, wind stress maxima occurring after frontal passage, the times for clockwise vector wind shifts associated with the frontal systems, and the systems' speeds, are estimated and emphasized in synoptic‐scale characterizations, since these can be related to observed ocean responses. The local ocean surface variability was observed to have an influence on regional boundary layer properties and on air‐sea interaction parameters even in the presence of the atmospheric storms.

Analysis of Tracer Data Collected during the SCCCAMP 1985 Intensive Measurement Periods

Abstract This paper contains an analysis of data obtained from measurements of the concentration of tracer gases released during the four intensive measurement periods of the 1985 South-Central Coast Cooperative Air Monitoring Program (SCCCAMP). These tracer experiments were designed to document mesoscale circulation patterns in the coastal region of Santa Barbara and Ventura counties in southern California. Analyses of these concentration data are aimed at evaluating the design of the experiments, describing the movement of the tracers and comparing transport patterns to measured winds, and evaluating the ability of trajectory calculations, which are based on winds from a diagnostic wind model to reproduce those patterns of transport. The study concludes that patterns of recirculation over the 2-day period of the tests are successfully documented, revealing transport in the Santa Barbara Channel that is consistent with the circulation about the midchannel eddy, and diurnal patterns of onshore–offshore fl...

Analysis of Mesoscale Airflow Patterns in the South-Central Coast Air Basin during the SCCCAMP 1985 Intensive Measurement Periods

An analysis of the mesoscale airflow patterns in the south-central coast air basin (SCCAB) was performed using data collected during the 1985 South-Central Coast Cooperative Aerometric Monitoring Program (SCCCAMP). Airflow within the SCCAB is strongly influenced by the diurnal sea-breeze/land-breeze cycle and by slope flows that develop along the steep terrain. Mesoscale airflow features observed during the four intensive monitoring periods include eddies along the coast and over the Santa Barbara Channel. An analysis of the transport patterns indicated that both recirculation of pollutants within the SCCAB and transport of pollutants from the south coast air basin (SOCAB) contributed to the observed high ozone concentrations on the intensive monitoring days.

Liquid-chromatography analysis of chloride and nitrate with "negative" ultraviolet detection: ambient levels and relative abundance of gas-phase inorganic and organic acids in southern California

A simple, cost-effective method is described for the determination of chloride and nitrate in environmental samples using conventional liquid chromatography equipment and negative photometry detection, i.e., the detection of weakly UV-absorbing analytes in a strongly UV-absorbing eluent. Method performance and validation are described, along with an example of application to the simultaneous measurements of gas-phase inorganic (nitric, hydrogen chloride) and organic (Formic, acetic) acids in ambient air. During a 10-day period of intensive measurements at a southern California smog receptor site, ambient levels of nitric acid and hydrogen chloride ranged up to 16.6 and 2.7 ppb, respectively (4-h samples). However, organic acids were more abundant than inorganic acids and accounted for 73.5% (ppb basis) of the total gas-phase acids.

Mesoscale hydrographic variability in the vicinity of Points Conception and Arguello during April–May 1983: The OPUS 1983 experiment

In April and May 1983, interdisciplinary oceanographic observations were made of upwelling events in the Point Conception area off southern California. The principal objective was to observe the structure and time dependence of the upwelling system. To accomplish this, two ships, two aircraft, moorings, drogues, and satellite imagery were all included in the observational effort. During the intensive measurement period three main upwelling events and two intervening relaxation or downwelling intervals were sampled during what was a period of overall longer‐term sea surface warming. Surface temperatures during upwelling were as low as 10.5°C in the upwelling center between Point Arguello and Point Conception, while during periods of nonupwelling winds, temperatures reached 14°–15°C in the same area. The upwelling center was also a source of higher‐salinity water (33.7‰) relative to the offshore waters that were anomalously fresh (33.3‰). Upwelling was observed off Point Arguello, Point Conception, and the area between with a possible lag of up to a day at Point Conception relative to the other areas. The upwelling plume as observed by surface mapping and remote sensing tended to move in a variety of directions from SE to SW. Part of the movement was usually into the Santa Barbara Channel, but other parts of the plume occasionally moved southwestward. There was no obvious correlation of plume direction with the wind. During relaxation events the entire region was covered by a 10‐ to 20‐m‐thick warm (14°–16°C), fresh (<33.5‰) buoyant layer. Spatial correlations of water temperature with 24‐hour lagged winds showed logical patterns, but the distributions were not as seen in other California studies.