			Home About us Contact

Diurnal Variability (diurnal + variability)

Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

Hourly surface wind monitor consistency checking over an extended observation period

ENVIRONMETRICS, Issue 4 2009
Scott Beaver
Abstract A consistency checking methodology is presented to aid in identifying biased values in extended historical records of hourly surface wind measurements obtained from a single station. The method is intended for screening extended observation periods for values which do not fail physical consistency checks (i.e., standard or complex quality assurance methods), yet nonetheless exhibit statistical properties which differ from the bulk of the record. Several specific types of inconsistencies common in surface wind monitoring datasets are considered: annual biases, unexpected values, and discontinuities. The purely empirical method checks for self-consistency in the temporal distribution of the wind measurements by explicitly modeling the diurnal variability. Each year of data is modeled using principal component analysis (PCA) (or empirical orthogonal functions, EOF), then hierarchical clustering with nearest neighbor linkage is used to visualize any annual biases existing in the measurements. The diurnal distributions for wind speed and direction are additionally estimated and visualized to determine any periods of time which are inconsistent with the typical diurnal cycle for a given monitor. The robust consistency checking method is applied to a set of 44 monitors operating in the San Joaquin Valley (SJV) of Central California over a 9-year period. Monitors from the SLAMS, CIMIS, and RAWS networks are considered. Similar inconsistencies are detected in all three networks; however, network-specific types of inconsistencies are found as well. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Regional-scale measurements of CH4 exchange from a tall tower over a mixed temperate/boreal lowland and wetland forest

GLOBAL CHANGE BIOLOGY, Issue 9 2003
Cindy Werner
The biosphere,atmosphere exchange of methane (CH4) was estimated for a temperate/boreal lowland and wetland forest ecosystem in northern Wisconsin for 1997,1999 using the modified Bowen ratio (MBR) method. Gradients of CH4 and CO2 and CO2 flux were measured on the 447-m WLEF-TV tower as part of the Chequamegon Ecosystem,Atmosphere Study (ChEAS). No systematic diurnal variability was observed in regional CH4 fluxes measured using the MBR method. In all 3 years, regional CH4 emissions reached maximum values during June,August (24±14.4 mg m,2 day,1), coinciding with periods of maximum soil temperatures. In 1997 and 1998, the onset in CH4 emission was coincident with increases in ground temperatures following the melting of the snow cover. The onset of emission in 1999 lagged 100 days behind the 1997 and 1998 onsets, and was likely related to postdrought recovery of the regional water table to typical levels. The net regional emissions were 3.0, 3.1, and 2.1 g CH4 m,2 for 1997, 1998, and 1999, respectively. Annual emissions for wetland regions within the source area (28% of the land area) were 13.2, 13.8, and 10.3 g CH4 m,2 assuming moderate rates of oxidation of CH4 in upland regions in 1997, 1998, and 1999, respectively. Scaling these measurements to the Chequamegon Ecosystem (CNNF) and comparing with average wetland emissions between 40°N and 50°N suggests that wetlands in the CNNF emit approximately 40% less than average wetlands at this latitude. Differences in mean monthly air temperatures did not affect the magnitude of CH4 emissions; however, reduced precipitation and water table levels suppressed CH4 emission during 1999, suggesting that long-term climatic changes that reduce the water table will likely transform this landscape to a reduced source or possibly a sink for atmospheric CH4. [source]

MASS LOAD ESTIMATION ERRORS UTILIZING GRAB SAMPLING STRATEGIES IN A KARST WATERSHED,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2003
Alex W. Fogle
ABSTRACT: Developing a mass load estimation method appropriate for a given stream and constituent is difficult due to inconsistencies in hydrologic and constituent characteristics. The difficulty may be increased in flashy flow conditions such as karst. Many projects undertaken are constrained by budget and manpower and do not have the luxury of sophisticated sampling strategies. The objectives of this study were to: (1) examine two grab sampling strategies with varying sampling intervals and determine the error in mass load estimates, and (2) determine the error that can be expected when a grab sample is collected at a time of day when the diurnal variation is most divergent from the daily mean. Results show grab sampling with continuous flow to be a viable data collection method for estimating mass load in the study watershed. Comparing weekly, biweekly, and monthly grab sampling, monthly sampling produces the best results with this method. However, the time of day the sample is collected is important. Failure to account for diurnal variability when collecting a grab sample may produce unacceptable error in mass load estimates. The best time to collect a sample is when the diurnal cycle is nearest the daily mean. [source]

Stomatal responses to CO2 during a diel Crassulacean acid metabolism cycle in Kalanchoe daigremontiana and Kalanchoe pinnata

PLANT CELL & ENVIRONMENT, Issue 5 2009
SUSANNE VON CAEMMERER
ABSTRACT To investigate the diurnal variation of stomatal sensitivity to CO2, stomatal response to a 30 min pulse of low CO2 was measured four times during a 24 h time-course in two Crassulacean acid metabolism (CAM) species Kalanchoe daigremontiana and Kalanchoe pinnata, which vary in the degree of succulence, and hence, expression and commitment to CAM. In both species, stomata opened in response to a reduction in pCO2 in the dark and in the latter half of the light period, and thus in CAM species, chloroplast photosynthesis is not required for the stomatal response to low pCO2. Stomata did not respond to a decreased pCO2 in K. daigremontiana in the light when stomata were closed, even when the supply of internal CO2 was experimentally reduced. We conclude that stomatal closure during phase III is not solely mediated by high internal pCO2, and suggest that in CAM species the diurnal variability in the responsiveness of stomata to pCO2 could be explained by hypothesizing the existence of a single CO2 sensor which interacts with other signalling pathways. When not perturbed by low pCO2, CO2 assimilation rate and stomatal conductance were correlated both in the light and in the dark in both species. [source]