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J. C. Kaimal

Bio: J. C. Kaimal is an academic researcher from National Oceanic and Atmospheric Administration. The author has contributed to research in topics: Capping inversion & Wind shear. The author has an hindex of 4, co-authored 4 publications receiving 217 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, the authors describe the motivation for those experiments, describes how they were conducted, and summarizes their results. But they do not discuss the performance of boundary-layer experiments.
Abstract: Two experiments conducted almost 20 years ago have come to be regarded as important milestones in boundary-layer research. This paper recounts the motivation for those experiments, describes how they were conducted, and summarizes their results.

105 citations

Journal ArticleDOI
TL;DR: In this paper, three in-situ and five remote sensing techniques for measuring the height of the daytime convective boundary layer were compared, and good agreement between the different systems when the capping inversion was steep and well defined, and some variability when the stratification was not so sharply defined.
Abstract: Three in-situ and five remote sensing techniques for measuring the height of the daytime convective boundary layer were compared. There was, as a rule, good agreement between the different systems when the capping inversion was steep and well defined, and some variability when the stratification was not so sharply defined. Two indirect methods for estimating boundary-layer heights from the length scales of convective motions in the layer are also discussed.

71 citations

Journal ArticleDOI
TL;DR: In this paper, the authors examined several features of wave and turbulence structure associated with disturbed nocturnal inversion and showed that the major contribution to the upward heat flux occurs at frequencies that would normally be considered characteristic of waves.
Abstract: Acoustic sounder and tower data obtained at the Boulder Atmospheric Observatory (BAO) are used to examine several features of the wave and turbulence structure associated with a disturbed nocturnal inversion. General features, including mean fields and Richardson number, for the case selected for this study are presented. Spectral analysis of the tower data reveals a separation of energy into wavelike and turbulent fluctuations. Analysis of the heat flux, however, shows upward counter-gradient fluxes in the vicinity of a low-level jet and near the top of the inversion. Cospectral analysis shows that the major contribution to the upward heat flux occurs at frequencies that would normally be considered characteristic of waves. In some cases, the upward flux is associated with a phase shift between vertical velocity w and fluctuating temperature θ different from the quadrature relation that would be expected of internal waves. Time series analysis reveals that these unexpected positive fluxes occur in relatively short bursts. Analysis of time series of θ and w in other cases, as well as inspection of acoustic sounder records, shows that sometimes such upward fluxes can result from a combination of wave motion and horizontal temperature advection. In this case the advection is associated with a shallow cold front.

45 citations

Journal ArticleDOI
TL;DR: In this article, a 5-yr continuous record of midtropospheric horizontal wind components from a radar wind profiler operating at Fleming, Colorado, shows a broad spectral peak centered around a period of 1 week and a minimum at about 4 months, in addition to the expected 1-yr peak.
Abstract: This study of a 5-yr continuous record of midtropospheric horizontal wind components from a radar wind profiler operating at Fleming, Colorado, shows a broad spectral peak centered around a period of 1 week and a minimum at about 4 months, in addition to the expected 1-yr peak. However, when the records are separated according to seasons, the pattern becomes more complicated, with several distinct peaks and clear differences between the summer and winter behavior emerging. In this paper the different spectral patterns observed are presented and the synoptic-scale features in the weather that could produce them are speculated on.

6 citations


Cited by
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TL;DR: The eddy covariance method is most accurate when the atmospheric conditions (wind, temperature, humidity, CO2) are steady, the underlying vegetation is homogeneous and it is situated on flat terrain for an extended distance upwind as discussed by the authors.
Abstract: The eddy covariance technique ascertains the exchange rate of CO2 across the interface between the atmosphere and a plant canopy by measuring the covariance between fluctuations in vertical wind velocity and CO2 mixing ratio. Two decades ago, the method was employed to study CO2 exchange of agricultural crops under ideal conditions during short field campaigns. During the past decade the eddy covariance method has emerged as an important tool for evaluating fluxes of carbon dioxide between terrestrial ecosystems and the atmosphere over the course of a year, and more. At present, the method is being applied in a nearly continuous mode to study carbon dioxide and water vapor exchange at over a hundred and eighty field sites, worldwide. The objective of this review is to assess the eddy covariance method as it is being applied by the global change community on increasingly longer time scales and over less than ideal surfaces. The eddy covariance method is most accurate when the atmospheric conditions (wind, temperature, humidity, CO2) are steady, the underlying vegetation is homogeneous and it is situated on flat terrain for an extended distance upwind. When the eddy covariance method is applied over natural and complex landscapes or during atmospheric conditions that vary with time, the quantification of CO2 exchange between the biosphere and atmosphere must include measurements of atmospheric storage, flux divergence and advection. Averaging CO2 flux measurements over long periods (days to year) reduces random sampling error to relatively small values. Unfortunately, data gaps are inevitable when constructing long data records. Data gaps are generally filled with values produced from statistical and empirical models to produce daily and annual sums of CO2 exchange. Filling data gaps with empirical estimates do not introduce significant bias errors because the empirical algorithms are derived from large statistical populations. On the other hand, flux measurement errors can be biased at night when winds are light and intermittent. Nighttime bias errors tend to produce an underestimate in the measurement of ecosystem respiration. Despite the sources of errors associated with long-term eddy flux measurements, many investigators are producing defensible estimates of annual carbon exchange. When measurements come from nearly ideal sites the error bound on the net annual exchange of CO2 is less than ±50 g C m−2 yr−1. Additional confidence in long-term measurements is growing because investigators are producing values of net ecosystem productivity that are converging with independent values produced by measuring changes in biomass and soil carbon, as long as the biomass inventory studies are conducted over multiple years.

2,210 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present a review of the literature on the analysis of profile measurements and the use of parameterisations and simple models, and suggest for the preprocessor development and for future research activities.

898 citations

Journal ArticleDOI
TL;DR: In this article, the roughness sublayer, surface layer, local similarity, z-less stratification and the region near the boundary-layer top are examined in the stable boundary layer.
Abstract: Various features of different stability regimes of the stable boundary layer are discussed. Traditional layering is examined in terms of the roughness sublayer, surface layer, local similarity, z-less stratification and the region near the boundary-layer top. In the very stable case, the strongest turbulence may be detached from the surface and generated by shear associated with a low level jet, gravity waves or meandering motions. In this case, similarity theory and the traditional concept of a boundary-layer break down. The elevated turbulence may intermittently recouple to the surface. Inability to adequately measure turbulent fluxes in very stable conditions limits our knowledge of this regime.

604 citations

Journal ArticleDOI
TL;DR: The universal length scale for exchange processes in the surface layer was the basis for the derivation of the similarity theory by Monin and Obukhov in 1954 as mentioned in this paper, and the current status of the theory is described, covering topics such as the accuracy of the universal functions and turbulent Prandtl number.
Abstract: This historical survey shows that Obukhov’s 1946 fundamental paper on a universal length scale for exchange processes in the surface layer was the basis for the derivation of the similarity theory by Monin and Obukhov in 1954. A brief overview of the experiments and findings used to formulate the universal functions in the presently used form is given. Finally, the current status of the theory is described, covering topics such as the accuracy of the universal functions and the turbulent Prandtl number.

538 citations

Book
28 May 2007
TL;DR: In this article, the authors present a list of principal symbols and abbreviations for parameterization schemes and their application in the terrestrial environment, including land surface-atmosphere parameterizations, water-surface-layer and turbulence parameterizations.
Abstract: Preface List of principal symbols and abbreviations 1. Why study parameterization schemes? 2. Land surface-atmosphere parameterizations 3. Soil-vegetation-atmosphere parameterizations 4. Water-atmosphere parameterizations 5. Planetary boundary layer and turbulence parameterizations 6. Convective parameterizations 7. Microphysics parameterizations 8. Radiation parameterizations 9. Cloud cover and cloudy sky radiation parameterizations 10. Orographic drag parameterizations 11. Thoughts on the future 12. References Index.

452 citations