Heat and moisture flux profiles in a region with inhomogeneous surface evaporation

Michels, B.I.; Jochum, A.M.

doi:10.1016/0022-1694(94)05095-f

Cited by 18 publications

(20 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The scalar entrainment flux is not coupled to the scalar surface flux, and therefore can have any value or sign and can dominate over the influence of the surface flux on scalar statistics. Examples of the ABL in which the statistics of scalars (e.g., water vapour, CO 2 and reactive species) are mainly determined by the entrainment process can be found in e.g., Druilhet et al (1983), Sorbjan (1991), Michels andJochum (1995), De Arellano et al (2004) and Jonker et al (2004).…”

Section: Introductionmentioning

confidence: 99%

Scaling Variances of Scalars in a Convective Boundary Layer Under Different Entrainment Regimes

Moene

Michels

Holtslag

2006

Boundary-Layer Meteorol

Self Cite

View full text Add to dashboard Cite

Abstract.For the presentation and analysis of atmospheric boundary-layer (ABL) data, scales are used to non-dimensionalise the observed quantities and independent variables. Usually, the ABL height, surface sensible heat flux and surface scalar flux are used. This works well, so long as the absolute values of the entrainment ratio for both the scalar and temperature are similar. The entrainment ratio for temperature naturally ranges from −0.4 to −0.1. However, the entrainment ratio for passive scalars can vary widely in magnitude and sign. Then the entrainment flux becomes relevant as well. The only customary scalar scale that takes into account both the surface flux and the entrainment flux is the bulk scalar scale, but this scale is not well-behaved for large negative entrainment ratios and for an entrainment ratio equal to −1. We derive a new scalar scale, using previously published large-eddy simulation results for the convective ABL. The scale is derived under the constraint that scaled scalar variance profiles are similar at those heights where the variance producing mechanisms are identical (i.e., either near the entrainment layer or near the surface). The new scale takes into account that scalar variance in the ABL is not only related to the surface flux of that scalar, but to the scalar entrainment flux as well. Furthermore, it takes into account that the production of variance by the entrainment flux is an order of magnitude larger than the production of variance by the surface flux (per unit flux). Other desirable features of the new scale are that it is always positive (which is relevant when scaling standard deviations) and that the scaled variances are always of order 1-10.

show abstract

Section: Introductionmentioning

confidence: 99%

Scaling Variances of Scalars in a Convective Boundary Layer Under Different Entrainment Regimes

Moene

Michels

Holtslag

2006

Boundary-Layer Meteorol

Self Cite

View full text Add to dashboard Cite

show abstract

“…The residual-layer moisture has a layered structure, and so a new humidity gradient is introduced whenever a new moisture layer was reached. This phenomenon was observed regularly in the EFEDA region (Michels and Jochum 1995;Jochum et al 2004). Compositing these profiles is possible using a multilayer normalization procedure, but this would introduce considerable errors resulting from the observational uncertainties of the individual layer depths.…”

Section: B Regional Fluxes From a Conservation Approachmentioning

confidence: 99%

“…The aircraft carried instrumentation to measure and derive basic meteorological parameters (temperature, humidity, pressure, and wind), turbulent fluxes (heat, moisture, and momentum), the four radiation flux components, water vapor and aerosol backscatter vertical profiles, and video images of the ground. Jochum (1993b) and Michels and Jochum (1995) describe the instrumentation, flight patterns, and analysis details. With high-resolution (100 Hz) sensors and sampling and at a typical low-level true airspeed of 135 m s Ϫ1 , scales down to 15 m are captured.…”

Section: B Measurements and Datamentioning

confidence: 99%

“…Potential errors arise from five fundamental sources, of which the first (instrumental accuracy) is not critical at all (Michels and Jochum 1995). The next two are related to inadequate sampling of turbulent eddies, either by missing the dominant wavelengths or by having too small a sample.…”

Section: Scenario IV In Tunementioning

confidence: 99%

“…Additional runs of the coupled canopy-ML slab model were made Michels and Jochum (1995). Lines with no symbols are from coupled canopy-ML model (MLm).…”

Section: A Comparison Of Regional Flux Estimatesmentioning

confidence: 99%

See 2 more Smart Citations

Area-Averaged Surface Fluxes in a Semiarid Region with Partly Irrigated Land: Lessons Learned from EFEDA

Jochum¹,

Bruin

Holtslag

et al. 2006

Journal of Applied Meteorology and Climatology

View full text Add to dashboard Cite

The European Field Experiment in a Desertification-Threatened Area (EFEDA) provides a comprehensive land surface dataset for a semiarid Mediterranean environment with natural vegetation and cultivated dry and irrigated land. This paper discusses the methods and practical aspects of deriving areaaveraged fluxes for a range of areas from the whole EFEDA region to several numerical weather prediction model grid cells (on 10-100-km scales). A time series of grid-scale surface fluxes for the entire observational period of 1 month was obtained from weighted surface averages, using a crop phenology-based land use classification together with a homogenized set of surface observations representative of the four major vegetation classes. The flux-aggregated surface observations were compared with two other approaches to obtain grid-scale fluxes (airborne flux observations and radiosondes in conjunction with a simple mixedlayer model). The area-aggregated fluxes (in particular of latent heat) depend strongly on the location of the area boundaries whenever a significant fraction of irrigated land is present. This result confirms clearly the importance of adequately accounting for tiles of irrigated land in surface schemes and corresponding physiographic databases of large-scale models. A simple way to accommodate for minimum information on the canopy water status is proposed in terms of the distinction of at least two seasonal classes of irrigated crops-one of spring and one of summer growing cycles. The main lesson from this aggregation exercise concerns the role of irrigation. First, this study quantifies the uncertainties in the space-time pattern and its effects on aggregated surface fluxes for the first time on the grounds of observational data. Second, it demonstrates practical ways to accomplish the parameterization of irrigation in flux aggregation schemes, by identifying the key data along with their possible sources and by defining a practical implementation procedure.

show abstract

Partitioning of radiation and energy balance components in an inhomogeneous desert valley

Malek

Bingham

1997

Journal of Arid Environments

View full text Add to dashboard Cite

Heat and moisture flux profiles in a region with inhomogeneous surface evaporation

Cited by 18 publications

References 15 publications

Scaling Variances of Scalars in a Convective Boundary Layer Under Different Entrainment Regimes

Scaling Variances of Scalars in a Convective Boundary Layer Under Different Entrainment Regimes

Area-Averaged Surface Fluxes in a Semiarid Region with Partly Irrigated Land: Lessons Learned from EFEDA

Partitioning of radiation and energy balance components in an inhomogeneous desert valley

Contact Info

Product

Resources

About