Hudson Valley Fog Environments

Fitzjarrald, David R.; Lala, G. Garland

doi:10.1175/1520-0450(1989)028<1303:hvfe>2.0.co;2

Cited by 67 publications

(56 citation statements)

References 23 publications

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“…Due to continuing evaporation as vertical mixing decreases, it is usual for the surface water vapour mixing ratio (r v ) to increase throughout the AET time frame (Fitzjarrald and Lala 1989;Acevedo and Fitzjarrald 2001;Busse and Knupp 2012;Bonin et al 2013). Such characteristic behaviour is considered here using the MIPS MPR.…”

Section: Data and Analysis Methodsmentioning

confidence: 99%

“…While they found the average sunset relative time for the initial r v increase to be about 30 min in summer and a few minutes in autumn before sunset, the normalized r v values in our investigation increase on average starting 80 min prior to sunset, with spring cases showing this start even 1 h earlier. This characteristic increase (often accomplished in the short-term "jumps") in surface water vapour was highlighted by Fitzjarrald and Lala (1989) and Acevedo and Fitzjarrald (2001); both studies used autumn observations from the Hudson River valley in the vicinity of Albany, New York State, and the latter also found temporal variations in the start of the increase among various observational sites. As vertical mixing is effectively reduced by the decreasing surface heat flux and evaporation near the surface continues, a build up of r v results that persists until eventual dew (or frost) formation later in the night.…”

Section: Surface Datamentioning

confidence: 99%

“…This upward trend in the mean r v continues even after sunset, implying that evaporation is the main contributor to the increase, since transpiration from plants requires photosynthesis. Fitzjarrald and Lala (1989) and the follow-up work of Acevedo and Fitzjarrald (2001) showed that near the time of maximum r v increase an inflection point in the surface temperature trace often occurs. The former mention the contribution of the net radiation term to temperature tendency (and the saturation specific humidity budget) during the transition, and we reiterate here that our cases were intentionally selected to only include clear-sky or nearly clear-sky days.…”

Section: Surface Datamentioning

confidence: 99%

“…Reductions in the surface heat flux lead to less vertical mixing, and the resulting decrease in turbulence is evident in this characteristic decrease. Continued evaporation near the surface as the depth of the mixed layer rapidly declines creates an increase in surface humidity that has been noted by several investigators (Fitzjarrald and Lala 1989;Acevedo and Fitzjarrald 2001;Busse and Knupp 2012;Bonin et al 2013). Once the surface heat flux has reversed signs, it is common for a temperature inversion to develop, primarily as a result of radiational cooling.…”

Section: Introductionmentioning

confidence: 99%

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Multi-platform Observations Characterizing the Afternoon-to-Evening Transition of the Planetary Boundary Layer in Northern Alabama, USA

Wingo

Knupp

2014

Boundary-Layer Meteorol

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Observations from the University of Alabama in Huntsville campus and groundbased scanning radar for over 140 total spring, summer, and autumn cases are studied to contribute to the relative scarcity of long-term datasets documenting the afternoon-to-evening transition of the planetary boundary layer. A sunset relative frame of reference is employed, focusing on the period 3 h before to 2 h after astronomical sunset, and several findings are consistent with previous investigations. Fluctuating components of wind and temperature computed from nearly collocated surface, Doppler wind profiler, and vertically pointing Doppler lidar measurements show a consistent decline as turbulence intensity diminishes through the transition. When normalized by their initial values, a pattern emerges: temperature variances decline slowly at first then quite abruptly after about 90 min before sunset. After the temperature variances begin to wane, vertical velocity fluctuations decrease, and the rate of their decay increases as vigorous thermal structures diminish. The fastest decline of the horizontal wind variance occurs after an accelerated vertical wind variance decrease, and the horizontal wind fluctuations display the slowest rate of decrease among these quantities. Near-surface humidity measurements show increases in mean water vapour mixing ratio as a steady rise generally beginning about 80 min prior to sunset. Composites of mean lidar vertical motion show final convective-type towers of upward motion occur about an hour before sunset and are coherent through 800 m (all heights a.g.l.). Lidar vertical motion variance at 195 m decreases by more than an order of magnitude approaching sunset, then remains below 0.01 m 2 s −2 for the rest of the studied time frame. Subtle, but steady, increases in both horizontal wind speed and radar-derived horizontal wind convergence above the surface layer (at 300 m) span the entire 5-h time frame. While the convergence results show a broad range, an increase in the mean is clear and found to be statistically significant. Implications

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Section: Data and Analysis Methodsmentioning

confidence: 99%

Section: Surface Datamentioning

confidence: 99%

Section: Surface Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Multi-platform Observations Characterizing the Afternoon-to-Evening Transition of the Planetary Boundary Layer in Northern Alabama, USA

Wingo

Knupp

2014

Boundary-Layer Meteorol

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“…It usually forms near the surface under clear skies in stagnant air in association with anticyclonic conditions (Gultepe et al, 2007). However, the mechanisms of radiation fog formation, development and dissipation are very complex and have been extensively studied with a series of numerical simulations and comprehensive observational programs including in situ measurements (Meyer et al, 1986;Fitzjarrald and Lala, 1989;Fuzzi et al, 1992Fuzzi et al, , 1998Gultepe et al, 2007;Zhou and Ferrier, 2008;Liu et al, 2011;Dupont et al, 2012). Recently, field experiments have been conducted to investigate dynamic, thermodynamic, microphysical, and radiative processes in Beijing and Nanjing, China (Liu et al, 2011), in Canada (Gultepe et al, 2009), and in Paris, France (Haeffelin et al, 2010;Dupont et al, 2012).…”

Section: Introductionmentioning

confidence: 96%

Development and application of a method for the objective differentiation of fog life cycle phases

Maier

Bendix

Thies

2013

Tellus B: Chemical and Physical Meteorology

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A B S T R A C T An objective classification of radiation fog in distinct evolutionary stages during its life cycle based on reliable criteria is essential for various applications, for example for numerical fog modelling and fog forecasting. However, there have been Á up to now Á merely qualitative approaches for the distinction of different evolutionary stages in radiation fog. Measurements of the microphysical fog properties with an optical particle counter obtained from droplet measurement technologies together with recordings of the horizontal visibility (VIS) are statistically analyzed to determine individual evolutionary stages of radiation fog with consistent microphysical properties. The developed three-stage approach is based on a statistical change point analysis of the double sum curves of the VIS, the liquid water content, the droplet concentration and the mean radius of the drop size distributions. It could be shown that each of the three recorded radiation fog occurrences could be split into three consecutive phases from formation to dissipation, regardless whether the VIS or the microphysical properties were considered. Having featured consistent microphysical patterns, it could be assumed that the three separated phases of the single fog occurrence could be aggregated for radiation fog. Although this classification is statistically reliable, the dataset still has to be extended for a generalization concerning the separated evolutionary stages.

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Fog as a Hydrologic Input

Bruijnzeel

Eugster

Burkard

2005

Encyclopedia of Hydrological Sciences

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This article reviews the hydrologic importance of fog in its various forms. Meteorologically, fog is defined as a ground-touching cloud with a visibility in the horizontal of less than 1000 m. The most widely occurring fog types include radiation fog, sea fog and steam fog, and advection fog, but often fog is also referred to by its location of occurrence (coastal, valley, or mountain fog). The physical processes underlying the various types of fog are described briefly. The use, advantages, and limitations of the most common types of fog collectors, fog detectors, and fog droplet spectrometers are dealt with before embarking on a discussion of techniques for the measurement and modeling of fog deposition on forest vegetation. Results of fog deposition measurements made at selected locations (representing coastal vs. inland, lowland vs. montane, and temperate vs. tropical conditions) are compared. The data confirm the importance of fog interception at many coastal and montane sites across the tropical to mediterranean and warm-temperate climatic spectrum. Under more continental conditions, contributions by fog are usually more modest except on windy mountain ridges and summits. Finally, the paper indicates the chief gaps in knowledge regarding the measurement and importance of fog as a hydrologic input.Encyclopedia of Hydrological Sciences. Edited by M G Anderson.

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Hudson Valley Fog Environments

Cited by 67 publications

References 23 publications

Multi-platform Observations Characterizing the Afternoon-to-Evening Transition of the Planetary Boundary Layer in Northern Alabama, USA

Multi-platform Observations Characterizing the Afternoon-to-Evening Transition of the Planetary Boundary Layer in Northern Alabama, USA

Development and application of a method for the objective differentiation of fog life cycle phases

Fog as a Hydrologic Input

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