Nocturnal Drainage Winds Research Articles

Potential for climate equity: Integrating nocturnal drainage winds into heat mitigation strategies in Portland

Limited adaptation options and local-scale heat mitigation measures to counter elevated nighttime temperatures have increased the need for effective and equitable city-scale cooling measures. I proposed that cold and dense air from surrounding high landscapes, called drainage winds, could be a potential city-scale nocturnal heat mitigation measure. I further suggest that this measure can moderate spatial disparities in heat mitigation capacity due to the unequal distribution of urban trees in Portland, Oregon. First, I conducted KLAM_21 wind simulations using grid cells of 30 m with elevation and historical and recent land use types. Then, I used census block groups including the proportion of tree canopy area, socioeconomic variables, and simulated wind attributes in statistical analysis. I found: (1) KLAM_21 simulation results generally align with actual wind observations, (2) urban development over the last two decades lowered the cold air layer, and (3) marginalized neighborhoods with less tree canopy coverage experience greater nocturnal cooling effects from drainage winds. These results emphasize the potential of drainage winds as an equitable heat mitigation option in Portland. Urban planners should integrate scenario-based simulated wind data into heat mitigation strategies to foster a more equitable and comfortable nighttime thermal environment in the long term.

Field Observations of Nocturnal Drainage Winds Blowing Down to the Fukuoka Plains

The vertical structures of nocturnal drainage winds that blow onto the Fukuoka Plains from mountains behind were examined on the basis of echo intensity and wind velocity obtained by using a Doppler sodar. Air and soil surface temperatures, wind velocity and net radiation near the ground surface were also measured to estimate the heat budget between the air and the ground. Though the nocturnal drainage winds have the depth of 250 m to 300 m, the shape of the fronts varies with the sea breeze and the surrounding flow. Twice in the nighttime, the occurrence of the horizontal wind with the maximum speed of 4 to 6 ms-1 was observed at the height about 150 m above the ground surface. Though the ascending currents with the speed of 0.2 to 0.4 ms-1 were also seen twice with the occurrence, the second current ascended higher than the first one. These phenomena may be due to the intermitted supply of cold air mass from a basin being in the upstream side. After the first occurrence, the air temperature near the ground surface reaches to the air temperature at a height of 30m. This reason is that the cold air near the ground surface formed by the radiational cooling is replaced with the upper warm air by the advection of the drainage winds. After then, the decreasing rate of the air temperature becomes smaller because the heat fluxes from the air toward the ground suppress the radiational cooling.

冷気流と冷気湖の動的相互作用に関する実測的研究

Field investigations of the dynamic interaction between nocturnal drainage winds and a cold-air lake were conducted in a hilly area near Fukuoka City, Japan. It was found that nocturnal drainage winds can be classified into two types according to where they occur, that is, below or above the surface of the cold-air lake. The nocturnal drainage wind which contributes to the development of the cold-air lake over a basin and flows down into the surface layer of the lake is one type of nocturnal drainage wind (NDW I). This type of flow, in general, has a thickness of more than 1O m, and a speed which oscillates with periods ranging from 30 to 60 minutes, though the cause of the periodicity has yet to be determined. Within the cold-air lake, that is, on the hillside buried in the lake, another type of drainage wind (NDW II) can be found, the thickness of which is less than about 10 m. Winds of this type also oscillate, with periods of 20 to 30 minutes and of about 40 minutes. These periods agree fairly well with those of internal gravity waves induced in the cold-air lake, suggesting that the periodic behavior of the NDW II type is associated with the wave-like movement of cold air in the lake. Although cold air is produced over the entire ground surface, nocturnal drainage winds, which are the flow of cold air down the sloping surfaces, exhibit different characteristics according to whether the slope is located above or beneath the surface of the cold-air lake.

斜面温暖帯に関する実測的研究

A thermal belt or a warm zone on a hillside, developing under calm weather conditions during the night, is one of the well-known local climatic phenomena. Although many models describing its fundamental concept have been constructed, very little observational data exists to support the models directly.The difficulty in studying local climatic phenomena lies mainly in collecting data. In the present study, an infrared radiation thermometer installed on the roof of a high building was used to obtain data for analyzing the air temperature structure in complex terrain. The altitude data set (Digital National Land Information, Japan) also was utilized to examine the dependence of air temperature on topography by applying multiple regression analysis.It is confirmed by observation that a thermal belt on a hillside is produced by nocturnal drainage winds and by a cold-air lake which is formed over the basin by the drainage wind and radiative cooling. The height and intensity of a thermal belt are subject to local and temporal variations due to topographical environments and weather conditions, and can vary from hill to hill, even in situations where they are located face to face. These results show that a thermal belt is a phenomenon produced dynamically by the movement of cold air.

Mesoscale Influences on Nocturnal Valley Drainage Winds in Western Colorado Valleys

Abstract The mesoalpha-scale upper-level sounding network data collected during the 1984 ASCOT meteorological and tracer experiments provided a unique opportunity to analyze the nocturnal drainage wind in four different valleys in western Colorado, and to examine the effects of the synoptic-and mesoscale ambient conditions on these valley drainage winds. The six experimental periods, although biased because of a “fair weather” selection process, provided an additional opportunity to examine “good” and “poor” drainage scenarios. The results show that drainage winds fill all four valleys up to 80%–l00% of their valley depths under favorable nocturnal radiative longwave cooling (1.0°–1.5°C h−1) and light (<5 m s−1) ambient winds. Valley drainage, once established, is rather resistant to erosion from above because of the large source regions of these valleys, their large volume fluxes and inertia, and the persistent stable conditions inside these valleys. Wind erosion was observed on three nights when the dra...

Comparative study of seasonal air pollutant behavior in a Mediterranean coastal site: Castellón (Spain)

Abstract During January, July and August 1988, two experimental campaigns were carried out in the surroundings of the Castellon industrial area located on the Spanish east coast. The main objective was to study the dispersion of the power plant plume located on this site. This work also forms part of a larger program intended to compose a mosaic of atmospheric mesoscale flows related to air pollution cycles for the whole of the Iberian peninsula. In this program, air pollutants have also been considered as tracers of opportunity of the atmospheric circulations, and the study of ground-level concentration cycles has been used to provide evidence for the meso-meteorological processes. On the Castellon coast, and for most of the year, surface atmospheric dynamics are dominated by local cycles of north-west nocturnal drainage winds and east to south-south-east daytime sea-breeze flows. This regime is particularly marked during the summer, while the effect of large scale synoptic conditions is more noticeable in winter and spring. A mobile laboratory was used to collect 10 min averaged values of O3, NO, NO2, and SO2. This unit was placed in the expected zone of influence of the coastal industries during the sea-breeze regime. Data obtained under summer and winter conditions have been compared and, while the temporal evolution of the concentrations of the compounds studied have similar structures, high ozone values have been detected in association with the onset of the sea-breeze during the summer.

Reducing Hydrostatic Truncation Error in a Mesobeta Boundary Layer Model

Tiny pressure gradient forces caused by hydrostatic truncation error can overwhelm minuscule pressure gradients that drive shallow nocturnal drainage winds in a mesobeta numerical model. In seeking a method to reduce these errors, a mathematical formulation for pressure gradient force errors was derived for a single coordinate surface bounded by two pressure surfaces. A nonlinear relationship was found between the lapse rate of temperature, the thickness of the bounding pressure layer, the slope of the coordinate surface and the location of the coordinate surface within the pressure layer. The theory shows that pressure gradient force error can be reduced in the numerical model if column pressures are sums of incremental pressures over shallow layers. A series of model simulations verify the theory and show that the theory explains the only source of pressure gradient force error in the model.

Smoke Flow Visualization in a Tributary of a Deep Valley

Smoke pot and oil fog smoke tracers have been used to plan meteorological instrument placement and quantitatively estimate air volume flow from a tributary during nocturnal drainage wind conditions. The estimated volume flow agrees well with estimates of the flow using tethered-balloon and remotely obtained wind velocity measurements. The smoke visualization shows a very complex flow structure caused by tributary flow interactions with the flow down the main valley. The magnitude of the outflow volume from the tributary was greater than expected. If the tributary studied is representative of the other tributaries in the valley, most of the volume flow in the main valley may enter through the tributaries.

Modelling-tracer study for risk assessment of a proposed sour gas facility

As an integral part of a risk assessment of a sour gas pipeline proposed for a recreational area in the Rocky Mountain foothills, the dispersion of hydrogen sulphide was assessed using meteorological monitoring, tracer gas concentration measurement and a complex terrain diffusion model. Sulphur hexafluoride was released into the nocturnal drainage winds of two valleys in the eastern slopes of the Alberta Rockies southwest of Calgary. The resulting concentrations were measured at several points on transects at various distances from the source. The NUVAL version of the dispersion model IMPACT (Integrated Model for Plumes and Atmospherics in Complex Terrain) was site tuned using the measured concentrations and concurrent meteorological data. Relative mean absolute errors of 24-50% were obtained. The Gaussian model (PLUMES) with modified stability classes gave relative mean absolute errors of 42-64% in predicting transect maxima. Dilution rates were found to be much larger than would be experienced under similar conditions over flat terrain.

Doppler Lidar Measurements of Winds in a Narrow Mountain Valley

Abstract During September and October of 1984, the Wave Propagation Laboratory of NOAA used its pulsed infrared Doppler lidar in support of the U.S. Department of Energy's Atmospheric Studies in Complex Terrain (ASCOT) program. The lidar measured winds channeled within a narrow mountain valley on seven experiment nights, between 2300 and 1100 MST. We were able to quantitatively define the structure of the nocturnal drainage winds, monitor their decay in the morning, and sense the formation of a thermally driven up-valley flow later in the day.

Numerical simulations of the night 2 data of the 1980 ASCOT experiments in the California Geysers area

A three-dimensional, time dependent hydrodynamic primitive equation model was used to simulate the distribution of nocturnal drainage winds, temperature, and turbulence in the California Geysers area. The case studied here (night 2) was under the condition that the ambient airflow was easterly and the direction of main drainage flow was westerly, The computed depth of drainage flow was less than 50 m at the ridge, and increased to 200 m at the valley, which agreed well with the observation. The computed wind speed at the ridge was smaller than the observation, but it agreed well at the valley site, Vertical wind variances measured by a doppler sodar indicated relatively large turbulence despite the fact that stable density stratification dominated throughout the night. The computed vertical wind variances were also larger than those observed over flat terrain, but smaller than the values recorded by the doppler sodar.

Experimental and model transport and diffusion studies in complex terrain with emphasis on tracer studies

The U.S. Department of Energy (DOE) Atmospheric Studies in Complex Terrain (ASCOT) program began in the fall of 1978 as a multiple DOE and other Federal Laboratory program devoted to developing a better physical understanding of atmospheric boundary layer flows in areas of complex terrain. The first technical challenge undertaken by the program was an investigation of atmospheric boundary layer phenomena associated with the development, continuation and breakup of nocturnal drainage wind flows. This paper discusses the general objectives the program has addressed during the past several years and focuses on results from a major field experiment conducted in 1980 in The Geysers area of northern California. Specifically, results from measurements of simultaneous tracer releases are compared to calculations from a mass-consistent wind field model coupled to a particle-in-cell transport and diffusion model. Results of these comparisons show that model calculations agree with measurements within a factor of 5 approximately 50 percent of the time. Part of the difficulty faced by the models in these comparison studies is associated with large variabilities between measurements made by samplers located one or two δx apart when compared to the resolution of the models. Space and time averaging improves the comparisons considerably, although the design of the field experiment did not allow the determination of optimum spacial and temporal averages.

Plume dispersion in a nocturnal drainage wind

A series of tracer experiments were conducted under nocturnal drainage wind conditions in a complex terrain setting in the Piceance Basin of western Colorado. Concurrent meteorological information including profiles of wind and temperature as well as gross turbulence fluctuations from fixed 2-m stations provided the basis to test plume growth and dilution prescriptions for this moderately complex site. Plume parameters exhibited slightly greater diffusion than would be indicated by simple stability-based prediction methods or the gross turbulence indicators. Two terrain-related mechanisms appear to contribute to the development of the plume. A meandering component immediately downwind of the confluence of two valleys gives the appearance of an abnormally wide time-integrated plume. Further downstream the mean wind direction stabilizes and the plume dimension reflects diffusive spread due to small-scale turbulence.

Interpretation of Meteorological Pollutant Roses in Areas Subject to Nocturnal Drainage Winds

Interpretation of Meteorological Pollutant Roses in Areas Subject to Nocturnal Drainage Winds