Incorporation of planetary boundary layer dynamics in a numerical model of long-range air-pollutant transport

In this paper, measurements of the first 150 m of the atmospheric boundary layer obtained by a high-frequency acoustic mini-sounder are compared with measurements obtained by a full complement of instruments including sonic anemometers mounted on the Boulder Atmospheric Observatory tower. The acoustic mini-sounder, starting as low as 6 m from the ground, measures in the monostatic mode the profiles of the vertical wind speed, w, and of the temperature structure parameter, C _T ² with enhanced height resolution of the order of 1 m and time resolution of the order of 30 s. The results of the comparison show that the high-frequency mini-sounder is an effective atmospheric boundary-layer profiler that is also portable and relatively inexpensive. Measurements of the spectrum of C _T ² are presented that provide information on the local isotropy of the temperature field. Statistics of the variability of C _T ² in both stable and unstable conditions are also given. The sounder's capabilities are further demonstrated by some detailed observations of the structure and time evolution of a thermal plume root at noon and of a nocturnal, stably stratified layer in which a dynamic instability develops. The plume starts at a height of less than 5 m, possesses substantial internal structure, and includes vertical velocities in excess of 2 m s^-1.     

Comparison of three methods for determining strong wind stress over Lake Flevo

The drag coefficient C _d (10 m) at the center of shallow Lake Flevo (20-km diam) is evaluated for wind speeds u between 5 and 15 m s^?1 independently by three methods. Trivane measurements of eddy-correlation fluxes agree with eddy flux data available for moderate wind speeds from other sites, and can together be represented by C _d(10 m) = 0.0007 μ^0.3. Additional evaluations of water-surface slope give C _d(10 m) ≈ 0.0024, indicating that the stress at the water-surface level may not be entirely accounted for by eddy-correlation measurements well above the waves. Neither the eddy-correlation stress, nor the water-surface stress appears to be accurately estimable from profile measurements of wind, temperature and humidity analyzed without regard to sea state, if u > 10 m s^?1.     

Tilt errors and precipitation effects in trivane measurements of turbulent fluxes over open water

For 390 ten-minute samples of turbulent flux, made with a trivane above a lake, the vertical alignment is determined within 0.1 ° through azimuth-dependent averaging. One degree of instrumental misalignment is found to produce an average tilt error of 9 ± 4% for momentum flux, and 4 ± 2% for heat flux. The tilt error in the vertical momentum flux depends mainly ons _u/u_*, and cannot be much diminished with impunity by high-pass pre-filtering of the turbulence signals. The effects of rain on trivane measurements of vertical velocity are shown to be negligible at high wind speeds, and adaptable to correction in any case.The normalized vertical velocity variance,s _w/u_*, appears to be proportional to the square root ofz/L for unstable stratification. For a wind speed range of 2 to 15 m s^–1, the eddy correlation stresses measured at 4- and 8-m heights can be reasonably well estimated by using a constant drag coefficientC _d=1.3 X 10^-3, while cup anemometer profile measurements give an overestimate of eddy stress at high wind speeds. A good stress estimate is also obtained from the elevation variance; it is suggested that trivane measurement of this variance might be made from a mobile platform, e.g., a moderately stabilized spar buoy.     

Air-sea bulk transfer coefficients in diabatic conditions

On the basis of recent data for the roughness Reynolds number of the sea surface, and using the Owen-Thomson theory on the transfers of heat and mass between a rough surface and the flow above it, the bulk transfer coefficients of the sea surface have been estimated. For a reference height of 10 m, the neutral-lapse transfer coefficient for water vapor is larger by only a few percent than that for sensible heat. When the wind speed at the 10-m height is u ₁₀>3 m s^–1, the coefficient for sensible heat C _H is larger by about 10% than that for momentum C _D . For u ₁₀<5 m s^–1, however, the value of C _D exceeds the value of C _H , and for u ₁₀=15 m s^–1 it is shown that C _H 0.8C _D . It may be also proposed that 10³ C _D =1.11 to 1.70, 10³ C _E =1.18 to 1.30, and 10³ C _H =1.15 to 1.26 for a range of u ₁₀=4 to 20 m s^–1. A plot of diabatic transfer coefficients versus wind speed is obtained by using a parameter of the sea-air temperature difference. For practical purposes, the coefficients are approximated by empirical formulae.     

Seasonal variation of volatile organic iodine compounds in the water column of Funka Bay,Hokkaido, Japan

Volatile organic iodine compounds (VOIs) emitted from the ocean surface to the air play an important role in atmospheric chemistry. Shipboard observations were conducted in Funka Bay, Hokkaido, Japan, bimonthly or monthly from March 2012 to December 2014, to elucidate the seasonal variations of VOI concentrations in seawater and their sea-to-air iodine fluxes. The bay water exchanges with the open ocean water of the North Pacific twice a year (early spring and autumn). Vertical profiles of CH₂I₂, CH₂ClI, CH₃I, and C₂H₅I concentrations in the bay water were measured bimonthly or monthly within an identified water mass. The VOI concentrations began to increase after early April at the end of the diatom spring bloom, and represented substantial peaks in June or July. The temporal variation of the C₂H₅I profile, which showed a distinct peak in the bottom layer from April to July, was similar to the PO₄ ^3? variation profile. Correlation between C₂H₅I and PO₄ ^3? concentrations (r = 0.93) suggests that C₂H₅I production was associated with degradation of organic matter deposited on the bottom after the spring bloom. CH₂I₂ and CH₂ClI concentrations increased substantially in the surface and subsurface layers (0–60 m) in June or July resulted in a clear seasonal variation of the sea-to-air iodine flux of the VOIs (high in summer or autumn and low in spring).     

Dynamics of lateral boundary meso-scale jet in the ocean and atmosphere

By using an ageostrophic shallow water model, it is pointed out that a kind of lateral boundary meso-scales jet can be established near the plateau or coast. The characteristic width of this kind of jet is proportional to the scale ofL _c=L₀(C₀/V_g), whereL ₀=C ₀/f is the radius of Rossby deformation,C ₀=(g ^* H)^1/2 the speed of gravity wave and g^* the reduced gravity. In general,L _c is of the order of one hundred kilometes and tens of kilometers in the atmosphere and in the ocean respectively. The large-scale geostrophic current is an important background condition for forming this kind of jet. From this view point it seems that this kind of atmospheric meso-scale jet only occurs in late spring and summer in the eastern part of Asia, because there is a large-scale south monsoon over there. For the ocean, this kind of meso-scale jet seems to be a semi-persistant system and not to show a significant seasonal variation, and it can be established on both sides of the ocean.     

Estimation of atmospheric surface layer parameters and numerical simulation using MM5 at Mangalore, West Coast of India

Atmospheric surface layer meteorological observations obtained from 20-m-high meteorological tower at Mangalore, situated along the west coast of India are used to estimate the surface layer scaling parameters of roughness length (z _o) and drag coefficient (C _D), surface layer fluxes of sensible heat and momentum. These parameters are computed using the simple flux–profile relationships under the framework of Monin–Obukhov (M–O) similarity theory. The estimated values of z _o are higher (1.35–1.54 m) than the values reported in the literature (>0.4–0.9 m) probably due to the undulating topography surrounding the location. The magnitude of C _D is high for low wind speed (<1.5 m s^?1) and found to be in the range 0.005–0.03. The variations of sensible heat fluxes (SHF) and momentum fluxes are also discussed. Relatively high fluxes of heat and momentum are observed during typical days on 26–27 February 2004 and 10–11 April 2004 due to the daytime unstable atmospheric conditions. Stable or near neutral conditions prevail after 1700 h IST with negative SHF. A mesoscale model PSU/NCAR MM5 is run using a high-resolution (1 km) grid over the study region to examine the influence of complex topography on the surface layer parameters and the simulated fluxes are compared with estimated values. Spatial variations of the frictional velocity (u _*), C _D, surface fluxes, planetary boundary layer (PBL) height and surface winds are noticed according to the topographic variations in the simulation.     

Bulk transfer coefficient over a snow surface

The drag coefficient C _D and the bulk transfer coefficient for sensible heat C _H over a flat snow surface were determined experimentally. Theoretical considerations reveal that C _D depends on the friction velocity u _* as well as on the geometrical roughness h of the snow surface. It is found that C _D increases with increasing u _* and/or h. The dependency of C _H on u _* and h is so small that it is possible to consider C _H as a constant for practical purposes: C _{H, 1} = 2.0 × 10^–3 for a reference height of 1 m. The bulk transfer coefficient for water vapor is estimated at C _{E, 1} = 2.1 × 10^–3 for a reference height of 1 m.     

The estimation of the energy balance of a lake from simple weather data

The energy balance of a lake with an area of approximately 46000 ha and a depth of 3 m has been estimated from simple weather data measured along the perimeter of the lake. These measurements are dry-bulb temperature and relative humidity, both at 1.5-m height, windspeed at 3-m height and sunshine duration. The estimated energy balance values were compared with the values computed from the measurements at the station situated at the centre of the lake. At this station, net radiation, water temperature, dry-bulb and wet-bulb temperature at a height of 2 m were measured. It is possible to estimate the daily evaporation from the lake with an error of 0.6 mm day^–1, if the location of measurement is downwind from the lake.     

Observation of wind shear during evening transition and an estimation of submicron aerosol concentrations in Beijing using a Doppler wind lidar

The wind speed and direction measured over six months by a Doppler wind lidar (Windcube-8) were compared with wind cup anemometers mounted on the 325-m Beijing meteorological tower (BMT). Five mountain–plain wind cases characterized by wind direction shear were selected based on the high-frequency (1.1 s) wind profile of the Windcube-8 and analyzed with 1-h mesoscale surface weather charts. Also analyzed was the relationship between in-situ PM₁ (aerodynamic diameter ≤ 1 μm) concentrations measured at 260 m on BMT and the carrier-to-noise ratio (CNR) of the co-located Windcube-8. The results showed that the 10-min averaged wind speed and direction were highly correlated (R = 0.96–0.99) at three matched levels (80, 140, and 200 m). The evening transition duration was 1–3 h, with an average wind speed of 1 m s^–1 at 80 m above the ground. In addition, there was a zero horizontal-wind-speed zone along the wind direction shear line, and in one case, the wind speed was characterized by a Kelvin–Helmholtz gravity wave. The variability of the PM₁ concentrations was captured by the CNR of the Windcube-8 in a fair weather period without the long-range transport of dust.     

On the extension of the wind profile over homogeneous terrain beyond the surface boundary layer

Analysis of profiles of meteorological measurements from a 160 m high mast at the National Test Site for wind turbines at Høvsøre (Denmark) and at a 250 m high TV tower at Hamburg (Germany) shows that the wind profile based on surface-layer theory and Monin-Obukhov scaling is valid up to a height of 50–80 m. At higher levels deviations from the measurements progressively occur. For applied use an extension to the wind profile in the surface layer is formulated for the entire boundary layer, with emphasis on the lowest 200–300 m and considering only wind speeds above 3 m s^?1 at 10 m height. The friction velocity is taken to decrease linearly through the boundary layer. The wind profile length scale is composed of three component length scales. In the surface layer the first length scale is taken to increase linearly with height with a stability correction following Monin-Obukhov similarity. Above the surface layer the second length scale (L _MBL ) becomes independent of height but not of stability, and at the top of the boundary layer the third length scale is assumed to be negligible. A simple model for the combined length scale that controls the wind profile and its stability dependence is formulated by inverse summation. Based on these assumptions the wind profile for the entire boundary layer is derived. A parameterization of L _MBL is formulated using the geostrophic drag law, which relates friction velocity and geostrophic wind. The empirical parameterization of the resistance law functions A and B in the geostrophic drag law is uncertain, making it impractical. Therefore an expression for the length scale, L _MBL , for applied use is suggested, based on measurements from the two sites.     

Coupled North Atlantic slope water forcing on Gulf of Maine temperatures over the past millennium

To investigate ocean variability during the last millennium in the Western Gulf of Maine (GOM), we collected a 142-year-old living bivalve (Arctica islandica L.) in 2004, and three fossil A. islandica shells (calibrated ¹⁴C_AMS = 1030 ± 78 ad; 1320 ± 45 ad; 1357 ± 40 ad) for stable isotope and growth increment analysis. A statistically significant relationship exists between modern GOM temperature records [shell isotope-derived (30 m) (r = ?0.79; P < 0.007), Prince 5 (50 m) (r = ?0.72; P < 0.019), Boothbay Harbor SST (r = ?0.76; P < 0.011)], and Labrador Current (LC) transport data from the Eastern Newfoundland Slope during 1993–2003. In all cases, as LC transport increased, GOM water temperatures decreased the following year. Decadal trends in the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO) influence GOM water temperatures in the most recent period, with water temperatures decreasing during NAO and AMO negative modes most likely linked to LC transport and Gulf Stream interaction. Mean shell-derived isotopic changes (δ¹⁸O_c) during the last 1,000 years were +0.47‰ and likely reflect a 1–2°C cooling from 1000 ad to present. Based on these results, we suggest that observed cooling in the GOM during the last millennium was due to increased transport and/or cooling of the LC, and decreased Gulf Stream influence on the GOM.     

The water and energy balances of Perch Lake (1969–1980)

Abstract

Since 1969, meteorological and limnological measurements required for evaporation estimates by the energy budget method have been made almost continuously during the open water season at Perch Lake, a small (0.45 km²), shallow (mean depth 2 m) lake on the Canadian Shield. Hydrological measurements required for water budget calculations have been made continuously since 1970. Since ground water input to the lake has been found to be significant, energy budget estimates of evaporation are used in the water budget equation to estimate ground water inflow. Results are summarized as the long‐term averages along with the ranges of variation of the budget components observed during the eleven‐year period.     

Microphysical and optical features of polluted cooling tower clouds

In November 1993 an airborne field study was performed in order to investigate the microphysical and radiative properties of cooling tower water clouds initiated by water vapour emissions and polluted by the exhaust from coal-fired power plants. The number-median diameter of the droplet size distributions of these artificial clouds was in the range of 13 μm. The concentration of smaller droplets (diameters d_D < 10 μm) increased with height and horizontal distance from the cooling towers. Close to the cooling towers, bimodal spectra were found with a second mode at 19 μm. The liquid water content (LWC) ranged between 2 and 5 g/m³ and effective droplet radii (R_e) between 6 and 9 μm were measured. LWC and R_e decreased with altitude, whereas the droplet concentration (N_D) remained approximately constant (about 2000 cm⁻³ ). An enrichment of interstitial aerosol particles with particle diameters (d_p) smaller 0.2 μm compared to the power plant plume in the vicinity of the clouds was observed. Particle activation for d_m > 0.3 μm. was evident, especially in cooling tower clouds further apart and separated from their sources. Furthermore, radiation measurements were performed, which revealed differences in the vertical profiles of downwelling solar and UV radiation flux densities inside the clouds.The effective droplet radius R_e was parameterized in terms of LWC and N_D using equations known from literature. The close agreement between measured and parameterized Re indicates a similar coupling of R_e, LWC and N_D as in natural clouds.By means of Mie calculations, volume scattering coefficients and asymmetry factors are derived for both the cloud droplets and the aerosol particles. For the cloud droplets, the optical parameters were described by parameterizations from the literature. The results show, that the link between radiative and microphysical properties of natural clouds is not changed by the extreme pollution of the artificial clouds.     

Spatial Variability of Both Turbulent Fluxes and Temperature Profiles in an Urban Roughness Layer

The spatial variability of both turbulent flow statistics in the roughness sublayer (RSL) and temperature profiles within and above the canopy layer (CL) were investigated experimentally in a densely built-up residential area in Tokyo, Japan. Using five towers with measuring devices, each tower isolated from the others by at least 200 m, we collected high-frequency measurements of velocity and temperature at a height z=1.8 z _H, where z _H, the mean building height in the area, is 7.3 m. Also, temperature profiles were measured from z=0.4 to 1.8 z _H. The ‘areal mean’ geometric parameters that were obtained for the areas within 200 m of each tower were fairly homogeneous among the tower sites. The main results are as follows: (1) The spatial variability of all RSL turbulent statistics, except the sensible heat flux, was comparable to that reported in a pine forest. Also, the variability decreased with increasing friction velocity. (2) The spatial variability of the RSL sensible heat flux was larger than that reported in a pine forest. Also, the variability depended on the time of the day and became larger in the morning. The difference among the sites was well related to the areal fraction of vegetation. (3) The spatial variability of the CL temperature profile depended on the time of the day and became larger in the morning. Nevertheless, the spatial standard deviation of CL temperature was always below 0.7 K. (4) It is suggested that the “warming-up” process in the morning when heat storage is dominant increases the spatial variation of RSL sensible heat flux and CL temperature according to the local properties around each tower and the variation decreases once there is further convective mixing in the midday     

Weakening sensible heat source over the Tibetan Plateau revisited: effects of the land�Catmosphere thermal coupling

The bulk heat transfer coefficient (C _H ) indicates the land?Catmosphere thermal coupling strength. We seek to detect its variability and changes on the Tibetan Plateau (TP) during 1981?C2006, particularly concerned with its effects on the sensible heat source. C _H is parameterized by Monin?CObukhov similarity theory combining routine meteorological measurements. The South Asian monsoon period is characterized by weak sensible heat flux (H), but strong thermal coupling (C _H ). Winter sees the greatest diurnal C _H range, roughly 0.001?C0.008. On average, C _H exhibits a notable nighttime increase (10% decade^?1) and a weak daytime decrease (?5% decade^?1). The strengthening thermal coupling at selected sites alleviates the weakening of H, because it enhances nighttime H increase and reduces daytime H decrease. Moreover, we confirm the finding in earlier studies that sensible heating is weakening on the TP, but find its trend less notable than empirically estimated using C _H ?=?0.004.     

Characteristics of air flow above and within soybean canopies

Air flow was observed above and within canopies of a number of kinds of soybeans. The Clark cultivar and two isolines of the Harosoy cultivar were studied in 1979 and 1980, respectively. Wind speed above the canopy was measured with cup anemometers. Heated thermistor anemometers were used to measure air flow within the canopy. Above-canopy air flow was characterized in terms of the zero-plane displacement (d), roughness parameter (z _o) and drag coefficient (C _d). d and z _o were dependent on canopy height but were independent of friction velocity in the range 0.55 to 0.75 m s^?1 · C _d for the various canopies ranged from 0.027 to 0.035. Greater C _d values were measured over an erectophile canopy than over a planophile canopy. C _d was not measurably affected by differences in leaf pubescence. Within-canopy wind profiles were measured at two locations: within and between rows. The wind profile was characterized by a region of great wind shear in the upper canopy and by a region of relatively weak wind shear in the middle canopy. Considerable spatial variability in wind speed was evident, however. This result has significant implications for canopy flow modeling efforts aimed at evaluating transport in the canopy. In the lower canopy, wind speed within a row increased with depth whereas wind speed between two rows decreased with depth. The wind speeds at the two locations tended to converge to a common value at a height near 0.10 m. The attenuation of within-canopy air flow was stronger in canopies with greater foliage density. Canopy flow attenuation seemed to decrease with increasing wind speed, suggesting that high winds distorted the shape of the canopy in such a manner that the penetration of wind into the canopy increased.     

Size-resolved aerosol chemical concentrations at rural and urban sites in Central California,USA

Aerosol size distributions were measured with Micro Orifice Uniform Deposit Impactor (MOUDI) cascade impactors at the rural Angiola and urban Fresno Supersites in California's San Joaquin Valley during the California Regional PM₁₀/PM_2.5 Air Quality Study (CRPAQS) winter campaign from December 15, 2000 to February 3, 2001. PM_2.5 filter samples were collected concurrently at both sites with Sequential Filter Samplers (SFS). MOUDI nitrate (NO₃⁻) concentrations reached 66 μg/m³ on January 6, 2001 during the 1000–1600 PST (GMT-8) period. Pair-wise comparisons between PM_2.5 MOUDI and SFS concentrations revealed high correlations at the Angiola site (r > 0.93) but more variability (r < 0.85) at the Fresno site for NO₃⁻, sulfate (SO₄⁼), and ammonium (NH₄⁺). Correlations were higher at Fresno (r > 0.87) than at Angiola (r < 0.7) for organic carbon (OC), elemental carbon (EC), and total carbon (TC). NO₃⁻ and SO₄⁼ size distributions in Fresno were multi-modal and wider than the uni-modal distributions observed at Angiola. Geometric mean diameters (GMD) were smaller for OC and EC than for NO₃⁻ and SO₄⁼ at both sites. OC and EC were more concentrated on the lowest MOUDI stage (0.056 µm) at Angiola than at Fresno. The NO₃⁻ GMD increased from 0.97 to 1.02 µm as the NO₃⁻ concentration at Angiola increased from 43 to 66 µg m^− 3 during a PM_2.5 episode from January 4–7, 2001. There was a direct relationship between GMD and NO₃⁻ and SO₄⁼ concentrations at Angiola but no such relationships for OC or EC. This demonstrates that secondary aerosol formation increases both concentration and particle size for the rural California environment.     

Sea surface stress measurements

Sea-surface stress measurements were made from a rigid tower in shallow water near San Diego, California, by both the direct covariance and inertial dissipation techniques. Stress estimates from the dissipation technique were generally higher than the directly measured values, with average drag coefficients of 0.99 x 10^-3 and 0.77 x 10^-3, respectively, for 8-m wind speeds of 5 to 7 m s^-1. In the inertial subrange, ratios of vertical to streamwise velocity spectra averaged 1.06 ± 0.16, significantly less than the isotropic value of 4/3 observed over land, suggesting that turbulence over water may be altered by the presence of waves.     

A theory for the scalar roughness and the scalar transfer coefficients over snow and sea ice

Although the bulk aerodynamic transfer coefficients for sensible (C _H ) and latent (C _E ) heat over snow and sea ice surfaces are necessary for accurately modeling the surface energy budget, they have been measured rarely. This paper, therefore, presents a theoretical model that predicts neutral-stability values of C _H and C _E as functions of the wind speed and a surface roughness parameter. The crux of the model is establishing the interfacial sublayer profiles of the scalars, temperature and water vapor, over aerodynamically smooth and rough surfaces on the basis of a surface-renewal model in which turbulent eddies continually scour the surface, transferring scalar contaminants across the interface by molecular diffusion. Matching these interfacial sublayer profiles with the semi-logarithmic inertial sublayer profiles yields the roughness lengths for temperature and water vapor. When coupled with a model for the drag coefficient over snow and sea ice based on actual measurements, these roughness lengths lead to the transfer coefficients. C _E is always a few percent larger than CH. Both decrease monotonically with increasing wind speed for speeds above 1 m s^–1, and both increase at all wind speeds as the surface gets rougher. Both, nevertheless, are almost always between 1.0 × 10^–3 and 1.5 × 10^–3.