Volume 1 - The Atmospheric Studies Group at TRC
Volume 1 - The Atmospheric Studies Group at TRC Volume 1 - The Atmospheric Studies Group at TRC
Turbulence Advection Option Gryning (1985) presents an overview of the Oresund experiments, and comments on particular features of the boundary layer resolved by measurements made during the June 5 experiment. There is evidence of vertical motion in the flow over the Oresund strait that may be associated with the changes in surface properties across the landsea boundary. There are also direct measurements of turbulence dissipation at a number of elevations along transects that cross the strait. One transect at about 270m on June 5 cited by Gryning shows a distinct and gradual lowering of the turbulence with distance across the strait, and an abrupt rise downwind of the far shoreline (over Copenhagen). Initial modeling of the Oresund experiments with CALMET/CALPUFF substantially overpredicts peak concentrations in five of the nine experiments, four of these by about a factor of 10. Peak concentrations predicted for the remaining four experiments are well within a factor of two. No application issues have been identified that can account for the overpredictions, but they are all associated with elevated (95m-high) non-buoyant tracer releases from a shoreline tower on the upwind side of the strait. The initial dispersion of these releases across the 20km distance to the opposite shore is controlled by the calculated overwater turbulence, which is much smaller than the turbulence calculated over land both upwind and downwind of the strait. This suggests that advected turbulence energy is an important factor to include in these simulations. CALMET includes the effect of advection on mixing heights and temperatures, but turbulence velocities are computed locally in CALPUFF. This local calculation can be broadened to incorporate a contribution from upwind cells. Vickers et al. (2001) discuss the decay of turbulence energy with downwind distance in offshore flow in terms of the local value of the friction velocity at a given height. They define an advective-decay timescale τ over which the friction velocity transitions from the (larger) overland value u *0 to the (smaller) overwater equilibrium value u *eq with transport time from the coast, t, and write: u 2 * 2 * eq 2 2 −t / τ ( u − u ) e = u + (3-52) *0 * eq We approximate the exponential decay as a linear decay to limit the number of upwind cells to process each sampling step and write: 2 2 ( σ − σ )( 1 − 0.7 τ ) 2 2 σ = σ + / (3-53) w, v w, vL w, vU w, vL t where the σ w,v refers to either σ w or σ v , subscript L identifies the local value at puff height, and subscript U identifies the upwind value at the same puff height. The local Final Report Vol.1 20
cell is the cell that determines the current puff properties. The time t is determined by the wind speed at puff height in the local cell and the distance from the center of the local cell to the particular upwind cell being processed. Only cells that are upwind and within the time horizon t = τ/0.7, and that have a turbulence velocity larger that the local turbulence velocity are processed, and only the largest increase in σ 2 (the second term on the right including the decay factor) is retained. The advective-decay timescale τ is entered as a control file input to CALPUFF. A value that is representative of the Oresund experiments can be estimated from aircraft measurements. Turbulence dissipation profiles at several heights during three of the experiments are shown in Figures 3-1 through 3-3. The upwind shoreline is at about grid coordinate 370 km and the transport is to the west or from right to left in these figures. A linear decay in turbulence is approximated by eye to obtain a subjective decay distance across the strait that ranges from 12-14 km on May 29 and June 4, and 14-16 km on June 5. CALMET wind speeds in the layer between 90m and 120m during the hour in which the flights were made are extracted near the upwind shore and halfway across the strait to estimate average transport speeds near the release height (95m). The easting component of these speeds average 11.4 m/s on May 29, 12.8 m/s on June 4, and 11.8 m/s on June 5. The corresponding decay times average 1145s, so the inferred timescale (τ = 0.7 t) is about 800s. The performance evaluation of CALPUFF using the 800s turbulence advective-decay timescale shows a substantial improvement. Final Report Vol.1 21
- Page 1 and 2: Development of the Next Generation
- Page 3 and 4: 1. INTRODUCTION The purpose of this
- Page 5 and 6: • Prognostic Meteorological Model
- Page 7 and 8: o 1: Maul (1980)-Carson (1973) o 2:
- Page 9 and 10: into 50 tiles (90 RUC grid-points/t
- Page 11 and 12: y H ( 1− 34.15z / L) 1/ 3 = (3-9)
- Page 13 and 14: During execution, the bulk algorith
- Page 15 and 16: Anemometer Height Adjustment for La
- Page 17 and 18: T (ºK) g (m/s 2 ) temperature grav
- Page 19 and 20: adjusted to account for the effect
- Page 21: Two methods of supplying the timesc
- Page 25 and 26: June 4 (1130-1230 CET) L. Turbulenc
- Page 27 and 28: 4. MODEL PERFORMANCE EVALUATION 4.1
- Page 29 and 30: The CALMET preprocessors TERREL, CT
- Page 31 and 32: All sampler locations are used as r
- Page 33 and 34: Table 4-2b Over-water Meteorologica
- Page 35 and 36: Meteorological data used in the OCD
- Page 37 and 38: . . CARPINTERIA, CA 3814 . UTM Nort
- Page 39 and 40: Year Month Day Table 4-4 Over-water
- Page 41 and 42: Datum: NAS-C (North American 1927)
- Page 43 and 44: Table 4-5 Source Characterization f
- Page 45 and 46: Table 4-6a Over-water Meteorologica
- Page 47 and 48: Geophysical Processing Gridded land
- Page 49 and 50: Table 4-7 Source Characterization f
- Page 51 and 52: tape format called GF-3. These data
- Page 53 and 54: . . Strait of Oresund 6230 6220 UTM
- Page 55 and 56: . . Strait of Oresund 6230 6220 UTM
- Page 57 and 58: Table 4-10 SEA.DAT Meteorological D
- Page 59 and 60: the numbers refer to ICOARE values,
- Page 61 and 62: that are simulated during the one-h
- Page 63 and 64: 4.3 Evaluation Results Cameron, Car
- Page 65 and 66: improve model performance relative
- Page 67 and 68: Figure 4-7. Graphical depiction of
- Page 69 and 70: Figure 4-8. Graphical depiction of
- Page 71 and 72: Figure 4-9. Graphical depiction of
cell is the cell th<strong>at</strong> determines the current puff properties. <strong>The</strong> time t is determined<br />
by the wind speed <strong>at</strong> puff height in the local cell and the distance from the center of<br />
the local cell to the particular upwind cell being processed. Only cells th<strong>at</strong> are<br />
upwind and within the time horizon t = τ/0.7, and th<strong>at</strong> have a turbulence velocity<br />
larger th<strong>at</strong> the local turbulence velocity are processed, and only the largest increase in<br />
σ 2 (the second term on the right including the decay factor) is retained.<br />
<strong>The</strong> advective-decay timescale τ is entered as a control file input to CALPUFF. A<br />
value th<strong>at</strong> is represent<strong>at</strong>ive of the Oresund experiments can be estim<strong>at</strong>ed from aircraft<br />
measurements. Turbulence dissip<strong>at</strong>ion profiles <strong>at</strong> several heights during three of the<br />
experiments are shown in Figures 3-1 through 3-3. <strong>The</strong> upwind shoreline is <strong>at</strong> about<br />
grid coordin<strong>at</strong>e 370 km and the transport is to the west or from right to left in these<br />
figures. A linear decay in turbulence is approxim<strong>at</strong>ed by eye to obtain a subjective<br />
decay distance across the strait th<strong>at</strong> ranges from 12-14 km on May 29 and June 4, and<br />
14-16 km on June 5. CALMET wind speeds in the layer between 90m and 120m<br />
during the hour in which the flights were made are extracted near the upwind shore<br />
and halfway across the strait to estim<strong>at</strong>e average transport speeds near the release<br />
height (95m). <strong>The</strong> easting component of these speeds average 11.4 m/s on May 29,<br />
12.8 m/s on June 4, and 11.8 m/s on June 5. <strong>The</strong> corresponding decay times average<br />
1145s, so the inferred timescale (τ = 0.7 t) is about 800s.<br />
<strong>The</strong> performance evalu<strong>at</strong>ion of CALPUFF using the 800s turbulence advective-decay<br />
timescale shows a substantial improvement.<br />
Final Report Vol.1 21
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