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3.5.13 Specifying Average Surface Roughness for the Long Term Model

 

     When using the dry deposition algorithms in ISCLT, the user must specify average values of surface roughness length following the AVEROUGH keyword.  The following syntax is used:

 

Syntax:

ME AVEROUGH  Aveper Z0

Type:

Optional, Repeatable

 

where the Aveper parameter specifies the long term averaging period for the following input, and must be one of the secondary keywords used on the Long Term AVERTIME card described in Section 3.2.3.2 (e.g., JAN, WINTER, ANNUAL, etc.).  The Z0 parameter is the average surface roughness length in meters for the specified averaging period.  Only one roughness length is supplied for each averaging period.  Surface roughness lengths representative of several land-use types are given in Table 3-2 by season.  Depending on the land-use type and climate, surface roughness may vary considerable by season, as shown for deciduous forests in Table 3-2.

                          TABLE 3-2

  SURFACE ROUGHNESS LENGTH, METERS, FOR LAND-USE TYPES AND

              SEASONS, FROM SHIEH ET AL., 1979

Land-Use Type

Spring

Summer

Autumn

Winter

1.Water Surface

0.0001

0.0001

0.0001

0.0001

2.Deciduous Forest

1.00

1.30

0.80

0.50

3.Coniferous Forest

1.30

1.30

1.30

1.30

4.Swamp

0.20

0.20

0.20

0.05

5.Cultivated Land

0.03

0.20

0.05

0.01

6.Grassland

0.05

0.10

0.01

0.001

7.Urban

1.00

1.00

1.00

1.00

8.Desert Shrubland

0.30

0.30

0.30

0.15

Definitions of Seasons:

 

Spring:Periods when vegetation is emerging or partially green.  This is a transitional situation that applies for 1-2 months after the last killing frost in spring.

 

Summer:Periods when vegetation is lush and healthy, typical of mid-summer, but also of other seasons where frost is less common.

 

Autumn:Periods when freezing conditions are common, deciduous trees are leafless, crops are not yet planted or are already harvested (bare soil exposed), grass surfaces are brown, and no snow is present.

 

Winter:Periods when surfaces were covered by snow, and when temperatures are sub-freezing.

 

201 - 202 - 203 - 204 - 205 - 206 - 207 - 208 - 209 - 210 - 211 - 212 - 213 - 214 - 215 - 216 - 217 - 218 - 219 - 220 - 221 - 222 - 223 - 224 - 225 - 226 - 227 - 228 - 229 - 230 - 231 - 232 - 233 - 234 - 235 - 236 - 237 - 238 - 239 - 240 - 241 - 242 - 243 - 244 - 245 - 246 - 247 - 248 - 249 - 250

 

 

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