_{E}
method

The
_{E}
method (Tables 6-8a and 6-8b) is a turbulence-based method which uses the
standard deviation of the elevation angle of the wind in combination with
the scalar mean wind speed.

The
criteria in Table 6-8a and Table 6-8b are for data collected at 10m and a
roughness length of 15 cm. Wind speed and direction data collected within
the height range from 20z_{0} to 100z_{0} should be used.
For sites with very low roughness, these criteria are slightly modified. The
lower bound of measurement height should never be less than 1.0 m; the upper
bound should never be less than 10 m. To obtain 1-hour averages, the
recommended sampling duration is 15 minutes, but it should be at least 3
minutes and may be as long as 60 minutes. The relationships employed in the
estimation methods assume conditions are steady state. This is more easily
achieved if the sampling duration is less than 30 minutes.

If
the site roughness length is other than 15 cm, the category boundaries
listed in Table 6-8a
may need to be adjusted. As an initial adjustment, multiply the Table 6-8a
values by:

(Z_{0}
/ 15)^{O.2}

where
z_{o} is the site roughness in centimeters. This factor, while
theoretically sound, has not had widespread testing. It is likely to be a
useful adjustment for cases when z_{o} is greater than 15 cm. It is yet
problematical whether the adjustment is as useful for cases when z_{o} is less
than 15 cm.

If
the measurement height is other than 10 m, the category boundaries listed in
Table 6-8a will
need to be adjusted. As an initial adjustment, multiply the lower bound
values by:

(Z/10)^{P}

where
Z is the measurement height in meters. The exponent P
is a function of the P-G stability category with values as follows:

The
above suggestions summarize the results of several studies conducted in
fairly ideal circumstances.
It is anticipated that readers of this document are often faced with
conducting analyses in less than ideal circumstances. Therefore, before
trusting the Pasquill category estimates, the results should be spot
checked. This can easily be accomplished. Choose cloudless days. In
mid-afternoon during a sunny day, categories A and B should occur. During
the few hours just before sunrise, categories E and F should occur. The
bias, if any, in the turbulence criteria will quickly be revealed through
such comparisons. Minor adjustments to the category boundaries will likely
be needed to tailor the turbulence criteria to the particular site
characteristics, and should be made in consultation with the reviewing
agency.

**6. METEOROLOGICAL DATA PROCESSING**

*
6.1 Averaging and Sampling Strategies *

6.2 Wind Direction and Wind Speed

6.2.1 Scalar Computations

6.2.2 Vector Computations

6.2.3 Treatment of Calms

6.2.4 Turbulence

6.2.5 Wind Speed Profiles

** ** *6.3 Temperature *

6.3.1 Use in Plume-Rise Estimates

6.3.2 Vertical Temperature Gradient

** ** *6.4 Stability *

6.4.1 Turner's method

6.4.2 Solar radiation/delta-T (SRDT) method

6.4.3
_{E} method

6.4.4 _{A}method

6.4.5 Accuracy of stability category estimates

** 6.5 Mixing Height **

6.5.1 The Holzworth Method

** ** **6.6 Boundary Layer Parameters **

6.6.1 The Profile Method

6.6.2 The Energy Budget Method

6.6.3 Surface Roughness Length

6.6.4 Guidance for Measurements in the Surface Layer

** 6.7 Use of Airport Data **

**6.8 Treatment of Missing Data **

6.8.1 Substitution Procedures

* 6.9 Recommendations *