The following equation provides the static stability:
sigma=(R/P)*(1000/P)^{R/cp
}*(partial theta/partial p)

Potential temperature was computed using Poisson's equation,
except at 1000 mb, where a lapse rate of 6.5K/km was used to bring the 850 mb
temperatures to 1000 mb using the 850 mb heights.
Partial theta/partial p is calculated using numerical differences. A forward
difference gives the static stability at 1000 mb:
partial theta/partial p _{p=p0}=
[theta(p_{0}+dp)theta(p_{0}
)]/dp

A centered unequal difference gives the static stability at 850 mb and 500 mb:
partial theta/partial p _{p=p0}=
[(dp_{2})theta(p_{0}
+dp_{1})+(dp_{1}
dp_{2})theta(p_{0}
)

(dp_{1})theta(p_{0}
dp_{2})]/(2*dp_{1}
*dp_{2})

At 200 mb, a backward difference gives the static stability:
partial theta/partial p _{p=p0}=
[theta(p_{0})theta(p_{0}
dp)]/dp

Units: m^{2} s^{2} kPa^{2}
