1972) mounted on the flying cablc of a tethered balloon or 011 ii f i x 4
support. This instrument measurcs the instantaneous values of the total
wind component (I.), the inclindtion of the wind to the horizontal (4). and
the temperature. The outputs werc sampled once ; i second and flic various
turbulcncc paranicters calculated after the removal of any linciir trends. Thc
nionientuni flux was dcrived froni the equation
riw' = ( I ' cos 4 - I ' cos $)( C sin 4 - I' sin 4)
and the vertical axis was dcfined either by reference to a sonic anemometer
(Florida data) or clsc by the assumption w = 0 (Cardington data). Since the
cquipmcnt was almost always mounted at least 150 m below the balloon the
rcwlts are considcred not to have been significantly affected by balloon
niowment (see Readings and HutIcr. 1972). All the rims considered in this
papcr were of one hour's duration and none of thcse measurements was
made in or above an inversion.
- _
2. THE VALUI~ 01. 6, I N riiE CONVECTIVE LIMIT
When the rate of buoyant production is much greater than the rate for
mechmical production, Eq. ( I ) simplifies to
- AtS' A,.! 3 - 1 3
(2)
0, -
' 2 -
But I:? = (11 T)w'O' where Q is the acceleration due to gravity. T is the absolute tcmprature. 0 is the potential temperature. and thc prime superscript
dciiotes a iluctuation about the mean. Thus Ey. (2) may be rewritten as
(3)
0, = Ad"3(g/T)1
If the assumptions are correct this equation should be applicable at high
Icvclq whcre the niechanical production term will often be negligible or at
low lcvelv when the atmosphere is very convective. For a given value of
( z w V ' ) ' ' 3 , Eq. (3) should give the rnirtinirtm value of a , since any mechanically gencrated turbuicnce would increase 0,. These predictions may be
tcsted by plotting a , against (zw'~')''.' (see Fig. 1). The data have been
classified according to the values of :,lL, where L, is the loctrl value of the
Monin-Ohukhov length (assuming von Khrman's constant, k = 0.4). It can
be seen that
(a) the less unstable points lie above the more unstable ones; and
(b) there is a tendency for the most unstable data to scatter about a
limiting line. just as would be expected if the conccpt of a convective limit is
correct.
support. This instrument measurcs the instantaneous values of the total
wind component (I.), the inclindtion of the wind to the horizontal (4). and
the temperature. The outputs werc sampled once ; i second and flic various
turbulcncc paranicters calculated after the removal of any linciir trends. Thc
nionientuni flux was dcrived froni the equation
riw' = ( I ' cos 4 - I ' cos $)( C sin 4 - I' sin 4)
and the vertical axis was dcfined either by reference to a sonic anemometer
(Florida data) or clsc by the assumption w = 0 (Cardington data). Since the
cquipmcnt was almost always mounted at least 150 m below the balloon the
rcwlts are considcred not to have been significantly affected by balloon
niowment (see Readings and HutIcr. 1972). All the rims considered in this
papcr were of one hour's duration and none of thcse measurements was
made in or above an inversion.
- _
2. THE VALUI~ 01. 6, I N riiE CONVECTIVE LIMIT
When the rate of buoyant production is much greater than the rate for
mechmical production, Eq. ( I ) simplifies to
- AtS' A,.! 3 - 1 3
(2)
0, -
' 2 -
But I:? = (11 T)w'O' where Q is the acceleration due to gravity. T is the absolute tcmprature. 0 is the potential temperature. and thc prime superscript
dciiotes a iluctuation about the mean. Thus Ey. (2) may be rewritten as
(3)
0, = Ad"3(g/T)1
If the assumptions are correct this equation should be applicable at high
Icvclq whcre the niechanical production term will often be negligible or at
low lcvelv when the atmosphere is very convective. For a given value of
( z w V ' ) ' ' 3 , Eq. (3) should give the rnirtinirtm value of a , since any mechanically gencrated turbuicnce would increase 0,. These predictions may be
tcsted by plotting a , against (zw'~')''.' (see Fig. 1). The data have been
classified according to the values of :,lL, where L, is the loctrl value of the
Monin-Ohukhov length (assuming von Khrman's constant, k = 0.4). It can
be seen that
(a) the less unstable points lie above the more unstable ones; and
(b) there is a tendency for the most unstable data to scatter about a
limiting line. just as would be expected if the conccpt of a convective limit is
correct.