In addition to surface atmospheric measurements, 217 upper-air rawinsonde profiles were performed from the Knorr. These represented the only rawinsonde measurements ever undertaken in the central part of the Labrador Sea. The upper-air profiles demonstrated that deep convection existed in the atmosphere as well as in the ocean (See figure below). The atmospheric boundary layers (ABLs) or mixed layers were considerably deeper than other extra-tropical marine regions, on the average. The figure shows three examples: the deepest ABL observed during the cruise (Feb. 9 0500 UT), a typical case in the same location a few hours later (Feb. 9, 1400 UT), and a relatively shallow ABL (for this cruise) just downwind of the ice edge (Feb. 22). In general, the ABL tended to be shallowest just off the upwind ice edge (see Feb. 22 case), but considerable temporal variability (e.g. the two Feb. 9 cases) prevented a detailed assessment of spatial variations in ABL characteristics from the ship data alone. One of the significant effects of the deep ABLs was that the temperatures and humidities required considerable time to adjust (i.e. become nearly equal) to the sea surface conditions due to the large quantity of air that had to be modified. In the Labrador Sea cold air outbreak situation, this means that temperatures and humidities remained low and large turbulent sensible and latent heat fluxes extended all the way across the Labrador Sea.
Caption: Potential temperature vs. height from the 1997
Knorr Labrador Sea cruise based on rawinsonde (weather balloon)
profiles. The atmospheric boundary layers (ABLs) are the regions
where the potential temperature is nearly constant with height.
The potential temperature in the
Feb. 9 0500 UT case increases
slightly between 1200 m and 4500 m (it follows the
"pseudo-adiabat") due to latent heat release within a cloud, but
the lower 4500 m is still well-mixed and hence within the ABL.
The ABL depths for the Feb. 9 1400 UT
and the Feb. 22
case are 1250 m and 980 m, respectively.
Other plots
Last update: 6/25/98
Please send all comments and suggestions to the author, Peter
Guest
Links out of here:
Acknowledgements:
Rawinsonde measurements performed by Peter Guest, Karl Bumke, Hauke Berndt, Uwe
Karger and Klaus Uhlig. The development of this web site and the cost of most
of the rawinsondes was supported by the Office of Naval Research grant number
N0001497WR30058.