Steve Koch on November
13, 1997 at 17:49:08:
A narrow band of intense but shallow convection (NCFR) is initiated
along anafronts (characterized by rearward relative flow) when sufficient
moisture and a strong low-level (LLJ) are present within 100 km
ahead of the cold front, even in the absence of any CAPE. The strength
of the lifting, which is associated with a circulation transverse
to the LLJ, is dependent upon (1) the strength of the LLJ, (2) the
magnitude of the deformation forcing in the Sawyer-Eliassen equation,
and (3) the cross-jet balance between the vorticity associated with
the vertical wind shear in the LLJ and the solenoidal vorticity
associated with any diabatic cooling source that may exist behind
Koch, S. E., and W. Clark, 1997: The dynamics of severe storm initiation
along a nonclassical cold front revealed by remote sensing observations
during COPS-91. J. Atmos. Sci. (submitted).
Adams, M. E., S. Businger, M. L. Kaplan, and S. E. Koch, 1997:
Extraction of geopotential height and temperature structure from
observed profiler winds over the Central Plains during STORM-FEST.
J. Appl. Meteor. (cond. accept.).
Karyampudi, V. M., S. E. Koch, J. W. Rottman, and M. L. Kaplan,
1995: The influence of the Rocky Mountains in the 13-14 April 1986
severe weather outbreak. Part II: Evolution of an internal bore
and its role in triggering a squall line. Mon. Wea. Rev 123, 1423-1446.
Koch, S. E., and P. J. Kocin, 1991: Frontal contraction processes
leading to the formation of an intense narrow rainband. Meteor.
Atmosph. Phys, 46, 123-154.
||Determine existence of the LLJ from WSR-88D and Profilers,
and estimate the thermal fields from thermodynamic retrieval applied
to the Profiler + WSR-88D combined network using the Adams et al.
(1997) & Karyampudi et al. (1995) divergence equation methodology.
Low-level aircraft traverses can be used to obtain greater spatial
resolution of these fields near to the front. Moisture distribution
are obtainable from ground and Mobile Mesonets, M-CLASS, and GOES8
cloud distributions. Vorticity balance will be evaluated from cross-front
wind shear using radars and profilers, but access to one or more 915
Mhz profilers is necessary to obtain information with sufficient detail
in lowest 2 km, based upon our experiences in COPS-91 (Koch and Clark
1997). I argue for this additional invaluable instrumentation, since
the emphasis in TIMEX is on low-level features.