NOAA/National Severe Storms Laboratory


Hypothesis (Atkins) regarding the interaction of horizontal convective rolls and a boundary for determining the locations of initial cloud development and subsequent deeper convection along boundaries

Nolan Atkins on December 29, 1997 at 09:27:23:

Initial cloud development and consequently deeper convection along a boundary is generated and organized by the boundaryís interaction with turbulent structures in the boundary layer, commonly horizontal convective rolls. Clouds will form at the intersection points of the boundary with the turbulent structures.


Recent studies (e.g., Wilson et al. 1992; Wakimoto and Atkins 1994; Atkins et al. 1997) have shown that clouds are initiated at preferred locations along boundary layer convergence zones. These preferred locations are also where boundary layer turbulent structures such as horizontal convective rolls intersect the boundary. Atkins et al. (1995) performed detailed dual-Doppler analysis along a sea-breeze front and showed that the intersection points of the sea-breeze with horizontal convective rolls were locations of vertical velocity maxima along the front. Close to the front, the horizontal convective roll axes were tilted upward and lifted by the frontal updrafts, creating a deeper and stronger updraft at the intersection point. Further observations of many different types of boundaries are required to assess the generality of the aforementioned results.


Atkins, N.T., R.M. Wakimoto, and T.M. Weckwerth, 1995: Observations of the sea-breeze front during CaPE. Part II: Dual-Doppler and aircraft analysis. Mon. Wea. Rev., 123, 944-969.

Atkins, N.T., R.M. Wakimoto, and C.L. Ziegler, 1997: Observations of the fine-scale structure of a dryline during VORTEX 95. Mon. Wea. Rev., In Press.

Wakimoto, R.M., and N.T. Atkins, 1994: Observations of the sea-breeze front during CaPE. Part I: Single-Doppler, satellite and cloud photogrammetry analysis. Mon. Wea. Rev., 122, 1092-1114.

Wilson, J.W., G.B. Foote, N.A. Crook, J.C. Fankhauser, C.G. Wade, J.D. Tuttle, C.K. Mueller, and S.K. Krueger, 1992: The role of boundary-layer convergence zones and horizontal rolls in the initiation of thunderstorms: A case study. Mon. Wea. Rev., 120, 1785-1815.

Superimpose photogrammetrically determined cloud positions on clear-air radar data. Radar data, collected by the DOWs and ELDORA, will map out the boundary and horizontal convective roll locations. Cloud locations will be determined from triangulation of photogrammetrically analyzed photographs of the cloud field taken from the photo sites. Three photo sites will be required. Two of the photo sites will be collocated with the two DOWs. The third photo site will be located on the opposite side of the boundary from the two other sites. If the cloud positions are located at the intersection points, the hypothesis is supported.

1) Clouds are not located at the intersection points of the boundary and turbulent structures.
2) Clouds form along the boundary in the absence of boundary layer turbulence.

The following appear in order; discussion points may directly refer to one or more comments preceeding it.


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