Geoscience Reference
In-Depth Information
For analyses of real thunderstorms the true value of vertical velocity is unknown, rendering
the calculation of RMSE_W impossible; however, RMSE_VR can be calculated. Therefore,
users could apply the variational multiple Doppler radar analysis approach to operational
scans if the vertical profile of RMSE_VR is used to validate upper-level vertical velocities.
The variational approach is a useful tool even for operational volume scans (less than 20
PPIs) because accurate three-dimensional winds can be retrieved at lower levels without
contamination from sampling error in upper level or uncertainty in the upper boundary
condition. These errors do not propagate vertically under the variational approach. Future
work should examine the dependence of the retrieved wind field on scan strategy using
observational datasets generated from real radar networks.
5. Conclusions
This chapter has introduced a variational multiple Doppler radar analysis for retrieving
three-dimensional wind fields in a severe thunderstorm. A simplified version of the
method presented by Gao et al. (1999) has been used to investigate the dependence of
retrieved vertical velocity on scan strategy. Three volume scan strategies have been
considered in this chapter: 1) a typical operational volume scan (17 PPIs), 2) a dense
operational volume scan (20 PPIs), and 3) an extremely dense volume scan (30 PPIs). The
variational approach has notable advantages over the upward integration method,
particularly the avoidance of error accumulation during the upward integration; however,
incomplete observations of the upper boundary condition can cause errors in estimates of
vertical velocity near the storm top even when the variational approach is used. Users
should limit their use of upper-level wind retrievals according to the root-mean-square
error of radial wind, as described in this chapter. The variational method provides
accurate estimates of the three-dimensional wind field at lower altitudes regardless of the
upper boundary conditions. The density of operational radar networks in metropolitan
regions has been increased in recent years to better monitor and forecast severe weather.
Together with this increase in operational radar network density, the variational analysis
method presented in this chapter will provide new information on the three-dimensional
structure of wind within thunderstorms, and advance understanding of the physical
mechanisms underlying heavy rainfall and severe winds.
6. Acknowledgment
The author thanks Dr. K. Iwanami of the National Research Institute for Earth Science and
Disaster Prevention (NIED) for providing useful suggestions regarding multiple Doppler
radar analysis. The model simulation was conducted at NIED using an SGI Altix 4700.
7. References
Armijo L. (1969). A theory for the determination of wind and precipitation velocities with
Doppler radars,
J. Atmos. Sci.
, 26, 570-573
Byre, H. R. & Braham, R. R. (1949).
Thunderstorms,
, U.S. Government Printing Office,
Washington D. C., 287 pp, USA.
Biggerstaff M. I. & R. A. Houze (1991). Kinematic and precipitation structure of the 10-11
June 1985 squall line,
Mon. Wea. Rev.
, 119, 3034-3065
