1. Reflections on Radar Observations of Mesoscale Precipitation
Sandra Yuter, North Carolina State University
David Mechem, University of Kansas
24 Jan 2017

2. After GATE: convective cells to convective+ stratiform transition in low shear
Leary and Houze (1979, JAS)

3. After PRE-STORM: Mature stage of MCS simplified
How did this large system form from a small area of convective cells?
Radar echo boundary
0°C level
Carefully explain convective and stratiform
Stratiform
Convective
Houze et al. 1989, BAMS

4. Time scales responsible for instantaneous observed radar field
Air flows
Precipitation particles
increasing time integration
Nearly instantaneous response to buoyancy and pressure perturbations
wparticles=wair-fallspeed
Particles take time to grow
Particles persist after growth stops

5. Distribution mean is not always the mode
average
average
Distribution mean is not always the mode
average
average

6. Distilling information on 3D structures Contoured Frequency by Altitude Diagram (CFAD)
Yuter and Houze (1995b, MWR)

7. Time Reflectivity Vertical Velocity
Florida: Reflectivity distributions indicate growth as snow particles fall while storm still developing strong updrafts and has no distinct stratiform region
Time
Kansas stratiform region
Yuter and Houze (1995ab, MWR)

8. Vertical air mass transport wair*air*area
Evolving Florida storm
Time
Vertical air mass transport
wair*air*area
Kansas stratiform region
Yuter and Houze (1995c, MWR)

9. Particle fountain conceptual model
Yuter and Houze (1995c, MWR)

10. 2D simulation using Bryan CM1 model with 250 m grid spacing
From Matt Parker,
North Carolina
State University

11. 2D simulation using Bryan CM1 model with 250 m grid spacing
From Matt Parker,
North Carolina
State University

12. Sustainability in tropical (low shear) Mesoscale Convective Systems
TOGA COARE result: Over periods of sustained convective cell activity, the cells never instantaneously occupied more than a small fraction of the radar domain. As cells weakened they evolved into stratiform precipitation, and the stratiform region grew as each cell finished its active convective phase and was added to the stratiform area. The sustainability of convective cells over time thus determined the overall size of a precipitation area.
Yuter and Houze, 1998, QJ

13. S-band Radar Data from Kwajalein
3 Rainy Seasons of
S-band Radar Data from Kwajalein
Monthly % total echo area > 20 dBZ
Aug-Sept 1999 and 2001 drier than 2001
With ± 2 dB calibration uncertainty
KWAJEX
Yuter et al. (2005, JAMC)

14. Typical Kwajalein MCS more irregular than idealized MCS
Particle Trajectories
Idealized
Typical of Kwajalein
Holder et al. (2008, MWR)

15. Limits on area fractions
Minimum stratiform area fraction increases with increasing total area
Maximum convective area fraction does not ever cover more than ~20% of the 300 km diameter radar domain
Increases then decreases with increasing total precip area
Holder et al. (2008, MWR)

16. Useful tools are adaptable
Image tool use

17. Model to Observation Comparisons – Storm Duration Aggregated
hail
1 km cloud resolving model with explicit microphysics (ARPS) of Ft. Worth Texas storm for time=0
(Smedsmo et al, 2004)
Smedsmo et al. (2004, JAM)

18. Compare among model sensitivity tests
Molthan et al. (2016, MWR)

20. Part of Houze’s legacy
Improved understanding of how mesoscale precipitation systems evolve from a small area of convective cells to large areas of convective cells + stratiform precipitation Adaptable tools for analyzing radar data used for a wide range of problems

21. Recommendation on top priority observation need for meteorology in general
Obtain profiles from the surface to ~2 km [800 mb] every 15 minutes with 10’s of km spacing within wintery mix storms and within inflow air for warm-season storms.
Such 3D thermodynamic observations would benefit nowcasting, forecasting, model evaluation, and data assimilation for many types of weather