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Polarimetric radar analysis of convection in northwestern Mexico Timothy J. Lang, Angela Rowe, Steve Rutledge, Rob Cifelli Steve Nesbitt.

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Presentation on theme: "Polarimetric radar analysis of convection in northwestern Mexico Timothy J. Lang, Angela Rowe, Steve Rutledge, Rob Cifelli Steve Nesbitt."— Presentation transcript:

1 Polarimetric radar analysis of convection in northwestern Mexico Timothy J. Lang, Angela Rowe, Steve Rutledge, Rob Cifelli Steve Nesbitt

2 Three radars in core Monsoon region during summer 2004 (NAME Tier I; NW Mexico) Network covered Gulf of California, Sierra Madre Occidental, Coastal Plain, Baja Peninsula, Pacific Ocean S-Pol – S-Band, Polarimetric, Doppler SMN – Cabo and Guasave radars (C-Band, Doppler)

3 Lang et al. (2007) reduced- dimension analyses Regime A Defined as enhanced rainfall over the Gulf and coastal plain Regime B Defined as enhanced northward coast-parallel movement of systems

4 Lang et al. (2007) Regime AB (both A and B occurring) More rainfall, with larger, more organized features

5 Rowe et al. (2008) Radar rainfall and vertical structure vs. topography More frequent, less intense rainfall at highest elevations Gulf ~12h out of phase with land More intense vertical reflectivity structure over low elevations

6 Conceptual Model Lang et al. (2007), Nesbitt et al. (2008), Rowe et al. (2008) Convection forms over highest terrain, then moves westward During disturbed regimes, convection organizes upscale, and persists after sunset into morning hours Question: How does the microphysical structure of convection vary with terrain and meteorological regime?

7 Storm Microphysics ~90 hours total spread over ~35 cases Usually 150-km range 2-3 PPIs with 0-1 RHIs in 15 min 360s @ rain-map angles (0.8,1.3,1.8°) Climatology Used most frequently; 200-km range Full-volume 360s, complete in 15 min Rain-map angles (0.8,1.3,1.8°) & 0.0° S-Pol 24-h Ops 7/8-8/21 Two Modes Only S-Pol data used in this study

8 ● Threshold on  HV,  (  DP ) – noise, clutter ● Threshold on Z H, Z DR – insects ● Threshold on LDR,  DP – second trip ● 21-pt (3.15 km) FIR filter on  DP, Adaptive linear fit to calculate K DP ● Z H, Z DR rain attenuation correction via  DP method (Carey et al. 2000) ● Z H corrected for gaseous attenuation (Battan 1973) ● Rainfall from CSU blended polarimetric algorithm (Cifelli et al. 2002) (Base Z-R: Z=133R 1.5 pol-tuned via Bringi et al. 2004) ● Blockage corrected via Cifelli et al. (2002) and Lang et al. (2007; 2008) ● Data gridded to 0.02° x 0.02° x 1 km 3-D grid, matched in horizontal to 2-D regional grids of Lang et al. (2007), using SPRINT ● 15-min temporal resolution (3801 volumes for entire project) ● Grids extend ~1.6° in each direction from S-Pol ● Grids include all polarimetric variables plus fuzzy-logic hydrometeor ID via Tessendorf et al. (2005) ● Convective/Stratiform partitioning via Rowe et al. (2008) ● Break down gridpoints by terrain (over water, 0-500 m land, 500-1500 m, and 1500+ m MSL) to investigate possible topographic influences ● Using lowest gridpoint containing rainfall, examine reflectivity, Z DR and D 0, K DP, and rainfall rate, following Carey et al. (2001) ● D 0 via D 0 = 1.529*(Z DR ) 0.467 ● Use Cifelli et al. (2002) to examine ice and liquid water mass contents DATA QC

9 Sanity check - S-Pol domain rainfall diurnal cycle results match well with previous studies

10 D 0 stratified by topography - Largest D 0 s occur most frequently over lowest elevations, and least frequently over water

11 Gulf has smallest D 0 and Z H values over full spectrum of rainfall

12 Gulf - least amount of ice mass, but relatively high water mass Land - Decreasing ice and water mass as elevation increases

13 Gulf - Reduced D 0 and Z H during Regime AB

14 During Regime AB, all terrain bands but 1500m+ have increased ice mass Ice Water Relatively large increases in water mass over Gulf and 0-500m during Regime AB

15 Polarimetric tuning via Bringi et al. (2004) Use Z H, Z DR, and K DP to estimate a in Z=aR 1.5 Examine distribution over all points Regime AB No Regime Lower a values over Gulf during disturbed regimes, with stratification by elevation over land In ordinary circumstances, variability in a with terrain is less obvious

16 Conclusions Land Convection has the largest D 0 s, along with ice and water mass, at the lowest elevations (0-500m) At highest elevations (1500m+), convection does not change much during disturbed regimes; lowest elevations show some change in terms of ice/water mass, D 0, etc. Consistent with inference from past studies of upscale organization during westward travel Water Storm microphysical structure is different over the Gulf of California than over the land Convection over water produces smaller drops via reduced ice phase microphysical processes compared to land During disturbed regimes, both warm and cold microphysical processes become more important, and net result is smaller drop sizes Warm rain processes more important over Gulf


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