1. Life Cycle of Warm-Season Midlatitude Convection Stan Trier NCAR (MMM Division)

2. Outline 1.Diurnal Cycle of Convection 2.Rainfall Episodes - Phase Coherence - Latitudinal Corridors 3.Propagating Nocturnal Convection (Model Composite Study) - Statistics - Evolving structure and propagation mechanism - Environmental characteristics

3. Amplitude and Phase of U.S. Diurnal Cycle of Thunderstorm Occurrence From Wallace and Hobbs (1977) Atmospheric Science: An Introductory Survey 0 6 12 18 LST

4. Hourly Average Rainfall Frequency (June-August 1996-2004) On WEB http://locust.mmm.ucar.edu/episodes/Hovmoller

5. Time/Frequency Diagram of United States Warm-Season Convection (1996-2004) On WEB http://locust.mmm.ucar.edu/episodes/Hovmoller

6. NOAA/CMORPH Rain Rate Boreal Summer - JJAS 2004 mm/hr Courtesy of Steve Nesbitt, presented at Warm Season Rainfall Workshop (9 June 2006)

7. From TRMM Tropics-wide observations: Over ocean, all types of precipitation features produce the most rainfall at night around 6 AM, mainly controlled by MCSs Over land, the total rainfall peaks in the afternoon when the atmosphere is least stable, however MCS rainfall peaks later at night, around midnight, due to their longer life cycle Nesbitt and Zipser (2003), Mon. Wea. Rev.

8. June 20-24 1998 Example of Coherent Rainfall Episodes Time (day/hr UTC) Stationary Locally Forced Propagating with Intermittency Continuous Propagation Latitudinal Corridor 115W75W95W30N36N42N48N On WEB http://locust.mmm.ucar.edu/episodes/Hovmoller Longitude Latitude

10. Documented Locations of Long-Lived Coherent Precipitation Episodes Radar+Sat Sat Only Courtesy of John Tuttle, presented at Warm Season Rainfall Workshop (9 June 2006)

11. Study Domains & Period Main Focus May - August 5-year (1999 to 2003) 2-year Sep-Oct: 1999, 2003 2-year Nov–Dec: 1999, 2003 Meteosat-7 IR, 30min May - Aug 0 20W 20E 20S 20N 0 40E 0.6 1.2 0 Average Elevation 35S - 20S (km) Nov - Dec Sep-Oct Average Elevation 0- 20N (km) 1.0 0 2.0 Courtesy of Arlene Laing, presented at Warm Season Rainfall Workshop (9 June 2006)

12. Tropical N. Africa: 16 – 30 June 2003 253K233K213K 16 18 20 22 24 26 28 30 Change in phase likely due to mesoscale convective vortex formation Courtesy of Arlene Laing

13. LATITUDE-TIME LATITUDE – PRESSURE CONVECTION MEAN ZONAL WIND (20W-35E) JUNE 2003 AEJ Mean Latitude of convection with zonal wind shear (associated with AEJ) Shear SN Courtesy of Arlene Laing

14. LATITUDE-TIME LATITUDE - PRESSURE CONVECTION MEAN ZONAL WIND (20W-35E) AUGUST 2003 TEJ W’ly AEJ Mean Latitude of convection with W’ly to E’ly shear (monsoon) Shear S N Courtesy of Arlene Laing

15. Comparing Continents Region (Longitude of Domain) Span (km) Duration (h)Phase Speed All episodes (ms -1 ) Contiguous US (37deg) 838 (1 per day mean) 18.5 (1 per day mean) Median – 13.6 East Asia (50deg)620( 1 per day mean) 11.6 (1 per day mean) Mean – 12.4 Europe (50 deg) Mean – 469.16Mean – 8.56Mean – 14.88 Median – 13.6 Africa (60deg)Mean - 1066 Median - 700 Mean – 25.5 Median – 18.0 Mean – 12.0 Median – 11.2 Courtesy of Arlene Laing

16. Span vs Duration for Four Continents Europe, 1999-2003 US Mainland, 1997-2000 East Asia, 1998-2001 Tropical N. Africa, 1999-2003 Courtesy of Arlene Laing

17. Common Features of Episodes Global phenomenon (on all continents with deep convec) Genesis along and immediately downstream of significant topography At least moderate vertical shear (10 m/s) in environment Most frequent and longest-lived at height of warm season Movement at speeds greater than synoptic disturbances (e.g., baroclinic waves) or low-middle tropospheric steering flow

18. Candidate Mechanisms for Long-Lived Coherent Propagating Convective Episodes Density currents Trapped gravity waves Gravity-inertia waves in the free troposphere Balanced circulations associated with and/or modified by convection (e.g., MCVs) Discussed by Carbone et al. (2002) J. Atmos. Sci

19. July-Aug 1998-2002 Radar + RUC Analysis Radar 900 mb Winds CAPE/Shear (600-900 mb) 300 mb Winds/Heights Corridors of Precipitation 0 6 12 18 24 TIME (UTC) 110 100 90 80 LONGITUDE WEST Propagating convection Locally forced Initiates at time of max solar heating over higher terrain Initiates during the night in the central plains From Tuttle and Davis (2006) To appear in Mon. Wea. Rev.

20. 22 LST Surface Potential Temp/Winds/Reflectivity In situ or weakly propagating Rapidly propagating

21. Days with strong LLJ (>12 ms -1 ) 45 days out of 310 900 mb Hgt Anom/Radar 300 mb Hgt Anom/Radar 900 mb Winds300 mb Winds/Hgts + - - + From Tuttle and Davis (2006) To appear in Mon. Wea. Rev.

22. Days with weak/no LLJ (<5 ms -1 ) 32/310 900 mb Hgt Anom/Radar 300 mb Hgt Anom/Radar 900 mb Winds300 mb Winds/Hgts + - - From Tuttle and Davis (2006) To appear in Mon. Wea. Rev.

23. Days with persistent corridors lasting 4 or more days 900 mb Hgt Anom/Radar 300 mb Hgt Anom/Radar 900 mb Winds300 mb Winds/Hgts + + 0 From Tuttle and Davis (2006) To appear in Mon. Wea. Rev.

24. Longitude 3-10 July 2003 Longitude vs Time Rainfall Frequency 0 3 6 9 12 15 18 21 0 3 6 9 12 15 18 21 0 Time (UTC hour) 105W100959085W 65 56 47 37 28 19 9 0% From Carbone et al. (2002; JAS) Diurnal Frequency Diagrams of Convection

25. July 3-10, 2003 500 hPa Height

26. Differing Regimes for Organized Convection Quasi-Stationary E-W Front PatternTranslating Synoptic Cold Front Pattern “Classic MCS pattern” (e.g., week-long BAMEX Case) Convection primarily nocturnal and early morning Large CAPE confined to frontal zone (restricts scale of convection) Supports both MCSs and long narrower linear convection Convection primarily afternoon and early evening Large CAPE both along and ahead (south and east) of frontal zone

27. 7-Day Simulations Using WRF (00Z 3 July to 00Z 10 July 2003) Initial and Boundary Conditions Obtained from ETA Analyses ( D t = 3h) Yonsei University PBL Scheme with Noah LSM Long and Shortwave Radiation Parameterization 4-km Simulation: - Central US Regional Domain (625 x 445 x 35) - Explicit Convection (No Cumulus Parameterization) - Lin et al. (1983) based Microphysical Scheme

28. Comparison of Simulated and Observed Precipitation Episodes From Trier, Davis, Ahijevych, Weisman, and Bryan (2006), To appear in J. Atmos. Sci.

29. Rainstreak Phase Speed Statistics (03-10 July 2003) Zonal Phase Speed (m/s) Frequency

31. Composite System-Relative Flow, Theta (Contours), Theta-e (Colors) Intensifying Stage (Early Evening) Mature Stage (Overnight) Weakening Stage (Around Sunrise) Distance (km) Height (km AGL)  Five Cases  40-km Along-Line Average

33. Rainstreak Propagation Rainstreak movement cannot be explained by advection by mean environmental flow through storm depth

34. Rainstreak Propagation (cont.)

35. Estimates of rain streak zonal phase speed based on mature stage cold-pool negative buoyancy (left) are systematically high Similar estimates based on the 16-km deep integrated buoyancy anomaly (right) are much closer to observed rain streak zonal phase speeds

36. Composites of the Mesoscale Environment for Mature Stage

37. Composite Vertical Cross Sections of the Mesoscale Environment

38. Trajectories from NETrajectories from SW 20 40 60 80 100 20 40 60 80 100 0.0 1.0 2.0 3.0 0.0 1.0 2.0 3.0 Height (km MSL) Relative Humidity (%) 03 00 2118 03 00 21 03 00 211803 00 21 Time (hr UTC) Forward Trajectory Analysis for a Strong Frontal Case Example

39. Diurnal Frequency and Composite Mesoscale Environment of Propagating Convection 850 hPa Temperature/Winds

40. Some Remaining Questions Are mechanisms for nocturnal propagation (a major component of long-lived episodes) similar on other continents? - e.g., poleward low-level jets (many continents, not Africa) Initiation of many major episodes in central U.S. tied to both topography and mobile short waves. Are they related? What governs intermittency (redevelopment along approximate same phase line in next heating cycle)? - amplification or refocusing free-tropospheric disturbance by convection? - density current dynamics/trapped gravity waves?