Abstract. The purpose of this research was to examine the environments conducive to heavy

Transcription

1 Abstract THURMAN, JAMES ARNOLD. Numerical Studies of Synoptic and Mesoscale Environments Conducive to Heavy Rainfall in Tropical and Extratropical Systems. (Under the direction of Yuh-Lang Lin.) The purpose of this research was to examine the environments conducive to heavy rainfall production, specifically a landfalling hurricane, Hurricane Floyd (September 1999) and an Alpine event, MAP IOP-2B (September 1999). In addition to studying the two events independently, a third study examined the link between Floyd's extratropical transition and IOP-2B given that the two events occurred a few days apart. Analysis of observations of both events led to the formation of the hypothesis that the coupling of transverse ageostrophic circulations over a preexisting low-level confluence zone was a key precursor to heavy rainfall production. In both cases, a low-level confluence zone was found based on the observations and simulations. For Floyd, the confluence zone developed as warm easterly winds ahead of the hurricane became juxtaposed with cooler northeast winds just inland over North Carolina and Virginia. In IOP-2B, the confluence zone developed as southerly winds from the Mediterranean became juxtaposed with easterly and southeasterly winds from eastern Italy. These easterlies and southeasterlies developed as southeast winds from the Adriatic Sea impinged upon the eastern Alps, and turned west in the form of a barrier jet. Also, in both cases, upper-level diffluence, due to a split flow, became juxtaposed over the low-level confluence, enhancing the upward motion. MM5 simulations for both events revealed coupled thermally direct and thermally indirect circulations over the low-level confluence zone with their rising branches coupled over the zone, proving the hypothesis. Simulations of Floyd's extratropical transition showed a link existed between Floyd and

2 IOP-2B. Parcels from Floyd's upper-level circulation reached Italy around the time the heavy rainfall developed in IOP-2B. Simulations with and without latent heat release demonstrated the importance of latent heat release in maintaining the upper-level jets and split flow which in turn, aided in the maintenance of convection. Latent heat release was also found to be important in maintaining the strength of the transverse ageostrophic circulations.

3 NUMERICAL STUDIES OF SYNOPTIC AND MESOSCALE ENVIRONMENTS CONDUCIVE TO HEAVY RAINFALL IN TROPICAL AND EXTRATROPICAL SYSTEMS by JAMES A. THURMAN A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements of the Degree of Doctor of Philosophy MARINE, EARTH, AND ATMOSPHERIC SCIENCES Raleigh 2003 APPROVED BY: Yuh-Lang Lin Chair of Advisory Committee Simon W. Chang Jerry M. Davis Michael L. Kaplan

4 Biography James Thurman was born in Kinston, NC on December 22, 1973 (what a Christmas present for his sister!). Growing up in Kinston, he graduated from South Lenoir High School in In the fall of that year, he began his undergraduate studies in meteorology at N.C. State University in Raleigh. In the spring of 1996, he received his B.S. in meteorology and in the fall of the same year began his master's degree study under Jerry Davis. James received his M.S. in meteorology in the fall of In 1999, James began work on a Ph.D. under Yuh-Lang Lin, also at N.C. State where he remained a full time graduate student until May, On May 7, 2001 James began working for Dyntel (now part of Computer Science Corporation) as an assistant systems analysist/programmer. On September 8, 2001, he married Alison Hall of Kinston and the couple moved to Garner in the summer of ii

5 Acknowledgements I would like to thank my committee members: Dr. Yuh-Lang Lin, Dr. Michael Kaplan, Dr. Jerry Davis, and Dr. Simon Chang for their valuable advice and direction during my research. I would also like to thank Dr. Davis and Dr. Charles Main of the Department of Plant Pathology for their guidance and support during my master's research and continuing support during the doctorate research and the free trip to Italy in I also thank Dr. Jay Charney for his help with the initial Floyd simulations on MASS and help with IOP-2B using MM5. Thanks also go to members, of the Mesoscale Dynamics Lab who made working there more fun, especially my partner in crime, Sam Chiao, Karl Pfeiffer, Jeff Cetola, Allan Huffman, Darrell Ensley, Kevin Lux, and Chris Hill. Sam and Karl were especially helpful with MASS and MM5 questions. I would also like to thank my co-workers at CSC for being great to work with and supportive during this time. Thanks to my boss, Lucille Bender for always making sure I was not neglecting research and threatening to fire me if I didn't get my degree. I also would like to thank Joe Touma of the U. S. EPA for advice and support during my research while working full time. Last but not least, I thank my family for their love and support throughout my academic career. My parents taught me to always do my best and trust the Lord and everything would work out. To my wife Alison, thank you for your love and support all these years while I finished my education. MAP IOP-2B research was funded by NSF Grant ATM NOGAPS analyses were obtained from the Fleet Numerical Meteorology and Oceanography Detachment website (navy.ncdc.noaa.gov). Floyd observations and radar imagery were obtained from iii

6 the Codiac service of UCAR. IOP-2B observations and satellite imagery were obtained from the MAP Data Centre ( Distance calculations in Chapter 2 were based on an algorithm from the website of Andrew Gray ( Simulations were performed on an SGI Origin at the North Carolina Supercomputing Center. iv

7 Table of Contents LIST OF TABLES...vii LIST OF FIGURES...viii 1. INTRODUCTION Introduction Purpose of research SYNOPTIC AND MESOSCALE ENVIRONMENTS CONDUCIVE TO HEAVY RAINFALL ASSOCIATED WITH A LANDFALLING HURRICANE: HURRICANE FLOYD (1999) Introduction Analysis of observations Upper-level analyses Surface analyses Radar analyses Features associated with heavy rainfall development Cool wedge and development of the coastal front Upper-level jets and interactions Numerical experiments Results CONTROL case NONBOGUS case Statistical analysis of CONTROL and NONBOGUS differences Terrain sensitivity simulation Statistical comparisons of CONTROL and FLOYD50 simulations Summary and conclusions SYNOPTIC AND MESOSCALE ENVIRONMENTS CONDUCIVE TO HEAVY RAINFALL ASSOCIATED WITH AN OROGRAPHIC RAIN EVENT: NUMERICAL SIMULATIONS OF MAP IOP-2B Introduction Mesoscale Alpine Programme (MAP) Observation analyses Surface analyses Upper air analyses Radar and rain gauge analyses Satellite analyses Summary of observations Model and simulations...91 v

8 3.5 Model results Sea level pressure and surface winds hpa features hpa heights and winds Surface and upper-level divergence Model soundings Rainfall Model vertical cross sections Trajectory analyses hpa back trajectories Time evolution of point 7 trajectories Summary and Conclusions THE EXTRATROPICAL TRANSITION OF HURRICANE FLOYD (1999) AND ITS EFFECT ON MAP IOP-2B Introduction Synoptic overview Numerical simulations Results Extratropical transition Sea level pressure and surface winds hpa heights and winds hpa potential vorticity IOP-2B Back trajectories Summary and conclusions SUMMARY AND CONCLUSIONS REFERENCES vi

9 List of Tables Table 2.1. Track errors (km) and minimum sea level pressure (MSLP, hpa) for Hurricane Floyd, CONTROL simulation, and NONBOGUS simulation for the period 0000 UTC 15 through 0000 UTC 17 September...42 Table 2.2. Summary of hypothesis tests between Floyd observations, CONTROL, and NONBOGUS simulations...43 Table 2.3. Summary of hypothesis tests between Floyd observations and FLOYD50 simulation...44 Table 2.4. Summary of hypothesis tests between the CONTROL and FLOYD50 simulations...45 Table hourly distances between FULL and AFRICA0 trajectories and between FULL and ZERO trajectories from 1200 UTC 20 back to 0000 UTC 19 September vii

10 List of Figures Figure 1.1. a) Terrain of the eastern U. S. with approximate Floyd track and b) location of Lago Maggiore and the terrain of the Italian Alps...5 Figure 2.1. Observed 48-hour accumulated rainfall (mm) for the period 0000 UTC 15 through 0000 UTC 17 September with the 6-hourly positions of Hurricane Floyd...46 Figure 2.2. Eta 300 hpa heights (m), isotachs (m s -1 ), and winds (m s -1 ) for a) 0000 UTC 15 and b) 0000 UTC 16 September...47 Figure 2.3. Subjective sea level pressure (hpa) analyses for a) 0600 UTC 15, b) 0000 UTC 16, c) 0600 UTC 16, d) 1200 UTC 16, and e) 1800 UTC 16 September...48 Figure 2.4. NEXRAD Doppler radar base reflectivities for the period 0300 UTC 15 through 0000 UTC 17 September...50 Figure 2.5. Location of key stations and cross sections referenced in Section Figure 2.6. Observed surface isotherms (ºC) for a) 0000 UTC and b) 0600 UTC 16 September...52 Figure 2.7. Observed sounding cross section of potential temperature (K) and winds (m s -1 ) from Springfield, MO to Morehead City, NC for a) 1200 UTC 15 and b) 0000 UTC 16 September...53 Figure 2.8. Morehead City, NC NEXRAD a) base reflectivity (dbz) and b) storm total rainfall (inches) and observed surface streamlines (m s -1 ) for 0000 UTC 16 September...54 Figure 2.9. a) observed surface velocity divergence (x10-5 s -1 ), b) observed 300 hpa velocity divergence (x10-5 s -1 ), and c) 850 hpa vertical moisture flux (x10-3 m s -1 g kg -1 ) for 0000 UTC 16 September...55 Figure Observed sounding cross section of temperature (ºC) and winds (m s -1 ) from Detroit, MI to Wallops Island, VA for a) 0000 UTC and b) 1200 UTC 16 September...57 Figure Observed surface frontogenesis (K 100 km -1 3 h -1 ) for a) 0000 UTC and b) 0600 UTC 16 September...58 viii

11 Figure Eta 0000 UTC 16 September 300 hpa a) total winds (m s -1 ) and isotachs (m s -1 ) and b) ageostrophic winds (m s -1 ) and ageostrophic isotachs (m s -1 )...59 Figure Eta cross section for 0000 UTC 16 September of a) horizontal winds (m s -1 ) and isotachs (m s -1 ) and b) velocity divergence (x10-5 s -1 ), ageostrophic circulation vectors, and ω (hpa s -1 )...60 Figure a) Area covered by model domains, b) terrain of CONTROL and NONBOGUS Domain 1, and c) FLOYD50 Domain 1 terrain...61 Figure CONTROL Domain 1 sea level pressure (hpa) and surface winds (m s -1 ) for a) 0000 UTC 15 and b) 0600 UTC 16 September. c) CONTROL Domain 1 surface streamlines (m s -1 ) and 6-hour rainfall (mm) for 0000 UTC 16 September...63 Figure a) TPC track and simulated tracks for the CONTROL and NONBOGUS simulations and b) TPC analyzed and simulated minimum central sea level pressures (hpa)...64 Figure CONTROL Domain 1 simulated a) cross section AB potential temperature (K), b) surface temperatures (ºC) and winds (m s -1 ), and c) 850 temperatures (ºC) and winds (m s -1 ) for 0000 UTC 16 September...65 Figure CONTROL Domain 1 simulated 300 hpa heights (m), winds (m s -1 ), and isotachs (m s -1 ) for a) 0000 UTC 15 and b) 0000 UTC 16 September. c) CONTROL Domain 1 cross section AB condensational heating (K h -1 ), isentropes (K) and ageostrophic circulation vectors for 0000 UTC 16 September...66 Figure CONTROL Domain 1 simulated a) surface divergence (x10-5 s -1 ), b) 850 hpa divergence (10-5 s -1 ), c) 300 hpa divergence (10-5 s -1 ), and d) 850 hpa vertical moisture flux (m s -1 g kg -1 ) for 0000 UTC 16 September...67 Figure CONTROL Domain 1 cross section CD isotherms (ºC) for a) 0000 UTC and b) 1200 UTC 16 September...68 Figure CONTROL Domain 1 Miller surface frontogenesis (K (100 km h) -1 ) for 0000 UTC 16 September with contributions from a) divergence and b) deformation...69 Figure CONTROL Domain 1 48 hour accumulated rainfall (mm) and selected observed rainfall totals for the period 0000 UTC 15 September through 0000 UTC 17 September...70 ix

12 Figure NONBOGUS Domain 1 sea level pressure (hpa) and surface winds (m s -1 ) for a) 0000 UTC 15 and b) 1200 UTC 16 September. NONBOGUS Domain 1 surface streamlines (m s -1 ) and 6-hour accumulated rainfall (mm) for c) 0000 UTC 16 and d) 1200 UTC 16 September...71 Figure As for Figure 2.17 except for NONBOGUS simulation...72 Figure NONBOGUS Domain 1 simulated 300 hpa heights and winds (m s -1 ) for a) 0000 UTC 15, b) 0000 UTC 16, and c) 1200 UTC 16 September...73 Figure NONBOGUS Domain 1 cross section AB with condensational heating (K h -1 ), isentropes (K), and ageostrophic circulation vectors for a) 0000 UTC and b) 1200 UTC 16 September...74 Figure As for Figure 2.19 except for NONBOGUS simulation...75 Figure As for Figure 2.20 except for NONBOGUS simulation...76 Figure As for Figure 2.21 except for NONBOGUS simulation...77 Figure NONBOGUS Domain 1 simulated a) 48-hour accumulated rainfall (mm) for the period 0000 UTC 15 September through 0000 UTC 17 September and b) CONTROL-NONBOGUS 48 hour accumulated rainfall difference (mm) for the same period...78 Figure As for Figure 2.17 except for FLOYD50 simulation...79 Figure FLOYD50 Domain 1 simulated a) 48-hour accumulated rainfall (mm) for the period 0000 UTC 15 September through 0000 UTC 17 September and b) FLOYD50-CONTROL 48 hour accumulated rainfall difference (mm) for the same period...80 Figure 3.1. Past Alpine rainfall events with MM5 derived terrain Figure 3.2. Subjective sea level pressure analyses (hpa) for a) 0000 UTC 19, b) 0000 UTC 20, c) 0600 UTC 20, and d) 1200 UTC 20 September Figure 3.3. Subjective height analyses (m) for 0000 UTC 19 September at the a) 850 hpa and b) 300 hpa levels Figure 3.4. As for Figure 3.3 except for 0000 UTC 20 September Figure 3.5. As for Figure 3.3 except for 1200 UTC 20 September x

13 Figure 3.6. Observed soundings for a) 1200 UTC 19 Cagliari, Sardinia, b) 0000 UTC 20 Cagliari, c) 0000 UTC 20 Milan, Italy, and d) 1200 UTC Milan Figure 3.7. Alpine radar composite rainfall rates (mm h -1 ) for a) 0000 UTC 19, b) 0000 UTC 20, c) 0600 UTC 20, and d) 1200 UTC 20 September Figure 3.8. Observed 48-hour accumulated rainfall (mm) for the period 0000 UTC 19 through 0000 UTC 21 September Figure 3.9. Infrared satellite imagery for a) 0130 UTC 19, b) 0130 UTC 20, c) 0600 UTC 20, and d) 1200 UTC 20 September Figure Water vapor satellite imagery for a) 0200 UTC 19, b) 0200 UTC 20, and d) 1200 UTC 20 September Figure a) Model area and domains, b) Domain 1 terrain, c) back trajectory starting points, and d) model terrain of North Africa for FULL simulation Figure September Domain 1 sea level pressure (hpa) and surface winds (m s -1 ) for FULL, AFRICA0, and ZERO simulations Figure As for Figure 3.12 except for Domain hpa heights (m), isotachs (m s -1 ), and winds (m s -1 ) Figure As for Figure 3.13 except for Domain hpa equivalent potential temperature (K) Figure As for Figure 3.13 except for Domain hpa relative humidity Figure FULL Domain hpa heights (m), isotachs (m s -1 ), and winds (m s -1 ) for a) 0000 UTC 19, b) 0000 UTC 20, c) 0600 UTC 20, and d) 1200 UTC 20 September Figure September FULL Domain 1 surface velocity divergence (10-5 s -1 ) for a) 0000 UTC, b) 0600 UTC and c) 1200 UTC. 300 hpa velocity divergence (10-5 s -1 ) and 700 hpa vertical velocity (cm s -1 ) for d) 0000 UTC, e) 0600 UTC, and f) 1200 UTC Figure As for Figure 3.17 except for AFRICA0 Domain Figure As for Figure 3.17 except for ZERO Domain xi

14 Figure Model soundings for Cagliari for a) FULL 1200 UTC 19, b) FULL 0000 UTC 20, c) AFRICA UTC 19, d) AFRICA UTC 20, e) ZERO 1200 UTC 19, and f) ZERO 0000 UTC 20 September Figure As for Figure 3.20 except for Milan for a) FULL 0000 UTC 20, b) FULL 1200 UTC 20, c) AFRICA UTC 20, d) AFRICA UTC 20, e) ZERO 0000 UTC 20, and f) 1200 UTC 20 September Figure September Domain 2 6-hour rainfall (mm) and surface winds (m s -1 ) for a-c) FULL, d-f) AFRICA0 and g-i) ZERO Figure Simulated Domain 2 48-hour accumulated rainfall (mm) from 0000 UTC 19 through 0000 UTC 21 September for a) FULL, b) AFRICA0, and c) ZERO simulations Figure Domain 2 48-hour accumulated rainfall differences (mm) for a) AFRICA0-FULL and b) ZERO-FULL Figure September Domain 2 cross section AB of potential temperature (K), potential vorticity (PVU), and ageostrophic circulation vectors for a) FULL 0000 UTC, b) FULL 0600 UTC, d) FULL 1200 UTC, e) AFRICA UTC, f) AFRICA UTC, g) AFRICA UTC, g) ZERO 0000 UTC, h) ZERO 0600 UTC, and i) ZERO 1200 UTC Figure a) Domain 1 Point 1 36-hour back trajectories, b) parcel heights (m), c) potential temperature (K), d) equivalent potential temperature (K), e) mixing ratio (g kg -1 ), and f) parcel temperature (ºC) for FULL, AFRICA0, and ZERO simulations Figure As for Figure 3.26 except for Point Figure As for Figure 3.26 except for Point Figure As for Figure 3.26 except for Point Figure As for Figure 3.26 except for Point Figure As for Figure 3.26 except for Point Figure Parcel positions and winds (m s -1 ) at parcel's pressure level for the three simulated trajectories for Point 7 from 1200 UTC back to 0300 UTC 20 September xii

15 Figure 4.1. a) NHC 6-hourly best track of Floyd 7-19 September and b) GOES-8 visible image for 1445 UTC 16 September Figure 4.2. NOGAPS sea level pressure (hpa) and surface winds (knots) every 12 hours from 0000 UTC 18 through 0000 UTC 21 September Figure 4.3. NOGAPS 300 hpa heights (m), isotachs (knots), and winds (knots) every 12 hours from 0000 UTC 18 through 0000 UTC 21 September Figure 4.4. Model domain of CNTRL and DRY simulations Figure 4.5. Initial simulation conditions at 1200 UTC 17 September for both the CNTRL and DRY simulations for a) sea level pressure (hpa) and surface winds (m s -1 ), b) 300 hpa heights (m), isotachs (m s -1 ), and winds (m s -1 ), and c) 300 hpa potential vorticity (PVU) Figure 4.6. CNTRL sea level pressure (hpa) and surface winds (m s -1 ) every 12 hours from 0000 UTC 18 through 0000 UTC 21 September Figure 4.7. As for Figure 4.6 except for DRY simulation Figure 4.8. CNTRL 300 hpa heights (m), isotachs (m s -1 ), and winds (m s -1 ) every 12 hours from 0000 UTC 18 through 0000 UTC 21 September Figure 4.9. As for Figure 4.8 except for DRY simulation Figure CNTRL 300 hpa potential vorticity (PVU) every 12 hours from 0000 UTC 18 through 0000 UTC 21 September Figure As for Figure 4.10 except for DRY simulation Figure CNTRL simulated 6-hour rainfall (mm) for a) 0900 UTC, b) 1200 UTC, c) 1500 UTC, and d) 1800 UTC 20 September Figure CNTRL and DRY sea level pressure (hpa) and surface winds (m s -1 ) for 0900 UTC through 1500 UTC 20 September Figure CNTRL and DRY 850 hpa heights (m), isotachs (m s -1 ), and winds (m s -1 ) for 1200 UTC and 1500 UTC 20 September Figure As for Figure 4.14 except for 850 hpa equivalent potential temperature (K) Figure As for Figure 4.14 except for 300 hpa heights, isotachs, and winds xiii

16 Figure CNTRL and DRY cross section AB of vertical velocity (cm s -1 ), potential temperature (K), and ageostrophic circulation vectors for 0600 UTC, 1200 UTC, and 1500 UTC 20 September Figure hour back trajectories for 0900 UTC 20 to 1800 UTC 18 September from northwest Italy for CNTRL and DRY simulations Figure UTC trajectory positions, sea level pressure (hpa), and 300 hpa isotachs (m s -1 ) for a) CNTRL and b) DRY simulations Figure CNTRL and DRY back trajectories diagnostics: a) absolute vorticity (x10-5 s -1 ), b) potential vorticity (PVU), c) wind speed (m s -1 ), d) parcel height (km), and e) vertical velocity (cm s -1 ) xiv