DISSERTATION
ON THE RELATIONSHIPS BETWEEN CONVECTIVE STORM
KINEMATICS, MICROPHYSICS, AND LIGHTNING
Submitted by
Timothy James Lang
Department of Atmospheric Science
In partial fulfillment of the requirements
for the Degree of Doctor of Philosophy
Colorado State University
Fort Collins, Colorado
Spring 2001
COLORADO STATE UNIVERSITY
December 1, 2000
WE HEREBY RECOMMEND THAT THE DISSERTATION PREPARED UNDER OUR SUPERVISION BY TIMOTHY JAMES LANG ENTITLED ON THE RELATIONSHIPS BETWEEN CONVECTIVE STORM KINEMATICS, MICROPHYSICS, AND LIGHTNING BE ACCEPTED AS FULFILLING IN PART REQUIRMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY.
Committee on Graduate Work
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ABSTRACT
ON THE RELATIONSHIPS BETWEEN CONVECTIVE STORM
KINEMATICS, MICROPHYSICS, AND LIGHTNING
Combined multiparameter radar, dual-Doppler, thermodynamic sounding, and lightning observations of 11 thunderstorms (6 from the mid-latitudes, 5 from the tropics) are presented. The thunderstorms span a wide spectrum of intensities, from weak monsoon-type to severe tornadic, and include both unicellular and multicellular convection. In general, the kinematically strongest storms featured lower production of negative cloud-to-ground lightning (typically < 1 min-1 flash rates for large portions of the storms’ lifetimes) when compared with more moderate convection, in accord with an elevated charge mechanism. The only significant differences between intense storms that produced predominately positive cloud-to-ground (CG) lightning for a significant portion of their lifetimes (PPCG storms), and intense storms that produced little CG lightning of any polarity (low-CG storms), was that PPCG storms featured much larger volumes of significant updrafts (both > 10 m s-1 and > 20 m s-1) and produced greater amounts of precipitation (both rain and hail). Otherwise, peak updrafts and vertical air mass fluxes were very similar between the two types of storms, and both types were linked by anomalously low production of negative CG lightning. It is suggested that PPCG storms may be caused by enhanced lower positive charge created by the larger volume of significant updrafts. Since both PPCG and low-CG storms are capable of being severe, anomalously low production of negative CG lightning (regardless of positive CG flash rate) may be a useful signature for use in the “nowcasting” of severe convection.
Timothy James Lang
Department of Atmospheric Science
Colorado State University
Fort Collins, Colorado
Spring 2001
ACKNOWLEDGEMENTS
I would like to thank the following people and organizations for their crucial help and support: my adviser, Dr. Steven Rutledge; my committee, Dr. William Cotton, Dr. Richard Johnson, and Dr. Ray Robinson; the CSU Radar Meteorology group, especially Paul Hein, Margi Cech, Dr. Larry Carey, Dr. Walt Petersen, and Dr. Rob Cifelli; the CSU-CHILL radar staff; the NCAR S-Pol radar staff; the NASA TOGA radar staff; the NASA Marshall Space Flight Center, especially Dr. Rich Blakeslee; New Mexico Tech, especially Dr. Paul Krehbiel; Ray McAnelly; and my fiancée Ashley Calvin. This work was supported under NSF grant ATM-9726464.
TABLE OF CONTENTS
Chapter/Section Title Page
1. INTRODUCTION 1
1.1 Background 1
1.2 Hypotheses 3
2. DATA AND METHODOLOGY 8
2.1 Overview 8
2.2 Observational Platforms 9
2.2a CSU-CHILL Radar 9
2.2b Pawnee Radar 10
2.2c SPOL Radar 10
2.2d TOGA Radar 10
2.2e Field Change Meters 10
2.2f National Lightning Detection Network 11
2.2g TRMM/LBA Advanced Lightning Direction Finder Network 11
2.2h New Mexico Tech VHF Lightning Mapper 12
2.2i Thermodynamic Soundings 12
2.3 Methodology 13
2.3a Radar Scan Strategy 13
2.3b Multiparameter Radar Analysis 13
2.3c Dual-Doppler Radar Analysis 17
2.3d Lightning Analysis 19
2.3e Sounding Analysis 20
2.3f Synthesis 20
3. CHILL-PAWNEE AND STEPS MID-LATITUDE THUNDERSTORMS 28
3.1 Overview of Storms 28
3.1a 1 July 1998 28
3.1b 15 July 1998 30
3.1c 21 July 1998 32
3.1d 25 July 1998 34
3.1e 30 July 1998 36
3.1f 29 June 2000 37
3.1g Summary 39
3.2 Comparison of Storm Environments 40
3.3 Vertical Structure 43
3.4 Testing of Elevated Charge Mechanism 49
3.5 Testing of PPCG Mechanisms 51
3.5a Tilted Dipole 51
3.5b Inverted Dipole 52
3.5c Precipitation Unshielding 53
3.6 Testing of Separated Updraft-Downdraft Mechanism 53
3.7 Summary 56
4. TRMM/LBA TROPICAL THUNDERSTORMS 132
4.1 Overview of Storms 132
4.1a 26 January 1999 132
4.1b 13 February1999 134
4.1c 15 February 1999 136
4.1d 17 February 1999 138
4.1e 20 February 1999 140
4.1f Summary 142
4.2 Comparison of Storm Environments 142
4.3 Vertical Structure 144
4.4 Testing of Elevated Charge Mechanism 148
4.5 Testing of PPCG Mechanisms 150
4.6 Testing of Separated Updraft-Downdraft Mechanism 150
4.7 Summary 151
5. SYNTHESIS AND DISCUSSION 211
5.1 Synthesis of Mid-Latitude and Tropical Results 211
5.1a Kinematic Intensity versus Cloud-to-Ground Lightning Production 211
5.1b Precipitation Intensity versus Cloud-to-Ground Lightning Production 214
5.1c Radar Reflectivity Intensity versus Cloud-to-Ground Lightning Production 215
5.1d Kinematic Intensity versus Precipitation and Reflectivity Intensities 216
5.2 Energy and Charge Considerations 217
5.3 Discussion and Conclusions 218
5.4 Suggestions for Future Research 223
BIBLIOGRAPHY 234
LIST OF TABLES
Table Caption Page
Table 2.1: Specifics of the radars used in this study. 22
Table 2.2: Overview of the algorithm used to calculate rain and hail rates from 23
CSU-CHILL and SPOL multiparameter radar data.
Table 2.3: Overview of the dual-Doppler algorithms employed in this study. 24
Table 3.1: Summary of kinematic, microphysical, and lightning observations for the 59
mid-latitude cases.
Table 3.2: CAPE (in J kg-1) and shear (in m s-1) calculations for the mid-latitude cases. 60
Table 3.3: Best correlation coefficients for reflectivity versus vertical wind speed, 61
considering various regions of the mid-latitude storms. Also shown are the times
of the radar volumes in which the best correlations were found (L – local/MDT;
Z – UTC).
Table 4.1: Summary of kinematic, microphysical, and lightning observations for the 153
tropical cases.
Table 4.2: CAPE (in J kg-1) and shear (in m s-1) calculations for the tropical cases. 154
Table 4.3: Best correlation coefficients for reflectivity versus vertical wind speed, 155
considering various regions of the tropical thunderstorms. Also shown are the times
of the radar volumes in which the best correlations were found (Z – UTC).
Table 5.1: Total kinetic energy (in 1013 J) contained in the vertical motions of the 225
thunderstorms in this study.
LIST OF FIGURES
Figure Caption Page
Figure 1.1: Schematic representation of the impact of the elevated charge mechanism 6
on lightning flash rates.
Figure 1.2: Schematic representations of the three mechanisms proposed to explain 7
PPCG thunderstorms. The top-left panel depicts the tilted dipole mechanism. The
top-right panel depicts the inverted dipole or enhanced lower positive charge mechanism.
The bottom panels depict the precipitation unshielding mechanism. From Williams (2000).
Figure 2.1: Schematic map of the operational area of the CHILL-Pawnee dual-Doppler 25
network. Pictured are the two dual-Doppler lobes. Landmarks include the two
radars (CHILL and Pawnee) as well as nearby cities and airports (map courtesy of P.
Kennedy).
Figure 2.2: Schematic map of the STEPS operational area. Pictured are the two dual- 26
Doppler lobes (bold circles) formed by CHILL and SPOL. Also shown are major
elevation contours. Landmarks include the three project radars (CHILL, SPOL, and
Goodland/KGLD) as well as nearby cities, airports, and other regional NEXRAD radars.
The shaded areas include other dual-Doppler and triple-Doppler lobes formed by the
CHILL-SPOL-KGLD network (map courtesy of Dr. J. Miller).
Figure 2.3: Schematic map of the TRMM/LBA operational area. Shown are the locations 27
of the radars (SPOL and TOGA), sounding site, rain gauge networks, ALDF sensors, and
profiler. Also shown are nearby cities and geographical regions. Topography is color-
coded. Black circles show the maximum ranges of both radars. The red dashed circles
show the dual-Doppler lobes (map courtesy of Dr. W. Petersen).
Figure 3.1: Horizontal cross-section of CHILL radar reflectivity at 0.5 km AGL, at 1850 62
MDT on 1 July 1998. Distances are relative to CHILL
Figure 3.2: Time-height cross-section of peak CHILL radar reflectivity for the 1 July 1998 63
storm. Values are in dBZ.
Figure 3.3: Time-height cross-section of maximum vertical velocity for the 1 July 1998 64
storm. Values are in m s-1.
Figure 3.4: Volume of 1 July 1998 storm containing updrafts within respective bins as a 65
function of time.
Figure 3.5: Rain production by the 1 July 1998 storm as a function of time. Values are 66
at 0.5 km AGL. Moderate rain is 20-60 mm h-1, and heavy rain is greater than 60 mm h-1.
Figure 3.6: Hail production by the 1 July 1998 storm as a function of time. Values are at 67
0.5 km AGL.
Figure 3.7: CG flash rate as a function of time for the 1 July 1998 storm. 68
Figure 3.8: Horizontal cross-section of CHILL radar reflectivity at 0.5 km AGL, 69
at 1925 MDT on 1 July 1998. Also shown are ground strike positions (plus signs
for positives, minus signs for negatives) of NLDN CGs that occurred during 1920-
1930 MDT. Distances are relative to CHILL.
Figure 3.9: Horizontal cross-section of CHILL radar reflectivity at 0.5 km AGL, at 70
1804 MDT on 15 July 1998. Distances are relative to CHILL.
Figure 3.10: Time-height cross-section of peak CHILL radar reflectivity for the 71
15 July 1998 storm. Values are in dBZ.
Figure 3.11: Time-height cross-section of maximum vertical velocity for the 15 July 72
1998 storm. Values are in m s-1.
Figure 3.12: Volume of 15 July 1998 storm containing updrafts within respective bins 73
as a function of time.
Figure 3.13: Rain production by the 15 July 1998 storm as a function of time. Values 74
are at 0.5 km AGL. Moderate rain is 20-60 mm h-1, and heavy rain is greater than 60 mm h-1.
Figure 3.14: Hail production by the 15 July 1998 storm as a function of time. Values are 75
at 0.5 km AGL.
Figure 3.15: CG flash rate as a function of time for the 15 July 1998 storm. 76
Figure 3.16: a) Horizontal cross-section of CHILL radar reflectivity at 0.5 km AGL, at 77
1804 MDT on 15 July 1998. Also shown are ground strike positions (plus signs for
positives, minus signs for negatives) of NLDN CGs that occurred during 1800-1810
MDT. b) Same as a) except for radar at 1840 MDT and CG lightning during 1840-
1850 MDT. Distances are relative to CHILL.
Figure 3.17: Horizontal cross-section of CHILL radar reflectivity at 0.5 km AGL, at 78
1531 MDT on 21 July 1998. Distances are relative to CHILL.
Figure 3.18: Time-height cross-section of peak CHILL radar reflectivity for the 79
21 July 1998 storm. Values are in dBZ.
Figure 3.19: Time-height cross-section of maximum vertical velocity for the 21 July 1998 80
storm. Values are in m s-1.
Figure 3.20: Volume of 21 July 1998 storm containing updrafts within respective bins as 81
a function of time.
Figure 3.21: Rain production by the 21 July 1998 storm as a function of time. Values are 82
at 0.5 km AGL. Moderate rain is 20-60 mm h-1, and heavy rain is greater than 60 mm h-1.
Figure 3.22: Hail production by the 21 July 1998 storm as a function of time. Values are at 83
0.5 km AGL.
Figure 3.23: CG flash rate as a function of time for the 21 July 1998 storm. 84
Figure 3.24: Horizontal cross-section of CHILL radar reflectivity at 0.5 km AGL, at 85
1516 MDT on 21 July 1998. Also shown are ground strike positions (plus signs for
positives, minus signs for negatives) of NLDN CGs that occurred during 1509-1519
MDT. Distances are relative to CHILL.
Figure 3.25: Total flash rate as a function of time for the 21 July 1998 storm. 86
Figure 3.26: Horizontal cross-section of CHILL radar reflectivity at 0.5 km AGL, at 87
1625 MDT on 25 July 1998. Distances are relative to CHILL.
Figure 3.27: Time-height cross-section of peak CHILL radar reflectivity for the 88
25 July 1998 storm. Values are in dBZ.
Figure 3.28: Time-height cross-section of maximum vertical velocity for the 25 July 1998 89
storm. Values are in m s-1.
Figure 3.29: Volume of 25 July 1998 storm containing updrafts within respective bins as 90
a function of time.
Figure 3.30: Rain production by the 25 July 1998 storm as a function of time. Values are 91
at 0.5 km AGL. Moderate rain is 20-60 mm h-1, and heavy rain is greater than 60 mm h-1.
Figure 3.31: Hail production by the 25 July 1998 storm as a function of time. Values are 92
at 0.5 km AGL.
Figure 3.32: CG flash rate as a function of time for the 25 July 1998 storm. 93
Figure 3.33: Horizontal cross-section of CHILL radar reflectivity at 0.5 km AGL, at 1640 94
MDT on 25 July 1998. Also shown are ground strike positions (plus signs for positives,
minus signs for negatives) of NLDN CGs that occurred during 1640-1650 MDT.
Distances are relative to CHILL.
Figure 3.34: Total flash rate as a function of time for the 25 July 1998 storm. 95
Figure 3.35: Horizontal cross-section of CHILL radar reflectivity at 0.5 km AGL, at 96
1716 MDT on 30 July 1998. Distances are relative to CHILL.
Figure 3.36: Time-height cross-section of peak CHILL radar reflectivity for the 97
30 July 1998 storm. Values are in dBZ.
Figure 3.37: Time-height cross-section of maximum vertical velocity for the 98
30 July 1998 storm. Values are in m s-1.
Figure 3.38: Volume of 30 July 1998 storm containing updrafts within respective bins 99
as a function of time.
Figure 3.39: Rain production by the 30 July 1998 storm as a function of time. Values 100
are at 0.5 km AGL. Moderate rain is 20-60 mm h-1, and heavy rain is greater than
60 mm h-1.
Figure 3.40: Horizontal cross-section of CHILL radar reflectivity at 0.5 km AGL, at 101
2325 UTC on 29 June 2000. Distances are relative to CHILL.
Figure 3.41: Time-height cross-section of peak CHILL radar reflectivity for the 102
29 June 2000 storm. Values are in dBZ.
Figure 3.42: Time-height cross-section of maximum vertical velocity for the 103
29 June 2000 storm. Values are in m s-1.
Figure 3.43: Volume of 29 June 2000 storm containing updrafts within respective 104
bins as a function of time.
Figure 3.44: Rain production by the 29 June 2000 storm as a function of time. 105