Charge Moments

Introduction.

• Postscript Version  (Highest Quality)
• PDF Version
  

Here is an extended version of the PowerPoint presentation I gave at the SLS conference.
I've added notes to the presentation so that reading through it would essentially simulate
what I would say.  This presentation has lots of material that is not covered in the preprint paper:

• SLS_2002_talk.ppt

The following are additional plots and analysis that would not fit  in the four page extended abstract.

This table gives the radar measurement thresholds used to classify hydrometeors.
This table is also given in Tessendorf and Rutledge (2002), which is also in the SLS
conference preprint volume.

Hydrometeor Classification Table

Hydrometeor Type	T	Zh	Zdr	LDR	Kdp	rho_hv
	(deg C)	(dBZ)	(dB)	(dB)	(deg/km)	...
Vertically Oriented Ice Crystals (VI)	<=-20	<40	not used	not used	<-0.25	not used
Snow (S)	<0	<=35	not used	not used	<0.5	>0.95
Graupel (G)	<0	35 to 55	not used	<=-20	<0.5	>0.95
Wet Hail (WH)	<0	>=55	not used	>=-20	-0.5 to 1.0	<0.97
Dry Hail (DH)	<0	>=55	not used	>-26	<0.5	>0.96
Drizzle (Drz)	>=0	<=35	not used	not used	not used	not used
Rain (R)	>=0	35 to 60	not used	not used	not used	not used
Large hail mixed with rain (L.h+r)	>=0	>=55	<1.0	>=-20	>=0.5	<=0.96
Large hail (LH)	>=0	>=55	<=0.5	>=-18	<0.5	<=0.96
Small hail mixed with rain (S.h+r)	>=0	>=50	<1.0	-27 to -20	>=0.5	<=0.98
Small Hail (SH)	>=0	>=50	<=0.5	<-18	<0.5	>0.96
Unclassified (UC)	.	.	.	.	.	.

In addition to this classification scheme, I have also developed a fuzzy logic
classification (FHC).  For the most part, the FHC 
is consistent with the look-up table method shown above.  
To read more about the FHC, follow this link.

The following two image loops give an overview of the storm.

• Loop of LMA point density from 21:30 to 00:30.
• Loop of vertical cross-sections of Horizontal Reflectivity (DZ), vertical velocity (W) and hydrometeor type.

This Figure shows the flash rates for the entire duration of the storm, from 21:30 to 04:00.  Note that radar coverage extended from only 21:30 to 01:20.  The top plot show total number of LMA sources each minute (black) with total counted flashes each minute (green).  Lower two panels show positive and negative cloud-to-ground flash rates.

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This figure shows time-height contours of hail echo volume above the melting level as determined by using the lookup table shown above and described in Tessendorf and Rutledge (2002, this volume).  Overlaid onto these contours are magenta plusses +  which are the source heights of positive cloud-to-ground (+CG) flashes as  determined by taking the mean height of the first 10 LMA points in the flash.  Compare with the figure immediately below.

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This figure shows time-height contours of hail echo volume as determined by my Fuzzy Logic Classification(FHC).


In the above figures, each time encompasses 6-7 minutes (the time required to complete a radar volume scan) starting from the time indicated on the axis.  To be consistent with this, I've taken all +CGs which occured after the time indicated but before the next time.  So, for example, there were 7 +CGs from 23:25 to 23:31.  All seven of these are plotted as +'s at 23:25.

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This table contains links to images of base (3 km MSL) reflectivity and precip type with CG strike locations overlaid.  The precip type in these images was determined using my Fuzzy Logic Classification (FHC) scheme.  Plus signs (+) indicate +CGs, and diamonds indicate -CGs.

The last column in this table has zoomed images of base reflectivity with CG strike locations overlaid and labeled by their source heights (as determined by the mean altitude of the first 10 points in the flash).  Black numbers(or +'s) correspond to +CGs and magenta numbers (or  -'s) correspond to -CGs.  For those CGs which were inextricably embedded in other lightning, we did not attempt to determine the source height; these CGs are labeled by + or - symbols.

The radar and CG times in the table correspond with those in the time-height contour figures.

For all skipped times in this table (e.g., from 21:30 to 22:39 and from 22:46 to 23:18), there was no CG activity.  This storm continued to produce CGs after 01:20, but there was no radar coverage after 01:20.

 

This figure shows histograms of the mean start altitude of both positive and negative CGs.  The mean start altitude is simply the mean of the first 10 points in each flash.  Note that this histogram includes only those CGs which I could isolate from other lightning.

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This Figure shows a histogram of the currents for only the +CGs in the June 29 storm.

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These two plots show the density of CGs (both positive and negative) in units of number of strikes per 25 square kilometers.  The left plot shows the density in terms of the NLDN strike point.  The right plot shows the density in terms of the LMA-inferred mean start point of the CG flashes.  Essentially, I constructed a 75X75 km grid with 5 km grid spacing and then found which grid point each CG was closest to.  Then I simply added up all the CGs in each grid point to make the contours you see above.  Contour interval is 1 flash per 25 km², with the 1, 5, and 10 contours extra thick.  The red color indicates where the density exceeded 10.   

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Charge Moments

Steve Cummer of Duke University provided these charge moment calculations.


Histogram of the +CG charge moments.  The bulk of them are
<200 C km, with a few larger ones.



Here's a scatter plot of the charge moments versus the peak current,
with +CGs in red and -CGs in green.  The fit line is for the +CGs only
and, as the plot title indicates, the correlation coefficient between peak
current and charge moment for the +CGs is about 0.6.  So there is some
tendency for +CGs with higher peak currents to have large charge moments,
but there is quite a bit of scatter.

This table provides information about CGs for which preliminary charge moments have been calculated.  Click on one of the times in the first column to see horizontal and vertical cross-sections of radar data with the lightning mapping points of the CGs overlaid.  Each image shows two horizontal cross-sections and two vertical cross-sections of horizontal reflectivity.  The red dots correspond to lightning mapping sources. The filled diamond symbols indicate the location of the first point of the flash.  The 'X' or diamond indicates the +CG or -CG strike point, as determined by the NLDN. 

Time  (UT)	Peak Current  (kA)	Charge Moment (Ckm)	Comments
22:42:07	17	31
22:44:52	21	32
22:52:11	10	0
22:55:46	12	7
23:24:57	23	15	In/near hail core. Initiates near 6 km MSL.  Positive charge region near 8 km MSL
23:26:03	34	24
23:28:17	71	129	A few km south of hail core.  Initiates near 6 km MSL. + charge regions near 6 and 8 km MSL
23:28:47	17	50
23:29:21	26	3
23:29:41	34	444
23:32:50	34	17
23:33:11	34	36	South of hail core during period of hail formation aloft.  Initiates near 5 km. + charge near 5 km.
23:33:20	29	42
23:34:01	17	42
23:34:25	21	25
23:34:38	16	17
23:35:15	38	48
23:38:18	40	168	In hail core. Initiates near 7 km MSL. + charge region near 6 km (in hail) and 8 km (downwind)
23:38:25	-14	21
23:39:46	27	7
23:40:19	27	1
23:41:21	26	0
23:42:23	18	1	Southeast of hail.  Initiates near 6 km and extends eastward into stratiform +charge from 5-7 km.
23:42:51	42	67
23:43:31	22	28
23:44:10	22	8
23:44:39	40	29
23:44:44	28	64
23:45:01	35	13
23:45:09	86	129	Concentrated in N portion of hail core.  Initiation and + charge near 6 km MSL.
23:45:21	31	46
23:45:47	33	193
23:46:13	55	126
23:46:29	22	0
23:46:55	39	20
23:47:01	36	18
23:48:06	36	92
23:48:23	36	105
23:48:40	45	104	Southeast edge of hail region.  Initiates and concentrates near 5 km MSL.
23:49:02	69	186
23:49:29	31	150
23:49:43	31	171
23:50:02	81	598
23:50:46	23	106
23:51:08	46	151
23:51:39	-19	15
23:53:24	31	49	Initiates at 7 km in hail.  Well-defined + charge below 5 km in hail core.
23:54:07	27	27
23:54:55	31	80	Initiates near 8 km downwind of main hail core.  + charge from 8-9 km, external to core.
23:55:07	100	255
23:55:23	61	38
23:55:33	56	122
23:55:51	28	43
23:56:15	65	164
23:56:23	23	27
23:56:35	15	49
23:57:00	48	186
23:57:58	36	29	Initiates near 7 km well east of core.  Extends east through + charge from 6-10 km.  Additional breakdown further north (maybe a different flash?)
23:59:04	47	150
23:59:26	18	3
23:59:52	27	132
00:00:17	27	57
00:00:58	21	7
00:01:03	31	259
00:01:41	59	126	Initiates near 5 km in region of developing hail, SE of core.  Continued breakdown through main hail region.  +charge near 5 km.
00:02:07	33	231
00:03:35	55	193	Initiates near 8 km MSL ENE of hail core.  + charge from 8-9 km and continued breakdown to the east.
00:04:34	47
00:05:25	50	64	Initiates near 5 km in possible secondary updraft and hail shaft ESE of main core. + charge from 4-7 km MSL in this secondary shaft.
00:05:29	17	0
00:06:05	46	171
00:06:27	26	39
00:07:02	13	0
00:07:30	66	360
00:07:59	-18	57	Initiates near 12 km MSL atop NW edge of main hail shaft.  Proceeds directly down through the hail.  Strong indication of + charge throughout this hail shaft.  This is a -CG.
00:08:10	103	304	Initiates near 8 km in main hail shaft and proceeds downward through hail shaft.  Similar path to the -CG immediately preceeding this flash.  Perhaps the preceding -CG allowed for abundance of + charge that was then dissipated by this +CG.  Current and charge moment are among the largest in the data set.
00:08:27	25	46
00:08:35	49	0
00:10:00	56	95	Initiates near 5 km on SE edge of hail echo, then proceeds at a near constant altitude of 5 km back north through the hail shaft.  Strong indication of + charge in hail at 5 km.
00:10:50	-17	53
00:10:51	-18	14
00:10:51	-24	57
00:11:19	-14	7
00:13:15	138	358	Similar to flash at 00:10.  Initiates near 4-5 km on SE portion of hail shaft then proceeds back north through the hail.  Entirely constrained within the hail.  Again, strong evidence of abundant low-level positive charge in the main hail region.  Current and charge moment are the largest of the data set.
00:14:26	23	120
00:16:33	100	297
00:17:24	60	97
00:18:00	45	46
00:20:42	45	95
00:22:28	29	18
00:22:33	54	151
00:22:40	63	25
00:23:28	78	109
00:23:46	30	39
00:24:41	112	304
00:25:09	42	36
00:26:17	29	136
00:26:19	54	158
00:27:14	16	0
00:28:38	-12	29
00:29:11	40	77
00:30:05	36	109
00:30:15	20	18
00:31:02	39	80
00:31:43	62	227
00:32:09	25	0
00:32:26	45	130
00:32:46	38	129
00:32:47	-18	27
00:33:05	28	78
00:33:16	26	56
00:33:44	43	244
00:33:54	25	270
00:34:03	49	162
00:34:17	25	22
00:34:43	49	294
00:35:03	29	0
00:35:19	32	64
00:35:25	22	185
00:35:50	20	38
00:36:06	42	97
00:36:20	18	71
00:36:32	32	66
00:37:05	31	87
00:37:40	35	91
00:38:06	48	260
00:38:23	70	395
00:38:51	43	101
00:39:17	37	94
00:40:37	51	494
00:40:51	48	99
00:41:10	50	144
00:41:43	91	479
00:43:09	21	57
00:43:32	41	161
00:43:52	42	112
00:44:24	20	32
00:45:06	-18	0
00:45:13	24	43
00:45:42	22	0
00:46:23	23	85
00:46:33	48	574
00:47:14	31	150
00:47:55	17	0
00:48:26	19	64
00:48:51	52	421
00:49:05	26	0	Initiates near 5 km on N edge of main hail shaft.  Proceeds south through low-level hail and positive charge.  Interesting that the current and charge moments were quite low compared with flashes at 00:10 and 00:13:15 when this flash appeared to be similar in structure.  Of course, this flash occured 30 minutes later during a more dissipative phase of the storm, so that coudl explain some of the difference in current and charge moment.
00:49:36	26	17
00:50:33	57	357
00:51:38	44	312
00:52:34	53	162
00:53:37	61	120
00:53:58	40	108	Initiates near 6 km and proceeds downward through the hail shaft.  Indication of + charge below 7 km MSL in the hail.
00:54:25	30	15
00:54:57	30	84
00:55:03	20	13
00:55:33	36	60
00:56:14	28	105
00:56:20	-18	73
00:57:06	-19	32
00:57:11	26	11
00:57:14	22	22
00:57:35	27	53
00:57:42	-15	15
00:58:04	-12	6
00:58:36	40	108
01:00:07	42	133
01:00:11	24	56
01:00:30	19	0
01:00:32	-17	3
01:00:57	29	43
01:01:51	33	108
01:01:52	-28	7
01:02:33	40	133
01:03:30	17	53
01:04:06	15	22
01:04:09	29	141
01:04:14	-21	34
01:04:56	33	85
01:05:22	40	176
01:06:18	52	148
01:06:38	-14	31
01:07:02	41	46
01:07:06	33	190
01:08:04	-28	10
01:08:29	17	15
01:08:41	103	239
01:09:15	22	90
01:09:31	40	141
01:10:19	28	6
01:10:30	44	99
01:10:50	33	21
01:11:21	25	4
01:11:39	37	48
01:11:48	57	104
01:12:50	22	76
01:13:07	51	291
01:13:27	87	206
01:13:43	41	288
01:13:59	25	136
01:14:09	28	34
01:14:15	23	34
01:14:36	34	113
01:15:12	48	88
01:15:43	59	164
01:15:57	48	78
01:16:02	34	63
01:16:12	23	29
01:16:35	30	35
01:16:39	27	25
01:16:51	70	111
01:17:01	-26	77
01:17:09	26	6
01:17:14	17	11
01:17:21	44	35
01:17:44	41	66
01:17:55	55	147
01:18:04	71	88
01:18:11	42	22
01:18:14	24	32
01:18:21	-17	10
01:18:47	37	46
01:18:59	26	41
01:19:03	59	158
01:19:21	65	179
01:19:25	84	190
01:19:29	67	134
01:19:39	64	172

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Last Updated:  21 March 2002.