ANALYSIS SUMMARIES for ABFM 2000

prepared by Jim Dye with help from Eric Defer

January --May 2001

E fields reported in the summaries below are based on the old matrix for determination of the three components of the field. The new matrix provided in April 2001 reduces the negative values of Ez as much as 40 to 60%. So the values reported herein may be too large. Positions are reported herein as (X,Y) coordinates relative to the WSR74-C radar.

Th total concentrations of particles measured by the 2D-C probe are denoted as N30 (ie. concentration of particles >30 microns which is heavily weighted towards smaller particles). N1 refers to the concentration of particles >1mm size, ie. the larger particles. Radar plots were available for only a few of the last summaries we prepared (June 4, 6, and 11). For other days some of the realtime radar plots were utilized but need to be verified.

Citation flight from 2013 to 2339 with the main area of investigation west of Vero Beach.

The first CG lightning from the storm complex was at ~1950 and the last was at ~2153 with the main period of CG activity occuring from 2100 to 2140 centered near (-30,-70). There were no LDAR data from this day.

From 2103 to 2121 the Citation made a spiral ascent from 7.6 to 10.7 km (-20 to –50C). centered at approx. (10, -75). For the first part of the ascent Ez was negative with fields of –50 to –69 KV/m. But at about 2109 to 2111 (9 to 9.3 km; -40C), Ez switched to + 30 to 50 KV/m throughout the upper part of the anvil. From 2125 to 2140 the plane initially flew to the eastern edge of anvil away from the core. It was briefly out of cloud, then turned and flew back toward the core, turning back east when it was 5 to10 km from the 40 dBZ core at its altitude. During this period it descended from 10.7 to 7.4 km. During the descent Ez was ~ +40 to 50 KV/m then at 8km Ez abruptly changed to ~ -60 KV/m. There is a suggestion of a screening layer (Ez changed from +ve to –ve and then back) at ~2124 and 2127 when the plane flew out of the cloud and then back in.

The Citation continued to fly in various part of this anvil until about 2305. The storm continued to develop new cells along its southern edge, especially on the SE part. E fields of 10s of KV/m persisted in the anvil throughout. It would be interesting to examine the E field structure at the time of the spiral ascent and after, but this case does not give opportunity to look at E field decay.

Lightning strike to Citation at ~2029:55 about 35 min after takeoff. A/C was at 7.6 km

(-21C) in cloud. Ez at time of strike was ~-70 kV/m but 2 s prior to the strike Ez had been ~-110 kV/m for the previous 7 s. Ex and Ey at time of strike were < +1 and ~ -4 kV/m, respectively. The reflectivity in the location of the strike was 10-15 dBZ, but was heading into stronger reflectivities of 20 to 30 dBZ 5 to 10 km away. Radar tops of that cell were about 12 km (maybe higher, Citation had made three earlier passes all at 7.6 km with Ez from ~-50 to +25 kV/m. 2D-C shows mm particles of 1- 5 /liter and total 2D conc. of 100 – 1000 /liter. Length of penetrations suggests small and maybe growing cell. [CHECK LWC & W]. Total conc. was >1000 /liter at time of strike. Strike took out the 2D probe. [CHECK]. Approx. location was over water just E of eastern tip of Cape Canaveral at approx. (16,12).

This flight was terminated early because of cabin pressure leak. Before the return to base a few passes were made in decaying anvils from a storm near Tampa. E fields were weak.

No LDAR data available.

1810—2000

The Citation took off to investigate the anvils of a storms. to the west which had produced lightning from roughly 1600 to 1700. There were more active cells NW of the storm which the Citation investigated. The main storm of interest had one cell near (-25,-50) which had produced several CGs as well as activity on LDAR from ~1600 to ~1640. Another cell near (-30,-30) also showed LDAR activity suggesting a few IC flashes from 1655 – 1705 but probably no CGs. Anvil from these cells was blowing off to the North. The Citation got to vicinity of these anvils near 1830 and orbited while waiting for clearance. From ~1844 to ~1905 the particle probe outputs shows the plane was in weak anvil at 8 km but in the eastern edge of the main anvil for about 50 km in the N-S direction. Comparison of track with radar plots shows that deepest penetration into the anvil was from ~1849 to 1852 barely in 5 to 10 dBZ. At this time the largest reflectivities in the main core of this anvil to the west were 10-15 dBZ. We probably couldn’t get clearance to go further north or west. E fields during all of the above period were very weak < 500 V/m. Most of this entire period the 2D-C shows no particles >1 mm, except perhaps for the 1849 to 1852 period. During this period the 2D-C was not operating.

Summary: The Citation found no enhanced E fields 1 ½ to 2 hours after the last lightning within roughly 40 -50 km of the eastern edge of this anvil in very weak reflectivities with few particles > 1mm size.

At ~1905 the Citation proceeded to a storm to the SSE of KSC near Vero Beach with anvil coming off to the north. Neither the LDAR nor the CGLSS detected any lightning from this complex which covered an area >50 x 50 km square with a number of cells. Max reflectivities at 6 km at 1900 were 25-30 dBZ but radar tops extended to 12 km. Regions of weak E fields with a max of ~ 2 KV/m were observed along parts of the northern edge of this complex from 1910 to 1945. No significant fields were observed. Maximum reflectivities flown through were probably 0 to 10 dBZ near 1925, with reflectivities up to 35 –40 dBZ at 4 km below the aircraft.

The Citation flight was from 1425—1755 with passes primarily at 7.9 km (-24C). It first investigated a small storm south of Daytona Beach at (-50,80) with 6 or 7 flashes (3 or 4 CGs) from 1433 to 1456. Another bigger storm developed to the SW with first lightning at ~1535 as A/C working first storm, but too active to work and couldn’t get clearance. First pass at 1450 shows Ez to –40 KV/m. Successive passes until 1607 show Ez >15 KV/m often as large as 40 to 60 KV/m (e.g. 1548 and 1553) even though no lightning after 1456. A/C continued passes until ~1725. Ez after 1630 <few KV/m and probably <1KV/m by 1700.

N30 = 200 –1000 /L until 1610 with N1 ~ 0.5 –1 /L. After 1615 N30 usually 100 /L or less and N1 ~ 0.1 to 1/L. After 1700 N30 ~50/L or less and N1 0.05 to0.5 /L. Realtime radar plots suggest radar tops in excess of 30,000 ft with 40 dBZ to 20,000 ft near 1530, but need to verify this. Last realtime RHI at 1637 suggests 20dBZ max at this time. Appears to be a case with weak updrafts which did produce lightning early on and continued to have charge separation occurring until ~1600-1605 with updrafts dying afterwards. May be interesting to look at Doppler data from 74C for hints of updraft strength.

CHECK: How well does radar show evidence of weak, but continued convection during the period with enhanced Ez and probable threat?

This is an excellent case in which the Citation investigated the anvil of an isolated, electrically active thunderstorm for over three hours starting at a time when the storm was still producing lightning through the time when the fields had decayed to a couple of KV/m. It is also an excellent case for examining the spatial/temporal decay of electric field downwind of the core of a storm.

The storm started producing lightning near 1930 about 100 km SW of KSC with an anvil blowing off to the NE. The anvil reached KSC at XXX? as reported by observers at the ROCC. The last CG flash occurred at ~2135, with LDAR sources continuing until 2150 to 2200. LDAR shows sources in the vicinity of the A/C during this period, but we are uncertain of their veracity. [The CTI listing of LDAR status for ABFM 2000 shows electromagnetic interference for this day, but the spatial and temporal coherence of most sources match well with CGLSS reports. Most of the data we find believable.] No LDAR sources are seen in that region after 2200. The core of the storm as viewed by the lightning activity remained in the same location centered near (-80,60) spreading 10 to 15 km away from that center. From ~2045 until 2225 the A/C made E—W reciprocal passes across the anvil while the storm was producing lightning and as the lightning stopped. It then commenced SW—NE passes along the axis of the anvil until about 2355. These passes extended over KSC and the field mill network and were at altitudes of 10.5, 8.7, and 7.9 km.

The E—W passes show strong fields with magnitudes from 10 to 50 KV/m both positive and negative. There is large horizontal variability, e.g. the passes from 2145 to 2200 show Ez as large as +35 and –50 KV/m. The fields diminish to a few KV/m by 2220. This decrease is partially temporal as the storm dies, but also spatial and dependent upon where the aircraft happens to fly relative to the storm.

The NE—SW passes show Ez to be less than 1 to2 KV/m except when flying near and over the decaying core region of the storm, where fields as large as 50 to 60 KV/m were observed. Larger fields in both the E—W and SW—NE passes tend to be associated with higher reflectivity at and below the aircraft. On the NE—SW passes the fields rapidly increase as the A/C approaches the higher reflectivity, but are weak and relatively uniform until that point. The measurements suggest that the charge causing the larger fields resides on falling precipitation below the aircraft.

2110 – 0021; All research legs flown at 8.8 km (-32C)

Anvil A – worked debris from storm over N part of KSC 2130 to 2200. Not sure if flashes associated with this debris, perhaps from CGs and LDAR at 1803 to 1810 at (-60,10) or maybe CGs at 1850 to 1900 at (-70,30) with LDAR sources spread to East over KSC. Very weak Ez (probably <2KV/m) and microphysics show very decayed anvil with N30 ~10 –90 /L and N1 0.05 to 0.3 /L.

NEED Radar plots to compare with flashes; expanded plots of E and 2D plots 1930-1945 If there was lightning in it, it is good case of advanced decay.

Anvil B – passes in residue of storm from ~2215 to ~2300. Again need radar plots to ascertain origin of anvil; possibility cell near (-80,-45) with produced CGs and LDAR from ~2130 to 2220. Ez weak except when got to NW near a newer cell (Storm C) (~-20KV/m at 2051); otherwise Ez <couple of KV/m; N30 up to 500 /L but usually less; N1 was 0.1 to 1 /L.

A good decayed anvil study, IF can identify storm which formed the anvil.

Anvil C – ~2300 to 2400

Anvil from storm at ~(-100,-15) producing CGs starting at ~2215 and continued until ~2231 with LDAR sources continuing in that locale until ~2330. [CHECK CGLSS to be sure it was OK from ~2230 to 2330] Initially N-S passes across anvil at different distances from core. Ez –50KV/m at 2316 30-40 km from core decreasing to few KV/m at 2323 at ~40-60 km from core. Later flew SE to NW along anvil axis but in weaker S part with Ez < few KV/m throughout; no 2D plots for this pass.

Good case to examine variation of Ez downwind of core, but limited number of passes.

A small maritime storm just to the east of KSC produced 3 CG flashes from1405 to 1417. At this time it had radar tops to 14 km with 35 dBZ extending to 9 km. There were two other somewhat smaller cells to the west and southwest of the cell with lightning that also contained reflectivities of 50 dBZ at low altitudes but weaker aloft. The NW cell did reach ~13 km radar tops but apparently produced no lightning. Then the cell with lightning collapsed although there may have been some convective bubbles within the decaying cell. The residual at 6 to 8 km from this cell slowly drifted to the west and merged with the cell to the west and by the time the aircraft arrived, it was hard to distinguish one from another.

These remnants drifted over the surface field mill network and between very roughly 1520 [CHECK] to 1600 produced elevated fields up to +3500 V at field mill site 26 at 1539.

The aircraft took off at 1600 and shortly after takeoff while still climbing from 5 to 6 km, it flew just below the eastern edge of some of the debris at ~ 1608 to 1610 but no discernable enhancements of Ez were detected. Radar shows main area of debris a little west of the Citation position. The plane climbed to 9.4 km and while making a pass from 1626 to 1629 through the top part of the debris, observing Ez of ~ +1.5 KV/m. On later lower passes at 1646 to 1651 and 1653 to 1658 at 7.5 km Ez fields of 3 to 3.5 KV/m were observed. Total 2D concentrations were < 100 /L and particles > 1mm size were ~0.1 to 0.2 /L.

This is a good case showing that by 2 to 2 ½ hours after lightning field strengths had decayed to a maximum of about 3 KV/m. More work can be done to examine the maximum reflectivities below the A/C for the different passes and compare to reflectivity over the surface network when it was showing enhanced positive fields. A rough early comparison suggests reflectivities over the surface network were ~25 dBZ, but by the aircraft arrived they had decayed to ~15 dBZ.

Initially flew in anvil of small storm roughly 255 to 260 deg and 60 to 100 km from WSR74C (a litle south of BOW ??) Anvils were blowing off to SW. The storm produced first LDAR sources ~1950 and first CG at 1958 and continued to produce lightning until ~2110 for LDAR and last CG probably 2047. Spiral at 2158 to 2204 from 7 to 8.5 km (-15 –30 C). Ez first +30 as setting up for spiral then +40 at lower part of spiral, then Ez of only few kV/m for 2+ min. followed by –40 kV/m. 2D-C shows strong variability and periodicity suggesting changes in Ez might be horizontally variability as much as vertical.

After the spiral from 2205 to 2230, apparently moved south [another anvil or same anvil, I can’t tell] and made 4 passes at 8.5 km . Ez in all passes <2-3 kV/m. N>30 was 100/L or less and N>1mm was <0.1 to 0.5 /L. From 2230 to 2320 made a series of passes at 8.5 km with Ez as large as –75 kV/m. When Ez was larger, N>30 was ~500-1000/L and N>1 was ~or>1 /L.

Without radar plots cannot tell what happened very well.

Flight from 1636 to 1910 made a few passes at 7.6 km in 2 decaying thunderstorms north of KSC and then flew in and near active cells while trying to land at Patrick AFB before diverting to Vero Beach. E field of +25 to –40 KV/m with large horizontal variations. The aircraft followed the E field decay to ~5 KV/m before the weak anvil disappeared.

Flight 1 from 1636 to 1957 in decaying anvils over KSC. Spirals were flown over the SLF and east.

Flight 2 from 2059 to 2342 in debris and decaying anvils over KSC.

Flight from 1705 to 1816 terminated early because of cabin pressure problem.

Flight 1 – 1404 to 1510

Couple of cells in a line NW and W of Vero Beach. The first CG and LDAR sources appear at ~1212. CGs continue at moderate rate until ~1250 with then a big gap until ~1320 when the last CG occurs. About 20 CGs total occurred. Ez ~2 KV/m at 2-4 km shortly after takeoff where A/C apparently flies under building storm which starts producing lightning near 1445.

A/C first enters cloud at ~1416 as it spirals up into anvil from ~4 to 7 km in the same approx. position that lightning had been occurring as recently as 1320. But Ez <1 KV/m and N30 ~1-10/L and N1 ~.01 to 0.1 /L. The A/C then flew back and forth in the anvil SSE – NNW headings until about 1500. Fields were all < 1 KV/m. Observer comments "cloud not very dense" and particle concentrations were max of N30 10-100 /L and N1 0.05 to 0.5 or less. While making the approach to PAFB rapid changes of ~ 1 KV/m characteristic of lightning were seen in Ez and the CGLSS and LDAR show lightning near the A/C.

Flight 2 – 1815 to 2132

All passes in these active cells had E fields of 10 –15 KV/m or more. Lots of lightning in these storms even where the A/C flew. The flight is not good for examining decay of E with space or time, but does show that when E is >10 KV/m N30 is at least 100-1000 /L or more and N1 is often >1 /L.

The Citation flew from 1224 to 1440 investigating cells off of Palm Beach out of range of the 74-C radar. No analysis has been pursued so far on this case.