August 04, 2004
More STEPS Summares
Here are some more daily summaries, similar to the last ones, but instead of plotting CG strike locations I plot the number of CGs of each polarity occurring during the allotted time period in 0.2 deg by 0.2 deg boxes. Positive CGs are the solid contours (levels are number of CGs per box - 5, 15, 25) and negative CGs are the dashed contours (levels are 5, 25, 50).
STEPS Summaries with CG Contours
(Edit: 5 Aug 04 - Thickened dashed lines to make them more visible)
Posted by Timothy at 04:46 PM
August 03, 2004
STEPS Daily Summaries
I have created GIF, PS, and PDF images of NEXRAD radar reflectivity factor and NLDN CG lightning strikes for nearly every day of June and July 2000. The files cover the 21-03 UTC (15-21 MDT) period, and feature maximum reflectivity factor and lightning strike locations within the greater STEPS region. I plan to add May 2000 when I obtain the NEXRAD national composities for this month. NEXRAD resolution is 2km horizontal. Positive CGs are Xs and negative CGs are triangles.
Posted by Timothy at 01:07 PM
May 28, 2004
Some examples of my MCS work
I have completed the basic form of a program that loops through all 11 June 2000 MCS lightning data, as measured by the LMA, and compares these data to a simple convective/stratiform partitioning of the KGLD NEXRAD radar data. The purpose is to understand gross differences between lightning occurring in the convective and stratiform regions of the MCS. The CS partitioning algorithm is still under refinement, but it basically looks for 30 dBZ echo at 6 km MSL (-10 C). This does a pretty good job of picking out the convective line vs. the stratiform region, as conventional algorithms get fooled by the intense stratiform echo in this storm. However, the algorithm currently lumps in weak/decaying convection with stratiform. What might be ideal is to get 3 categories working - stratiform, convective, and transitional - that would be consistent with the 3 basic zones of an MCS.
The first plot is a simple histogram of VHF source altitudes in convective and stratiform regions, from 10 minutes of data starting at 2140 UTC (early part of storm). Note how stratiform sources are distributed lower in altitude than convective sources.
The next plot shows density of convective, stratiform, and unclassified (i.e., no radar data in same location) sources in the horizontal, for the same time period. This is more a sanity check than anything, to make sure the algorithm is working as wished. Note that I require a 5-km radius to no convective pixels before I will classify an LMA source as stratiform or unclassified (red is convective, yellow is stratiform, white unclassified).
Here is a plot of the mean initiation locations of convective-, stratiform-, and unclassified-initiated flashes. If 50%+ of a flash's first 10 points or first 10% of points (whichever is smaller) fall within convective (stratiform) echo, then the flash is called convective(stratiform)-initiated. If this threshold is not reached, it is an unclassified-initiated flash. The location is determined from the mean of the first 10 points or first 10% of points, so sometimes the initiation location may appear in what appears to be the wrong echo, if the initial points skirt the boundary between the two types of echo. Note how within the convective region there are definite "hot spots" of flash initiation. It will be interesting to examine kinematic and microphysical data from the radar network in the context of these "hot spots."
This plot shows a simple time series of the number of LMA sources per category. Note how convective sources dominate the overall number, as expected, and there is a distinct peak after 2200 UTC, as well as a late-lifetime recovery. Interestingly, the stratiform source numbers are volatile but with a fairly flat long-term trend, despite the fact that stratiform echo grew significantly with time in this storm. Finally, the third panel, which is unclassified points, shows a 2300-0000 UTC spike caused by the MCS passing over the KGLD radar.
This last plot shows 2140 UTC data again. Now we are looking at just the propagation characteristics of convectively initiated flashes with significant stratiform components. The idea is to see how such a flash behaves vertically as it propagates into the stratiform region (represented by horizontal distance from flash initiation point). For example, is there downward sloping as might be expected by theorized charge structures? This plot is similar to many other times from this storm, and shows that downward sloping does occur, but by no means is universal.
(Edit: Fixed last figure due to problems with original algorithm.)
Posted by Timothy at 01:51 PM
May 25, 2004
Testing an image
Here's an example figure from my STEPS research, showing a plot of lightning relative to convective and stratiform areas of an MCS.
Here is the figure, from 2150 UTC on 11 June 2000:
Posted by Timothy at 06:59 PM