Dr. Timothy J. Lang

AMS Tropical Conference Talk

Here is a NAME-related talk I will give at next week's AMS conference on tropical meteorology.

TRMM Conference Poster

Here is a poster presented at the recent TRMM conference in Las Vegas. I contributed the NAME ground radar analysis.

Statisical Framework Presentation

Here is a presentation I made on our research into the creation of a framework for the statistical analysis of large radar and lightning datasets, recently presented at the AMS annual meeting in New Orleans.

Statistical Framework Presentation

20 June 2007 Bow Echo Radar Mosaics

I created 3-D mosaics of radar data from 4 NEXRAD radars in Oklahoma, for analysis of a bow echo MCS that occurred on 20 June 2007. The mosaics cover a period of significant sprite production by the storm. These mosaics will be analyzed in order to characterize the spatial and temporal evolution of the storm structure, which will then be compared to sprite production. I have linked below to a movie of the lowest altitude horizontal cross-sections of reflectivity in these mosaics.

Movie of radar mosaics

Pictures from Taiwan Site Survey

Here are some pictures I took during my recent trip to Taiwan. Of particular interest will be pictures from the survey of potential S-Pol sites, which you will find about halfway through the album.

Pictures at KodakGallery.com

S-Pol Blockage Simulations for Taiwan

Here are blockage pattern simulation results for the two proposed TiMREX S-Pol sites, Air Force Academy and Levee. AFA has less blockage overall, but Levee has a nice view up the river valley. Both blockage patterns are much worse than anything we saw in NAME. It may be difficult to perform QPE in the eastern sector, beyond about 50 km range.

AFA 0.5-deg Elevation
AFA 1.0-deg Elevation
AFA 1.5-deg Elevation
AFA 2.0-deg Elevation
AFA 2.5-deg Elevation
AFA 3.0-deg Elevation

Levee 0.5-deg Elevation
Levee 1.0-deg Elevation
Levee 1.5-deg Elevation
Levee 2.0-deg Elevation
Levee 2.5-deg Elevation
Levee 3.0-deg Elevation
Levee 3.5-deg Elevation
Levee 4.0-deg Elevation
Levee 4.5-deg Elevation

NCAR TiMREX website

RHI Sector Gridding Test

In TiMREX, S-Pol will likely scan RHI sectors on a regular basis. I tested the feasibility of using REORDER to grid RHI sector scans, similar to how we usually do with PPI sectors. The test was successful, with the RHI sectors gridding with few artifacts. Here are some examples using CHILL data from a hailstorm on 10 May 2005.

2332 UTC RHI Sector Horizontal Cross-Section
2335 UTC PPI Sector Horizontal Cross-Section
2332 UTC RHI Sector Vertical Cross-Section
2335 UTC PPI Sector Vertical Cross-Section

Publications updated

Please find selected new publications listed on the right side of the main page.

Latest NAME Posters

These posters review much of my most recent NAME research.

AMS 2007 Radar Conference
Taiwan ICMCS-VI Conference

CSU Radarmet's NAME research page

C3VP AMFR QC Reports

These reports cover the current state of the AMFR radar quality control process.

Initial AMFR QC Report - 26 June 2007
King/AMFR Intercomparison - 7 July 2007
AMFR Intercomparison Report - 25 October 2007

CSU Radarmet C3VP Research Page

Kdp in the 05 August 2004 NAME Storm

I am currently testing out Kdp calculation and thresholding with the NAME S-Pol radar data. Here is a nice example from the 05 August 2004 mesoscale convective system.

]]> Here we see large Kdp values aloft, below the melting level - over 5.5 deg/km in fact! This is likely due to the presence of melting hail, and represents either the wet hailstones or shed water drops. Note the negative Zdr and high LDR values above the Kdp maximum, indicating large hail above the melting level. Interestingly, the Kdp values decline toward the ground. This could be partly due to some evaporation, but more likely there are some size distribution effects on Kdp. That is, a distribution of large water-coated ice particles may have inherently larger Kdp values than the same amount of water in drop form. Thus, as the water-coated hailstones further melt and form regular rain, Kdp values would be expected to decrease, as observed. This is a hypothesis that will be investigated using a T-matrix scattering model.

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)

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.

STEPS Daily Summaries

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.)

Template Finished!

OK, the major updates to the website template are done. Minor ones may occur in the future, however. Now I can get on with posting my research!