US Composite Lightning Daily Total from Natl Lightning Network
US Composite Lightning 15min Total from Natl Lightning Network
| These data are restricted to collaborators that have a working relationship with the NASA Marshall Space Flight Center (MSFC) Lightning Group. |
Table of Contents
Introduction
This README file contains information on lightning data produced by the U.S. National Lightning Detection Network (NLDN). The lightning product, the file format (Hierarchical Data Format or HDF), instructions for accessing the HDF library, and pertinent scientific references are provided here. The U.S. National Lightning Detection Network is a commercial lightning detection network operated by the Vaisala Group whose webpage is at (LightningStorm.com). A network of more than 150 antenna stations are connected to a central processor that records the time, polarity, signal strength, and number of strokes of each cloud-to-ground/in-cloud lightning flash detected. The Improved Performance Combined Technology (IMPACT) Antenna system uses a combination of time-of-arrival of radio frequencies and direction finding technology to geo-locate the flash. Depending on the location within the network, Vaisala claims a location average accuracy of 500 meters, with a detection probability between 80-90 percent, varying slightly by region. The NLDN raw lightning datasets are a continuous record from 3 Jan 1988 through the present. Data from 1988 through 1994 are NOT quality controlled, and are in the standard 6 field format. (second data). These data are listed as "GAI Lightning Ground Strikes". Data from 1995 through present ARE quality controlled by Vaisala, and are in an expanded 12 field format (millisecond data). These data are listed as "Vaisala US NLDN Lightning Flash Data", and have been archived as version 2 data. On March 1, 2008, the data were promoted to version 3. In version 3 data, a thirteenth field was added, which is a Cloud-to-Ground / In-Cloud Discriminator (G, C). These QCed data are ingested on DVD directly from Vaisala each month. Additional information about the "GAI Lightning Ground Strikes" dataset can be found here: http://ghrc.nsstc.nasa.gov/uso/ds_docs/nldn/gai_dataset.html.
Additional information about the "Vaisala US NLDN Lightning Flash Data" dataset can be found here: http://ghrc.nsstc.nasa.gov/uso/ds_docs/vaiconus/vaiconus_dataset.html
This document deals primarily with the lightning products derived from the NLDN lightning data..
Citing NLDN Data
Our data sets are provided through the NASA Earth Science Data and Information System (ESDIS) Project and the Global Hydrology Resource Center (GHRC) Distributed Active Archive Center (DAAC). GHRC DAAC is one of NASA's Earth Observing System Data and Information System (EOSDIS) data centers that are part of the ESDIS project. ESDIS data are not copyrighted; however, in the event that you publish our data or results derived by using our data, we request that you include an acknowledgment within the text of the article and a citation on your reference list. Examples for general acknowledgments, data set citation in a reference listing, and crediting online web images and information can be found at: http://ghrc.nsstc.nasa.gov/uso/citation.html
U.S. Composite Lightning Product
| NOTE: There has been an improvement in the method of calculation for Peak Current Amplitude, which takes effect on july 1, 2004.
Peak Current Amplitude Improvements:
When estimating peak-current amplitudes, the NLDN uses a simple power-law model to compensate for signal attenuation due to propagation over finite-conductivity soil. This is sufficient for lightning events within 400 km of a sensor but underestimates propagation losses for more distant events. By modifying the parameters used in the algorithm, we can significantly reduce the random error for individual sensor measurements. At the same time, we will re-calibrate the NLDN peak-current estimate using rocket-triggered lightning data obtained in Florida in 2002-2003. The mean value for return strokes will increase by approximately 15% as a result of these changes, once implemented. With this re-calibration and propagation correction, we will reduce the overall expected error in peak current down to 15-20%, nearly a factor-of-two improvement from earlier years. |
The Global Hydrology Resource Center (GHRC) generates a gridded lightning product from the data collected from the U.S. National Lightning Detection Network. This lightning product is created by binning the number of flashes that occur over a 15 minute period to pixels. Each pixel is 0.0718954 degrees latitude by 0.0765027 degrees longitude (approximately 8 km x 8km). The data spatial range is from 20N to 53N (459 pixels) and from 60W to 130W (915 pixels). Therefore, the northwest corner is located at 53N latitude, 130 W longitude.
Pixel values can range from 0-254 which corresponds to the number of flashes detected in that pixel in a 15 minute period. A value of 255 denotes that 255 or more flashes occurred within that pixel during the 15 minute interval. Although the pixel values can range from 0-254 flashes, generally the maximum pixel value observed in the products is about 100 flashes. This product is produced four times each hour for the following periods past the hour:
(1) 00:00:00 - 00:14:59.99 UTC,
(2) 00:15:00 - 00:29:59.99 UTC,
(3) 00:30:00 - 00:44:59.99 UTC,
(4) 00:45:00 - 00:59:59.99 UTC.
A daily composite is also produced from the 15 minute data over the continental United States. For the daily product, the value in each pixel is the number of flashes occurring in that pixel area during a 24 hour period (from 00:00:00 UTC to 23:59:59 UTC). The binned values are scaled by 3 such that a value of 1 corresponds to 1-3 flashes, 2 from 4-6, etc. A value of 255 indicates 765 or more flashes occurred in the pixel over the 24 hour period.
These products (daily and 15 minute) are processed and archived from Quality checked data received from Vaisala.
HDF File Structure
The sole purpose of the HDF raster image format is for a space-saving technique. Although an image may be created with default parameters, this HDF file contains only pixel data and summary information. If an image is desired, the corresponding product in the GIF (Graphical Interchange Format) should be ordered.
Fifteen minute Lightning Product HDF file structure
Each 15 minute lightning product file contains:
| Item |
HDF Object Type |
HDF Ref. No. |
| Version Descriptor |
N/A |
1 |
| Date/end time of image |
HDF Label |
2 |
| 15 minute Lightning image |
RIS8 image |
3 |
| Summary file |
Annotation |
4 |
The summary file indicates whether the image was generated in real time or was reprocessed using quality assured data.
The RIS8 image contains the following levels:
| Level |
# flashes/pixel/15 min |
| 0 |
0 |
| 1 |
1 |
| 2 |
2 |
| 3 |
3 |
| . . . |
. . . |
| 254 |
254 |
| 255 |
>254 |
Daily Lightning File Structure
Each daily lightning product file contains:
| Item |
HDF Object Type |
HDF Ref. No. |
| Version Descriptor |
N/A |
1 |
| Daily Lightning image |
RIS8 image |
2 |
| Date/end time of image |
HDF Label |
3 |
| Summary file |
Annotation |
4 |
The summary file contains the indication whether the image was generated in real time or was reprocessed using quality assured data. (All products are now generated from QC data)
The RIS8 image contains the following levels:
| Level |
# flashes/pixel/day |
| 0 |
0 |
| 1 |
1 - 3 |
| 2 |
4 - 6 |
| 3 |
7 - 9 |
| 4 |
10 - 12 |
| . . . |
. . . |
| 254 |
760 - 762 |
| 255 |
>762 |
Latitude/Longitude Values
The navigation for the RIS8 images (15 minute and daily) is as follows:
| Rows in image: |
459 |
Columns in image: |
915 |
| Northern boundary: |
53 N |
Southern boundary: |
20 N |
| Western boundary: |
130 W |
Eastern boundary: |
60 W |
The lightning array has a horizontal (East-West) dimension of 915 and a vertical (North-South) dimension of 459. The latitude bounds are from 20N to 53N in the North-South direction and from 130W to 60W in the East-West direction. The latitude and longitude can be computed for the center of each pixel in the following manner:
N latitude = 53. - ((row# - 1/2) x (0.07189542484))
W longitude = 130. - ((col# - 1/2) x (0.07650273224))
For example:
The (row#,col#) of the upper left hand (northwestern corner) pixel is (1,1). Therefore, the latitude and longitude of the center of pixel (1,1) is:
N latitude = 53. - ((1 - 0.5) x (0.07189542484)) = 52.96405228759
W longitude = 130. - ((1 - 0.5) x (0.07650273224)) = 129.9617486339
The (row#,col#) of the lower right hand (southeastern corner) pixel is (459,915). Therefore, the latitude and longitude of the center of pixel (459,915) is:
N latitude = 53. - ((459 - 0.5) x (0.07189542484)) = 20.03594771242
W longitude = 130. - ((915 - 0.5) x (0.07650273224)) = 60.03825136612
Fifteen minute lightning product file naming convention
The 15 minute products have the following naming convention:
NhhmmZyyyy.ddd_cglitn_vx.hdf
where
hh = hour (UTC)
mm = minutes
yyyy = year
ddd = day of year
x = version number (represents the version of the raw data the product was made from)
NOTE: Version 2 raw data is QCed millisecond data in a 12 field format; we went to version 3 when a 13th field was added, the cloud-to-ground/cloud-to-cloud discriminator.
For example, N1600Z1995.132_cglitn_v2.hdf. Using the example file name, the file contains the lightning product for the 15 minute period ending 1600 UTC on day 1995.132 (May 12, 1995 from 15:45:00 to 15:59:59).
Daily lightning product file naming convention
The daily products have the following naming convention:
Ndailyyyyy.ddd_cum_cglitn_vx.hdf
where
yyyy = year
ddd = day of year
x = version number (represents the version of the raw data the product was made from)
For example, Ndaily1995.182_cum_cglitn_v2.hdf.
In the daily case, the day corresponds to the 24 hour period beginning at 00:00:00 UTC on the day of year indicated. In the example given then the daily file contains the binned 24 hour lightning for the period beginning 00:00:00 UTC on 94182 (July 1, 1994) and ending 23:59:59.
How to Get the HDF Library and Tools
See http://hdf.ncsa.uiuc.edu.
References
Cummins, K. L., M. J. Murphy, E. A. Bardo, W. L. Hiscox, R. B. Pyle, and A. E. Pifer, 1998. A Combined TOA/MDF Technology Upgrade of the U. S. National Lightning Detection Network, J. Geophys. Res., 103, 9035-9044. Idone, V. P.,
D. A. Davis, P. K. Moore, Y. Wang, R. W. Henderson, M. Ries, and P. F. Jamason, 1998. Performance evaluation of the U. S. National Lightning Detection Network in eastern New York, 1, Detection Efficiency, J. Geophys. Res., 103, 9045-9056.
Contact Information
To order these data or for further information, please contact:
Global Hydrology Resource Center
User Services
320 Sparkman Drive
Huntsville, AL 35805
Phone: 256-961-7932
E-mail: support-ghrc@earthdata.nasa.gov
Web: http://ghrc.nsstc.nasa.gov/
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