LIS/OTD 2.5
Degree Low Resolution Time Series (LRTS)
LIS/OTD 2.5 Degree Low Resolution Time Series
0.1
The product is a 2.5 deg
x 2.5 deg gridded composite of daily time-series of total (IC+CG) lightning
bulk production, expressed as a flash rate density (fl/km2/day). Separate gridded time series from the 5-yr
OTD (4/95-3/00) and 5-yr LIS (12/97-2/03) missions are included, as well as a
combined OTD+LIS product. Lowpass
temporal filtering (110-day for OTD, 98-day for LIS, 110-day for combined) and
spatial moving average filtering (7.5 deg) have been applied, as well as
best-available detection efficiency corrections and instrument
cross-normalizations, as of the product generation date (4/21/03).
The product is
distributed in HDF (Hierarchical Data Format).
HDF is accessible from C or Fortran using interfaces provided by NCSA (http://hdf.ncsa.uiuc.edu), or through
various commercial software packages, such as IDL or Noesys (http://www.rsinc.com). All data in this product are stored in HDF
Scientific Data Sets. Note that inline (HDF internal) GZIP compression
has been applied. Users should verify
that their NCSA HDF library distribution or third-party software application
versions are current enough to transparently decompress inline-compressed HDF
grids.
This
preliminary dataset is being made available to the community prior to full
intercomparison of the overlapping OTD and LIS time series. The variance in the separate time series
products, and in the combined product, has not yet been quantified. Users should note that these data are
experimental. Inclusion of the product
version number in citations is strongly recommended for traceability.
In
presentations or publications, users are to acknowledge the dataset as follows:
The
v0.1 gridded time series satellite lightning data were produced by the NASA
LIS/OTD Science Team (Principal Investigator, Dr. Hugh J. Christian, NASA /
Marshall Space Flight Center) and are available from the Global Hydrology
Resource Center (http://ghrc.msfc.nasa.gov).
a.
Approach
Bulk lightning
production, expressed in fl/km2/day, is calculated as a “counting
experiment”. The calculation procedure
is as follows:
1.
For
each day of each mission, the viewing of each sensor is recorded (in km2
sec) on a 0.5 deg grid. The number of
flashes observed by each sensor, weighted by the inverse of the instantaneous
instrument detection efficiency [see below] is also recorded on a 0.5 deg
grid. These daily high resolution grids
are generated for each day from 5/4/95 – 2/28/03.
2.
“Combined”
grids are generated for each day by adding the flash totals and viewtime totals
for each mission. The “combined” grids
only contain joint data from 12/97-04/00.
3.
A
boxcar moving average of duration [110, 110, 98] days is applied to the flash
and viewtime grids for the [combined, OTD, LIS] products, respectively. This reduces aliasing of the local diurnal
cycle due to precession of the instruments’ host platform orbits, which would
otherwise fatally bias the time series with spurious high frequency signals. A window of 110 days is used for the
combined product since the OTD sampling dominates over LIS (4x greater).
4.
The
data are resampled at 2.5 deg resolution to limit product size. Each 2.5 deg daily grid cell value is thus
the average of 25 0.5 deg grid cell values over +/- [55, 55 or 49] days.
5.
A
further spatial moving average of +/- 1 2.5 deg grid cell (7.5 deg total) is
applied to reduce sample variance.
6.
2.5
deg flash rate estimates are
calculated as weighted flash sums divided by total viewing time.
7.
A
further lowpass filter with cutoff [110, 110, 98] days is applied to each map
location’s time series in order to eliminate residual high frequency noise.
8.
The
results of step 7 occasionally introduce negative flash rates into the time
series, typically near the beginning/end of them missions, the “top” and
“bottom” of orbits, and in very low lightning production regions (cold ocean
gyres, deserts) or regions with extreme seasonality. These are reset to “0” flash rate.
The
final products are thus daily, 2.5 deg resolution maps of estimated flash rate
density, whose estimates contain 7.5 deg spatial moving average and [110, 110
or 98] day lowpass filtered observations (approximately 3-month windows). Due to LEO instrument undersampling,
instrument and/or host platform operational dropouts, etc., higher spatial or
temporal resolution can not yet be recommended to users for quantitative
analysis.
The
grids contain 3287 daily maps, one for each day from 1/1/95 to 12/31/03. Note that grids prior to the start of the
OTD mission and after 2/28/03 are included for simplicity, but are empty or
contain data using less than a [110 or 98] day sample. The recommended start/end dates (daily grid
indices) of useful data are listed in section 10.
The
HDF file contains 7 Scientific Data Set (SDS) grids compressed internally (and
transparently) using GZIP lossless compression. These include:
·
LRTS_COM_FR Combined Flash Rate [3287x144x72, float, fl/km2/dy]
·
LRTS_OTD_FR OTD-only Flash Rate [3287x144x72, float, fl/km2/dy]
·
LRTS_LIS_FR LIS-only Flash Rate [3287x144x72, float, fl/km2/dy]
·
LRTS_COM_VT Combined Viewing [3287x144x72, float, km2
dy]
·
LRTS_OTD_VT OTD-only Viewing [3287x144x72, float, km2
dy]
·
LRTS_LIS_VT LIS-only Viewing [3287x144x72, float, km2
dy]
·
LRTS_AREA Grid cell areas [144x72, km2]
The
LRTS_xxx_FR products are the primary data products. The LRTS_xxx_VT products are included for user reference to
demonstrate the variable instrument viewing; users are encouraged to review
these grids to understand the relative variability in the input data sampling. The LRTS_AREA product is included for
convenience.
Best-available calibrations for
instrument detection efficiency (as of 4/21/03) have been applied in the v0.1
product, as a function of mission date, local time of day, and location relative
to the South Atlantic Anomaly. These
are documented in Boccippio et al, 2002 and Christian et al, 2003, and
summarized in the documentation for the High Resolution Full Climatology
(LISOTD_HRFC) product, also available from the GHRC. The HRFC product also contains the spatially and temporally
variant detection efficiency grids applied to the LRTS data.
Users wishing to cite
this calibration procedure may use or modify the following:
Observations in the LIS/OTD v0.1 time series gridded
products have been corrected by the LIS Science Team by estimated flash
detection efficiency, applied as a function of sensor, local hour, date of
mission, and (for the OTD) geographic location. For the entire dataset, these corrections correspond to average
flash detection efficiencies of 47% (OTD) and 82% (LIS). The adjustments derive from a combination of
laboratory calibration, ground-validation and cross-normalization between the
two instruments. Uncertainty in these
corrections is estimated as +/-10%. The
calibration procedure is described in the dataset documentation. The gridded time series products
additionally have been averaged spatially (7.5 deg, at 2.5 deg resolution) and
temporally ([select 110 or 98 days as appropriate] low pass filters have been applied).
Consistency
between modeled and ground-validated detection efficiency suggests that the
applied corrections are know within about +/- 10%. This is thus the minimum uncertainty in the gridded data, arising
from possible bias in the correction. A
much higher source of uncertainty in the time series products is undersampling
of a given grid location, even with the severe spatial and temporal averaging
that has been applied. Intercomparison
of OTD and LIS time series during the missions’ overlap window readily
illustrates this undersampling effect.
It is not yet known if the total uncertainty in the time series products
will preclude quantitative use of the data.
However, qualitative interannual variability has been observed [e.g., Goodman
et al, 2000] which appears consistent with known ENSO effects on local
meteorology.
All
OTD and LIS orbits undergo both automated and manual quality assurance. For the preliminary reanalysis, the most
stringent orbit rejection criterion was applied: any orbit which was assigned a
manual Q/A “warning” flag has been rejected from the reanalysis.
Each
OTD flash is further assigned an automated quality index (the ‘Thunderstorm
Area Count’ or ‘Density Index’), indicating its likelihood of being lightning
rather than optical or radiation noise.
For this reanalysis, only flashes with values of the metric >= 140
have been included. This is the same cutoff
value used in all validation and science analysis published by the LIS science
team to date. This filter removes most
radiation noise from the data; a slight residual “ring” artefact of very low
spurious flash rates remains at the periphery of the South Atlantic Anomaly
(southeast Pacific and southeast Atlantic).
There
are no restrictions on the use of these data.
However, v0.1 is an experimental reanalysis, intended to support
imminent analysis needs among users and to test the validity of the data
product. Users should treat the v0.1
data with caution during quantitative analysis.
PLEASE
NOTE that these grids do not answer
the question “what lightning occurred on a given day” (see “Approach”,
above). Instantaneous lightning
occurrence can be derived from the OTD and LIS mission online browse images and
interactive flash data extraction tools.
Users desiring
“seasonal” estimates should recall that moving averages and lowpass filtering
have already been applied to these
data, even though the data are recorded as daily grids (there is thus much
redundancy in the full resolution data product). A “seasonal” estimate for, e.g., DJF ’95-’96 would thus be the
daily grid corresponding to Jan 15, 1996, which would contain data from the
previous and following 55 or 49 days (depending on whether the combined, OTD or
LIS time series was selected). The
daily grid index for this grid would be 379 (indices for 1995 span [0,364]; Jan
1, 1996 would be [365]; Jan 15, 1996 would be [379]. Note that leap days are included in this product (1996 and 2000).
Below is a table of useful
daily grid indices. “n/d” indicates no
data available. “First data” is the
date of the first input daily (unsmoothed) grid for each mission. “First useful” is the “first data” date + 55
days [OTD, combined products] or 49 days [LIS product], i.e., the date of the
first useful time-smoothed daily grid.
“Last useful” and “last data” are the converse. Grids before “first useful” or after “last
useful” should be ignored.
|
|
Jan 1 |
DJF center |
MAM center |
JJA center |
SON center |
OTD first data / first
useful |
OTD last useful / last
data |
LIS first data / first
useful |
LIS last useful / last
data |
|
1995 |
n/d(0) |
n/d(14) |
n/d(104) |
195 |
287 |
122 / 177 |
- |
n/d |
n/d |
|
1996 |
365 |
379 |
470 |
561 |
653 |
- |
- |
n/d |
n/d |
|
1997 |
731 |
745 |
835 |
926* |
1018 |
- |
- |
1066 |
- |
|
1998 |
1096 |
1110 |
1200 |
1291 |
1383 |
- |
- |
1115 |
- |
|
1999 |
1461 |
1475 |
1565 |
1656 |
1748 |
- |
- |
- |
- |
|
2000 |
1826 |
1840 |
1931 |
2022 |
2114 |
- |
1854 / 1909 |
- |
- |
|
2001 |
2192 |
2206 |
2296 |
2387 |
2479 |
n/d |
n/d |
- |
- |
|
2002 |
2557 |
2571 |
2661 |
2752 |
2844* |
n/d |
n/d |
- |
- |
|
2003 |
2922 |
2936 |
n/d |
n/d |
n/d |
n/d |
n/d |
n/d |
2936 / 2981 ** |
* Note that severe instrument/platform
dropouts may compromise data quality in the JJA97 (OTD) and SON02 (LIS)
seasons; see the online OTD and LIS browse images (or the included LRTS_xxx_VT
grids) for details of the dropout dates.
** Note that the
DJF02-03 season center (day 2936) does not include data beyond 2/28/03; this is
a 94, not 98 day, sampling window. The
bias effects should be minimal.
The
current product version is v0.1. All
subsequent versions of this dataset (both minor and major revisions) will
maintain the same product definition, resolution and file format. Additional years of LIS data may be added
into the product for future revisions, as minor version updates, but will not
alter file format. Product definitional
changes will be finalized with the v1.0 release, which will also be contingent
upon publication in a refereed journal of the methodology and results. Subsequent major version updates will only
occur if later version OTD or LIS orbit data are used as inputs to this product
(the currently used orbit data versions are 1.1 for OTD; 4.0 for LIS).
Questions regarding
dataset ordering, media issues, file handling or HDF file access (input/output)
should be directed to the Global Hydrology Resource Center (ghrc@msfc.nasa.gov). Questions regarding the science data
processing, viewing, calibration and variance should be addressed to Dennis.Boccippio@nasa.gov. Questions regarding the OTD or LIS missions
themselves should be addressed to the OTD/LIS Principal Investigator, Hugh.J.Christian@nasa.gov.
Instrument and Calibration/Validation:
Goodman,SJ; Christian,HJ; Rust,WD (1988): A comparison of the optical
pulse characteristics of intracloud and cloud-to-ground lightning as observed
above clouds. J. Appl. Met. 27, 1369-1381.
Christian,HJ; Blakeslee,RJ; Goodman,SJ (1989): The Detection of
Lightning from Geostationary Orbit. J. Geophys. Res. 94, 13329-13337.
Christian,HJ; Blakeslee,RJ; Goodman,SJ (1992): Lightning imaging sensor
for the Earth Observing System. (TM-4350.) NASA. 44 pages. Available from
Center for Aerospace Information, P.O. Box 8757, Baltimore Washington
International Airport, Baltimore, MD 21240.
Christian,HJ; Driscoll,KT; Goodman,SJ; Blakeslee,RJ; Mach,DA;
Buechler,DE (1996): The Optical Transient Detector (OTD). Proc. 10th
International Conference on Atmospheric Electricity, Osaka, Japan.
Kummerow, C; Barnes, W; Kozu, T; Shiue, J; Simpson, J (1998): The
Tropical Rainfall Measuring Mission (TRMM) sensor package. J. Atmos. Oc. Tech.
15, 809-817.
Christian,HJ; Blakeslee,RJ; Goodman,SJ; Mach,DA; Stewart,MF;
Buechler,DE; Koshak,WJ; Hall,JM; Boeck,WL; Driscoll,KT; Boccippio,DJ (1999):
The Lightning Imaging Sensor. Proc. 11th Intl. Conf. on Atmospheric Electricity
(NASA), Guntersville, AL, 7-11 June. 746-749.
Ushio,T; Driscoll,KT; Heckman,S; Boccippio,DJ; Koshak,WJ; Christian,HJ
(1999): Initial comparison of the Lightning Imaging Sensor (LIS) with Lightning
Detection and Ranging (LDAR). Proc. 11th Intl. Conf. on Atmospheric Electricity
(ICAE), Guntersville, AL, 6-11 June. 738-741.
Christian,HJ; Blakeslee,RJ; Goodman,SJ; Mach,DM (eds.) (2000): Algorithm
Theoretical Basis Document (ATBD) for the Lightning Imaging Sensor (LIS). http://eospso.gsfc.nasa.gov/atbd/listables.html Posted: 1 Feb 2000. (NASA
/ Marshall Space Flight Center, AL 35812)
Koshak,WJ; Bergstrom,JW; Stewart,MF; Christian,HJ; Hall,JM;
Solakiewicz,RJ (2000): Laboratory calibration of the Optical Transient Detector
and Lightning Imaging Sensor. J. Atmos. Oc. Tech. 17, 905-915.
Boccippio,DJ; Driscoll,KT; Koshak,WJ; Blakeslee,RJ; Boeck,WL; Mach,DA;
Buechler,DE; Christian,HJ; Goodman,SJ (2000): The Optical Transient Detector
(OTD): Instrument characteristics and cross-sensor validation. J. Atmos. Oc.
Tech. 17, 441-458.
Thomas,RJ; Krehbiel,PR; Rison,W; Hamlin,T; Boccippio,DJ; Goodman,SJ;
Christian,HJ (2000): Comparison of ground-based 3-dimensional lightning mapping
observations with satellite-based LIS observations in Oklahoma. Geophys. Res.
Lett. 27, 1703-1706.
Boccippio, DJ; Koshak, WJ; Blakeslee, RJ (2002): Performance assessment
of the Optical Transient Detector and Lightning Imaging Sensor: I. Predicted
diurnal variability. J. Atmos. Oc. Tech. 19, 1318-1332.
LIS/OTD-Enabled Science & Applications:
Christian, HJ et al (2003): Global frequency and distribution of
lightning as observed by the Optical Transient Detector. J. Geophys. Res, 108
4005, doi: 10.1029/2002JD002347.
Boccippio,DJ; Wong,C; Williams,ER; Boldi,R; Christian,HJ; Goodman,SJ
(1998): Global validation of single-station Schumann resonance lightning
location. J. Atmos. Sp. Terr. Phys. 60, 701-712.
Christian,HJ; Blakeslee,RJ; Boccippio,DJ; Boeck,WL; Buechler,DE;
Driscoll,KT; Goodman,SJ; Hall,JM; Koshak,WJ; Mach,DM; Stewart,MF (1999): Global
frequency and distribution of lightning as observed by the Optical Transient
Detector (OTD). Proc. 11th Intl. Conf. on Atmospheric Electricity (ICAE),
Guntersville, AL, 7-11 June. 726-729.
Driscoll,KT (1999): A comparison between lightning activity and passive
microwave measurements. 11th International Conf. on Atmospheric Electricity
(ICAE), Guntersville, AL, 7-11 June 1999. 523-526.
Cecil, DJ; Zipser, EJ (2000): Relationships between tropical cyclone
intensity and satellite-based indicators of inner core convection: 85 GHz
ice-scattering signature and lightning. Mon. Wea. Rev., 111, 979-996.
Buechler,DE; Driscoll,KT; Goodman,SJ; Christian,HJ (2000): Lightning
activity within a tornadic thunderstorm observed by the Optical Transient
Detector (OTD). Geophys. Res. Lett ., 27, 2253-2256.
Goodman,SJ; Buechler,DE; Knupp,K; Driscoll,KT; McCaul,EW (2000): The
1997-98 El Nino event and related wintertime lightning variations in the
Southeastern United States. Geophys. Res. Lett. 27, 541-544.
Jeker,DP; Pfister,L; Thompson,AM; Brunner,D; Boccippio,DJ; Pickering,KE;
Wernli,H; Kondo,Y; Staehelin,J (2000): Measurements of nitrogen oxides at the
tropopause: Attribution to convection and correlation with lightning. J.
Geophys. Res., D 105, 3679-3700.
Boccippio,DJ; Goodman,SJ; Heckman,S (2000): Regional differences in
tropical lightning distributions. J. Appl. Met. 39, 2231-2248.
Williams,ER; Rothkin,K; Stevenson,D; Boccippio,DJ (2000): Global
lightning variations caused by changes in thunderstorm flash rate and by
changes in the number of thunderstorms. J. Appl. Met. 39, 2223-2230.
Nesbitt,SW; Zipser,EJ; Cecil,DJ (2000): A census of precipitation
features in the tropics using TRMM: Radar, ice scattering and lightning
observations. J. Clim. 13, 4087-4106.
Rodgers, E; Olson, W; Halverson, J; Simpson, J; Pierce, H (2000):
Environmental forcing of supertyphoon Paka’s (1997) latent heat structure. J.
Appl. Met., 39, 1983-2006.
Boccippio,DJ; Cummins,KL; Christian,HJ; Goodman,SJ (2001): Combined
satellite and surface-based estimation of the intracloud / cloud-to-ground
lightning ratio over the continental United States. Mon. Wea. Rev. 129,
108-122.
Toracinta, ER; Zipser, EJ (2001): Lightning and SSM/I ice-scattering
mesoscale convective systems in the global tropics. J. Appl. Met. 40, 983-1002.
Boccippio, DJ; Heckman, S; Goodman, SJ (2001): A diagnostic analysis of
the Kennedy Space Center LDAR network. 2: Cross-sensor studies. J. Geophys.
Res. 106, 4787-4796.
Chang, DE;Weinman, JA; Morales, CA; Olson, WS (2001): The effect of
spaceborne microwave and ground-based continuous lightning measurements on
forecasts of the 1998 Groundhog Day storm. Mon. Wea. Rev., 129, 1809-1833.
Ushio,T; Heckman,S; Boccippio,DJ; Christian,HJ (2001): A survey of
thunderstorm flash rates compared to cloud top height using TRMM satellite
data. J. Geophys. Res., D, 106, 24089-24095.
Boccippio,DJ (2002): Lightning scaling laws revisited. J. Atmos. Sci.
59, 1086-1104.
Bond, DW; Zhang, R; Tie, X.; Brasseur, G.; Huffines, G; Orville, R.E;
Boccippio, DJ (2001): NOx production by lightning over the
continental United States. J. Geophys. Res, 106, 27701-27710.
Koike, M.; Kondo, Y.; Akutagawa, D.; Kita, K.; Nishi, N.; Liu, S.C.;
Blake, D.; Kawakami, S.; Takegawa, N.; Ko, M.; Zhao, Y.; Ogawa, T. (2003)
Reactive nitrogen over the tropical Western Pacific: Influence from lightning
and biomass burning. J. Geophys. Res, 108, 8403, doi:10.1029/2001JD00823.
A set of Interactive Data Language (IDL)
routines to extract the LIS/OTD Low Resolution Time Series (LRTS) and other
gridded products are distributed with the data. The IDL syntax is roughly similar to C or FORTRAN and porting of
these routines should be relatively straightforward.
Note: These routines are being provided as a courtesy to the
user community. The GHRC and LIS
Science Team cannot guarantee technical support or compatibility with IDL
version updates or platform-specific implementations.
GETGRID.PRO:
GETGRID, HDF_NAME,
SDS_NAME, GRID, [DIMS, DIMNAMES, DIM0…]
Retrieves a scientific
data set (and optionally, its dimensions) from one of the HDF climatology
files.
LONLAT_TO_XY.PRO:
RESULT =
LONLAT_TO_XY([LON,LAT],RESOLUTION)
Converts a [lon,lat]
pair to a grid [x,y] index, for a given grid resolution (e.g., 2.5 deg in the
LRTS product).
RESULT =
XY_TO_LONLAT([X,Y],RESOLUTION)
Converts a grid [x,y] pair to a grid cell center [lon,lat], for a given grid resolution (e.g., 2.5 deg in the LRTS product).