Field Campaigns and Ground Validation
Over the past two decades, the GHCC Lightning Team has been involved in numerous field campaigns around the globe. By measuring the the electrical properties of thunderstorms, members of the GHCC Lightning Team have helped advance the field of Atmospheric Electricity while providing insight into key elements of the global hydrological cycle.
During the early and mid 1980s, many of the field measurements recorded by the GHCC Lightning Team were used to verify that optical signals produced during a lightning discharge are powerful enough to be viewed from a space. These measurements led to the design and deployment of the Optical Transient Detector and the Lightning Imaging Sensor. From the late 1980s, the airborne and ground based measurements of lightning activity have been used to support field campaigns which were designed to investigate storm convection and precipitation in various climatological regimes. In the future, our involvement in field programs will include the validation of the data obtained by the space based lightning detection instruments, such as OTD and LIS.
The COoperative Huntsville Meteorological EXperiment was conducted in the vicinity of Huntsville, Alabama during June-July, 1986. The objectives of this field experiment were to investigate the morphology, dynamics, microphysics, and electrical evolution of storms and the relation of storm electrical activity to precipitation and dynamical processes. The primary instrumentation used in quantifying storm electrification included the ER-2 LIP, 4-station MSFC lightning direction finder network, NCAR research radars, and T-28 field mills.
Airborne Field Mill (ABFM) Project, summer 1990, 1991; winter 1992 in the vicinity of Kennedy Space Center, Florida. The purpose of this study was to determine when weakly convective or layered cloud systems are electrified and to produce remote sensing tools to predict the electrification. The study was designed to address the existing launch commit criteria for eleectrified clouds that had the potential to cause triggered lightning discharges. An instrumented Lear 28/29 jet was used to penetrate developing cumulus clouds and measure the vector electric field and some simple cloud parameters. The airborne measurements were compared to radar to determine some of the conditions necessary for cumulus cloud electrification.
The Convection and Precipitation/Electrification field experiment was conducted between 8 July to 18 August 1991 in east central Florida in the vicinity of Cape Canaveral. The objectives of this field experiment were to 1) identify relationships between co-evolving wind, water, and electric fields within convective clouds and 2) determine the meteorological and electrical conditions in which natural and triggered lightning can/cannot occur. Research instruments included the ER-2 LIP, NCAR research radars, KSC field mill network, and KSC LDAR.
The U. S. Weather Research Program, formerly the STormscale Operational and Research Meteorology (STORM) program, conducted an experiment called the STORM-FEST (Fronts Experiment Systems Test) from 1 February to 15 March 1992. The objectives were to study the mesoscale structure and dynamics of wintertime fronts, associated precipitation, and severe weather over the Central U.S. with the latest observing systems. During this program, the Lightning Instrument Package (LIP) was flown aboard the ER-2 high altitude aircraft.
The Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) was designed to improve our understanding of the coupled ocean-atmosphere system. A coordinated study of thunderstorms and lightning was conducted during the intensive 4-month observing period November 1992 to February 1993. A network of cloud-to-ground lightning sensors was installed with sites on Kapingamarangi Atoll and near the towns of Rabul and Kavieng, Papua New Guinea. Electrical measurements were also made from the NASA ER-2 and DC-8 airplanes.
The first two CAMEX field studies were conducted at Wallops Island, Virginia during September 1993, and 21 August to 2 September 1995. The third in the series of CAMEX field studies (CAMEX-3) is planned for August to September 1998. CAMEX-3 will be devoted to the study of Atlantic hurricane tracking and intensification using NASA-funded aircraft remote sensing instrumentation. The NASA ER-2 Lightning Instrument Package (LIP) is used to measure the DC and transient (i.e., lightning) electric fields, optical pulses, and atmospheric conductivity as the aircraft flies over the tops of storms. These data will be used to 1) investigate lightning-storm relationships and 2) provide validation for the TRMM mission.
The Maritime Continent Thunderstorm Experiment (MCTEX) was conducted from 13 November to 10 December 1995 over the Bathurst and Melville Islands (the ``Tiwi Islands''), located approximately 50 km off the coast of Australia's Northern Territory. This international experiment was designed to study the vigorous life cycle dynamics, microphysics, and lightning produced by these island thunderstorms. The characteristics of these thunderstorms were obtained with a 4-station cloud-to-ground lightning network, surface electric field instruments, and a doppler radar.
In the spring of 1998, the ER-2 LIP will be flown in a 3 to 4 week field campaign called the TExas FLorida UNderflight (TEFLUN) experiment in support of validation of the Tropical Rainfall Measuring Mission (TRMM). This field campaign will focus on the U.S. Gulf Coast and especially on the priority TRMM ground validation (GV) sites in Texas and Florida.
Tropical "Ocean" Field Campaign (Kwajalein)
In the summer of 1999, there are plans to conduct a tropical ocean campaign in the vicinity of Kwajalien atoll in the Republic of the Marshall Islands (RMI). During this program, the convective aspects of the northern component of the ITCZ which occuring in the central Pacific Ocean will be investigated. The Lightning Instrument Package (LIP) will fly on the NASA DC-8, and cloud-to-ground lightning measurements will be obtained from a three station ALDF network operated by Aeromet, Corporation. For TRMM ground truth, MSFC is looking at the possibility of modifying the existing systems or expanding the coverage of the network.
Tropical "Land" Field Campaign (Brazil)
During January and February 1999, there are plans to conduct a tropical land campaign during the wet season in Brazil to coincide with the wet phase of the Large-scale Boisphere_atmosphere (LBA) experiment. The experiment will focus on the convection occurring in the rain forest region of Rhondonia (11 S, 62 W) in Brazil. Plans include the implementation of a dual Doppler radar and a four station Advanced Lightning Direction Finder (ALDF) network. The network is located in the vicinity of Ji Parana and will begin to collect data for a TRMM validation field campaign. The lightning network will continue to operate for a minimum of 12-18 months with the assistance of Brazilian scientists.
Lightning Detection Instruments
Advanced Lightning Direction Finder
These sensors detect cloud-to-ground lightning strikes and determine their location by triangulation of two or more lines of bearing. An ALDF automatically detects more than 90% of all cloud-to-ground lightning occurring within a range of 100 km. Other lightning, such as cloud-to-cloud and intracloud lightning, is ignored. The National Lightning Detection Network (NLDN) is a network of more than 130 of these ALDF sensors.
Lightning Detection and Ranging (LDAR)
Located at the Kennedy Space Center, the LDAR consists of seven antennas that detect electromagnetic pulses at 66 MHz, which allows it to detect 99% of all flashes (both intracloud and cloud-to-ground flashes) within 10 km of the antenna network. The accuracy of source locations is a function of position relative to the receiving array, generally decreasing (particularly along the radial axis with respect to the array center) with distance. The RMS error for LDAR lightning source locations varies from 100 meters inside the network to about 10 km at a range of 90 km (about 1/3 the width of the Florida peninsula).
KSC Electric Field Mill Network
Thirty-one advanced field mills developed by NASA/MSFC are deployed at sites around the Kennedy Space Center (KSC) and Cape Canaveral Air Station provide data on lightning activity and surface electric fields induced by charge aloft. This data helps forecasters determine when electric charge aloft may be sufficient to create triggered lightning during launch, and to determine when to issue and cancel lightning advisories and warnings.
Airborne Electric Field Mill
In several field campaigns, these field mills have been installed on the top and bottom of a DC-8 and an ER-2 aircraft. With this configuration, the field mills are used to measure the vertical component of the electric field as the aircraft flies in the vicinity of electrified clouds. The dynamic range of these instruments extends from the fair weather fields (a few tens of V/m) to large thunderstorm fields (thousands of V/m). Using these field mills, it is possible to detect both intracloud and cloud-to-ground lightning from the abrupt electric field changes in the data. The field mills were developed by NASA/MSFC.
Airborne Conductivity Probe
During numerous flights, a conductivity probe has been installed on the superpod nose cone of the ER-2 aircraft and has been used to measure the conductivity of the atmosphere. The probe consists of a pair of Gerdien capacitor type sensors so that the contributions to the total conductivity due to positive and negative ions are obtained simultaneously throught each flight. Storm electric currents have been derived using electric field and air conductivity measurements.
Airborne Optical Pulse Sensor
The optical pulse sensor consists of a photodiode at the focus of a wide angle field-of-view lens, and was used to observe the bright flashes of light produced during a lightning discharge. During the mid 1980s, this instrument was flown on a high altitude aircraft to observe lightning from above cloud top. A bandpass filter was installed at the front of the lens and was used to pass one specific lightning spectral line, such as the neutral atomic oxygen line (777.4 nm) or the neutral atmoic nitrogen line (868.3 nm).
This instrument is an Ebert spectrometer which was used to measure the spectral characteristics of lightning discharges. The spectral range of this instrument is from below 600 nm to almost 900 nm (infrared spectrum). This instrument was also flown on a high altitude aircraft during the mid 1980s.
The following proposals are in response to NASA Research Announcement NRA-97-MTPE-03:
Interpretation of Lightning Observations for Understanding the Meteorological Properties of Clouds
- Steven Goodman (MSFC)
- Ravi Raghavan (USRA)
- Earle Williams (MIT)
- Mark Weber (MIT)
The emphasis of this proposed research program is the interpretation of total lightning observations to understand the meteorological properties of clouds. In this context, our focus will be to explore quantifiable relationships between lightning and other cloud and environmental variables. Using these relationships, we will then develop algorithms that can use lightning observations on a global scale to diagnose cloud kinematics, morphology, and storm severity. This improved understanding of the relationships among the processes that lead to the electrification of clouds and subsequent lightning activity is highly desired to better interpret global cloud measurements.
We propose to take advantage of currently available surface and space based data sets to jump start the development, testing, assessment and validation of algorithms that employ total lightning observations. Initial data sets will be acquired at the Tropical Rainfall Measuring Mission (TRMM) ground truth site in Florida. In 1999, similar multi-sensor data bases (including total lightning) will be available from Huntsville, AL, the Rondonia region of the Brazilian Amazon, and the Kwajalein Atoll region of the Pacific Ocean as part of future validation campaigns. Thus, total lightning and storm observations will be collected from extratropical land, tropical land, and tropical ocean environments. The new knowledge from this study will be applicable to lightning observations acquired from future missions such as the proposed Lightning Mapper on GOES N-P.
Cross-Sensor Validation of the Lightning Imaging Sensor
- Dennis Boccippio (MSFC)
- Monte Bateman (USRA)
- Nilton Renno (University of Arizona)
An effort to perform a detailed, quantitative validation of the Lightning Imaging Sensor (LIS) is being proposed as a collaborative effort between personnel of the National Aeronautics and Space Administration (NASA) Marshall Space Flight Center (MSFC) and the Universities Space Research Association (USRA) at the Global Hydrology and Climate Center (GHCC) and the University of Arizona. The focus of the study will be the determination of LIS precision, accuracy, sensitivity (detection efficiency), biases and variance in previously unexplored lightning regimes and problematic observation zones. The investigation will build on preliminary work and lessons learned during validation of the prototype Optical Transient Detector (OTD). The benefits of this study to the Mission to Planet Earth (MTPE) program will be the delivery of a well-calibrated, bias free dataset of tropical and mid-latitude total lightning, with specified observation variances (errors). Such a dataset will play an important role in quantifying tropical surface temperature changes and lightning-related NOx emissions, and key rate-related meteorological parameters such as convective mass flux and cirrus anvil detrainment rates, which are difficult to determine by passive (IR and microwave) measurements during rapid flybys.
The specific objectives of this proposal are to: 1) rigorously assess the reduction in LIS detection efficiency due to noise contamination, 2) optimize the existing adaptive noise filters, 3) assess the largely unknown intracloud (IC) flash detection efficiencies of both OTD and LIS, 4) cross-calibrate the OTD and LIS sensors to extend the temporal baseline of global lightning observations, 5) validate and/or improve the flash grouping algorithms currently employed to delineate convective cells, 6) assess the sampling-related variance in observations of global and regional flash rates, and 7) utilize concurrent TRMM ground truth and satellite data and fully validated LIS observations to lay a groundwork for relating observed flash rates to other convective parameters. The proposed work makes extensive use of existing algorithms and methodology developed for OTD, as well as observations from sensors already fielded or planned in other field campaigns.
LIS Validation Studies Using Lightning at the KSC-ER
The ground based electric field mill (FM) network and the Lightning Detection and Ranging (LDAR) system at the NASA Kennedy Space Center (KSC) and USAF Eastern Range (ER) will be used to characterize and validate the Lightning Imaging Sensor (LIS) data set. The validation activities will focus on quantifying and improving the LIS geolocation accuracy and lightning detection efficiency. As part of this activity, an intensive investigation will be made of the characteristics of lightning charges, lightning radio sources, thunderstorm current sources, and theoretical (model) calculations of photon transport inside clouds. Also, measurements of the absolute radiance on the ground will be correlated with LIS. Particular emphasis will be given to possible relationships between the amount of charge involved in a lightning flash (derived from the FM network) and the total optical energy that is measured by the LIS.