SR SSD 2000-10
4/2000

Technical Attachment

Automated Lightning Detection and Ranging System:
An Introduction and Overview

Introduction

The Federal Aviation Administration has put in place via contracts with commercial vendors and thru software improvements the ability for FAA sponsored ASOS sites to begin reporting cloud-to-ground lightning information. This system, known as the Automated Lightning Detection and Ranging System (ALDARS) is currently being implemented at FAA sponsored ASOS sites with full implementation expected later this year.

In a nutshell, the FAA has contracted with Global Atmospherics Inc. (GAI) for the purchase of their cloud-to-ground lightning information. This is the same vendor that the NWS uses for our own National Lightning Detection Network (NLDN) lightning graphics.

Through a process which I will explain in more detail later on, the lightning data is made available to the ASOS Acquisition Control Unit (ACU). If the ASOS site has version 2.6 software installed (most FAA sponsored sites have this already installed), the ACU will process the information and perform the following:

a) If the cloud-to-ground lightning strike is within 5 miles of the ASOS, the ASOS will take a SPECI observation, begin thunder, and carry "TS" for thunderstorm in the body of the observation in the present weather field. "TS" will continue to be carried in the present weather field in subsequent METAR observations until no cloud to ground lightning strikes are observed for a 15 minute period. At that time, the ASOS will take a SPECI observation and end the thunder.

b) If the cloud-to-ground lightning strike is between 5 miles and 10 miles of the ASOS, the ASOS will take a SPECI observation, and carry "VCTS" for thunderstorm in the vicinity in the body of the observation in the present weather field. "VCTS" will continue to be carried in the present weather field in subsequent METAR observations until no cloud-to-ground lightning strikes are observed for a 15 minute period. At that time, the ASOS will take a SPECI and end the "VCTS."

The ASOS will carry either "TS" or "VCTS", whichever is closer to the ASOS.

c) Separate from the above, or independently, if the cloud-to-ground lightning strike is between 10 miles and 30 miles of the ASOS, the ASOS will carry a "DSNT LTNG xx" remark indicating distant lightning, with "xx" being the direction of the lightning in octants. This will be appended as appropriate on all SPECI and/or METAR observations.

Again, it must be emphasized that ONLY FAA sponsored ASOS sites have this capability. This is because the lightning information is being throughput to the ASOS ACU by means of FAA communications channels. NWS ASOS sites do not have access to this.

The following Web site lists the FAA locations that have ALDARS activated as of April 7, 2000. This site will be updated on a regular basis by the NWS ASOS Operations and Monitoring Center (AOMC): http://www.nws.noaa.gov/aomc/aldars.htm

Overview

The attachment shows in graphical form how the lightning data is delivered to the ASOS ACU:

1) The GAI lightning sensors detect the cloud-to-ground lightning strikes (please note this system ONLY detects cloud-to-ground strikes).

2) The GAI lightning sensors transmit the data to a satellite.

3 and 4) The satellite downloads the data to the GAI downlink in Tucson, Arizona for processing.

5) The GAI processing site accepts the data and assimilates it and parses the information so that each strike is assigned a latitude and longitude.

6) The data are retransmitted back to the satellite.

7) The data is then sent to all FAA Air Route Traffic Control Centers (ARTCCs). All FAA sponsored ASOS sites communicate via MCI leased phone line with the AWOS/ASOS Data Acquisition System (ADAS) that resides at the ARTCC in whose airspace the ASOS is located in.

The lightning information with latitude/longitude data arrives at the ADAS at each ARTCC. The ADAS has programmed into it the latitude/longitude of all ASOS sites within its airspace.

8) If the ADAS determines that the lightning strike is within 30 miles of an ASOS site within its airspace based on latitude/longitude information, the ADAS will transmit the ALDARS data via leased phone line to the ASOS ACU.

9) If the ASOS site has software version 2.6 installed, the ASOS ACU will process the data, append the appropriate information onto the SPECI or METAR observation, and then disseminate the information back thru the leased phone line to the ADAS system. The ADAS system will then throughput the observation onto the FAA Weather Message Switching Center Replacement (WMSCR) and then onto GATEWAY, and then to all external users, including the NWS and AWIPS.

It must be emphasized that the above ALDARS cycle and all polling between the ADAS and the ASOS site updates once every minute.

Questions concerning the ALDARS may be directed to Victor Murphy, NWS Southern Region ASOS Focal Point at (817) 978-7777 x 130.