“NASA wanted a technology developed by the Agency that’s useful to somebody outside NASA,” Moore says of the project’s origins. She notes that NASA, and particularly the Earth Science Technology Office, has long worked to help the public predict and respond to natural hazards.
The entire project builds on a network of GPS stations installed in the 1990s for the study of seismic movement and later also used to gather some meteorological data. The geodetic modules developed by the team at Scripps calculate the IPW estimates onsite and transmit them, rather than sending raw data back to a central facility for interpretation. “Each site individually computes its location and water vapor and transmits that directly,” Moore says.The system is still considered a prototype and a test bed for developing and demonstrating the technology, which is likely to later be more heavily integrated into local forecasters’ tools and NOAA’s Advanced Weather Interactive Processing System. Benefits On the afternoon of July 18, 2013, weather balloon soundings indicated enough monsoonal moisture from the Gulf of Mexico had reached Yuma, Arizona, to cause heavy rains, but it had not, or at least not yet, arrived in San Diego. It was early in the monsoon season, which in Southern California runs from July until mid-September. “In meteorology, we try to determine how much rain we can get out of the atmosphere by looking at how much moisture is in the atmosphere,” Small says. “When we see IPW really start to go up on the GPS data, that’s when we can make some decisions on how much rain we’re going to get and if we should issue a flash flood watch.” Whether that moisture is coming from the Gulf of Mexico or the Gulf of California, there’s little warning due to scarce meteorological observations in Mexico. [Monsoon rains flood Highway 78 just south of Borrego Springs in San Diego County in late July 2013. Credits: National Oceanic and Atmospheric Administration] Before the Earth System Research Laboratory started incorporating data from the meteorological GPS network, forecasters in Southern California relied on data from four weather balloon sites in San Diego, Yuma, Phoenix, and Las Vegas, which report twice a day. Now, though, there were five GPS stations along the Mexican border between Yuma and San Diego, transmitting data every half hour. By the morning of July 19, the balloon sounding at San Diego showed the moisture had arrived, but it would have been difficult to characterize its movement and extent because no data were available yet from Yuma. Using the GPS dataset, though, forecasters were able to track moisture distribution in real time. Water vapor content began to spike around El Centro, California, between San Diego and Yuma, to levels higher than at either of those other cities. Based on the information, a flash flood watch was eventually issued for the area, followed, indeed, by several flash flooding events carrying large rocks into the roadway, including two that trapped about 30 drivers on Route 78 northeast of San Diego and another that strewed debris across Sunrise Highway, just east of the city. “It definitely contributed to their ability to have situational awareness as to how vapor was moving around and to predict flash flooding,” Moore says. [Photo Credit: Twitter/NWSAlbuquerque] Small says the enhanced density of sensor sites and frequency of reports has demonstrably helped the office with its most important public safety function of issuing flash flood watches and warnings during fast-changing and hard-to-predict events like monsoons. “We can let them know which days are not good days for hiking in the canyons and mountains in our deserts.” The office’s warnings and forecasts go out to all local television and radio stations. “It’s a big hit with the forecasters,” Small says of the new system. Forecasters are now working with the project scientists to refine the interpretation of data and develop tools to use it, including the IPW tools being planned for a revision to NOAA’s weather processing system. Meanwhile, with the accelerometer sensors in the GPS network, which detect seismic motion, JPL and Scripps hope to demonstrate a technology that could save lives in the event of an earthquake. The ability to predict the arrival and intensity of the quake that follows a primary wave would leave between half a minute and a minute and a half, depending on a population center’s distance from the quake, to shut down elevators and gas lines, bring bullet trains to a halt, cease any surgical operations, and otherwise take potentially lifesaving precautions, Moore says. “There are a lot of things you can do if you have 30–90 seconds.” Edited for WeatherNation by Meteorologist Mace Michaels