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Daily rainfall over Sumatra related to greater atmospheric phenomena



  Daily rainfall over Sumatra related to major atmospheric events
Rain and clouds in Indonesia. Credit: Pixel PlaceboCC BY-NC 2.0

Worldwide, communities are concerned about rain and storms. The area known as the "Sea Continent", which includes major islands such as Sumatra, Java, Borneo, Papua New Guinea, along with a galaxy of smaller islands, is experiencing heavy rainfall, including periodic monsoonal rains and lightning floods.


In a new study led by atmospheric scientist Giuseppe Torrey of the University of Hawaii (UH) at the Manoa School of Ocean and Earth Sciences and Technology (SOEST), researchers revealed details about the relationship between a larger atmospheric phenomenon called the the Madon-Julian oscillation (MJO) and the daily precipitation patterns of the continent.

The MJO orbits the globe around the tropics and can affect weather on weekly to monthly time scales, alternating cloudy, rainy weather, and sunny, drier periods.

Tori and co-authors find that the influence of MJO on daily precipitation patterns in Sumatra is quite significant. When the MJO operated near the Maritime Continent, there was more water vapor ̵

1; and therefore greater potential for significant rain events – and more variations of water vapor during the day compared to the suppressed phase. Also, clouds and rain seem to move ashore at night faster during the MJO active phase.

The team relies on data from a network of GPS stations that were installed on Sumatra and on neighboring islands by a team of scientists interested in monitoring the tectonic activity along the west coast of Sumatra. As it turns out, the GPS signal is distorted by the amount of water vapor in the atmosphere. This distortion is bad news for people who are interested in location information – GPS technology has been invented. Scientists, including UH Mānoa atmospheric science professor Stephen Bussinger, realized that distortion could tell us something about the state of the atmosphere and pioneered its use as a data source.

  Daily rainfall over Sumatra related to major atmospheric phenomena
Clouds over the Indonesian field. Credit: Wilson Loo CC BY-NC-ND 2.0

With the extensive coverage of GPS stations on Sumatra Island, the team had a data set that provided a very detailed picture of daily atmospheric changes.

"Given the existing scientific literature, we felt that the MJO had influenced the local convection of the maritime continent," Torrey said. "One thing that surprised me was how well we could see the convection spreading to the coast in the late evening. This is thanks to the density of GPS network stations we looked at. "

The MJO is probably one of the most important phenomena on the planet and can affect the weather and climate of regions that are even thousands of miles from the Marine Continent. A better understanding of MJO and a good way to simulate it are key to a better understanding of our current and future climate.

As this study expands the understanding of the effects of MJOs on clouds and rainfall over Sumatra, Tori will team with SOEST atmospheric scientist Alison Nugent to investigate the causes of these impacts and the mechanisms that control the spread of rainfall at sea.


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More information:
Giuseppe Torri et al., On the Daily Cycle of Sedimentary Water Vapor Obtained by GPS over Sumatra, Journal of Atmospheric Sciences (2019). DOI: 10.1175 / JAS-D-19-0094.1

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University of Hawaii at Manoa
Reference :
Daily precipitation over Sumatra related to greater weather (2019, September 20)
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