Imagine a river in the sky - one made of water vapor, instead of liquid water. That’s an atmospheric river and it can transport moisture long distances.
Over the North Pacific, atmospheric rivers transport water vapor over the ocean to the West Coast of North America. When the moisture gets to land, it’s pushed upward, which causes much of the water vapor to condense, forming intense precipitation. The heavy rain and snow can cause hazards like floods, but is also beneficial for agriculture and drinking water supplies.
Why is it called the Pineapple Express?
The atmospheric river pattern over the North Pacific is often called the “Pineapple Express” because it moves moisture from Hawaii, where pineapples are grown, to the west coast of the United States and Canada, where it can cause heavy rain and snow.
The event on November 6-8, 2006
In this activity, students analyze humidity and rainfall data from a particularly intense atmospheric river over the Pacific that caused heavy precipitation in northwest Oregon, Washington state, and southern British Columbia from November 6-8, 2006. Mudslides and flooding were widespread. Eleven counties in Washington were declared national disaster areas. In Mount Rainier National Park, floods washed out roads and campgrounds.
About COSMIC satellites and data
COSMIC is a group of small satellites (called microsatelites) that measures how radio waves from GPS satellites bend while traveling through the atmosphere in order to deduce the characteristics of the atmosphere, such as the temperature and amount of water vapor. Because COSMIC is able to make these measurements for different altitudes in the atmosphere and over the ocean - places where weather data is sparse - the data has an important role in helping meteorologists predict weather and is added to weather models to make forecasts more accurate.
This data exploration is based on the weather events and COSMIC data described in two papers:
- Ma et al. (2011) Assimilation of GPS Radio Occultation Data for an Intense Atmospheric River with the NCEP Regional GSI System, Monthly Weather Review, v. 139, pp. 2170-2183.
- Neiman et al. (2008) Diagnosis of an Intense Atmospheric River Impacting the Pacific Northwest: Storm Summary and Offshore Vertical Structure Observed with COSMIC Satellite Retrievals, Monthly Weather Review, v. 136, pp. 4398--4420.