What Are Atmospheric Rivers and How Does NOAA Study Them?

  January 15, 2023

Photo Credit: NOAA RESEARCH NEWS 

                            NOAA– Recent heavy rains and flooding along the U.S. West Coast may have made you aware of atmospheric rivers. The heavy rain and mountain snow that contribute to the area water supply can cause serious disruption from these naturally occurring air currents, but they can also be of immense value. On average, just a few atmospheric river episodes account for between 30 and 50 percent of the yearly precipitation in the west coast states. In order to enhance forecasting skills as well as our comprehension of how atmospheric rivers affect populations and the physical environment, NOAA investigates atmospheric rivers.

Long, concentrated areas in the atmosphere called atmospheric rivers carry moist air from the tropics to higher latitudes. High wind speeds and the wet air combine to generate heavy rain and snow as it hits the ground, especially over steep territory. These intense precipitation events have the potential to cause catastrophic harm to people and property in the form of mudslides and flash floods. When atmospheric rivers cross land, they may produce hurricane-like conditions, including heavy and swift rain, cyclone-force winds, and noticeably taller waves. An atmospheric river event that struck California in October 2021 had a significant negative impact on the San Francisco Bay region. The low pressure system quickly intensified, resulting in record rainfall, gusts of up to 80 mph, and waves of up to 60 feet. In California, some locations have already received more than 18 inches of rain in the previous week, comparable to the circumstances that are presently present throughout the west coast. Almost the whole state of California has had rainfall that is 400–600% over normal.

The Science behind atmosphere rivers (NOAA)

In order to improve the forecasting of atmospheric river intensity and duration to support water resource management decisions, NOAA and partners manage facilities like the NOAA Hydrometeorology Testbed and conduct targeted field campaigns using satellite measurements, offshore aircraft reconnaissance, and land-based atmospheric river observatories. For reconnaissance missions into atmospheric rivers, the NOAA Aircraft Operations Center and the U.S. Air Force 53rd Weather Reconnaissance Squadron "Hurricane Hunters" provide specially outfitted aircraft. Modern technology is used by the U.S. Air Force Reserve WC-130J and the NOAA G-IV jet to collect atmospheric data during storm events. Dropsondes are used on these trips by NOAA researchers and their collaborators to gather information on numerous atmospheric factors. Then, a central repository that supplies information for worldwide weather predictions receives this data. The NOAA Atmospheric River Portal is a helpful tool for getting information, images, analyses, diagnostics of current conditions, forecasts, and projects related to atmospheric rivers. It is a comprehensive collection of current conditions and forecast models.

Satellite imaging makes it simple to discern atmospheric rivers over the ocean, but it is more challenging to see their structure after they cross land. In order to close these data gaps, NOAA created on-the-ground atmospheric river observatories that are outfitted with equipment that measures snow depth, wind profiles, and water vapour. Data are used to develop thresholds for landfalling atmospheric rivers, enabling forecasters to keep track of the conditions related to atmospheric rivers. These thresholds are combined with imagery from NOAA's GOES-18 and GOES-16 geostationary satellites.

In order to enhance forecasting skills and our comprehension of the effects of atmospheric rivers and how they can alter over time due to climate change, NOAA conducts research on atmospheric rivers. Research to enhance the capacity to forecast atmospheric rivers weeks to months in advance is supported by NOAA's Modeling, Analysis, Predictions and Projections (MAPP) and Climate Variability and Predictability (CVP) Programs. Since the effects of these weather events are so extensive, these forecasts can be useful to many facets of society, such as giving local emergency officials and reservoir management actionable information.

An animated depiction of a dramatic river occurrence from January 2017 (Credit: NOAA Physical Sciences Laboratory)

The frequency of atmospheric rivers, which are naturally occurring components of our planet's weather systems, may start to shift as a result of climate change. Using information from regional climate models, NOAA concluded last year that climate change is expected to modify atmospheric rivers in ways that would make water management more challenging. Models boosted low-elevation precipitation, but anticipated reduced high-elevation precipitation, according to researchers. Decision-makers in places where the availability of water may already be stretched might benefit greatly from studies like these that simulate probable changes in atmospheric river occurrences over the next century.

In December 2022, NOAA Corps pilots conduct a research expedition into an atmospheric river off the West Coast of the United States. Source: NOAA

Under the terms of a Creative Commons licence, this article has been taken from NOAA Research News. Go here to read the original article.