Meteorologists investigate Airborne jet streams bringing both floods and drought relief

A satellite image showing water-vapour concentration reveals an atmospheric river (yellow) streaming northeast across the Pacific Ocean.

Californians call it the Pineapple Express: a weather pattern that zips across the Pacific Ocean from Hawaii, delivering not baskets of tropical fruit, but buckets of rain and snow.

In meteorological terms, the Pineapple Express is an atmospheric river, a narrow band of air that carries huge amounts of moisture.

For the next six weeks, meteorologists will be plying the eastern Pacific by air and sea, in the hope of catching several atmospheric rivers barrelling towards the coast.

It is the biggest push yet to understand these phenomena, which have received serious scientific attention only in the past decade.

Atmospheric rivers get their start over warm tropical waters; they then flow eastwards and towards the poles a kilometre or two above the ocean surface.

They may stretch for thousands of kilometres, but are only a few hundred kilometres wide. When they hit land, they start to drop their moisture in torrential downpours or blizzards.

“When we have too many atmospheric rivers, floods can occur, and when we don’t have enough we gradually fall into drought,” says Marty Ralph, a meteorologist at the Scripps Institution of Oceanography in La Jolla, California, and a leader of the field campaign.

In Europe, atmospheric rivers affect mostly the western part of the continent, but they can be felt as far inland as Poland.

In North America, the entire west coast is affected, and parts of the central and eastern United States occasionally feel the effects of atmospheric rivers that develop over the Gulf of Mexico.

The moisture is often welcome, bringing up to half of the year’s water supply in affected areas1.

A 2013 study found that as many as three-quarters of all droughts in the Pacific Northwest between 1950 and 2010 had been brought to an end by atmospheric-river storms2.

California has been stricken by drought for years (Nature 512, 121–122; 2014), but last month, an atmospheric river dropped enough rain to erase one-third of the water deficit of one major reservoir in just two days.

Climate change may bring stronger and more frequent atmospheric rivers, because the warmer the atmosphere is, the more water it can hold, says David Lavers, a meteorologist at Scripps who is not involved in the project.

“The more you know about how the atmosphere behaves,” he says, “the better position you’re in to prepare for extreme events.”

Read the full article on Nature website - Nature 517, 424–425 (22 January 2015) doi:10.1038/517424a

NASA GPM: Contributing to Earth observations from space

The NASA NPOL radar station (left) and D3R Radar station (right) precipitation radars deployed south of Waterloo, Iowa, for the Iowa Flood Studies ground measurement campaign. 

Credit: NASA/Matt Schwaller

The Global Precipitation Measurement (GPM) Core Observatory, launched on Feb. 27 from Tanegashima Space Center in Japan, will help advance our understanding of Earth's water and energy cycles, improve the forecasting of extreme events that cause natural disasters, and extend current capabilities of using satellite precipitation information to directly benefit society.

The GPM mission will provide unprecedented data on rain and snowfall. The science instruments on the GPM Core Observatory will provide data that will yield the greatest clarity on rain and snow yet gathered from orbiting spacecraft.

With GPM, scientists will gather vast amounts of precipitation data on a global scale. But, how do they know how to interpret the data? How do scientists know the data is correct?

This is where ground validation contributes to the mission. Using instruments that complement and correlate with those on the spacecraft, scientists on the ground gather similar precipitation data.

These data are directly compared with that from satellites to improve the models relying on the satellite data.

Walt Petersen, GPM ground validation scientist from NASA's Wallops Flight Facility at Wallops Island, Va., said, "GPM ground validation is a) the process by which we identify uncertainties in satellite-based precipitation products compared to ground observations"

"b) how we improve satellite-based methods of estimating precipitation by better understanding precipitation physics."

"c) how this physics relates to what the instruments 'see,' and d) assess the utility of GPM products in monitoring the global water cycle, flood and weather prediction, and e) al this adds to and aids our understanding of climate change."

This is an artist's depiction of NASA's Global Precipitation Measurement mission's Core Observatory. 

Credit: NASA

The GPM program uses remote campaigns and a Precipitation Science Research Facility at Wallops to supplement and correlate the data gathered by Earth-orbiting satellites.

"Ground validation is central to understanding the quality of GPM precipitation products, how the products can be improved, and evaluating the utility of the measurements in a variety of earth system science applications," Petersen said.

The remote campaigns, using instrumented aircraft and ground-based instruments, allow scientists to monitor precipitation under a variety of conditions and geographic regions.

Petersen said, "The Wallops Precipitation Research Facility collects multi-frequency dual-polarimetric radar observations of precipitation rates, types, sizes and shapes through the depth of the troposphere."

"We collect high quality, concentrated rain gauge network measurements of area-mean rainfall, and use networks of imaging instrumentation to observe the number and distributions of the size, shape and type of precipitation particles falling to ground."

"Collectively, these measurements enable us to describe precipitation physical properties over scales ranging from that of an individual rain drop or snowflake to that of the Delmarva and Chesapeake Bay regions."

With ground validation, scientist will be able to gauge the quality of Earth observations from space using GPM and improve combined space- and ground-based data products used to understand global precipitation.

Water Evidence for Mars Floods has dried up!

Lava, not water, may have carved the biggest channels on Mars.

Ever since NASA's Mariner 9 spacecraft beamed back the first images of the channels in the 1970s, most people have assumed they were created by massive floods. 

David Leverington of Texas Tech University in Lubbock says flowing water would have left behind much more sediment than is seen. There are also few minerals that form in liquid water present.

Lava, however, is known to have carved big channels on the moon. And Leverington points out that some of the channels on Mars start on the flanks of volcanoes and end in large deposits of solidified lava (Geomorphology, DOI: 10.1016/j.geomorph.2011.05.022).

Kelin Whipple of Arizona State University (ASU) in Tempe agrees that lava probably carved the huge channels, such as Kasei Valles (shown). He says the study calls into question the case for huge volumes of water – and possibly an ocean – on ancient Mars.

Phil Christensen, also at ASU, says clays and fans of sediment still point to the existence of smaller Martian lakes and rivers. These would be better places to search for life, he says, because they would have held water for longer periods than the giant channels, where floods – if there ever were any – would have been fleeting. "Lakes and deltas are probably the places people are going to look for life," he says.

Solar cycle may drive Venice's floods

If you want to see Venice while keeping your feet dry, don't go when the sun has lots of spots. Peaks in solar activity cause the city to flood more often, apparently by changing the paths of storms over Europe.

Several times a year, but most commonly between October and December, Venice is hit by an exceptional tide called the acqua alta.

David Barriopedro at the University of Lisbon, Portugal, and colleagues were intrigued by studies showing the tides followed an 11-year cycle, just like the sun, showing peaks when the sunspots were most abundant.

They looked at hourly observations of sea level between 1948 and 2008, which confirmed that the number of extreme tides followed peaks in the solar cycle (Journal of Geophysical Research Atmospheres, DOI: 10.1029/2009JD013114).

NASA MODIS: Satellite Pictures of Floods in Spain

By late February 2010, flooding had forced the evacuation of more than 1,000 people in southern Spain, according to the Dartmouth Flood Observatory.

Heavy rains affected the provinces of Cordoba, Jaen, and Seville, blocking roads as well as flooding homes.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured these images of southern Spain on March 9, 2010 (top), and March 8, 2009 (bottom).

Both images use a combination of infrared and visible light to increase the contrast between water and land. Vegetation appears bright green. Clouds appear sky blue. Water ranges in color from electric blue to navy. Bare ground appears tan.

Much of the flooding in the province of Seville occurred along the Guadalquivir River, which flows past the city of Sevilla (Seville) en route to the Golfo de Cádiz.

Before emptying into the gulf, the river feeds wetlands along the coast, and the most conspicuous difference between the image from March 2010 and the image almost exactly a year earlier is the soggier appearance of these wetlands. Whereas patches of bright green cluster around discrete water bodies in the 2009 image, electric blue—suggestive of standing water—surrounds the deeper water bodies in 2010.

Away from the wetlands, in the direction of Costa del Sol, several water bodies appear swollen in 2010. Overall, the landscape appears greener in the later image, indicating that greater precipitation in 2010 spurred plant growth in the normally arid region.

NASA image courtesy MODIS Rapid Response Team at NASA GSFC. If you wish to see more pictures from the NASA Earth Observatory website click here.

Rising water levels engulf Netherlands

Much of the European coast would be affected by 2 metres (red) of sea level rise.

Sea levels should take a couple of thousand years to rise by 25 metres (red).

The map show the areas that lie within 2 and 25 metres of present sea levels.

(Image: Google – Map data © 2009 PPWK, Tele Atlas. Overlay: heywhatsthat.com)