Archive for May, 2013

« Older Entries

Iowa Flood Studies: Multi-wavelength View of Mammatus

May 30th, 2013 by Brenda Dolan

Although the significant convection stayed well south of the IFloodS area of study on the evening of 28 May, the multiple wavelength radars at the NPOL site captured the large anvil spreading out from the convection and the associated undulations beneath, known as mammatus. Mammatus clouds are often (but not necessarily) associated with severe weather and form on the underside of anvils due to large temperature, density and wind shear gradients between the cloud and the air. These types of clouds are very photogenic, especially at sunset.

Panorama of wavy mammatu clouds

May 28, 2013. Panorama of D3R (left) scanning mammatus at sunset. Copyright B. Dolan, Colorado State University

The NPOL radar against a bacground of wavy clouds at sunset.

May 28, 2013.The NPOL radar under a large anvil with mammatus. Copyright Brenda Dolan, Colorado State University.

This case provides an interesting perspective from three different radar wavelengths.  The S-band NPOL radar, with the longest wavelength of 10 cm, is less prone to attenuation (fading out over distance) and is most sensitive to precipitation-sized hydrometeors. NPOL captures the larger domain out to 135 km, with some indications of the undulations on the under side of the anvil and fingers of virga (rain evaporating before reaching the surface) beyond 50 km in range.

Range height indicator (RHI) of NPOL reflectivity through the anvil of a mescoscale convective system displaying small undulations on the underside (mammatus).

Range height indicator (RHI) of NPOL reflectivity through the anvil of a mescoscale convective system displaying small undulations on the underside (mammatus). Credit: NASA

 

The shorter wavelengths of the D3R are more sensitive to smaller hydormeteors, but subject to more significant attenuation and only see out to 40 kilometers. The Ku-band (2.2 cm) shows the incredible structure in this type of cloud, while the shortest wavelength Ka-band (0.85 cm) is somewhat attenuated by water vapor in the atmosphere, resulting in less reflectivity than the Ku-band frequency. Using these three wavelengths in concert helps to provide a more complete picture of these beautiful clouds.

Reflectivity RHI from D3R’s Ku-band radar.

Reflectivity RHI from D3R’s Ku-band radar. Credit: NASA

Reflectivity RHI from D3R’s Ka-band radar.

Reflectivity RHI from D3R’s Ka-band radar. Credit: NASA

From May 1 to June 15, NASA and Iowa Flood Center scientists from the University of Iowa will measure rainfall in eastern Iowa with ground instruments and satellites as part of a field campaign called Iowa Flood Studies (IFloodS). They will evaluate the accuracy of flood forecasting models and precipitation measurements from space with data they collect.

Brenda Dolan is a Research Scientist at Colorado State University, Fort Collins Colo. in the Radar Meteorology group. Her interests include cloud microphysics and polarimetric radar. During IFloodS, she is spending nearly two weeks as the overnight radar scientist at NPOL and sent these observation notes from the NPOL site near Traer, Iowa.

Iowa Flood Studies: Tiny Things Matter

May 23rd, 2013 by Bo Chen

When I heard that student volunteers were needed for IFloodS, I knew I wanted to take part. I had had little experience with fieldwork in the past. Most of my graduate work has been spent in front of a computer, conducting data analysis and performing hydrological modeling. I had difficulty visualizing the information I was working on — I didn’t have a good sense of how much 20 mm of rainfall is. I wanted to get outside and see for myself!

I was one of three Iowa Flood Center students who helped set up the NASA NPOL radar near Waterloo. It was a wonderful experience. The radar is really impressive — the antenna is 10 meters in diameter! I got to talk with some of the NASA representatives about the radar. It represents the next generation of radar systems, and will provide much more accurate rainfall estimates.

Putting together a radar dish

Apr. 25, 2013. IFloodS has provided students at the University of Iowa a unique opportunity. Graduate student, Bo Chen (far right), helps install the NASA NPOL radar Credit: Aneta Goska, Iowa Flood Center.

It was chilly in the morning when we started work, but it warmed up a lot as the day progressed — we all got sunburned! I didn’t have a good idea what kind of clothes to wear for fieldwork — I learned that it’s best to wear clothes you don’t care too much about. We got pretty dirty.

I also helped install four observation stations (three rain gauges each) near Shueyville, south of Cedar Rapids. We go to Shueyville once a week to clean and maintain the gauges — since the instruments are deployed in farm fields, they get dirty very quickly. It’s important to clean them up regularly. We saw dust in the buckets in just a few days’ time. While we’re there, we also download the data from the data logger. It is then uploaded into the IFloodS portal where the science teams can access it and displayed on Iowa Flood Information System, IFIS.

Gilles Molinié, Université Joseph Fourier and Witold Krajewski, Jim Neimeier, and Bo Chen, Iowa Flood Center, discuss the location for a disdrometer for the IFloodS campaign. Molinié brought the disdrometer from Switzerland to collect data during the IFloodS campaign. Credit: Fred Ogden, University of Wyoming.

Gilles Molinié, Université Joseph Fourier and Witold Krajewski, Jim Neimeier, and Bo Chen, Iowa Flood Center, discuss the location for a disdrometer for the IFloodS campaign. Molinié brought the disdrometer from Switzerland to collect data during the IFloodS campaign. Credit: Fred Ogden, University of Wyoming.

I worked with Jim Niemeier to install three rain gauges at an experimental Iowa State site near Des Moines. It was a tough day! We saw a lot of mice, and Jim explained that sometimes animals like to burrow in under the platforms. When we remove the platforms, who knows what might be waiting for us? Perhaps a scared and threatened animal. Animals also sometimes chew the wires, so we have to watch out for that.

For me, this fieldwork experience has been really fun. I now understand the importance of getting out into the field. Tiny things do matter — if it’s not done right, the data can be biased. I learned that careful fieldwork is vital for research. For instance, I learned that I can’t sit on the base of the rain gauges, because my body weight could destroy the level and bias the measurement. I caught myself just before I sat down. I jumped up and thought, “No, I can’t do that!”

I also learned that my professors in Engineering do make efforts to collect reliable firsthand data. I also found that fieldwork is difficult, and we have to be very careful in order to collect good data. Exposure to experiments like IFloods may help to build up our knowledge about fieldwork, and ultimately advance our understanding of complex natural processes.

Bo Chen is a doctoral student in the Civil and Environmental Engineering Department at the University of Iowa working with Professor Witold Krajewski. His research interests include enhancing flood prediction and hydrologic modeling, specifically the hillslope hydrological process and channel routing. During the IFloodS campaign, he is heading up a group of University of Iowa students in servicing and collecting data from one of the field sites.

Iowa Flood Studies: XPOL Radars in Iowa’s Turkey River basin

May 17th, 2013 by Dan Ceynar

Finding a location for two of the four University of Iowa XPOL radars was easy. They will remain at their current home base locations near Iowa City and Cedar Rapids overlooking the Clear Creek Watershed for the IFloodS campaign.  For the other two destined for the Turkey River basin in northeast Iowa — well, there was work to be done.

As is typical, finding the “ideal” radar locations proved to be challenging.  The primary goal was simple enough — a high spot with a good view.  Then we add in the need for power, communications, and access, and it becomes more complicated.

The Turkey River basin, unaltered by glaciers, is rugged and hilly by Iowa standards. Lots of great views, but the ruggedness that makes some of the land difficult to farm, and also means there are a lot of obstructions on the tops of hills, namely tall trees. This image is the “radar’s eye “ view  from the St. Olaf site and demonstrates why it was chosen. Credit: Iowa Flood Center

The Turkey River basin, unaltered by glaciers, is rugged and hilly by Iowa standards. Lots of great views, but the ruggedness that makes some of the land difficult to farm, and also means there are a lot of obstructions on the tops of hills, namely tall trees. This image is the “radar’s eye “ view from the St. Olaf site and demonstrates why it was chosen. Credit: Iowa Flood Center

After much planning, looking at satellite images, talking with local cities and groups, it was time to visit the basin for a reality check.  Many sites that had appeared so promising became distant memories, but new possibilities arose with help of local individuals from the City of Decorah, the City of Calmar, local IDNR staff, Northeast Iowa Community College, and others.  We are grateful for their “touring the countryside” time and cooperation.  In the end, two very attractive locations were secured, one in Calmar and one south of St. Olaf.

 

April 30, 2013, Calmar site: The XPOL installation at Calmar went smoothly enough. It was very windy, but sunny, with mild temperatures. For the follow-up installation of the communications, we dealt with very windy conditions and ice-covered surfaces. Credit: Iowa Flood Center

April 30, 2013, Calmar site: The XPOL installation at Calmar went smoothly enough. It was very windy, but sunny, with mild temperatures. For the follow-up installation of the communications, we dealt with very windy conditions and ice-covered surfaces. Credit: Iowa Flood Center

 

May 2, 201, St. Olaf Site:  The St. Olaf installation was a bit better, 38 degrees F (warm??) , overcast, and very windy, with rain all day. Visiting scholar Jacopo Grazioli, Dan Ceynar, and Radek Goska of the Iowa Flood Center adjust the radar position on the cribbing. Credit: Iowa Flood Center

May 2, 201, St. Olaf Site: The St. Olaf installation was a bit better, 38 degrees F (warm??) , overcast, and very windy, with rain all day. Visiting scholar Jacopo Grazioli, Dan Ceynar, and Radek Goska of the Iowa Flood Center adjust the radar position on the cribbing. Credit: Iowa Flood Center

As many visiting researchers and NASA and scientist are now fully aware, the weather in Iowa is constantly changing, often between extremes. The weather during the installation of the XPOL radars was challenging, ranging mostly from cold, windy, and rainy to windy and icy. Very challenging indeed. Tenacity prevailed, and both new radar locations were successfully installed at the beginning of the month despite the adverse weather conditions.

From May 1 to June 15, NASA and Iowa Flood Center scientists from the University of Iowa will measure rainfall in eastern Iowa with ground instruments and satellites as part of a field campaign called Iowa Flood Studies (IFloodS). They will evaluate the accuracy of flood forecasting models and precipitation measurements from space with data they collect.

Dan Ceynar is a staff engineer at the Iowa Flood Center. He coordinates many of the Iowa Flood Center’s instrumentation networks across Iowa including stream sensors, rain gauges, and XPOL radars. This spring, he has been busy working with NASA and IFC staff to deploy instruments for the IFloodS campaign.

Iowa Flood Studies: Witek’s World

May 10th, 2013 by Witold Krajewski

Last year, when working with the NASA GPM team in the planning stages for the Iowa Flood Studies project, more affectionately known as IFloodS, I worried — a lot.

2012 was a year of historic drought in Iowa. IFloodS is all about studying and measuring precipitation. What if drought continued into 2013? In short, what if it didn’t rain?

Turns out my fears were unfounded. The spring of 2013 has turned out to be wet. Very wet. In mid-April, Iowa City got 4.5 inches in a single day, while nearby North Liberty’s rainfall totaled a whopping 8.3 inches that has less than 1% chance of being exceeded in any given year.

Despite a drought in 2012, the NASA NPOL radar near Waterloo has been able to capture information from multiple precipitation events in Iowa this spring. Credit: Vitek Krajewski / Iowa Flood Center

May, 2013. Despite a drought in 2012, the NASA NPOL radar near Waterloo has been able to capture information from multiple precipitation events in Iowa this spring. Credit: Witold Krajewski / Iowa Flood Center

OK, so I am no longer worrying that we’ll set up some of the most sophisticated instrumentation in the world for measuring precipitation, only to find ourselves measuring dust.

This last weekend I got the chance to drive around the state and see firsthand what heavy rainfall was doing to Iowa’s streams, rivers, and landscape. I drove north out of Iowa City to the NASA NPOL radar site near Waterloo. As I crossed many streams and rivers in the Cedar River basin, I observed water running high and fast.

May, 2013. Many Iowa streams are bank full this spring after heavy April rain events. Credit Witold Krajewski / Iowa Flood Center

May, 2013. Many Iowa streams are bank full this spring after heavy April rain events. Credit Witold Krajewski / Iowa Flood Center

Later on, I drove south to pick up my wife from a horseback outing, and I saw more elevated stream levels and saturated farmland.  Many streams were overflowing the banks.  It reminds me that everything we do at the Iowa Flood Center cannot completely prevent floods and the damage they bring. We can better inform people about impending floods, and we can improve mitigation strategies to lessen the damage. These are all worthwhile activities that I believe in wholeheartedly. But it’s worth remembering, even as we are in the midst of this exciting project, that it’s not the state-of-the-art technology or the groundbreaking studies that matter the most — it’s the people we serve, the citizens of Iowa and citizens of the world, who are living with floods.

Witold Krajewski is the director of the Iowa Flood Center, based at the University of Iowa in Iowa City. He is a professor in the Department of Civil and Environmental Engineering and serves as the Rose & Joseph Summers Chair of Water Resources Engineering. His scientific interests concern measuring, modeling, and forecasting precipitation using radar and satellite remote sensing.

Iowa Flood Studies: Spring Data Collection Features a Winter Mix

May 8th, 2013 by Walt Petersen

The big science highlight so far is that over May 2 through May 4, the GPM Ground Validation team finally collected a coordinated, co-scanned multi-radar frequency and dual-polarimetric dataset with the D3R and NPOL radars and we did it in one of the most complex multi-day precipitation events that we’ll measure in mid and high latitudes – a mixture of rain, snow and sleet.

The NASA D3R radar looking over an Iowa field lightly dusted with snow.

May 3, 2013. The D3R radar, which measures precipitation at similar frequencies as the radar on the GPM Core satellite, measured rain, snow, and sleet at the Traer site in Iowa. Credit: Walt Petersen / NASA

In fact, the snowfall portion of the storm turned out to be a record event for Iowa in May. The fact that D3R and NPOL co-scanned the event is important because you have a longer wavelength, high power reference radar (NPOL) with dual-polarization (both vertical and horizontal scans), and hence enhanced capability to discern specifics on precipitation shapes, sizes and numbers, scanning coincident with a radar (D3R) that carries the same higher frequencies that the DPR radar will carry on the GPM Core Satellite.

The higher frequencies of the D3R are more sensitive, but will often attenuate, or dissipate, faster in the mixture of precipitation we sampled. So, you can test how well you can correct for that attenuation and retrieve the complex precipitation structure from the D3R, which is our proxy for the space-borne radar, against your reference platform, the NPOL. At the same time, we learn a great deal about the precipitation physics when we look at things with 3 different frequencies and in dual-polarization modes.

Map of field locations of IFLoodS instruments. The NPOL and D3R radars are located dead center and a ray of disdrometers and rain gauges stretches southeast toward Iowa City in the bottom right. Other rain sensors are distributed throughout the Turkey River basin in the north east and the south fork of the Iowa river west of Traer. Credit: Iowa Flood Center

Map of field locations of IFloodS instruments. The NPOL and D3R radars are located dead center and a ray of disdrometers and rain gauges stretches southeast toward Iowa City in the bottom right. Other rain sensors are distributed throughout the Turkey River basin in the north east and the south fork of the Iowa river west of Traer. Credit: Iowa Flood Center

Moreover, we did this over a “reference” 100 km-long ray of disdrometers, vertically pointing micro rain radars, and rain gauges – all in all, what will probably amount to a great deal of information to interpret.

From May 1 to June 15, NASA and Iowa Flood Center scientists from the University of Iowa will measure rainfall in eastern Iowa with ground instruments and satellites as part of a field campaign called Iowa Flood Studies (IFloodS). They will evaluate the accuracy of flood forecasting models and precipitation measurements from space with data they collect. Walt Petersen, a scientist based at NASA’s Wallops Flight Facility, is the Ground Validation Scientist for the Global Precipitation Measurement (GPM) mission.

Notes from the Field