Iowa Flood Studies: Waiting for the Rain near Traer, Iowa

From May 1 to June 15,  the Iowa Flood Studies, or IFloodS campaign is taking place in eastern Iowa. NASA and the Iowa Flood Center at the University of Iowa are measuring rainfall with ground instruments, ground radar, and satellites, and then evaluating flood forecasting models and precipitation measurements from space.

We have been waiting for rain at the NPOL site. Yesterday evening it got very close- within 50 km or so. In the interim, we were waiting for convective cells to develop along what is called a radar “fine-line”.  Fine-lines are little boundaries in the lowest part of the atmosphere associated with small changes in wind, temperature and/or humidity that often work to focus bugs. They are very visible to the radar and are often (though not always) associated with a line of cumuliform clouds which will sit over the top of the boundary. The clouds form in response to convergence and mixture of the moisture along the fine line and tend to “ride” it as it propagates along. Often, deeper more vigorous rain cells will develop along these lines as they intersect other cloud rolls or boundaries.

May 1, 2013. Clouds along the “fine-line”, a boundary that means a change in wind, temperature and/or humidity is occurring. Credit: Walt Petersen / NASA

At any rate, we watched one of these boundaries for quite some time yesterday with the radar. It passed NPOL in the afternoon (below) and I went out to take a quick picture of the clouds along it (above; which were unimpressive…..alas).  However, southwest of Des Moines there were a few severe storms that developed along the same line; just didn’t happen in our area.

NPOL radar view of the “fine-line.” Clouds and rain are shown in blue. The NPOL position is labeled in white and the line of green sites show where the ground instruments are located. Credit: NASA

Today (currently) we are awaiting a major storm system that is sitting just to our west and northwest and producing rain mixed with snow in the northwest corner of Iowa — the same system that was producing snow in Colorado early this morning. It looks to be wet and cold here for the next few days after the storm arrives. If and when we get the rain/snow mix, we will focus very hard on coordinated scanning with the D3R as this will be a very unique opportunity for us to collect data in a mixed-phase event with three different radar frequencies at dual-polarization. Since this situation happens more often in the mid-latitudes, and GPM will extend our rain and snowfall measurement capability into the mid-latitudes, this could be a great case for looking at the famous “rain-snow line” transition and how our GPM radar and radiometer algorithms will work in this situation.

Walt Petersen is the Ground Validation Scientist for the Global Precipitation Measurement (GPM) mission, based at NASA’s Wallops Flight Facility in Virginia.

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Iowa Flood Studies: Meet the 2-D Video Disdrometer

A rain gauge will collect how much rain falls, but how exactly do scientists measure the size, shape, and fall speed of raindrops near the ground? Patrick Gatlin of NASA’s Marshall Space Flight Center, sent us a couple photos from Iowa of the instrument that does exactly that: a two-dimensional video disdrometer.

Patrick Gatlin (NASA/MSFC) and Merhala Thurai (Colorado State Univ.) perform calibration tests on a NASA two-dimensional video disdrometer (2DVD) being used to measure the size, shape and fall speed of raindrops for the IFloodS campaign. Credit: NASA

Shaped like a giant pizza box, the disdrometer has a medium sized square opening in the center. Along two adjacent sides at 90 degrees from each other are two video camera systems that record the raindrops as they fall. With a front view and side view of the droplets, scientists can determine their size and shape, and get an idea of how many of differing sizes are falling.

Hamburger shaped raindrop viewed by the disdrometer software from the front (left) and side (right). Credit: Patrick Gatlin / NASA

“A common misconception is that raindrops are shaped like a tear-drop, but actually they are shaped more like a hamburger bun similar to the 5 mm sized raindrop shown here,” Gatlin says. During IFloodS, millions of raindrops will be measured by these type of rainfall sensors. Scientists will examine all these raindrops in order to provide better estimates of rainfall from weather radars probing the atmosphere from the ground up and those looking down on Earth from space, like the eventual GPM Core satellite.

Apr. 8, 2013. NASA and Iowa Flood Center staff set up about 20 disdrometers throughout the field area in April. Credit: Aneta Goska / Iowa Flood Center

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Iowa Flood Studies: NPOL Radar Site near Traer, Iowa

Walt Petersen is the Ground Validation Scientist for the Global Precipitation Measurement (GPM) mission, based at NASA’s Wallops Flight Facility in Virginia. He manages all of GPM’s ground validation operations, the field campaigns that ensure that satellites measure rainfall and precipitation from space accurately.

From May 1 to June 15, he is leading the Iowa Flood Studies, or IFloodS campaign in eastern Iowa. He and his team, as well as their partners at the Iowa Flood Center at the University of Iowa are measuring rainfall with ground instruments, ground radar, and satellites, and then evaluating flood forecasting models. Over the next few weeks, Walt and others on the ground will be sending us their notes from the field.

4/29/2013, NPOL Radar Site near Traer, Iowa

Apr 29, 2013. The NASA Polerametric (NPOL) precipitation radar (center) scans for rainfall in both the horizontal and vertical planes to measure precipitation throughout the whole volume of the air column. The smaller D3R radar is to the far left. Credit NASA

This morning, my first full day around the area of Waterloo, Iowa. Quite appropriately, we were greeted by severe thunderstorms with some ping pong ball-sized hail in the area. Luckily for my rental car,  and even more luckily for the NPOL and D3R antennas, that hail stayed north of the radar site (large hail, rental cars, and/or radar antennas not being the best mix). I thought it an appropriate welcoming to the experiment. I drove out to the radar for the first time this morning in my little Nissan rental car. I’ll be curious to see how it does on the gravel/dirt road after it rains a few inches.

Apr. 25, 2013. A team of NASA staff and Iowa Flood Center and University of Iowa students assist with the NPOL setup in eastern Iowa. Credit: Aneta Goska, Iowa Flood Center.

Things are impressive out here. The NPOL and D3R guys did a very nice job of getting the NPOL and D3R set up. We are still in the midst of tweaking small things prior to getting down to serious data collection. For example, we need to make certain that the NPOL is well-calibrated (doing that now), and then we need to test the timing of our scan sequences to make sure we are making the requirement that we sample the rain field in a 360 degree circle once every 3 minutes or less. The objective is to make rapid maps of rainfall (out to a range of say, 150 km, from the NPOL) at high time and space resolution, and then in between making those rain maps, do coordinated scanning of the precipitation in the vertical plane with the D3R radar or over other river basins of interest. The rapidly collected rain maps serve as a reference for doing our comparisons to satellite products and to test products for hydrologic modeling of runoff (e.g., flood forecasting).

Apr. 29, 2013. The science trailer where data from the radars is collected. From left to right, Walt Petersen, Dave Wolff, and Delbert Willie. Credit: NASA

The coordinated scanning with the D3R is done for a slightly different reason. These scans are collected along a line that has many raingauges and disdrometers located at different points so that we can connect the dots between the rainfall we are measuring near the ground (for example, rainfall rates and raindrop sizes, numbers and shapes) to the physics happening in the column of the atmosphere above those points (e.g., how the rain is made). We care about this from the perspective of testing algorithms designed to retrieve precipitation estimates from space using the GPM DPR radar (which has similar frequencies to the D3R) which will fly on the GPM Core satellite.

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Greenland Aquifer Expedition: Tracking Temperatures in the Aquifer

By Clément Miège

Hi there! Today I have another story to share with you! It’s about the tracking of the temperature evolution of the firn aquifer temperature by using two thermistor strings that we set up in the two holes made by Jay (see Jay’s post on drilling for details).

By tracking temperatures over a year, we will observe the firn heating mechanisms in the summer with the melt from the surface of the ice followed by water infiltration in the firn. In the winter, we will get a sense of the refreezing processes from the cold surface air, which cools the upper part of the firn and we will observe the persistence of the firn aquifer over the years.

To achieve this, we installed two thermistor strings with two different lengths: 30 and 60 meters. The shorter string has 60 sensors on it, sampling every half-meter. The longer one will only get a temperature reading every 2.5 meters but it will record deeper temperatures. Both strings are set to collect data every hour for an entire year, assuming the batteries last that long (hopefully!) The temperature chain is called a thermistor string because each sensor is a thermistor, a type of resistor sensitive to temperature changes. After measuring a resistance change, calibration curves allow us to retrieve temperature changes.

The thermistor-string story started in Utah, when we received the equipment late from the manufacturers, giving us only 5 days to work on it before leaving for Greenland. We realized that integrating the whole system together with the satellite uplink would take most of our last prep days.

It was definitely too late to ship the thermistor equipment with the rest of our gear, so Rick and I traveled with it in our checked luggage! I ended up with a 50 lbs of spool coiled with about 60 meters of cable in a suitcase. Rick had a black pelican case as his checked bag, with the second thermistor string, datalogger, ARGOS antenna and other pieces of hardware. We learned how to travel light, bringing minimal clothing, and wearing the cold-weather clothes in the airplane so we were able to meet the airline luggage restrictions – it definitely made for fun travels!

At the Kulusuk Hotel, in southeast Greenland, we finished integrating the thermistor string, mostly by picking the right data-transmission rate to the satellite in regards to our battery consumption estimates. Having the ARGOS satellite uplink will let us receive temperature data via email every day from the field site and tell us almost in real time what the temperatures are in the two holes.

In the field, shortly after drilling each hole (to avoid water refreezing due to cold air down the hole), we lowered the thermistor string down and backfilled the hole with surface snow. Then, we used the Felics drill to make a 4-meter hole to anchor the long pole that holds the ARGOS antenna.

Lowering the second thermistor string down the 30-meter hole.

On that day, the 20-knot katabic winds were blowing a lot of snow, so we used a mountain tent as a snow-proof environment to work with the electronics before dropping off the case in its hole. To give you a taste of the wind speed: Rick was charging one of the thermistor-string battery and the wind was so strong that it blew the small 1kw generator off…. crazy! When the winds finally died down, we buried the case in a 2-meter deep snow pit, because we wanted to prevent the case from being exposed to surface densification and melt during the summer.

Digging a deep snow pit for the thermistor case.

Last check on the electronics, to make sure all the wires are tightened before closing the box — next opening in one year!

That is it! The box is down the hole.

After backfilling the snow pit, the only evidence at the surface of the temperature strings is the top of the pole with the ARGOS antenna and a red flag!

We are hoping to recover the case with the datalogger next year, but we are not sure if the ARGOS antenna will still be sticking out, because this sector of the ice sheet is getting a lot of snow accumulation in the winter. We will use a metal detector to find the metal pipes left near the case.

Because this is likely my last post for this expedition’s blog, I would like to thank the all team for this great adventure and everybody that was supporting this exciting research. Until next time!

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Greenland Aquifer Expedition: Back in the Office

By Lora Koenig

Watching dogsleds go by in Kulusuk.

Well, I am back in Greenbelt, Maryland, typing with warm fingers in a climate-controlled office with high-speed Internet and drinking fountain just down the hall. After fieldwork, I am always thankful for things I generally take for granted, like being able to charge my laptop by simply plugging it into an outlet. There is no longer a need fill a generator with gas and then start it just to charge batteries. Aw, the comforts of home!  (We all had safe trips back to the US and have returned to our home institutions last week.)

For the last blog post of the season, I decided to pull together a few of my favorite photos from our trip to give you a sampling of the great fun we get to have while doing this kind of research. The most fun I had during this trip was on our final day in Kulusuk: we were invited to the Kulusuk School to with the children in the upper grades (who speak some English) about our work. I regret that we do not have any pictures of this event, but we were giving our presentation and letting the students run our small ice core drill, thus neglecting picture taking. The school in Kulusuk has about 70 students and includes all grades. The building has lots of windows and is very bright inside — it is one of the prettiest schools I have been in, with lots of open space, a small kitchen, library and a gym. I especially liked the entrance to the school, which was equipped with plenty of coat hangers and boot racks for the students to shed their cold weather gear as soon as they come inside. Though we were there talking about science, the school in Kulusuk is known for their art. We were hosted by the art teacher, Anne-Mette Holm, and after our talk got to attend one of her classes where the students were making wooden sculptures. We also got to see other student projects including weaving, toy making and furniture making. Quite a portfolio!  The students’ art has traveled the world, being shown at different expeditions across the Arctic. (Check out pages 11 -15 of this document for some examples of the children’s art work under Anne-Mette’s tutelage.)

While our visit to the school was definitely the top highlight of the trip here are a few others highlights in pictures.

The northern lights (Aurora) never got old and were out almost every night.

The view out the window from our dinner table in Kulusuk at sunset.

Sunset in Kulusuk.

Seeing mountains from our campsite on the ice sheet, a nice change from the typical flat white ice sheet.

Watching Clem dig a really big hole for the thermistor control boxes.

Seeing the transition between the flat ice sheet and the fast flowing outlet glaciers.

Catching a ride in the airport luggage carts.

So those were some of the highlights of the field work and now it is time to work with the data we gathered. In the week we have been back, we have already started to analyze our data. We see that, as expected, the densities in the firn (aged snow) above the aquifer are higher than expected and that there is more water than originally predicted. We still need more data to fully understand what this water trapped in the Greenland ice sheet means for sea level rise. We need many years of data to understand how and if the aquifer is changing with time… but remember this was an exploratory mission. When we set out, we were not even sure if our drills would even work. There was a chance they would have just frozen in place and we would not have gotten any data. This was a high-risk mission due to the weather in the region and all the new things we were trying. We came back with all the data we set out to get and, quite frankly, I am surprised. We had a large team that helped with this project including the field team, logistics support, airport support, the NASA and NSF support teams and all of you for your well wishes and interest in our research. Thanks to all! Until next time, stay cool

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