Mar 212017
 

Retrieving fall streaks within cloud systems using Doppler Radar

 

Abstract: Interaction of the ice crystals with super-cooled liquid droplets in mixed-phase clouds leads to an enhanced growth of the ice particles. However, such processes are still not clearly understood although they are important processes for precipitation formation in mid-latitudes. To better understand how ice particles grow within such clouds, changes of microphysical parameters of a particle population falling through the cloud have to be analyzed. The Transportable Atmospheric Radar (TARA) can retrieve the full 3-D Doppler velocity vector based on a unique three-beam configuration. Using the derived wind information, a new fall streak retrieval technique is proposed so that microphysical changes along those streaks can be studied. The method is based on Doppler measurements only. The shown examples measured during the ACCEPT campaign (Analysis of the Composition of Clouds with Extended Polarization Techniques) demonstrate that the retrieval is able to capture the fall streaks within different cloud systems. These fall streaks can be used to study changes in a single particle population from its generation (at cloud top) till its disintegration. In this study fall streaks are analyzed using radar moments or Doppler spectra. Synergetic measurements with other instruments during ACCEPT allow the detection of liquid layers within the clouds. The estimated microphysical information is used here to get a better understanding of the influence of super-cooled liquid layers on ice crystal growth. This technique offers a new perspective for cloud microphysical studies.

The full text of the paper from L. Pfitzenamier et. al., 2017, can be found in the here on the J-Tech web page

 

Aug 242015
 

londonreading

During the last 4 weeks I was for a secondment at the University of Reading. Main goal was to learn more about microphysical retrievals of cloud properties. But also exchanging knowledge and ideas was on the agenda. So I was very glad that I got the chance to work with Chris Westbrook and his colleagues.

houseSince the very successful ACCEPT campaign I have plenty of data to look into and develop ideas. One of them was to retrieve mean ice particle size using the wavelength ration of the operated radars  (3 GHz and 35 GHz). The group in Reading was really helpful in answering questions and discuss first preliminary results. They already had experience with such retrievals.

Discussion with other PhDs and Scientists brought also some very fruitful and promising input. I exchange some of the ACCEPT and hope that the collaboration will go on in the future. An improvement of my retrieval for retrieving fall-streaks within radar data was tested on a different data set. This improved the understanding of my own retrieval and helped to validate it.

So all in all a successful exchange for both sides. I thank once again the colleagues from Reading for the collaboration and all the rest. And I hope that the collaboration will go on in the future

Apr 202015
 

Last week Stephanie Prianto Rusli and Lukas Pfitzenmaier presented posters at the European Geoscience Union in Vienna. This conference gave a grate opportunity to meet a brought range of scientists from all kinds of Geoscience and come into discussion. It also gave the opportunity to go into interdisciplinary sessions and generate new ideas.

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Stephanies poster was in the the session: Remote Sensing of Clouds and Aerosols: Techniques and Applications and its title: Multi-sensor approach to retrieving water cloud physical properties and drizzle fraction  (poster here)

Lukas poster could be find in the new session about Observing and modeling processes in moderately supercooled clouds and was dealing with Effect of cloud microphysics on particle growth under mixed phase conditions  (poster here). Discussions and comments within the supercooled cloud community where very fruitful and caused quite some attention. So the changes are high to have a second one in the next EGU 2016.

 

Oct 312014
 

Today we went to Cabauw to fix some  radar issues that we have. The weather forecast of today was good for lidar measurements too we started the Raman-lidar CAELI as well. As you can see as all the measurement quick-looks for the lidar systems (Polly and CAELI) we had some nice cirrus layer over Cabauw. So we expected also that our colleagues from Munich would have a good change to observe some HALOs within the cirrus clouds. But the conditions where that good, that we could also observe this HALOs over Cabauw.

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Halos are optical reflections produced by hexagonal oriented ice crystals within ice clouds. This reflections produce a ring around the sun and also some bright dots next to the sun. Observations of such HALOs make it possible to get information about the ice crystal shape and their orientation. Lidar measurements could also give such information. Combining the measurements of the lidar systems and the HALO-camera in de Bilt will hopefully produce some nice results.

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Oct 252014
 

Yesterday, Fr 24-10-2014, was a realy nice measurement day. A lot of mid-level clouds over Cabauw and all instruments where running and measuring smothly. Only the lidar systems where not able to penetrate the clouds, because of the precipitation that was present during the whole day. The overpassing front systems produced the whole day real nice clouds that we measured. To capture the vertical structure of the cloud system and the atmosphere we launched some radiosondes. So all in all we are happy that we could measure this clouds. With those information I wish a nice weekend!

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Oct 232014
 

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The last days have been quite windy and rainy. That is also the reason why we didn’t spend so much time on the site. We launched some days ago some weather balloon. Such a radiosonde takes about 30 minutes of preparations before it is launched. First the balloon has to be filled with the right amount of Helium. Then the parachute attached and finally the sonde itself has to be tied up to the parachute. One important point to take into account before the launch is the wind speed and the direction. This prevents the sonde from being caught by trees or one cable of the Cabauw tower.

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With such a radiosonde it is possible to get vertical information about temperature, pressure, humidity and wind as the balloon is ascending in the atmosphere. This information help us to define thermodynamic conditions under which some of the microphysical processes can take place and some don’t. Several launches after each other also contain information about the variability of the atmospheric state. So all in all this small device is a real useful tool for our campaign.

Oct 172014
 

On Monday, we had a visit form a photographer (Rob Doolaard) to shoot some pictures from our work there. Because of ‘bad’ weather conditions, we were most of the time inside one of the instrumental cabins to prepare our daily meeting and later on to also do the meeting. Actual plan had been, that we do lidar measurements and launch a weather balloon as well, but the conditions were too bad, so we skipped it. The first two pictures are taken inside the TARA radar cabi. The other two are outside during one of our discussions. They illustrate quite well, that a measurement campaign includes a lot of ‘IDLE state’ as well. And if the weather is not nice you wait inside 🙂

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Oct 122014
 

Now the first week is over already. It was an interesting one and we learned a lot from it.

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One thing is that hardware for wireless connection is not always waterproof. So we bought new ones and installed them and now everything works again. Network problems also costs us some missing of raw-data with TARA yesterday, but now everything seems to work again. The biggest issue we had so far is that both cloud radars stop working at the same. So right now we try to repair them with the support from METEK. One is already back and measuring. For the second on we hope to get it done soon.

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We also performed our first measurements with CAELI on Friday. We took almost 3 hours of measurements with it. At the beginning some low cumulus clouds were present. This made it difficult to align the lidar properly but after a short stop and a short readjustment it worked fine. Also in the afternoon the low cloud disappeared and we could measure the cirrus clouds.

All in all the first week was quite busy and I hope that the next weeks will be busy as well. But it would be nice to have less errors to fix and take more measurements instead.

Oct 092014
 

On the 7th of October we had a very nice Kick-Off. I think we all got a good impression about the campaign and about the clouds we want to observe. We all got wet around noon when a convective cell overpassed the site. But it desappeared as fast as it appeared. So thanks to Tim for giving us the nice pictures (the big ones in the middle). He took both pictures within less then 2 hours difference. With those to pictures you already can get an impression about how variable the weather was on the 7th of October over Cabauw.

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During this precipitation event one of the radars stopped working. This was fixed in the evening and it is now working continuously. But now one of our network connections is broken and we are working to fix that at the moment. The new equipment is bought and installed. And now waterproof!

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We also measured some nice clouds that morning, so the first data are taken. We hope for more nice and cloudy days like that morning. Now the sun is shining and we hope for a nice sunset later

Oct 062014
 

During the weekend we took the first measurements. For this all radar systems were pointing to the zenith that the measurements can be compared. The results of the comparrison will be the first data to look into. It will be a nice test to see different sensitivities of the instruments.

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Today we put back the antenna elevation of TARA to 45 degree elevation and also put back the webcam. The pictures show that moving the antennas of TARA isn’t a fast process and even need some muscle power to make it work. Luckily also the weather turned into more cloudy conditions. So let’s hope , at least from our point of view, that it will become rainy and cloudy autumn. This would be nice for some nice measurements… Let’s see what the Kick-Off tomorrow will bring.

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