WG 1 workshop on the LAPBIAT Atmospheric Sounding campaign at the Finnish Meteorological Institute in Helsinki, September 2-3, 2010.

WG 1 workshop on the LAPBIAT Atmospheric Sounding campaign at the Finnish Meteorological Institute in Helsinki, September 2-3, 2010. Venue: Finnish Meteorological Institute (FMI), Erik Palmenin aukio 1, Helsinki, Finland Aqua room Local organizer: Rigel Kivi E-mail: rigel.kivi@fmi.fi Meeting Report Accurate measurements of water vapor in the upper troposphere and stratosphere are needed for the climate studies. As the water vapor mixing ratio varies five orders of magnitude from ground to the mesosphere, different measurement techniques are applied. Intercomparison of various measurement techniques and methods allows the assessment of the measurement uncertainties and is a prerequisite for improved instruments and data analysis methods. Atmospheric water vapor measurement is the topic of WG1 of COST Action ES0604, Atmospheric Water Vapor in the Climate System (WaVaCS). In January-June 2010 the LAPBIAT atmospheric sounding campaign took place in Sodankylä, northern Finland (67.4º N, 26.6º E) to perform profile and column measurements of water vapor and aerosols in the troposphere and stratosphere by various in situ and remote sensing instruments. The campaign involved balloon borne research grade water vapor instruments such as the Cryogenic Frost point Hygrometer (CFH) and the Lyman- alpha fluorescence hygrometer FLASH- B. The climate research radiosonde Vaisala RR01, which is currently under development, was flown in the same payload with the cryogenic frost point hygrometer and the fluorescence hygrometer. The remote sensing instruments participating in the campaign included the microwave radiometer for water vapor measurements MIAWARA-C. This instrument was operated for a six month period, until mid-june 2010. The aerosol in situ profile measurements were made by the new COBALD instrument and by a well established balloon borne aerosol backscatter sonde. The particle measurements in the stratosphere were made simultaneously with the water vapor measurements. The purpose of the workshop in FMI Helsinki during 2-3 September 2010 was to discuss different measurement techniques, campaign results and future cooperation. Workshop started on Thursday, 2. September 2010 at 9:00 at FMI Helsinki First session: Thursday, 2. September 2010, morning session Session chair: Holger Vömel Session report: Franz Immler Rigel Kivi (FMI) welcomed all participants to the WG1 workshop at FMI Helsinki and announced the logistical information. Leif Backman (FMI) gave an overview of the structure and activities of the Finish Meteorological Institute (FMI). The FMI is a governmental institution with more than 600 employees, more than 1

half of which are scientists. FMI provides a number of services for the public and the economy. It is divided into two departments: the weather and safety department and the department for research and development. The latter has eight units, one of which is the arctic research unit. Rigel Kivi's (FMI) presentation provided an overview of the LAPBIAT campaign, starting with a history of similar activities at the FMI Arctic Research Centre in Sodankylä. In 2004 the LAUTLOS campaign took place, where a number of radiosondes and specialized sensors like the cryogenic frost point hygrometer (CFH) were flown. The motivation of the LAPBIAT Atmospheric Sounding Campaign in 2010 was firstly to improve and develop new instruments capable of accurate measurements of water vapor and aerosol profiles, especially in the upper troposphere and in the stratosphere. Secondly the aim was to investigate atmospheric processes, such as formation of polar stratospheric clouds and dynamical processes leading to redistribution of water vapor in the stratosphere. The balloon campaign took place in January to March 2010, this time period coincided with the RECONCILE aircraft campaign. January 2010 was particularly suitable to observe PSCs in the Arctic stratosphere, for example temperatures down to -90º C were observed in the lower stratosphere. New Vaisala Reference Radiosonde RR01 prototype was flown in the same payload with the cryogenic frost point hygrometer CFH and FLASH-B Lyman-alpha fluorescence hygrometer. The payloads also included the newest versions of radiosondes by Vaisala (RS92), Graw (DFM-09) and Intermet. For detecting the aerosol and cloud particles two backscatter sondes were compared, the COBALD developed at ETH Zurich and Aerosol Backscatter sonde developed at the University of Wyoming by James Rosen and Norman Kjome. The latter is a well established instrument and was used here for the comparisons with the newly developed Cobald sonde. Overall 33 multi-sensor balloon payloads were launched; total number of individual in-situ instruments was 172. In January 2010 a series of unique observations of PSCs and water vapor were made using combination of water vapor and aerosol sensors in balloon payloads. Among the remote sensing instruments, participating in LAPBIAT, in particular the compact microwave spectro-radiometer MIAWARA-C from the Institute of Atmospheric Physics at the University of Bern was run for extended time period: from mid-january until mid-june 2010. Rigel Kivi presented results of water vapor and PSC measurements; total water vapor comparisons between sondes, GPS, FTS and MIAWARA-C; comparisons of the CFH and MLS retrievals. Holger Vömel (DWD) gave an introduction to the GCOS Reference Upper-Air Network (GRUAN). The detection of climate change poses strict requirements on the accuracy and stability and accuracy of observations. In particular in the upper atmosphere the networks that were operated in the past did not provide reliable data to detect changes of temperature and other variables. The main reason for this was that these networks were not designed for that purpose but for providing input to short or medium term weather forecast models. Therefore the Global Climate Observation System (GCOS) decided to install an Upper-Air reference network for providing accurate data for climate models as well as for the calibration and validation of other observational systems including those on satellites. The GRUAN lead centre that was installed at the Lindenberg Observatory together with the Working Group for Atmospheric Reference Observations (WG-ARO) worked out the guiding principles of GRUAN observation which are traceability to standards, estimation of measurement uncertainty and comprehensive documentation. An important part of this effort is inter-comparisons of instruments that are needed to assess instrument performance and to validate uncertainty estimates. In this context the LAPBIAT campaign was an important effort to help GRUAN fulfilling its tasks. Hannu Jauhiainen (Vaisala Oy) provided an overview of the development of the Vaisala 2

radiosondes. He presented technical details on each sonde type used since 1930s. This information is very important to understand challenges of data homogenization for trend studies. Over the years the radiosondes were improved, however a climate study using time series by radiosondes should take into account changes in radiosonde generations. Alexander Kotik (GRAW radiosondes) reported from the newest improvements of Graw operational radiosonde DFM-09. This sonde was tested in LAPBIAT campaign in March 2010 and some problems with the temperature measurements were detected. Obviously the radiation effect on the sensor was larger than expected. Based on this information Graw improved the coating of the sensor with the new coating being a lot smoother and therefore having a higher reflectivity than the old one. Also the new radiosonde, which is an upgrade of the DFM-06 has improved its data processing in particular the time synchronization and lag-correction. The sensors are calibrated in the factory to references that are traceable to SI units. Temperature is calibrated in the range from - 80 to 40 C at 12 points and humidity from 0% to 95% relative humidity at 5 points. Franz Immler (DWD) analyzed the data of the RS92 radiosondes in comparison to the references in order to derive uncertainties. At first a methodology was presented that provides the framework for proper uncertainty estimation and inter-comparison. The goal is to derive a data product that complies with the GRUAN standards described earlier. The temperature sensors are calibrated with an accuracy better than 0.1. Some additional accuracy comes in from aging of the sensors. The main source of uncertainty however is the radiation effect during daytime. Measurements of this effect performed in Lindenberg were presented. From this lab experiment a radiation correction scheme was established that to a large extend agrees with that used by the manufacturer. The important part of this work is not only to establish a correction scheme but to also assess the uncertainty of the correction that feeds into the overall uncertainty budget of the sensor. The overall uncertainty is 0.1 to 0.2 K in the troposphere and reaches 0.6 above 30 km altitude. Concerning the humidity measurements there is also a radiation effect that needs to be corrected, but there is also a dry bias at night time with respect to the CFH data that need to be accounted for. Additionally the time-lag correction adds to the uncertainty budget. For both variables the correction schemes were developed and the uncertainty estimates for each individual profiles can be calculated. Thus a GRUAN data product can be established based on RS92 radiosonde profiles. Second session: Thursday, 2. September 2010, afternoon session Session chair: Franz Immler Session report: Sergey Khaykin Sergey Khaykin (Central Aerological Observatory of Roshydromet, Russian Federation) reported the new design of FLASH-B hygrometer. An upgraded version of the FLASH-B instrument has been developed and is now undergoing laboratory and flight tests. The upgraded instrument is equipped with new hydrogen lamp developed to meet all the requirements for emission stability, the new crush-proof optics based on plastic Fresnel lenses, the new electronics built on modern highquality components and the new elaborated firmware. A built-in pressure sensor controls the photomultiplier power to keep it off below 2 km altitude allowing for easy launch procedure. The uncertainty of the instrument does not exceed 10% for upper tropospheric and stratospheric conditions. The hygrometer has interfaces to Vaisala RS-92 sonde and Meisei RS06G sonde. The upgraded FLASH-B instrument integrated with Meisei radiosonde has been flown 3 times at Biak, Indonesia in January 2010 during SOWER campaign, providing accurate measurements of water vapor down to 1.5 ppmv. Another batch of new FLASH-B sondes with interface to Vaisala RS92 has been successfully flown from Ny-Alesund during the Winter 2009/2010. Comparison of new FLASH-B upper tropospheric data to Vaisala RS92 and Meisei RS06G reveals good agreement. 3

Terhi Lehtola (Vaisala Oy, Finland) presented Vaisala Reference Radiosonde prototype in LAPBIAT. In January 2009 Vaisala launched a program to develop an operational reference-grade radiosonde for climate studies and other applications where enhanced radiosonde performance is required (especially the GRUAN network). The program first focuses on upper-air measurements of humidity. The first version of the operational reference radiosonde (RR01) is based on Vaisala Drycap sensor, a new capacitive thin-film sensor originally developed for measuring ultra-dry gases in industrial applications. After piloting, the instrument will be further developed according to the feedback gained from the international scientific community. Measurement range of the DRYCAP sensor is from -30 to -90 C frost point temperature. Sensor is operated at a constant temperature above the ambient, meaning that response time is not temperature dependent and there is no need for temperature correction. The on-flight auto-calibration procedure reduces sensor drift. The sensor is protected by the wind and radiation shields. During LAPBIAT the RR01 was flown together with CFH and in dual soundings. Comparison of RR01 frost point data to CFH showed the difference between 1 and 3 C frost point temperature. Twin soundings with two RR01 exhibit excellent repeatability. Isaac Moradi (Dept. of Space Science, Lulea University of Technology, Sweden) gave a talk on application of satellite observations from microwave sensors to evaluate the quality of radiosonde humidity data in the upper troposphere. Microwave and infrared satellite data provide valuable humidity observations in the upper troposphere with global coverage. Satellite IR and microwave data have been compared to radiosondes for many years. Soden and Bretherton (1993) developed a method to retrieve Upper Tropospheric Humidity (UTH) from IR satellite data. This relation was modified by Buehler and John (2005) for satellite data from microwave sensors, especially data from Advanced Microwave Sounding Unit (AMSU-B) and Microwave Humidity Sounder (MHS) sensors. Many studies have shown that satellite and radiosonde UTH are consistent. The talk by Isaac Moradi focused on the two later studies. In the first comparison the radiosonde data from three tropical and one mid-latitude station from the Atmospheric Radiation Measurement (ARM) program dataset were used. Good agreement was found between the two datasets. The satellite data were slightly moister than the radiosonde data, with a mean difference of 1-2.3% RH, depending on the radiosonde site. In the second comparison, which is still ongoing, the AMSU/MHS UTH data was used to evaluate the quality of humidity data from the Integrated Global Radiosonde Archive (IGRA) dataset. Overall assessment of IGRA data showed that some operational radiosonde data had very good accuracy and some showed a large bias. The bias seemed to be regional dependent, but this result still needs more investigation. Kalev Rannat (Tallinn University of Technology) presented retrievals of atmospheric precipitable water using the GPS technique. The water vapor calculations were based on the data from IGS and EUREF GPS-stations, which extend from the Arctic area up to Crete in Greece. Usually the determination of Integrated Precipitable Water Vapor (IPWV) needs a network-linked PC, L1, L2 band GPS-receiver with a well-installed geodetic antenna and appropriate software for geodetic calculations (like Bernese, GAMIT/GLOBK, Gipsy). Some experimental GPS-meteorological stations were installed in Finland and Estonia. The goal is to develop a complementary and cheaper 1-band technique for better coverage of the monitoring area. The IPWV measured by the new experimental receiver were validated by the data from independent measurements. During LAPBIAT the results of GPS-data analysis showed good agreement with the sonde measurements. Several additional short presentations were made. Holger Vömel pointed out that to be a reference GRUAN type of observations must include the measurement uncertainty. The GRUAN analytical approach is threefold: to analyze all sources of uncertainty; to synthesize one uncertainty estimate for each data point and to verify this estimate in comparisons. Evaluation of uncertainty sources for CFH instrument shows that the largest source is controller stability, which depends on PID 4

parameters, electronic controller noise, frost point morphology, mirror clearing signals etc. The morphology of the frost point layer has been investigated using electronic microscope during AquaVit intercomparison campaign. In most soundings the proper clear signals occur before launch increasing measurement uncertainty before second clear signal. Point by point uncertainty, time response and averaging in stratosphere need to be refined. Franz Immler (DWD) showed results from the Lindenberg Upper-Air Method intercomparison (LUAMI). A large number of in-situ and remote sensing instruments were operated in Lindenberg and other sites during the LUAMI. Air-borne lidar WALES was used to inter-compare ground-based lidars at four sites across Europe in one flight. CFH and WALES water vapor agree over the entire troposphere and CFH and FLASH agree between tropopause and 25 km altitude. RS92 correction and uncertainty estimates developed using LUAMI (and other) inter-comparison provides a preliminary GRUAN data product. Johanna Lentonen (Vaisala Oy, Finland) noted that the Vaisala RS-92 radiosonde provides an interface for scientific instruments, which is open for users. The interface parameters such as data bandwidth can be adjusted according to requirements from scientific community. The new Reference Radiosonde based on DRYCAP sensor needs further improvements and comprehensive tests before the start of mass production. The metadata is of great importance for analyzing the results of soundings and intercomparisons. Third session: Friday, 3 September 2010, morning session Session chair: Niklaus Kämpfer Session report: Corinne Straub Brigitte Tschanz (University of Bern) presented integrated water vapor analysis from MIAWARA- C measurements. MIAWARA-C is a campaign instrument for middle atmospheric water vapor profiling from whose spectra integrated water vapor (IWV) can be retrieved as a side product using an empirical formula. The agreement of IWV over Sodankylä in winter 2009/2010 derived from MIAWARA-C was compared to values determined from GPS and radiosonde-measurements. The general agreement between the three techniques is good. But if the comparisons are regarded in more detail, differences between the MIAWARA-C data and the values from the other two techniques become visible, but only on certain days with high liquid water content. The reason for the difference is that MIAWARA-C cannot distinguish between integrated and liquid water in the troposphere. Therefore its IWV measurements are only reliable under dry tropospheric conditions. Corinne Straub (University of Bern) had analyzed middle atmospheric water vapor measured by the microwave radiometer MIAWARA-C. MIAWARA-C was operated in Sodankylä from mid January to mid June 2010. With the present retrieval setup the instrument delivered a time series of daily middle atmospheric water vapor profiles at an altitude range of 35 to 75 km. Outside of this altitude limit, contribution of a-priori information gets substantial. In the end of January MIAWARA-C captured a Stratospheric Sudden Warming event (SSW) visible in a sharp increase in mesospheric water vapor, which can be explained by transport of mid latitudinal air to Polar Regions. Investigations of wave coupling between different atmospheric layers during this SSW event are part of the ongoing research. Martin Brabec (ETH Zürich) presented results from intercomparison of COBALD and Rosen- Kjome Backscatter sonde. The Compact Optical Backscatter Aerosol Detection sonde (COBALD) is a new, compact and light instrument using a similar measurement technique as the Rosen-Kjome (Wyoming) Backscatter sonde from the late 80s, which is not produced anymore. COBALD is designed to detect Aerosols, PSC's and Cirrus clouds and for LIDAR calibrations/intercomparisons. 5

During the LAPBIAT and RECONCILE campaigns COBALD measurements were validated against the Wyoming backscatter sonde, where one of the goals was to find an appropriate calibration scheme for COBALD. The investigation of the calibration scheme is still going on. The first comparisons between the two sondes showed nice agreement in Backscatter ratio up to the PSC layer in the red channel and a slight drift in the blue channel. Within the PSC layer there is a slight offset between the two instruments, which is attributed to the slightly different properties of the sondes, and at high altitudes the COBALD profiles are a little bit noisier than the ones from the Wyoming sonde. Ines Engel (ETH Zürich) reported COBALD polar stratospheric cloud observations in the Arctic winter 2009/2010. During the LAPBIAT and RECONCILE campaign 24 COBALD sondes have been flown (Ny-Alesund 13 and Sodankylä 11) with different matching goals. There were successful time and space matches between COBALD and a LIDAR (MAL) aboard the Geophysica aircraft. The goal of these matches is to observe the evolution of PSC's. The work on this data is in progress. First comparisons with CALIPSO showed that COBALD measures similar structures within PSC's. Detailed model studies will follow to verify/falsify the PSC-classification scheme by CALIPSO. The advantage of COBALD compared to CALIPSO is that it can be flown on the same balloon as a water vapor sonde and therefore structures in the H2O-profile detected by the H2Osonde can be clearly attributed to a PSC. Holger Vömel (DWD) showed CFH hygrometer observations of dehydration in the Arctic Polar vortex. In the first part of the LAPBIAT campaign, at the end of January, there was a long period of very cold temperatures in the stratosphere with clear evidence of PSC (type I and II) with the according dehydration and rehydration events. These events were measured with CFH/FLASH and COBALD in the same payload. The rehydration events are explained with the vertical redistribution of water vapor and the sedimentation of ice particles at a level lower than the PSC layer. Comparisons with MLS show that the satellite also detects most of these events, even if its altitude resolution is poorer than the one of the sondes. Fourth session: Friday, 3 September 2010, afternoon session Session chair: Rigel Kivi Session report: Tina Christensen Sergey Khaykin (Central Aerological Observatory of Roshydromet, Russian Federation) analysed FLASH hygrometer observations of dehydration and rehydration in the Arctic Polar Vortex 2010 from both in situ balloon and air-borne measurements. The cold winter of 2010 was well-monitored by the LAPBIAT balloon campaign and the RECONCILE aircraft campaign. Extremely cold temperatures in the Polar vortex 2010 resulted in: formation of distinct dehydration layer at 20-24 km with H 2 O reduction of up to 1.2 ppmv; formation of rehydration layer at 18-21 km with H 2 O enhancement up to 1.1 ppmv; redistribution of water vapor within 18-24 km with ice particles having sedimented 2 km down. The effect on water vapor was observed during 17-29 January by all operated hygrometers Backward trajectory analysis showed that dehydrated layer observed in H 2 O profiles was formed during 17-20 January period North-East from Scandinavia. FLASH-A, FLASH-B, FISH and CFH instruments demonstrated good inter-consistency and close agreement between the data sets. Leif Backman (FMI) presented a model study for the winter 2009/2010 focusing on water vapor in the Arctic stratosphere. Chemical transport model FinROSE showed a dry bias of 0.5-1.0 ppmv of water vapour profiles compared to MLS, and a wet bias compared with the Sodankylä soundings. FinROSE has PSC parameterization (no microphysics). Dehydration is seen in the models runs, but weaker than what is seen in the satellite data. Also the ozone depletion was studied with FinROSE. 6

Franz Immler (DWD) provided an introduction of Mobile Aerosol Raman Lidar (MARL). The Lidar was built in 1996 and has measured in many locations. It is listed in NDACC as a mobile device. It is now installed at FMI, Sodankylä, for at least one year period. Pekka Verronen (FMI) presented details of Sodankylä Ion Chemistry (SIC) model and FinROSE model. Energetic particle precipitation can create NOx and HOx and thus result in ozone loss. With the FinROSE-ctm and the Sodankylä Ion Chemistry (SIC) model the effect of solar proton events on OH and O3 profiles were studied. Discussion topics included LAPBIAT interaction with other projects, campaigns. Ines Engel and Sergey Khaykin will participate in RECONCILE meeting in November. Slides to be presented may be sent to Sergey. From several sides it was expressed that LAPBIAT is a unique campaign, combining instrument development and geophysical research. It has been very fruitful and collaboration should continue along these lines. For example there will be possibilities related to the metrology research program as noted by Heikki Turtiainen from Vaisala Oy. There were CIMO - campaigns in Mauritius 2005 and recently in China in summer 2010. LAPBIAT database environment is ready and instrument PI:s can start uploading the data. Deadline for data uploads is end of 2010. It was suggested to include README file with contact person(s) and person(s) to be acknowledged. Also information about data level (level 1, level 2, uncertainties) is strongly encouraged. Possible LAPBIAT papers were discussed. The topics include water vapor column density comparisons; PSCs and dehydration processes; analysis of stratospheric warming event; mesospheric water vapor; BKS/COBALD intercomparison; Reference Radiosonde RR01 development; FinROSE model study. It was noted that there will be an ACP special issue for RECONCILE and related projects which may be relevant for some of the LAPBIAT publications. The meeting was closed at 16:00 on Friday, September 3, 2010. 7