De Bilt, Netherlands

The Royal Netherlands Meteorological Institute is the Dutch national weather forecasting service, which has its headquarters in De Bilt, in the province of Utrecht, Netherlands.The primary tasks of KNMI are weather forecasting, monitoring of climate changes and monitoring seismic activity. KNMI is also the national research and information centre for climate, climate change and seismology. Wikipedia.

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News Article | April 17, 2017

Meteorologists have long struggled to forecast storms and flooding at the level of streets and neighborhoods, but they may soon make headway thanks to the spread of mobile-phone networks. This strategy relies on the physics of how water scatters and absorbs microwaves. In 2006, researchers demonstrated that they could estimate how much precipitation was falling in an area by comparing changes in the signal strength between communication towers1. Accessing the commercial signals of mobile-phone companies was a major stumbling block for researchers, however, and the field progressed slowly. That is changing now, enabling experiments across Europe and Africa. The technology now appears ready for primetime. It could lead to more precise flood warnings — and more accurate storm predictions if the new data are integrated into modern weather forecasting models. Proponents also hope to use this approach to expand modern weather services in developing countries. The newest entry into this field is ClimaCell, a start-up company in Boston, Massachusetts, that launched on 2 April. The 12-person firm says that it can integrate data from microwave signals and other weather observations to create more accurate short-term forecasts. It notes it can provide high-resolution, street-level weather forecasts three hours ahead, and will aim to provide a six-hour forecast within six months. The company has yet to make information on its system public or publish it in peer-reviewed journals. ClimaCell will start in the United States and other developed countries, but plans to move into developing countries including India later this year. “The signals are everywhere, so basically we want to cover the world,” says Shimon Elkabetz, ClimaCell’s chief executive and co-founder. But the fledgling company faces competition from researchers in Europe and Israel who have tested systems at multiple scales, including countries and cities, over the past several years. The scientists recently formed a consortium to advance the technology using open-source software. Coordinated by Aart Overeem, a hydrometeorologist at the Royal Netherlands Meteorological Institute in De Bilt, the group is seeking nearly €5 million (US$5.3 million) from the European Commission to create a prototype rainfall-monitoring system that could eventually be set up across Europe and Africa. “There is a lot of evidence that this technology works, but we still need to test it in more regions with large data sets and different networks,” Overeem says. Although ClimaCell has made bold claims about its programme, Overeem says he cannot properly review the company's technology without access to more data. “The fact that a start-up company and commercial investors are willing to put money into this technology is good news, but I believe there is room for all,” says Hagit Messer, an electrical engineer at Tel Aviv University in Israel, who led the 2006 study. She is part of the research consortium led by Overeem. Previous projects by members of the consortium that tested the technology have met with success. In 2012, for instance, Overeem and his colleagues showed that the technology could be applied at the country level using commercial microwave data in the Netherlands2. And in 2015, the Swedish Meteorological and Hydrological Institute (SMHI), headquartered in Norrköping, launched a prototype real-time ‘microweather’ project in Gothenburg. It collects around 6 million measurements in the city each day in partnership with the telecommunications company Ericsson and a cellular tower operator. The result is a minute-by-minute estimate of rainfall on a 500-metre-resolution map that encompasses the city. Jafet Andersson, an SMHI hydrologist, says that the project has helped to advance the technology. For example, he notes that microwave data often overestimate rainfall by as much as 200–300%. But the team has worked out how to correct for that bias without relying on reference measurements from rain gauges or ground-based radar. This will make it easier to extend the technology to developing countries. “It will take some time, but we are in the process of industrializing it on a country scale, or even a global scale,” Andersson says. Researchers with the consortium have deployed the technique in African countries that do not have access to ground-based radar and extensive rain-gauge networks. A team led by Marielle Gosset, a hydrologist at the French Institute for Development Research in Toulouse, demonstrated a proof-of-concept system in Burkina Faso3 in 2012 and has since branched out to other countries including Niger. Working with French telecoms giant Orange, and with funding from the World Bank and the United Nations, her team hopes to expand into Morocco and begin using real-time microwave data in Cameroon this year. The technology is attracting interest in Africa because conventional weather-monitoring systems such as radar are too expensive, Gosset says. Weather forecasts based on microwave signals give developing countries a similar system, but for less money, she says. Access to commercial data is getting easier, too. Researchers say that telecommunication companies are beginning to see the value of releasing the data, and the consortium plans to create a central repository for processing the information. Project scientists hope to create a model that will enable a smooth partnership with the industry. “I think that this door is just about to open,” says Andersson.

News Article | October 26, 2016

A diagram lost for more than 350 years documents a spectacular sky of 1630. Around midday on 24 January 1630, seven suns seemed to blaze over Rome. Many onlookers took the phenomenon as a celestial omen of good or ill fortune, but an adherent of the scientific revolution also took note of the kaleidoscopic sky. Jesuit scholar Christoph Scheiner recorded the phenomenon, along with a similar one seen ten months earlier. His work helped to inspire seventeenth-century Dutch astronomer and philosopher Christiaan Huygens to develop the first theories of how such 'halo effects' might arise naturally, but the 1630 diagram was thought to have been lost. A librarian in Germany has now uncovered what seems to be a copy of the picture, and reports the find in Applied Optics1. Halo effects are caused by particles of ice in the atmosphere refracting and reflecting light, and they often manifest as rings, circles or arcs around the Sun or Moon. Sometimes 'mock suns' known as parhelia appear at certain points along the rings. This is what Scheiner recorded in 1629 and 1630, although he didn't know the cause. Scheiner's letters and diagrams depicting the halos passed among his contemporaries for interpretation, influencing luminaries such as French philosopher and mathematician René Descartes to try to explain similar atmospheric phenomena. But the originals of both diagrams had vanished by 1658, when Huygens came to the subject. He worked from a book by French astronomer Pierre Gassendi, which included a copy of the 1629 diagram and a written description of the 1630 display. Huygens drew his own reconstruction of the 1630 diagram. For centuries, Huygens's reconstruction was the earliest known diagram of the 1630 halos. In the 1890s, an original print of Scheiner's picture surfaced at the Munich University Library in Germany — only to be destroyed when bombs hit the building in 1943. But earlier this year, Eva Seidenfaden, scientific librarian at the Trier Municipal Library in Germany, was browsing the digitized collection of Herzog August Library in Wolfenbüttel, Germany, when she spotted an intriguing halo diagram in the Herzog archives. She recognized the picture's Latin caption from her research into the subject2 with Walter Tape, a retired mathematician at the University of Alaska Fairbanks, and Günther Können, former head of climate analysis at the Royal Netherlands Meteorological Institute in De Bilt. Seidenfaden alerted Tape, who used the surviving Munich University Library records to confirm that it was a copy of the same diagram. The find "was a stunning surprise", says Tape. Fokko Jan Dijksterhuis, a historian of science at the University of Twente in the Netherlands, says that the diagram is particularly interesting "because it concerns one of the first well recorded observations of halos. Consequently it adds not only to our historical knowledge, but also to our scientific body of knowledge". He compares it to finding old astronomical or meteorological data, crucial for reconstructing the past. Making a preliminary comparison between the Scheiner and Huygens diagrams, Können says, "The halo displays on the two diagrams are very close — there are no halos in the original that are missed in Huygens's reconstruction." This is not so surprising, he adds, given that Scheiner was meticulous in his description. In her announcement of the find1, Seidenfaden proposes that more of Scheiner's work might be uncovered by tracing how the diagram made its way to the Herzog library. She says that there is even a possibility, albeit remote, that further investigation might turn up a draft of Scheiner's own interpretation of his observations.

Bintanja R.,Royal Netherlands Meteorological Institute | Van Oldenborgh G.J.,Royal Netherlands Meteorological Institute | Drijfhout S.S.,Royal Netherlands Meteorological Institute | Wouters B.,Royal Netherlands Meteorological Institute | Katsman C.A.,Royal Netherlands Meteorological Institute
Nature Geoscience | Year: 2013

Changes in sea ice significantly modulate climate change because of its high reflective and strong insulating nature. In contrast to Arctic sea ice, sea ice surrounding Antarctica has expanded, with record extent in 2010. This ice expansion has previously been attributed to dynamical atmospheric changes that induce atmospheric cooling. Here we show that accelerated basal melting of Antarctic ice shelves is likely to have contributed significantly to sea-ice expansion. Specifically, we present observations indicating that melt water from Antarctica's ice shelves accumulates in a cool and fresh surface layer that shields the surface ocean from the warmer deeper waters that are melting the ice shelves. Simulating these processes in a coupled climate model we find that cool and fresh surface water from ice-shelf melt indeed leads to expanding sea ice in austral autumn and winter. This powerful negative feedback counteracts Southern Hemispheric atmospheric warming. Although changes in atmospheric dynamics most likely govern regional sea-ice trends, our analyses indicate that the overall sea-ice trend is dominated by increased ice-shelf melt. We suggest that cool sea surface temperatures around Antarctica could offset projected snowfall increases in Antarctica, with implications for estimates of future sea-level rise.

De Haan S.,Royal Netherlands Meteorological Institute
Journal of Geophysical Research: Atmospheres | Year: 2011

Wind, temperature, and humidity observations from radiosonde and aircraft are the main sources of upper air information for meteorology. For mesoscale meteorology, the horizontal coverage of radiosondes is too sparse. Aircraft observations through Aircraft Meteorological Data Relay (AMDAR) sample an atmospheric profile in the vicinity of airports. However, not all aircraft are equipped with AMDAR or have the system activated. Observations inferred from an enhanced tracking and ranging (TAR) air traffic control radar can fill this gap. These radars follows all aircraft in the airspace visible to the radar for air traffic management. The TAR radar at Schiphol airport in Netherlands has a range of 270 km. This Mode-S radar contacts each aircraft every 4 s on which the transponder in the aircraft responds with a message that contains information on flight level, direction, and speed. Combined with the ground track of an aircraft, meteorological information on temperature and wind can be inferred from this information. Because all aircraft are required to respond to the TAR radar, the data volume is extremely large, being around 1.5 million observations per day. Note that there are no extra costs for this data link. The quality of these observations is assessed by comparison to numerical weather prediction (NWP) model information, AMDAR observations, and radiosonde observations. A preprocessing step is applied to enhance the quality of wind and temperature observations, albeit with a reduced time frequency of one observation of horizontal wind vector and temperature per aircraft per minute. Nevertheless, the number of observations per day is still very large. In this paper it is shown that temperature observations from Mode-S, even after corrections, are not very good; an RMS which is twice as large as AMDAR is observed when compared to NWP. In contrast to the temperature observations, the quality found for wind after correction and calibration is good; it is comparable to AMDAR, slightly worse than radiosonde but certainly very valuable for mesoscale NWP. Copyright 2011 by the American Geophysical Union.

Schneider P.,Norwegian Institute For Air Research | Van Der A R.J.,Royal Netherlands Meteorological Institute
Journal of Geophysical Research: Atmospheres | Year: 2012

A global nine-year archive of monthly tropospheric NO2 data acquired by the SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) instrument was analyzed with respect to trends between August 2002 and August 2011. In the past, similar studies relied on combining data from multiple sensors; however, the length of the SCIAMACHY data set now for the first time allows utilization of a consistent time series from just a single sensor for mapping NO2 trends at comparatively high horizontal resolution (0.25). This study provides an updated analysis of global patterns in NO2 trends and finds that previously reported decreases in tropospheric NO2 over Europe and the United States as well as strong increases over China and several megacities in Asia have continued in recent years. Positive trends of up to 4.05 (0.41) × 1015 molecules cm-2 yr-1 and up to 19.7 (1.9) % yr-1 were found over China, with the regional mean trend being 7.3 (3.1) % yr -1. The megacity with the most rapid relative increase was found to be Dhaka in Bangladesh. Subsequently focusing on Europe, the study further analyzes trends by country and finds significantly decreasing trends for seven countries ranging from -3.0 (1.6) % yr-1 to -4.5 (2.3) % yr -1. A comparison of the satellite data with station data indicates that the trends derived from both sources show substantial differences on the station scale, i.e., when comparing a station trend directly with the equivalent satellite-derived trend at the same location, but provide quite similar large-scale spatial patterns. Finally, the SCIAMACHY-derived NO2 trends are compared with equivalent trends in NO2 concentration computed using the Co-operative Programme for Monitoring and Evaluation of the Long-range Transmission of Air Pollutants in Europe (EMEP) model. The results show that the spatial patterns in trends computed from both data sources mostly agree in Central and Western Europe, whereas substantial differences are found in Eastern Europe.

Van der Veen S.H.,Royal Netherlands Meteorological Institute
Monthly Weather Review | Year: 2013

The cloud mask of the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) is a nowcasting Satellite Application Facility (SAF) that is used to improve initial cloudiness in the High-Resolution Limited-Area Model (HIRLAM). This cloud mask is based on images from the Meteorological Satellite (Meteosat) Second Generation (MSG) satellite. The quality of the SAF cloud mask appeared to be better than initial HIRLAM clouds in 84% of the cases. Forecasts have been performed for about a week in each of the four seasons during 2009 and 2010. Better initial clouds in HIRLAMalways lead to better cloud predictions. Verification of forecasts showed that the positive impact is still present after 24 h in 59% of the cases. This is remarkable, because initial dynamics was kept unchanged. The magnitude of the positive impact on cloud predictions is more or less proportional to the initial cloud improvement, and it decreases with forecast length. Also, forecast 2-m temperatures are affected by initial clouds. The generally positive bias of the 2-m temperature errors becomes a few tenths of a degree larger during the night but it decreases a comparable amount during daylight, because MSG tends to increase the cloud amounts in HIRLAM. The standard deviation of the errors often improves slightly in the first part of the forecast, indicating that forecast temperatures correlate better with observations whenMSGis used for initialization. For longer lead times, however, standard deviations deteriorate a few tenths of a degree in seven of the eight verification periods, which all had a length of about a week. © 2013 American Meteorological Society.

The response of the tropical atmosphere to a collapse of the thermohaline circulation (THC) is investigated by comparing two 5-member ensemble runs with a coupled climate model (CCM), the difference being that in one ensemble a hosing experiment was performed. An extension of the Held-Hou-Lindzen model for the Hadley circulation is developed to interpret the results. The forcing associated with a THC collapse is qualitatively similar to, but smaller in amplitude than, the solstitial shift from boreal summer to winter. This forcing results from reduced ocean heat transport creating an anomalous cross-equatorial SST gradient. The small amplitude of the forcing makes it possible to arrive at analytical expressions using standard perturbation theory. The theory predicts the latitudinal shift between the Northern Hemisphere (NH) and Southern Hemisphere (SH) Hadley cells, and the relative strength of the anomalous cross-equatorial Hadley cell compared to the solstitial cell. The poleward extent of the Hadley cells is controlled by other physics. In the NH the Hadley cell contracts, while zonal velocities increase and the subtropical jet shifts equatorward, whereas in the SH cell the opposite occurs. This behavior can be explained by assuming that the poleward extent of the Hadley cell is determined by baroclinic instability: it scales with the inverse of the isentropic slopes. Both theory and CCM results indicate that a THC collapse and changes in tropical circulation do not act in competition, as a possible explanation for abrupt climate change; they act in concert. © 2010 American Meteorological Society.

De Haan S.,Royal Netherlands Meteorological Institute
Quarterly Journal of the Royal Meteorological Society | Year: 2013

Wind, humidity and temperature observations from aircraft and radiosondes are generally used to find the best initial state of the atmosphere for numerical weather prediction (NWP). To be of use for very-short-range numerical weather forecasting (or numerical nowcasting), these observations need to be available within several minutes after observation time. Radiosondes have a typically observation latency of over 30 min and arrive too late for numerical nowcasting. Zenith Total Delay (ZTD) observations obtained from a ground-based network of Global Navigation Satellite System (GNSS) receivers can fill this gap of lacking rapid humidity information. ZTD contains information on the total amount of water vapour. Other rapidly available observations, such as radial wind estimates from Doppler weather radars, can also be exploited. Both observations are available with a delay of less than 5 min with adequate spatial resolution. In this article, the impact of assimilation of these humidity and wind observations in a very-short-range regional forecast model is assessed over a four-month summer period and a six-week winter period. As a reference for the impact, GNSS observations are also assimilated in a three-hourly NWP scheme with longer observation cut-off times. The quality of the forecasts is evaluated against radiosonde observations, radar radial wind and hourly precipitation observations. Assimilation of both GNSS ZTD and radar radial winds resulted in a positive impact on humidity, rainfall and wind forecasts. © 2013 Royal Meteorological Society.

News Article | August 22, 2016

Detecting turbulence remains the Achilles' heel of modern-day aviation. The reports submitted by pilots, subjective and often very inaccurate, are the least expensive and the most frequently used method for trying to predict where it will occur. Scientists from the Faculty of Physics, University of Warsaw, have demonstrated that turbulence can be detected in a much faster and more precise way, using data already routinely broadcast by the aircraft operated by commercial airlines. Anyone who has experienced turbulence on an airplane certainly knows that it's no fun ride. Despite advancements in technology, methods used to detect these dangerous atmospheric phenomena are still far from perfect. However, there is every indication that data allowing pilots to avoid turbulence and even to forecast such occurrences are already being routinely recorded. In fact, this has been done for many years! Jacek Kopec, a doctoral student at the Faculty of Physics, University of Warsaw, and a member of the staff of the University's Interdisciplinary Center for Mathematical and Computational Modelling (ICM), has managed to extract this valuable information from the flight parameters routinely broadcast by the transponders installed in most of the modern commercial aircraft. This new method for detecting turbulence is so original and potentially easy to implement on a large scale that the article describing it has been featured in the "highlight articles" section of the journal Atmospheric Measurement Techniques. "Today's commercial aircraft fly at altitudes of 10 to 15 km, where the temperatures fall to -60 °C. Conditions for measuring atmospheric parameters are very difficult, which explains why such measurements are not taken systematically or extensively. A lack of sufficiently accurate and up-to-date information not only exposes aircraft and their passengers to danger, it also restricts the development of theories and tools for forecasting turbulence," Jacek Kopec says. At present, pilot reports (PIREPs), relayed by radio and provided to pilots of other aircraft by air traffic controllers, are a basic source of turbulence data. Since these reports are based on the subjective opinions of pilots, the data collected in this way are often marred by substantial inaccuracies as to both the area of turbulence and its intensity. More accurate readings are provided by aircrafts involved in the Aircraft Meteorological Data Relay (AMDAR) program. This method is nonetheless costly, so data collected at cruising altitudes are transmitted relatively rarely. In practice, this prevents such reports from being used to detect and forecast turbulence. Passenger aircraft are fitted with sensors that record a variety of flight parameters. Unfortunately, most of the data are not made publicly available. Publicly available reports include only the most basic parameters such as the position of the aircraft (ADS-B transmissions, which are also used by the popular website FlightRadar24) or its speed relative to the ground and the air (Mode-S data). Meanwhile, detecting turbulence requires knowledge of the vertical acceleration of aircraft. "Vertical accelerations are especially strongly felt both by the passengers and by the aircraft," Jacek Kopec explains. "Unfortunately, there is no access to materials regarding vertical accelerations. That was why we decided to check if we could extract such data from other flight parameters, accessible in Mode-S and ADS-B transmissions. The research aircraft in a project in which I participated was fitted with a suitable transponder, so we took advantage of that fact. By coincidence, our coauthor, Siebren de Haan from the Royal Netherlands Meteorological Institute, recorded the transmissions received from the transponder," he adds. Scientists from the Faculty of Physics tested three algorithms of turbulence detection. The first relied on information about the position of aircraft (ADS-B transmissions). However, preliminary tests and their comparison against the parameters registered in the same area by the research aircraft failed to produce satisfactory results. As for the remaining two algorithms, each of them used, though in somewhat different ways, the parameters received approximately every four seconds through Mode-S transmissions. In the second approach, the parameters were analyzed using the standard theory of turbulence. In the third approach, the scientists adapted a method for determining turbulence intensity previously used to measure turbulence on a very small scale in the understory of forests. It turned out that once wind velocity in the vicinity of the aircraft was determined and its changes were analyzed in successive readings, it was possible to use the latter two theoretical approaches to locate turbulence areas with an error of only 20 km. Passenger aircraft need around 100 seconds to travel this distance, so this level of accuracy would allow pilots to maneuver their aircraft to effectively avoid turbulence. By harnessing existing data, this system of turbulence detection developed at the Institute of Geophysics (Faculty of Physics, University of Warsaw) therefore requires no significant investments in aviation infrastructure. In order to be operational, the system needs adequate software and a computer connected in a simple way to the devices that receive Mode-S transmissions from the transponders on board aircraft. Such devices are standard equipment in air traffic control institutions in Europe. In this system, passenger aircraft act as sensors by creating a dense network of measurement points above Europe. "In the coming months, we will be working to improve the software. Nevertheless, we have already achieved our most important goal: we have proved that the method for detecting turbulence we have proposed really works and can provide pilots with information enabling them to avoid dangerous areas in the atmosphere. Turbulence detection will also help improve aviation forecasting methods," stresses Prof. Szymon Malinowski from the Faculty of Physics, Jacek Kopec's doctoral dissertation advisor and one of the authors of the publication. The turbulence detection system has been developed under a grant from Poland's National Science Center (NCN). Data for the research was collected in a flight test campaign financed from the Seventh Framework Programme of the European Union.

News Article | September 8, 2016

Human-caused climate change likely doubled the chances of the torrential rains that caused deadly flooding in Louisiana and damaged 60,000 homes in the state, a new study has found. Less than a month after the deluge that killed 13 people, a team of scientists have just published an analysis of rainfall records going back to the 1930s alongside computer model simulations. Lead author of the study Dr. Karin van der Wiel, a research associate at both Princeton University and the National Oceanic and Atmospheric Administration, said the extra greenhouse gases in the atmosphere had now “changed the odds” for Louisiana being hit by torrential downpours. Compared to the year 1900, the model analysis had clearly shown that the extra greenhouse gases in the atmosphere had increased the chances of a torrential downpour in that Gulf Coast region. Van der Wiel told DeSmog, “The odds for a comparable event have now changed by at least 40 per cent, and our best estimate is a doubling. That is because of the increases in greenhouse gases.” The study has been published in the European Geophysical Union’s journal Hydrology and Earth System Sciences and will now go through an open peer review process, meaning the conclusions could change. Rain started falling in central parts of Louisiana around August 10, with areas around Baton Rouge among the hardest hit. The area of Watson registered more than 31 inches of rain in one day. The Red Cross, which said its own relief efforts would cost $30 million, described the floods as the worst natural disaster in the U.S. since Hurricane Sandy in 2012. Thousands of Louisiana families were evacuated, tens of thousands of homes were flooded, and more than $100 million-worth of crops were ruined. In the study, the research team analyzed rainfall records and found that last month’s Louisiana event was likely a 1-in-550 year downpour. The chances of a similar storm unfolding anywhere in the central Gulf Coast area was now one-in-30 years. Van der Wiel said the best way to understand the role of climate change on extreme weather was to ask how greenhouse gas emissions were altering the chances of events happening. “Climate change has changed the odds of us getting an event like this,” she said. To gauge the role of greenhouse gases in the rainfall, the researchers took data from global climate modelling carried out at NOAA’s Geophysical Fluid Dynamics Laboratory. The team, part of the World Weather Attribution (WWA) project, compared the results from models that included the extra greenhouse gases now in the atmosphere to models that ran without the human influence. Dr Geert Jan van Oldenborgh, of the Royal Netherlands Meteorological Institute and a co-author of the analysis, said, “This was by far the hardest, fast attribution study we have done, given all the different small-scale weather types that cause precipitation in the region.” “It was encouraging to find that our multi-model methods worked even for such a complicated case.” The WWA team used similar methods to work out the role of greenhouse gas emissions in the devastating coral bleaching on Australia’s Great Barrier Reef in late 2015 and early 2016. That analysis found the record warm conditions that caused the bleaching were now 175 times more likely to occur because of the extra greenhouse gases in the atmosphere.

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