Convective weather phenomena, such as summer thunderstorms, result from the rising and sinking of air masses. Their forecasting is generally part of ‘nowcasting’, which means the provision of forecasts for the next few minutes up to two hours ahead. For this purpose, the DWD verifies and analyses a whole set of different input information.
This includes data from the thunderstorm cell detection and tracking systems CellMOS (Cell identification and tracking based on Model Output Statistics) and KONRAD (Konvektionsentwicklung in Radarprodukten); 3D radar data relating to the vertically integrated liquid water content (VIL) in the atmosphere; lightning detection data; data from the precipitation forecasting system RADVOR-OP (Radar-Online-Niederschlagsvorhersage); SYNOP reports (from stations in the surface measurement network) as well as high resolution numerical model data. All these data and systems provide a comprehensive basis for detecting these rapidly developing mesoscale weather phenomena.
In order to be able to efficiently process and exploit the rapidly changing information used for nowcasting, a new pre-processing system called NowCastMIX has been developed. It provides a new categorisation as well as an optimised, consistent warning proposal every five minutes, in particular for summer thunderstorms. It is important for warning services to be able to continuously track thunderstorm movements and issue timely and risk-specific warnings for the regions and areas likely to be affected. To this end, the information from the various tracking systems and the paths of radar signals are combined in the best possible way.
The aim – optimum warning proposals
NowCastMIX uses a fuzzy logic approach, which in this context means that uncertainties and imprecisions of non-specialist descriptions are modelled in order to assess the probability and intensity of accompanying elements such as gale force gusts, hail and heavy precipitation. These are combined to obtain a categorised assessment of the local thunderstorm intensity. A spatial filter is applied to produce an optimum warning proposal offering the greatest ease of use for the meteorologist in the warning unit.
In this form, the system’s outputs constitute an invaluable source of input data for the AutoWARN system currently under development. AutoWARN is designed to combine a most varied range of meteorological information and give the best possible automated support for the issuing of warnings of hazardous weather. The automatically generated warning proposals are constantly checked by a meteorologist and revised if necessary. The manually revised warning proposals are finally transformed into textual and graphical warnings for distribution to customers.
Significant improvement in forecast skill
A quality verification study was conducted for the 2011 convective summer season. The forecasts produced showed high forecast skill and represented a significant improvement when compared directly with persistence forecasts, e.g. forecasts made according to the principle ‘Tomorrow same as today’. This proves that the system provides nowcasting with an invaluable synthesis of available data.
New technology is also being used which represents the vertical liquid water content in the atmosphere, whereby the values given are estimates of local precipitation potentials. VIL helps nowcasting to evaluate the likelihood of hail and detect those areas where heavy precipitation is possible. Rapidly decreasing VIL contents could hint at a collapsing cell and the related strong downdraft wind.
Supercell storms detected
Another feature DWD has explored is the detection of mesocyclones. This method relies on searching Doppler radar wind data for rotation signatures such as those typically associated with the rotating updraft in supercells. Rotations are revealed by strong shear in the wind measured by the radar and can be detected using pattern recognition methods.
The mesocyclone detection algorithm, which includes an upstream quality control, has been in real-time operation since the convective season of 2011 and reports detected mesocyclones together with the level of intensity. A large number of supercells were detected correctly during the past convective season, including the one which had formed on July 13, 2011 in the area north of Munich up to the Bavarian Forest, which caused an F2 tornado in Sautorn-Plattling in the Deggendorf district.
Thanks to their polarisation technology, new radar systems will help to gain an even better understanding of the structure and physics of precipitation processes. In addition to improvements in the quality control of radar data and the quantitative determination of precipitation, the new systems also enable a classification according to precipitation type – rain, hail, snow, sleet – and differentiation from non-meteorological echoes, such as those from birds. This opens up new avenues for better assessing the development of thunderstorm cells and further improvements to nowcasts.
Impacts of climate change on the construction industry – Report 2
The simulations from global and regional climate models show that further warming will continue to be the key feature of climate change until the end of the 21st Century. This will increasingly affect the construction industry. According to current opinion, the warmer climate is expected to lead to changes in the frequency of extreme weather events, with the possibility of more frequent heat waves, heavy rainfalls, winter storms or thunderstorms with hail and gale force gusts. All this will most likely affect existing and future buildings and their construction, as well as the performance and strength of construction materials.
The growing need for adaptation in the construction sector was mentioned in the German Strategy for Adaptation to Climate Change (Deutsche Anpassungsstrategie, DAS) adopted by the Federal Cabinet in December 2008. Specialist products have since been developed to support decision makers and institutions in the construction industry, as well as engineers and architects in their efforts to implement building techniques that are adapted to climate change.
Optimum indoor air quality – minimum energy consumption
The question of how to ensure an acceptable indoor air quality in buildings even at rising outside temperatures will be increasingly important in the future. The main issue here is to create a comfortable environment for people inside the building as well as special indoor conditions which meet the requirements of goods or devices stored and installed there. Taking into account that energy resources are limited and that CO2 emissions must be reduced, both the refurbishment of existing buildings and the planning of future ones must aim for optimum indoor air conditioning while ensuring that as little energy as possible is consumed.
In order to meet this objective, planners and engineers need reliable information on the climate conditions that are typical for the location of the building. Given the changing climate, it is also important to know what the conditions will be like in the future, as buildings are designed to last many decades. So far, appropriate data sets consisting of hourly values of parameters such as air temperature, cloud cover, wind speed and global radiation – referred to by the expert community as test reference years – had been provided by the DWD only on the basis of past measurement and observation data series.
Avoid expensive refurbishment of buildings
On behalf of the Federal Institute for Research on Building, Urban Affairs and Spatial Development (BBSR), the test reference years have now been updated and, for the first time, complemented by a data set which, based on five regional climate models, describes expected developments of the climate until the middle of this century. It is hoped that the new data set will enable planners, engineers and architects to design buildings in a way that their functionality is maintained even under changing climate conditions, avoiding expensive refurbishment projects and excessive energy consumption – and ultimately contributing to climate change mitigation.
Not only the buildings but also their construction are subject to climate/weather related restrictions. Many construction materials such as concrete, mortar, sealants, adhesives or paints can be worked at certain temperatures only. Heavy rainfalls can damage parts already built as moisture might penetrate the structure, or materials might get washed away. In addition to this, adverse weather conditions may also pose a danger to the people working on the site.
Fewer bad weather days
Weather related downtime of construction work often leads to significant additional costs. It is expected that the frequency of such impediments will change as a result of climate change. A study suggests that the key elements of ‘bad weather days’ are frost, heavy rain and snow cover.
On the basis of a model ensemble of 19 regional climate models, the spatial distribution and the number of days on which construction sites are affected by inclement weather was examined. In the lowlands, weather conditions currently affect the work on construction sites an average of 10 to 20 days. Analyses indicate little change for the near future, meaning that at first the number of days on which construction is possible in the year is expected to increase by just a few days almost everywhere in Germany.
Around the end of the century, however, the number of days on which construction is possible is expected to rise significantly. Depending on the region, a decrease of around ten days is foreseen in the number of bad weather days, with the greatest change in the eastern and southern parts of Germany. Downtime days due to too low temperatures will decrease significantly so that presumably the work on building sites will not have to be interrupted as often as before.
Revisiting the Fukushima disaster – Report 3
The German Precautionary Radiation Protection Act (StrVG) stipulates that the responsibility for monitoring air and precipitation for radioactivity and forecasting the dispersion of radioactive substances lies with the Deutscher Wetterdienst. To this end, the DWD operates a Germany-wide network of 48 stations where radioactivity is measured. These observations are complemented by measurements from aircraft if necessary.
For the daily routine operation this means measuring and analysing radioactivity in the air and precipitation on a continuous basis, using various devices at different sites, even when no radioactive incident has been reported. The time intervals for taking air and precipitation samples vary from two hours up to a month.
In the event of an incident resulting in radiological consequences for Germany, the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) orders the start of intensive measurements as laid down by the Precautionary Radiation Protection Act. The frequency of measurements is consequently increased, and data transmitted to the Integrated Measuring and Information System for Environmental Radioactivity Monitoring (IMIS) every two hours. IMIS is operated by the Federal Office for Radiation Protection (BfS) in its role as the federal coordination centre. The BfS is also responsible for publishing the data.
Prepared for crisis
The following exciting sequence of events summarises the period from mid March to mid June, during which we provided measurements and dispersion calculations. Conducting a routine crisis exercise every quarter, the exercise we planned for the first quarter of 2011 was on March 11 – exactly the day Japan was rocked by an earthquake and a tsunami inundated large areas of the north eastern parts of the country, which ultimately caused the nuclear disaster at Fukushima.
From March 12, 2011, there was the risk of radioactivity leaking into the atmosphere. On April 12, 2011 – a month later – the incident was rated as a major nuclear accident, which is the highest level (level 7) on the scale of the International Atomic Energy Agency (IAEA).
While still running the routine exercise on March 11, we immediately raised the measurement frequency in consultation with the BfS and BMU. It was judged, however, that the increase in the radioactivity levels over Germany due to the nuclear accident at Fukushima would be small. Emergency was therefore not declared, but the sampling and measuring intervals were shortened in order to always have the most recent data available.
March 12-15, 2011
On Saturday March 12 we were alerted by the BMU and computed possible dispersions. Our crisis management team came together for its first meeting on March 14.
From March 15 we published an assessment of the ‘Meteorological situation and dispersion conditions in Japan’ on the home page of our website.
This included a relative distribution graphic computed from an assumed emission level, as there was no information available about the actual radiation load at Fukushima that could be used in the calculations. These were performed twice daily, at 00:00 and 12:00 UTC, using our emergency response dispersion model with an assumed source height of 250m.
The results were computed and visualised at six hourly intervals for a forecast period of up to 72 hours ahead. The information presented provided an animated loop showing the dispersion graphics for the next three days, illustrating the direction of where an estimated amount of radioactive emissions would be dispersed depending on the prevailing weather conditions and how they would be diluted over time.
Based on the relative concentration and dispersion forecasts, the morning and afternoon reports provided information on the weather situation in Japan and the resulting dispersion conditions in German and in English.
Considering the dispersion forecasts, our meteorologists estimated that radioactive air from Fukushima could arrive in Germany in about ten days.
March 21, 2011
From this date air samples taken at Offenbach showed an increased activity concentration of xenon-133. The levels recorded are up to a hundredfold higher than normal xenon-133 activity. Despite this, the resulting dose didn’t pose a health risk.
The isotope xenon-133 is a nuclear fission product of uranium-235 or plutonium-239. It is a noble gas, which on its way through the atmosphere is not washed out by rain. Xenon-133 is rapidly transported over long distances and therefore helps in the detection of released radioactivity at an early stage. Xenon-133 has a half-life of just five days, which means that this isotope is detectable for a short time only. After an estimated transport time of ten days, only about a quarter of the original xenon-133 activity was left to be measured.
March 23, 2011
Together with the Corporation for Airborne Target Representation (GFD), we carried out a measurement flight using a Learjet. On this flight the jet was accompanied in close formation by the research aircraft Falcon of the German Aerospace Center (DLR). No increased radioactivity concentrations were measured over Germany during this first measurement flight.
March 24, 2011
From this day, the air filters of our high volume samplers recorded increased values of iodine-131, caesium-137 and caesium-134.
The measurement of the radioactive iodine and caesium nuclides was of particular importance, as these are easily absorbed by the human body and thus have great physiological effects in the long term. The particle concentrations were increased, yet still at a level which posed no health risk to people.
Significantly increased activity concentrations were recorded from March 26 to April 1, 2011 and from April 5-10, 2011.
March 30, 2011
We took a second aircraft measurement. From this day on, increased iodine-131 activity was also observed in precipitation samples, varying at levels between the limit of detection and about 3.3 Bq/l. Apart from iodine-131, there was no trace of any other radioactive element in the precipitation.
The analysis of the air samples at the central laboratory in Offenbach showed increased concentrations of iodine-131. The measurements taken by the aircraft were within the range of values resulting from the air samples taken on the ground.
June 14, 2011 onwards
Our measurements showed no further irregularities. The frequency of measurements was reduced back to routine operation.
Large interest from Japan
Immediately after we had conveyed all measurement results to the relevant authorities, the data were published on our home page and the access numbers spoke for themselves: in April alone, the dispersion calculations were accessed more than four million times from Japanese servers, and even in May, the number of accesses from Japan was still at about 3.5 million. Even when the service stopped at the end of July, a total of close to two million accesses were recorded. In addition, nearly 9,000 emails, mainly from people in Japan, asked for the publication of data to be continued.
Virtually everyone is interested in the weather and virtually every area of our lives is affected by weather and climate. As the reference for meteorology in Germany, the Deutscher Wetterdienst (DWD) is the competent contact point not only for all the issues discussed above. The range of tasks is many and varied. It records, analyses and monitors the physical and chemical processes in our atmosphere. It holds information on all meteorological occurrences, offers a diverse range of services both for the general public and for special user groups, and operates the national climate archive.
In its role as a national meteorological service, the DWD is also a provider of scientific and technical services and a competent and reliable partner for public and private associates in the field of meteorology. The increasing demands of its customers not only oblige the DWD to supply high quality products and services, but also are a continuous incentive to improve product quality, customer orientation, and profitability.
In the Fukushima based work cited above, both the dispersion forecasts and the measurements taken by the DWD were at the highest technical and scientific levels. The high sensitivity of the measuring instruments made it possible to detect increased activity concentrations for the particles in air and precipitation samples.
Published: 27th Nov 2012 in AWE International