The weather balloons measure to what height the heat in the city differs measurably from the temperatures outside the city, also known as the 'urban heat island'. Measurements of the urban climate are normally carried out from the ground, via weathers stations on street level or on building roofs. Releasing weather balloons in the city is unique. The last time vertical observations in the urban environment were collected was by helicopter, more than 50 years ago in New York. Then a helicopter was used for this purpose.
“In the scientific literature this 50 year old research is still used as the point of reference. With these measurements we are going to write a piece of Amsterdam history in the meteorological field”
The main goal of the researchers is to find out to what height the urban heat island extends. Parallel to the measurements above the Amsterdam city centre, measurements are also taken from a rural area just outside Amsterdam. The researchers aim to identify the crossover point: the altitude in the atmosphere at which the city's heat island is no longer noticeable and the temperature is equal to the temperature of the rural area. This research adds these vertical measurements to the observations of the weather stations in the city, in order to create a better understanding of the urban weather model.
Why is understanding the urban climate important?
As a result of climate change, heat is causing more and more pressure on cities. In addition, due to the ever increasing urbanization, a growing number of inhabitants of these cities are exposed to the impact of this heat. In the city, heat is trapped in stones, roads and buildings, and the city itself produces a lot of heat.
“It is often underestimated how much impact heat stress has on, for example, the vitality and productivity of inhabitants. Understanding the urban climate and the predictability of a city's weather profile is therefore becoming increasingly important”
Program Developer Climate Resilient Cities
The urban heat research on the Dam
The weather balloons are launched every two hours from Dam Square in Amsterdam. In the atmosphere the weather balloons will grow to a diameter of two metres. The measurements start Tuesday evening after sunset and continue for 24 hours until Wednesday after sunset. The balloons measure temperature, humidity, wind speed and direction. A measurement is registered every two seconds. The measurements are recorded up to an altitude of 2.5 kilometres.
From the observations of the balloons it can be derived what the thickness of the so called mixing layer is. This is the lowest layer of the atmosphere and the height to which the influence of everything that happens on the surface is noticeable, such as heat and air pollution. Above that, the free atmosphere begins.
“The mixing layer is thicker during hot days and provides a kind of lid on the city. As a result, air pollution remains trapped in the city longer on summer days and this has an impact on the health of residents”
Also wind speed will be measured
In addition to releasing the weather balloons from the Dam Square, a SODAR device is placed on the roof of the home location of AMS Institute at Marineterrein Amsterdam to measure wind speed. In cities, wind is often blocked by the concentration of buildings and their height. Wind and wind variations are vital at high temperatures to ensure pleasant cooling, but also to spread air pollution more quickly.
The SODAR will send out sound waves and listens to reflections that come back as a result of temperature variations in the atmosphere. Every 10 to 30 minutes, the SODAR measures the wind speed of the atmosphere in blocks of approximately 10 metres up to an altitude of around 200 metres.
When will the results of the research activities be available?
The results of the two research methods (weather balloons and SODAR) will be used in addition to the collaborative research project Amsterdam Atmospheric Monitoring Supersite (AAMS). This project monitors the horizontal weather profile of the city using 25 measuring stations. The research results will be incorporated in a data visualization developed by design agency Clever°Franke. The visualization will be launched at the beginning of September. In addition, the Wageningen researchers are preparing a scientific publication that can be used to improve the urban climate of cities worldwide.
In the news
The measurements on Dam Square created a buzz in the Dutch media. Selection of items: