KITcube is the highly sophisticated, integrated atmospheric observation system of the Institute for Meteorology and Climate Research, Troposphere Research Division (IMK-TRO). KITcube consists of a mobile system for worldwide deployment and a stationary observatory for continuous monitoring.

The mobile KITcube combines high-resolution measurements of scanning remote sensing systems (e.g. wind lidar, X-band precipitation radar, humidity and temperature profilers, sun photometers, water vapour and cloud camera systems, and many more) with classical in situ instruments on measurement masts and on weather balloons (local measurements). Fully coordinated scans of the systems make the KITcube a very well suited observation system for studies of thunderstorms, atmospheric convection, clouds and precipitation. The mobile KITcube main site during the Swabian MOSES measurement campaign is located in Rottenburg am Neckar, the X-band precipitation radar is installed in Nürtingen.

The stationary KITcube at KIT Campus North in Eggenstein-Leopoldshafen north of Karlsruhe consists, among other things, of the 200 meters high meteorology mast, which has been measuring air temperature, humidity, wind and turbulence in continuous operation since 1972, and a modern C-band precipitation radar. The stationary KITcube is part of the AERONET measurement network, providing data for the station "Karlsruhe". The mobile KITcube can be used as additional temporary station during measurement campaigns such as Swabian MOSES ("KITcube_Rottenburg"). Thus, both contribute to a worldwide database of aerosol and radiation measurements.

Aerosol Lidar

With an aerosol lidar (Light Detecting and Ranging) the spatial distribution of aerosol particles and droplets in the atmosphere can be measured contactless. This is achieved by tracking the backscattered radiation of a laser over distances of several kilometres, using a telescope-like device.

During the Swabian MOSES measurement campaign, a slewable Raman lidar is used, which can measure aerosol particles and cloud base over distances of 6-15 kilometres. The device emits an invisible laser beam (wavelength: 355 nm) whose photons are scattered by aerosol particles and cloud droplets. A 20-centimeter telescope is used to receive the backscatter signal. The laser beam and telescope can be swivelled to determine the spatial distribution of aerosol particles. Polarization of the backscattered laser light provides information about the shape of the particles.

Compared to ground-based measurements (see below), the information obtained with lidar measurements shows the vertical structure of particle distributions, the transport direction of aerosol clouds, cloud base and the extent of the well-mixed atmospheric layer above ground.

In situ aerosol meters

Condensation particle counters (CPC) can be used to reliably determine the number of aerosol particles larger than three nanometers (billionths of a meter) at a specific site (in situ). Aerosol particles are placed in a container saturated with alcohol or water, by condensation the particles increase in diameter such that they can be detected via light scattering.

Two methods are used to determine the size of the aerosol particles (see photo):

1. With a scanning mobility particle sizer (SMPS) aerosol particles can be selected according to their electrical mobility. Subsequently the particles are counted by a condensation particle counter (CPC). This works for particles in the size range of approx. 8-1200 nanometers.
2. An optical particle counter (OPC) measures the light scattered from individual aerosol particles. Using scattered light pulses, the size distribution of the particles can be calculated. This works for particles in the size range of approx. 300 nanometres to 40 micrometres (millionths of a metre).

Mobile cloud chamber PINE

PINE (Portable Ice Nucleation Experiment) is a mobile cloud chamber for the investigation of ice nucleating particles (INPs), which are relevant for ice crystal formation in mixed phase clouds (temperature range -10°C to -35°C, water saturated conditions) and cirrus clouds (temperature range -35°C to -60°C, water saturated conditions). An optical particle counter (fidas-pine, Palas GmbH, Karlsruhe) installed downstream in the chamber can detenct the forming ice crystals (the INPs) due to their larger diameter compared to cloud droplets and non-activated aerosol particles. This allows the determination of a temperature-dependent INP concentration. Further information.

Authors: Dr. Harald Saathoff, Dr. Ottmar Möhler, IMK-AAF

Balloon soundings in the atmosphere

The higher atmospheric layers can be measured best with helium-filled weather balloons. Various instruments can be attached to the balloons, which measure various parameters as the balloon ascends (and also as it sinks later on). Depending on their size, the balloons rise to an altitude of 20 to 35 kilometres and thus fly much higher than most aircraft. The balloon sonde ascends until its balloon bursts, then the descent begins during which a parachute is often used used to slow down the sonde. This prevents damage, but also allows measurements under controlled conditions during the descent.

In the simplest case, a so-called radiosonde is attached to a weather balloon. It measures temperature, humidity, air pressure and the spatial position (GPS) and sends the information via radio to a ground station. In addition to the radiosonde, further instruments can be attached to the weather balloon. These include e.g. an ozone instrument, which can be used for measuring the stratospheric ozone layer, or a precise hygrometer, which can be used to accurately determine vapour concentrations at the transition zone from troposphere to stratosphere (tropopause) at an altitude of about 12 kilometres, where water vapor concentrations are especially low. Depending on the specific situation, a particle measuring instrument is used to precisely locate cloud droplets, ice crystals or dust particles in the atmosphere.

Another method for measurements from a weather balloon, used during the Swabian MOSES measurement campaign, is based on so-called AirCores (see research objectives). This can be compared to the principle of an ice core, but instead of ice, air collected with a very long and thin tube is used. This tube fills with ambient air from the stratosphere and the troposphere below as the balloon descends. After landing, the special tube is collected and the air inside is analysed in a laboratory for various trace gases such as carbon dioxide (CO₂), carbon monoxide (CO) or methane (CH4). This method can also be used to measure other gases such as ozone-depleting substances.

Author: Dr. Christian Rolf, Research Centre Jülich (FZJ)

Autosonde system Stuttgart-Schnarrenberg

At the radiosonde station Stuttgart-Schnarrenberg the German Weather Service (DWD) operates an autosonde system type AS15 of the company Vaisala Oyj. Currently three radiosonde ascents per day (at 00 UTC, 06 UTC and 12 UTC) are carried out with the autosonde system. In case of critical weather conditions, the supervisor at the forecast and operations centre (VBZ) in Offenbach am Main can also request an additional radiosonde ascent at 18 UTC. The autosonde system can stock up to 24 radiosondes and balloons and performs radiosonde ascents fully automatically. A monitoring of the radiosonde ascents is performed in 24-hour shift operation.

For the Swabian MOSES campaign, additional radiosondes will be launched with start time at 08:15 UTC (08 UTC) and start time 14:15 UTC (14 UTC). The radiosonde data will be acquired at an ascent rate of approximately 300 meters per minute and provided in FM94 BUFR format with a temporal resolution of 2 seconds. In addition to the radiosonde ascent (BUFR 309057), descent data (BUFR 309056) will also be recorded and encoded. The autosonde system uses the Vaisala RS41-SGP radiosonde (with pressure sensor) and a TOTEX TA600 balloon with an integrated parachute. Helium 4.6 is used as the carrier gas.

Author: René W. Reitter, German Weather Service (DWD), Measurement Technology Division - TI 22

Measuring probes

During flood events, hydrological and water chemical parameters change within a very short time. In order to record these dynamics, nine continuously measuring probes are installed at three locations in the rivers Ammer, Steinlach and Goldersbach. For example, the CTD turbidity probe (see photo) measures electrical conductivity, water temperature, water level and turbidity. Other probes measure the parameters oxygen, pH and chlorophyll. A third probe developed by the UFZ outputs information on dissolved organic carbon and nitrate levels.

ISCO Autosampler

For all water quality parameters that cannot be measured with probes, automatic samplers, so-called autosamplers from ISCO (Model 3700; see photo), are used. An integrated pump draws water samples at predefined time intervals and fills glass bottles located inside the device. Autosamplers generate composite water samples, by e.g. pumping a volume of 250 milliliters into the same 1-liter bottle four times per hour (every 15 minutes), that reflect changes in water chemistry over time. Since river water is usually very turbid during floods, suspended solids are also sampled. In addition to automatically generated composite water samples, manual sampling will be conducted at some sites, primarily to decipher pollutant inputs from specific sources such as urban areas or road runoff, and to investigate the extent to which rivers are sources of greenhouse gases in relation to the degree of land use in the catchment (see research objectives).

Chemical and bioanalytical methods

Samples collected during rain events will be processed in the laboratory of the Geo- and Environmental Research Centre of the University of Tübingen. Using instrumental analysis, complex chemical mixtures in the water will then be identified and their toxic effects determined using bioanalytical methods. In this process, pollutants dissolved in water and chemicals bound to particles are separated from each other by filtration and examined separately. Analyses at the University of Tübingen include nutrients such as nitrate, particle size distribution and the determination of dissolved carbon.

At the UFZ Department of Cell Toxicology in Leipzig, the high-throughput platform CITEPro (Chemicals in the Environment Profiler) is used to analyse the effects of chemical mixtures, using cell-based in vitro bioassays. In addition, organic chemicals are identified and their concentrations determined using high-resolution mass spectrometry (HR-MS). At the UFZ in Magdeburg, trace elements such as zinc, copper, iron and gadolinium are analysed, which can be used as indicators for certain substance input pathways, e.g. from urban areas. In addition, at the UFZ Leipzig, ultra-high resolution mass spectrometry (FT-ICR-MS) is used to characterise dissolved organic material from various sources in the catchment area in more detail. At the KIT branch in Garmisch-Partenkirchen, analyses of greenhouse gases such as nitrous oxide are performed.

Authors: Dr. Clarissa Glaser, University of Tübingen; Dr. Stephanie Spahr, University of Tübingen/IGB Berlin & Dr. PD Ralf Kiese, KIT

Due to weather patterns atmospheric surface pressure is continuously fluctuating, which is also recorded by many amateur meteorologists. Besides slow fluctuations that can be recorded with a barometer, sudden pressure fluctuations can arise from thunderstorm cells. These rapid pressure fluctuations are sources of infrasound waves that can propagate in the atmosphere over long distances. The infrasound range adjoins the audible range at lower frequencies; the transition between the infrasound range and the acoustic sound range is around 20 Hertz (audible range spans from approx. 20 to 20,000 Hertz, depending on age and volume).

The sensor unsed in the measurement campaign can detect pressure fluctuations in a frequency range from about 0.02 to 100 Hertz, hence can detect infrasound waves and acoustic waves in the lower audible range. For detection, a sensitive differential pressure sensor is used (Sensirion SPD816-125Pa), which measures the pressure difference between a sealed reference vessel (a glass vessel with a volume of 5 liters) and the environment. This is achieved by allowing a small flow of air driven by the pressure difference between the reference volume and the outside air through a narrow channel. A heat source is located in the duct, and air temperature is measured on both sides of the source. From the temperature difference, the flow velocity can be derived and subsequently the pressure difference.

The figure on the right shows the sensor: the reference vessel is wrapped with thermal insulation to prevent rapid temperature fluctuations of the reference - which would also simulate pressure fluctuations. The actual sensor element is located in the metal housing above the reference vessel. The data is automatically recorded using a laptop and transferred to the campaign's data server via an LTE connection.

Only a few measurements have been carried out so far to investigate the infrasound signals of convective events. Within the Swabian MOSES campaign, infrasound measurements will be combined with the long-range diagnostics of the KITcube instruments to gain additional information on the flow events in a thunderstorm cell.

Author: Dr. Frank Hase, IMK-ASF

MoLEAF (Mobile Land-Ecosystem-Atmosphere Flux) is a mobile measuring system that is used to measure the fluxes of energy and matter between the land surface and the atmosphere. This system consists of a trailer mast, which is equipped with various measuring instruments and can be pneumatically extended to a height of 30 metres. The second important component of the MoLEAF system is a mobile laboratory cabin that can be transported on a pickup truck and can dropped at the measurement site. It contains a computer workstation, the power supply for the measurement system, and the internet connection. Together this enables the rapid deployment of the measuring system in the event of extreme weather events with a short warning time and self-sufficient operation on site. Thus, measurements can start within a few hours after arrival at the site.

The central measuring unit of the MoLEAF is a so-called eddy covariance system, which is based on a common and widely used method for measuring and calculating vertical turbulent fluxes within atmospheric boundary layers. The eddy covariance method analyzes high-frequency wind and scalar atmospheric data series, gases, energy, and momentum to determine the vertical fluxes of these quantities. This statistical method in commonly used in meteorology and other applications (micrometeorology, oceanography, hydrology, agricultural sciences, industrial and regulatory applications, etc.) to determine the exchange fluxes of trace gases over natural ecosystems and agricultural fields and to quantify gas emission rates. The method is also widely used to verify and calibrate climate and weather models, complex biogeochemical and ecological models, and remote sensing estimates from satellites and aircraft. Due to its mathematic complexity the covariance method requires considerable care in setting up and processing data.

Via the eddy covariance system the exchange of sensible heat, i.e. the energy used to heat the air, the exchange of CO₂, and evaporation can be determined. In addition, the MoLEAF has measuring instruments for recording the radiation balance, which is composed of short-wave and long-wave radiation, for determining the soil heat flux, the soil water content, the air temperature and the air humidity. Wind speed and direction are also recorded. All measurements are continuously and automatically operated during measrement campaing, with a high temporal resolution (0.1 seconds for turbulent quantities and 1 minute for non-turbulent quantities) and can also be monitored remotely via the Internet.

Author: Dr. Matthias Mauder, IMK-IFU

A network of soil moisture sensors enables the continuous measurement of soil moisture and soil temperature at different depths. The mobile devices used in the campaign consist of individual sensor nodes, to each of which six soil moisture sensors are connected. The sensors are installed in pairs, so that the soil moisture and soil temperature can be measured at each location at three different depths. The measured data is transferred to a database via mobile radio and visualised.

The soil moisture sensors work according to the TDT principle (Time Domain Transmission), which is based on the influence of the dielectric properties of the soil on the propagation speed of an electromagnetic signal that is transmitted as a pulse to the sensors. Water is characterized by a high dielectricity compared to dry soil. A high water content in the soil and thus a high dielectricity slows down the propagation speed of the electromagnetic signal. Including further parameters such as soil temperature, the soil moisture can be determined from the propagation speed.

Why are these measurements important? Soil moisture is an important parameter of natural soils, which is not only of great importance for agriculture (see research objectives). Due to the pronounced heterogeneity and complexity of soils, soil moisture is also characterized by a high temporal and spatial variability. Single measurements often do not adequately represent such changes. Wireless sensor networks allow an investigation of the temporal and spatial dynamics of soil moisture.

Authors: Matteo Bauckholt, Prof. Dr. Peter Dietrich, UFZ

Precipitation measurements with radars such as the KITcube X-band radar provide information with very high spatial and temporal resolution, which cannot be achieved with a ground measurement network of precipitation gauges. Radar measurements however suffer from typical measurement errors, which can be minimized by calibrating the radar with the (relatively few) in-situ measurements.

For Swabian MOSES, a network of 23 optical distrometers (parsivels) will be set up for the first time. While conventional rain gauges only provide information on the amount of precipitation, the use of distrometers also provides information on the composition of precipitation in respect to size and type of the hydrometeors.This information can also be estimated from the measurements of the polarimetric KITcube X-band radar. By comparison with the distrometers which are distributed in the entire measurement area, the radar-based information can be verified and improved via calibration (also of the polarimetric measured quantities).

Author: Dr. Jan Handwerker, IMK-TRO

Despite the massive damage caused by severe hail events, especially in the Swabian MOSES study area, hail is not measured directly at many weather stations in Germany. However, the size distributions of hailstones, so-called spectra, are relevant for several applications. Precipitation radars in principle also measure hail, but only provide a complete signal (or several signals in the case of modern dual-pole devices) for the atmosphere at an altitude of around 1 kilometre.

Observed spectra can be used to improve the conversion methods of the radar signal to hail at the surface. The hail spectra are also crucial for damage to buildings, vehicles and agricultural crops and are therefore needed for the most accurate calculation of hail damage and hail risk. Finally, long-term measurements of hailstones can be used to determine possible trends caused by climate change.

The newly developed measuring device HailSens can measure hail spectra with high temporal resolution. When a hailstone hits the receiving surface, the surface is set into vibration, which is recorded by a piezoelectric microphone mounted under the receiving surface. From this, the number and size of hailstones impacting the receiving surface can be derived. Each impact of a hailstone is registered and automatically sent to a server. The data is then available almost in real time.

As part of the Swabian MOSES field measurement campaign, a total of 10 hail measurement devices have been installed - precisely at the locations where, according to the IMK's radar analyses, hail occurs most frequently.

Author: Prof. Dr. Michael Kunz, IMK-TRO

The measurement of wind as a vector quantity (wind speed and direction) with strong spatial and temporal variability poses great challenges to the measurement concept and measurement technology, but is of fundamental importance for understanding the energy and material balance of the atmosphere.

Doppler lidar instruments determine the velocity of scatterers (aerosol particles) which are moving with the wind, based on the Doppler effect along a laser beam. This works for scatterers in a distance of up to 10 kilometers. To determine the wind vector as well as vertical and horizontal profiles, the laser beam is directed into different directions of the half-space above the instrument via a controllable mirror system (scanner). Additional benefit results from the combined and synchronized use of the instruments, by which either small-scale flow patterns (e.g. in valleys) can be measured with high resolution or, as in the case of the Swabian MOSES measurement campaign, larger-scale flow properties in more extensive investigation areas can be analysed. Like this, advection and flow convergence can be determined, which are important for thunderstorm formation (see research objectives).

Within the framework of Swabian MOSES, the IMK-TRO operates Doppler lidar devices with data transmission in near real time to determine the wind profile up to heights of 3 kilometres at a total of 7 locations in the study area between the eastern Black Forest, Neckar valley and western Swabian Alb. In June and July these will be extended by an airborne scanning Doppler lidar (see research aircraft). Instruments of the project partners IMK-IFU and University of Hohenheim complete the network with two additional sites.

Author: Dr. Andreas Wieser, IMK-TRO

Cosmic-Ray Neutron Sensing (CRNS) is a mobile, contactless technology for determining mean soil moisture in a vicinity of about 15 hectares. The method is based on the detection of neutrons "reflected" in the soil. Since neutrons are particularly sensitive to hydrogen atoms, a direct dependence of the neutron intensity on the water in the root zone around the sensor can be derived. Since the neutrons originate from cosmic events, such as stellar explosions, this measurement method is called Cosmic-Ray Neutron Sensing.

The sensor typically contains detector gases (e.g. helium) which react to neutrons passing through and generate an electric current pulse. These pulses are counted and saved by the data logger along with information such as GPS coordinates, temperature, air pressure and humidity. From the collected information, soil moisture can be estimated.

The stationary sensors are already successfully used in research and agriculture to measure hourly changes in soil moisture over several years. To obtain information about an entire field or a specific catchment area, the detector can be used in mobile "roving" mode. In this mode, the sensor is installed in a vehicle and simply counts the neutrons while driving. Measurement data and coordinates are collected every 10 seconds so that an average soil moisture can be calculated for the distance travelled.

A good estimate of soil moisture at the landscape scale is relevant e.g. for hydrological modelling. It can be used to predict future weather developments, to estimate the risk from droughts, heat waves or floods (see research objectives).

Authors: Mandy Kasner, Prof. Dr. Peter Dietrich, UFZ

Additional information on Cosmic Ray Neutron Sensing & Roving and its use in other projects: Homepage

The vertical temperature and humidity profile of the atmosphere is important for the formation and intensity of thunderstorm events. In addition, the three-dimensional (3D) wind field especially in the upwind region of a thundercloud, determines the intensity of precipitation in the form of rain or hail (see research objectives).

By using small (size of a yoghurt cup) and light (12 gram) swarm probes of Sparv, vertical profiles of air temperature, humidity, pressure and the 3D wind field can be measured directly in a thundercloud. The sondes transmit the measured parameters every 4 seconds via radio to the mobile ground station. A real-time map continuously shows the position of all probes. The swarm probe is a new type of measuring instrument that provides several series of measurements in a defined air volume for up to one hour. Up to 17 balloon-borne probes can be launched simultaneously or in close proximity, for example directly in front of a thundercloud. The probes ascend to a user-defined height and then follow the flow in the thundercloud on so-called Lagrangian paths.

The individual probes can be separated from the balloons in the further course either by remote command or from a further, previously defined height and thus fall to the ground. Due to their low weight, the fall velocity and thus the momentum when hitting the ground is low, so that the probes can be used several times (if they are recovered).

Author: Prof. Dr. Michael Kunz, IMK-TRO

The Wingcopter Eddy Covariance Drone is a measuring system developed to determine the exchange of greenhouse gases between the atmosphere and ground-level sources or sinks (such as vegetation, soil organisms or mofettes).

For this purpose, it is equipped with a five-hole probe wind measuring instrument, a fine-wire thermometer that measures particularly quick and sensitive, and a combined carbon dioxide/water vapour sensor. In future is is planned to add a laser methane sensor.

The Eddy covariance method is the methodological and mathematical basis of the measuring system. In the presence of a vertical gradient of an atmospheric variable (such as a gas concentration), it describes the systematic relationship between the vertical movement of air parcels with which this variable is transported and its resulting change at a given measurement height.

This vertical motion is determined as a component of the three-dimensional wind field with the five-hole probe instrument. This instrument uses the differences of the dynamic pressures, which are applied directionally to the slightly inclined pressure holes of the probe, in order to measure the relative inflow of the drone flying horizontally at about 50 meters above the ground at a speed of about 80 km/h. At the same time, the exact flight attitude of the drone is determined. The atmospheric wind field in which the drone is moving is then determined by simultaneously recording its exact flight attitude and movement using inertial and satellite navigation. Rapid determination of gas concentrations in the air parcels moving with the wind field is achieved by measuring the concentration-dependent absorption of infrared radiation by these gases inside the measurement system.

Over areas that are particularly relevant to the climate system and worthy of consideration for climate research, the Wingcopter Eddy Covariance Drone can thus be used to quantify the vertical fluxes of humidity, heat and, in particular, of the greenhouse gases mentioned, and thus to study and balance them in greater detail (see research objectives).

Author: Prof. Dr. Torsten Sachs, GFZ