PHILEAS campaign successfully completed

HALO research aircraft has provided valuable contributions to research into the effects on the climate of the Asian Summer Monsoon and the wildfires in Canada

16 October 2023


Touchdown for the PHILEAS mission: Following the removal of the instruments from the HALO research aircraft in Oberpfaffenhofen in Bavaria, the measurement campaign has been completed on schedule. Over the past eight weeks, a team of researchers coordinated by Forschungszentrum Jülich and Johannes Gutenberg University Mainz (JGU) has been investigating the impacts of the Asian Summer Monsoon on global climate, fully achieving the ambitious measurement objectives. The wealth of exceptional data collected will allow profound insights into how the Asian Summer Monsoon and so-called pyroconvection transport airborne pollutants. With regard to the latter, large-scale fires of the type seen in Canada generate powerful convection and also pyrocumulonimbus or thunderstorm clouds that can aggravate the situation. Initial results of the analysis of the data should be available in a couple of months.

The main objective of this PHILEAS campaign was to study the effects of the Asian Summer Monsoon on climate. Convective systems tend to predominate vertical transport in this massive weather system and these can convey highly contaminated air from the near-surface atmosphere in Southeast Asia to elevations of up to 15 kilometers. From there, the polluted air spreads to the west into the area above the Eastern Mediterranean and to the east over the Pacific.

During the first measurement phase from early to mid-August, the researchers were able to analyze monsoon air containing a large proportion of the pollutants present over the Eastern Mediterranean, roughly in a location above Israel and Jordan. In the second campaign phase involving flights from Anchorage in Alaska, the transport of contaminated air over the Pacific, Alaska, and Canada was investigated.

Professor Martin Riese, Director of the Stratosphere section at the Institute of Energy and Climate Research (IEK) at Forschungszentrum Jülich, was pleased by the outcome: "PHILEAS has been remarkably successful. Our predictions as to where we would find air masses from the Asian monsoon turned out to be accurate and we were able to precisely target these during the measurements flights. As all the instruments worked perfectly, we now have a unique set of data at our disposal. The monsoon air that was examined was characterized by increased concentrations of greenhouse gases such as methane and nitrous oxide, of natural climate gases such as water vapor, and of atmospheric pollutants including carbon monoxide and ammonia."

This is the first time that scientists can study in detail an extensive quantity of polluted monsoon air at higher latitudes, in this case in the lower stratosphere. They monitored and analyzed the same air masses on successive days. Riese continued: "Contaminants can persist for longer in the stratosphere and thus have a more marked influence on the climate. This also happens with aerosols, such as solid particles of ammonium nitrate. These particles act as ideal condensation nuclei for ice clouds. The formation and distribution of ice clouds play a major role when it comes to climate sensitivity – in other words, to what extent exactly our climate becomes warmer in response to increasing levels of atmospheric carbon dioxide."

"We also had the unique opportunity when in Anchorage to assess the impact of the wildfires in Canada. These were particularly severe in the Northwest Territories around Yellowknife. We were even able to measure, near the fire sources, the pyroconvection currents taking the products of combustion up as far as the stratosphere. As was the case when it came to measuring the monsoon air, the combined use of the GLORIA remote sensing device with in-situ instruments that use various methods to analyze the air where the aircraft is located proved to be especially effective," stated Professor Peter Hoor, head of the Airborne Measurements group at the Institute of Atmospheric Physics of JGU.


Now all the data needs to be inspected and evaluated. Following an in-house workshop by the PHILEAS team in November, initial results might first be presented in early winter at conferences of the international atmosphere and climate research community in San Francisco and Baltimore.

Determination of the effects on climate will require considerable time as the associated modeling will be very complex. This will be the task of the TPChange Collaborative Research Center at Mainz University, for which the PHILEAS data will represent a core element. In addition to the aerosol-related processes, a particular challenge for climate modeling will be the distribution of water vapor in the tropopause independently of the monsoon system. This is to be investigated in more detail, again with the help of HALO, in a follow-up PHILEAS project involving collaboration between Forschungszentrum Jülich and JGU.

The partners

PHILEAS is a joint project of Forschungszentrum Jülich and Johannes Gutenberg University Mainz together with the Karlsruhe Institute of Technology (KIT), the German Aerospace Center (DLR), the Leibniz Institute for Tropospheric Research (TROPOS) in Leipzig, the Max Planck Institute for Chemistry in Mainz as well as the universities of Frankfurt and Wuppertal. A team of some 70 researchers supports the airborne measurement flights.


The High Altitude and Long Range Research Aircraft HALO is a joint initiative of several German environmental and climate research institutions. HALO is funded by grants from the German Federal Ministry of Education and Research (BMBF), the German Research Foundation (DFG), the Helmholtz Association, the Max Planck Society, the Leibniz Association, the Free State of Bavaria, the Karlsruhe Institute of Technology (KIT), Forschungszentrum Jülich, and the German Aerospace Center. The latter is both owner and operator of the aircraft.