Clouds as a factor influencing the climate
by Staff Writers
Hamburg, Germany (SPX) Jan 20, 2020
The almost six-week-long EUREC4A (Elucidating the role of clouds-circulation coupling in climate) field campaign will begin on 20 January 2020. The aim is to test theories about the role of clouds and convection in climate change by conducting comprehensive measurements in the atmosphere and ocean.
In addition, EUREC4A will examine how fine-scale features in the ocean - eddies and fronts - interact with the atmosphere. Five research aircraft and four research ships will be deployed to the east and south of the Caribbean island of Barbados, together with ground measurement stations and satellite-based remote sensing, as part of the German-French initiative that involves over 40 partners.
The world's largest study to date of low-level clouds and their local interactions with the atmosphere and ocean will be conducted by the Max Planck Institute for Meteorology (MPI-M) in Hamburg and the Laboratoire de Meteorologie Dynamique (LMD) in Paris. It will build upon decades of collaboration with the Caribbean Institute for Meteorology and Hydrology (CIMH).
The German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt; DLR) is an important partner, with experiments on the ground and on board the High Altitude and LOng Range (HALO) research aircraft. DLR is also responsible for operating the research aircraft.
Low-level clouds in the trade-winds region
In order to verify these, the researchers have a particular requirement for observational data relating to the dynamics of the atmospheric and oceanic conditions in which clouds form and dissipate. The extensive measurements conducted during the EUREC4A field campaign will allow them to study the lifecycle of convective clouds in the trade-wind regions in great detail and obtain a picture that is as complete as possible.
How do clouds react to climate change?
If so, it would imply that higher estimates of the expected warming from increasing carbon dioxide levels are more plausible. Regarding the question of cloud response to climate change, there is still much uncertainty. We hope that EUREC4A will change this." The geographical extent and scope of the measurements offers the opportunity to evaluate a new generation of climate models and satellite data products.
In numerical models, trade-wind clouds have so far reacted differently to climate disturbances. Complex climate models predict that the area covered with low-level clouds will be highly sensitive to the prevailing conditions, while simpler process models show the opposite. Understanding and resolving these contradictions serves as the starting point for the EUREC4A field study.
The most important research questions are as follows. How resilient or susceptible is the amount of shallow cumulus cloud cover to variations in the strength of convective mixing, surface turbulence and large-scale circulations? How do the radiative effects of water vapour and clouds influence shallow circulations and convection? What are the implications for the spatial arrangement of clouds and convection in the tropics, and ultimately for climate sensitivity - that is, the vulnerability of the climate system to a given perturbation, such as the presence of additional greenhouse gases?
"Estimates of climate sensitivity remain very uncertain, and most of this uncertainty stems from the response of low-level clouds in the tropics, especially in the trade-wind regions," explains Co-principal investigator Sandrine Bony of LMD. "The low-level clouds over Barbados are typical of the cloud cover that can be found in trade-wind regions throughout the tropics. Therefore, what we learn from EUREC4A will not only enhance our understanding of clouds off Barbados, but also tropical clouds more generally."
Studying water vapour with an airborne laser
More importantly, it enables us to measure the water vapour that surrounds the clouds; this has a significant impact on the way in which they grow and behave. Humid layers of air above the clouds also have an indirect influence on their formation due to radiative effects and can be accurately captured by the lidar," explains DLR researcher Martin Wirth.
In addition to a better understanding of the coupling processes between clouds and circulation, the campaign will provide a reference dataset containing extensive measurement data. This will serve as a benchmark for improving the modelling and satellite-based remote sensing of clouds and circulation.
Felix Ament of the University of Hamburg says: "The information about clouds and their interactions with the atmosphere that we will capture during EUREC4A will be more detailed, multifaceted and comprehensive than ever before. We want to provide a reference point that will serve as a touchstone for encouraging and inspiring scientists over the coming decades."
Campaign processes and measurement platforms
EUREC4A is largely focused around the deployment of three research aircraft on Barbados. The first of these is the French ATR-42, which will be used for in-situ and remote sensing in the lower troposphere. It will be joined by the DLR HALO research aircraft, which has a range of over 8000 kilometres and a maximum operating altitude of 15 kilometres.
HALO is equipped with an extensive suite of modern instruments for remote sensing - including radar and lidar - as well as a system for ejecting dropsondes. Finally, the Twin-Otter operated by the British Antarctic Survey (BAS) will focus on measuring aerosols and the turbulent and microphysical cloud structure.
In addition, the Lockheed WP-3D Orion research aircraft belonging to the US National Oceanic and Atmospheric Administration (NOAA) and the aircraft of the Regional Security Service (RSS), which is permanently stationed on Barbados, will also support the measurements. The WP-3D flights will, among other things, complement those of HALO by determining the large-scale conditions and connecting them with measurements performed by the ships.
The data acquired by the aircraft will be complemented by measurements performed at the BCO and using the flexibly controllable Polarisation Diversity Doppler Radar (POLDIRAD) system. POLDIRAD will be stationed on a high plateau eight kilometres southeast of the BCO during the campaign.
Martin Hagen of the DLR Institute of Atmospheric Physics says: "POLDIRAD allows us to record the development of precipitation with high temporal and spatial resolution at a range of up to 250 kilometres to the east of Barbados. The measurements conducted at the BCO, from the ships and along the flight paths, can thus be considered within the spatial and temporal context of the large-scale distribution and development of precipitation."
Unmanned aerial systems will take off from ships
The research ships serve as remote sensing and in-situ platforms for atmospheric and ocean observations. These may include radiosondes, lidar and radar technologies, tethered balloons and unmanned aerial systems.
"Spatial variability at the sea surface is an important boundary condition for the development of the overlying atmosphere and thus also for cloud formation," says Johannes Karstensen from the GEOMAR Helmholtz Centre for Ocean Research Kiel, who is the Expedition Leader on the Maria S.
Merian. "We want to understand the coupling between oceanic and atmospheric processes, especially in the case of large eddies and frontal zones, and thus make these easier to represent in model simulations."
Evolving landscape added fuel to Gobi Desert's high-speed winds
New York NY (SPX) Jan 13, 2020
On February 28, 2007, harsh winds blew 10 train cars off a track running near China's Hami basin, killing three passengers and seriously injuring two others. Hurricane-force gusts of 75 mph or more scour this basin every 15-20 days or so, on average, and can reach maximum speeds of more than 120 mph. A study published last week in Nature Communications has documented a new feedback loop that may have helped to make this basin in the Gobi Desert one of the windiest places in China. "It's an odd-loo ... read more
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