Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Air pollution and volcanic ash cause more efficient freezing of clouds

14.11.2011
In clouds of the northern hemisphere ice is formed at much higher temperatures than in southern-hemispheric clouds.

This conclusion was drawn based on laser-aided measurements at Leibniz Institute for Tropospheric Research (IfT) in Leipzig, Germany, at Magellan University in Punta Arenas, Chile, at Stellenbosch University in South Africa and during transatlantic cruises of the German research vessel Polarstern. In a recent publication in the scientific journal Geophysical Research Letters the authors state that their study documents the relevance of aerosol particles for the formation of ice crystals in shallow cloud layers in the northern hemisphere.

The strong air pollution in the northern hemisphere is suspected to contribute to the observed effect.

Also volcanic ash particles have a strong influence on the ice formation in clouds. This finding was revealed in a second, collaborative study of IfT Leipzig and Ludwig-Maximiliams University Munich, which used data from the eruption of the Eyjafjallajökull volcano in Iceland in April 2010 and was recently published in the scientific journal Journal of Geophysical Research.

To investigate the differences between the northern and southern hemisphere, scientists at IfT Leipzig analyzed data from the cruises of the Polarstern to Antarctica and back in 2009 and 2010 and compared the findings with an already existing data set from Leipzig. During the cruises to Punta Arenas in Chile and Kapstadt in South Africa they observed the formation of clouds with laser. For that purpose a so-called LIDAR system developed at IfT emits laser pulses at wavelengths of 355, 532, and 1064 nm which are than reflected back to the LIDAR by particles suspended in atmosphere. From the rotation of the oscillation direction of the reflected light, so-called depolarization, the phase state of the clouds can be determined. The comparison of the collected data with the data set of Leipzig revealed strong contrasts in the amount of ice-containing clouds.

Above central Europe 70 percent of all clouds contain ice already at temperatures of above -18 degree Celsius. At these temperatures clouds above southern Chile and South Africa form ice only in 20 and 35 percent of the cases, respectively. The reason for such a contrast is most likely the larger amount and larger variety of aerosol particles, so-called ice nuclei, in the northern hemisphere which are a basic requirement for the freezing of cloud droplets at temperatures between -40 and 0 degree Celsius. These ice nuclei typically consist of mineral dust, soot, or fine ash originating from the numerous deserts or areas with forest fires, but also man-made air pollution from industry and biomass burning activity are a possible source of ice nuclei. “Compared to the polluted atmosphere in the northern hemisphere the air above Punta Arenas in the vicinity of Antarctica is virtually clean. The largest city at the southern tip of America is located right within the Antarctic deep-pressure belt. During most of the time of the year, the air comes from the west – right from the Pacific Ocean”, explains Thomas Kanitz PhD, student at IfT.

It is well known that small aerosol particles are needed as nuclei for cloud droplet condensation and ice crystal formation. Pure, particle-free cloud droplets would not freeze before temperatures decrease to below -40 degree Celsius. This threshold temperature can be significantly increased via contact of the cloud droplet with insoluble particles or specific types of bacteria. However, it remains unclear to which extent ice formation is influenced by these particles or by other meteorological processes, and whether global climate models are capable of reproducing this effect. Related to this point is the question, whether the formation of clouds and thus precipitation in regions with strong pollution differs from the situation in less-polluted regions. In the midlatitudes of the northern hemisphere the free troposphere between 2 and 12 kilometer height is strongly loaded with aerosol particles stemming from man-made air pollution, desert dust and biomass burning. In the southern midlatitudes these particles are mostly absent because the surface area is dominated by oceans and comparably few regions with industry, forests, or deserts.

Also volcanic eruptions can influence ice formation in clouds. During the eruption of the Eyjafjöllajökull volcano in Iceland in April 2010 the scientists at Leipzig studied the effect of the volcanic ash on cloud glaciation with two LIDAR systems located at Leipzig and at Maisach, close to Munich, Germany. “When there is volcanic ash in the atmosphere, ice can obviously form at relatively high temperatures as soon as enough humidity is available”, reports Dr. Patric Seifert, scientist at IfT. Without volcanic ash, ice is usually formed only at temperatures below -25 degree Celsius.

Tilo Arnhold

Publications:
Kanitz, T., P. Seifert, A. Ansmann, R. Engelmann, D. Althausen, C. Casiccia, and E. G. Rohwer (2011), Contrasting the impact of aerosols at northern and southern midlatitudes on heterogeneous ice formation, Geophys. Res. Lett., 38, L17802, doi:10.1029/2011GL048532.
http://www.agu.org/pubs/crossref/2011/2011GL048532.shtml
The studies were supported by funding of the “Pakt für Forschung und Innovation“ of the Leibniz Association.
Seifert, P., et al. (2011), Ice formation in ash-influenced clouds after the eruption of the Eyjafjallajökull volcano in April 2010, J. Geophys. Res., Vol. 116, D00U04, 14 PP., doi:10.1029/2011JD015702.
http://www.agu.org/pubs/crossref/2011/2011JD015702.shtml
The studies were supported by the Europeean Commission in the frame oft he lidar research networkk EARLINET.
Additional Information:
Thomas Kanitz/ Dr. Patric Seifert
Leibniz Institute for Tropospheric Research (IfT), Optical Remote Sensing group
Tel. 0049-341-235-2149, -2460, -2918, -2411, -2411
http://www.tropos.de/ift_personal.html
Links:
Worldwide observations with the portable Raman lidar systems (Polly)
http://polly.tropos.de/lidar/index.php
Lidar Research Network EARLINET:
http://www.earlinet.org/

Tilo Arnhold | idw
Further information:
http://www.tropos.de/eng/ift_news.html

More articles from Earth Sciences:

nachricht Novel method for investigating pore geometry in rocks
17.06.2018 | Kyushu University, I2CNER

nachricht Decades of satellite monitoring reveal Antarctic ice loss
14.06.2018 | University of Maryland

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: AchemAsia 2019 will take place in Shanghai

Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.

Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...

Im Focus: First real-time test of Li-Fi utilization for the industrial Internet of Things

The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.

Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.

Im Focus: Sharp images with flexible fibers

An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.

Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...

Im Focus: Photoexcited graphene puzzle solved

A boost for graphene-based light detectors

Light detection and control lies at the heart of many modern device applications, such as smartphone cameras. Using graphene as a light-sensitive material for...

Im Focus: Water is not the same as water

Water molecules exist in two different forms with almost identical physical properties. For the first time, researchers have succeeded in separating the two forms to show that they can exhibit different chemical reactivities. These results were reported by researchers from the University of Basel and their colleagues in Hamburg in the scientific journal Nature Communications.

From a chemical perspective, water is a molecule in which a single oxygen atom is linked to two hydrogen atoms. It is less well known that water exists in two...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Munich conference on asteroid detection, tracking and defense

13.06.2018 | Event News

2nd International Baltic Earth Conference in Denmark: “The Baltic Sea region in Transition”

08.06.2018 | Event News

ISEKI_Food 2018: Conference with Holistic View of Food Production

05.06.2018 | Event News

 
Latest News

A sprinkle of platinum nanoparticles onto graphene makes brain probes more sensitive

15.06.2018 | Materials Sciences

100 % Organic Farming in Bhutan – a Realistic Target?

15.06.2018 | Ecology, The Environment and Conservation

Perovskite-silicon solar cell research collaboration hits 25.2% efficiency

15.06.2018 | Power and Electrical Engineering

VideoLinks
Science & Research
Overview of more VideoLinks >>>