IMPACT OF THE SCANDINAVIAN MOUNTAINS ON A HIGH-IMPACT CYCLONE IN AUGUST 2003

In August 2003, Central Norway was hit by extreme precipitation. The cyclone that caused the precipitation has been simulated with a high-resolution model, and several sensitivity studies have been carried out. The simulations reveal that the release of latent heat had a major impact on the development of the cyclone. The cyclone occurred during a period of anomalously high sea surface temperatures (SST). Numerical tests show however that the development of the cyclone and the extreme precipitation are fairly insensitive to the SST. Removing the orography of Scandinavia leads to a deformation of the cyclone; when the orography is present a lee trough is formed over SE-Norway and the pressure gradient to the west of the low as it moves over SE-Norway is stronger than in the run with no mountains. The results will be helpful in analysing similar events in coarse-resolution climate simulations, where the mountains are poorly resolved

DYNAMICAL PROCESSES RELATED TO CYCLONE DEVELOPMENT NEAR GREENLAND

A cyclone that caused heavy snowfall and winds exceeding 30 m/s over E-Greenland and N-Iceland on 20-21 September 2003 is investigated. Numerical simulations are conducted to assess the role of Greenland\u27s orography for the development, as well as to evaluate the significance of other factors such as latent heating, SST and SST gradients. The simulations reveal that the cyclone evolution is strongly affected by the orography of Greenland. When orography is removed, a deep, well organized baroclinic low develops rapidly and moves eastward at 75°N. Conversely, in the control run the evolution of the primary baroclinic low is greatly suppressed by the orographic retardation of the warm air ahead of and the cold air behind the low. At the same time, a secondary low off Greenland’s east coast at 68°N intensifies due to a coupling between an approaching upper level PV-anomaly and a lower level PV-anomaly generated from lee effects. This secondary low then moves eastward and causes extreme weather conditions, as observed. Further sensitivity experiments show that latent heating contributes to deepen the low, while SST gradients and SST in general contribute relatively little

THE GREENLAND LEE-LOW AND A FORECAST ERROR OF THE 8 JANUARY 2005 DENMARK WINDSTORM

Forecasts of the 8 January Denmark Windstorm are compared. In a wrong forecast, the Greenland-lee low is far to shallow, there is less outflow of cold air from west of Greenland and consequently a poor development of the upper trough that fed the windstorm. The analysis of the forecasts and an ETKF analysis support that a correct analysis of the atmosphere in the region between Iceland and Greenland would have been of importance to get a correct forecast of the windstorm over Denmark 3 days later

DYNAMICAL PROCESSES RELATED TO CYCLONE DEVELOPMENT NEAR GREENLAND

A cyclone that caused heavy snowfall and winds exceeding 30 m/s over E-Greenland and N-Iceland on 20-21 September 2003 is investigated. Numerical simulations are conducted to assess the role of Greenland\u27s orography for the development, as well as to evaluate the significance of other factors such as latent heating, SST and SST gradients. The simulations reveal that the cyclone evolution is strongly affected by the orography of Greenland. When orography is removed, a deep, well organized baroclinic low develops rapidly and moves eastward at 75°N. Conversely, in the control run the evolution of the primary baroclinic low is greatly suppressed by the orographic retardation of the warm air ahead of and the cold air behind the low. At the same time, a secondary low off Greenland’s east coast at 68°N intensifies due to a coupling between an approaching upper level PV-anomaly and a lower level PV-anomaly generated from lee effects. This secondary low then moves eastward and causes extreme weather conditions, as observed. Further sensitivity experiments show that latent heating contributes to deepen the low, while SST gradients and SST in general contribute relatively little

THE GREENLAND LEE-LOW AND A FORECAST ERROR OF THE 8 JANUARY 2005 DENMARK WINDSTORM

Forecasts of the 8 January Denmark Windstorm are compared. In a wrong forecast, the Greenland-lee low is far to shallow, there is less outflow of cold air from west of Greenland and consequently a poor development of the upper trough that fed the windstorm. The analysis of the forecasts and an ETKF analysis support that a correct analysis of the atmosphere in the region between Iceland and Greenland would have been of importance to get a correct forecast of the windstorm over Denmark 3 days later

Strong constraints on aerosol-cloud interactions from volcanic eruptions.

Aerosols have a potentially large effect on climate, particularly through their interactions with clouds, but the magnitude of this effect is highly uncertain. Large volcanic eruptions produce sulfur dioxide, which in turn produces aerosols; these eruptions thus represent a natural experiment through which to quantify aerosol-cloud interactions. Here we show that the massive 2014-2015 fissure eruption in Holuhraun, Iceland, reduced the size of liquid cloud droplets-consistent with expectations-but had no discernible effect on other cloud properties. The reduction in droplet size led to cloud brightening and global-mean radiative forcing of around -0.2 watts per square metre for September to October 2014. Changes in cloud amount or cloud liquid water path, however, were undetectable, indicating that these indirect effects, and cloud systems in general, are well buffered against aerosol changes. This result will reduce uncertainties in future climate projections, because we are now able to reject results from climate models with an excessive liquid-water-path response

Kabul Times. (Kabul, Afghanistan), 1968-07-22

Kabul Times. (Kabul, Afghanistan), 1968-07-22; Volume 7; Number 10