Transverse cirrus bands in weather systems: a grand tour of an enduring enigma

Abstract

thunderstorm systems were formed over the ocean near to the western coast of Portugal and moved slowly towards the Lisbon region throughout the night, between the late hours of 17 February and the early hours of 18 February. By the time those convective cells reached the Lisbon area, deep cloud systems had moved and passed slowly over the study area for more than eight hours, being responsible for intense precipitation activity that resulted in accumulated values exceeding 100 millimetres.The effects of the storm in the Lisbon metropolitan region were harmful and in some cases even ruinous. A large number of urban inundations and country flash-floods have caused loss of life and serious damage to property, demonstrating some lack of preparedness on the part of the city to respond suitably to these natural hazards and risks. These facts show the importance of studying with more detail the impacts and consequences of an extreme rainstorm in Lisbon, in order to prevent future disasters and to propose suitable mitigation measures. References

Satellite Observations of an Unusual Cloud Formation near the Tropopause

“…6. We notice the resemblance of this feature of cloud organization into lines to modeling studies of mammatus clouds in sheared environments (Kanak and Straka 2009) and to cirrus bands close to the jet stream (Knox et al 2010). Where the mammatocumulus formations are organized into cloud lines, we suggest that they be termed mammatocumulus lucullus.…”

A View of Tropical Cyclones from Above: The Tropical Cyclone Intensity Experiment

“…The waves could potentially be ducted in the outflow layer, similar to what was seen in thunderstorm anvils by Fovell et al (2006). Knox et al (2010) described bands in the upper troposphere of a hurricane with a similar horizontal wavelength, but no vertical structure could be identified in their study. To our knowledge this is the first time such features have been resolved by dropsondes in a hurricane.…”

Convectively Induced Transverse Band Signatures in Satellite Imagery

“…In the case of multistorm events, each individual storm was analyzed for the existence of transverse bands. Previous studies of the transverse band feature (Ellrod 1985;Knox et al 2009) and other unpublished Web-based satellite feature interpretation guides/examples were used as visual aides to subjectively identify the presence of bands in visible and IR window imagery. Convective events in which transverse bands did form and were sustained for a significant period of time (at least 30 min) were entered into the 2006 Storm Database, where the life cycle of the storm and its transverse band evolution were documented.…”

“…Areas of strong atmospheric turbulence over large regions are often characterized by extensive cloud cover, which sometimes contain well-defined transverse cirrus bands that can be observed in visible or infrared satellite imagery (Ellrod 1985). The occurrence of transverse band (or ''radial cirrus'') signatures in satellite imagery is not an uncommon feature in the life cycle of a thunderstorm, but they are also present within jet streams, tropical cyclone outflow, and the warm conveyor belt of midlatitude cyclones (Knox et al 2009). Knox et al pro-vide a comprehensive literature review and present detailed examples of the transverse band signature in high-resolution satellite imagery, but also indicate that ''there is no consensus on why transverse bands form.''…”