Springtime Cloud Properties in the Taiwan Strait: Synoptic Controls - - PowerPoint PPT Presentation
Springtime Cloud Properties in the Taiwan Strait: Synoptic Controls and Local Processes Mien-Tze Kueh and Pay-Liam Lin Department of Atmospheric Sciences, National Central University, Chungli HKMS25: 2013 Nov 2 Outline Background
Department of Atmospheric Sciences, National Central University, Chungli
HKMS25: 2013 Nov 2
Primary source: Kueh and Lin: Springtime cloud properties in the Taiwan Strait: synoptic controls and local
The springtime is a high-occurrence season for low-clouds and fog events in the area.
The fogs and very low clouds can impact the local marine and aviation transportation due to their low visibility.
Remarkable northwestward decreasing SST and wind channeling effect are commonly observed over the strait.
General features in the spring season:
SST gradients over the shelf seas.
larger cloudiness located on the upwind side.
ISCCP
Cold air surge: Separation of low cloud layers Frontal system: Vertical extension
cold air surge versus frontal system
Cold air surge:
and alto clouds associated with prevailing northeasterly.
no fog observed. Frontal system:
dominate.
for stratus.
with southwesterly
cold air surge versus frontal system
Significant divergence and convergence within the boundary layer in TS are remarkable for cold surge and frontal conditions, respectively. Northward increasing stabilities are found for both conditions, and a more stable environment emerges from the cold surge condition. Backing (veering) wind observed within the TS is indicative
(warm) air advection emerges from the cold surge (frontal) condition.
Frontal condition: warmer and moister thermal structure is subjected to the warm air advection and dynamical lifting that arose from the deep layer of the southwesterly flow. Vertical extension
Cold surge: cold and dry air surge along with the local convergence aloft, serves to compensate for the near-surface strong divergence and thus produce a subsidence warming (result in a drying layer) locally within the TS. Separation of low cloud layers
Cold surge: Thicker clouds Frontal system: More rainfall
The springtime clouds over the TS are commonly a mixture of stratocumulus and alto clouds, with a preponderance of stratocumulus over the strait. A separation of low cloud layers is recognized during cold air surge, whereas vertical development of low cloud layers is commonly observed with frontal passage.
(e.g., wind channeling effects and sea temperature conditions) within the TS is fundamentally dependent on synoptic-scale flow patterns. The most distinct difference between the local cloud formations associated with the two synoptic conditions is the suppression of very low cloud and fog along with cold air surge. Stratus cloud and fog are present within the northward prefrontal airflow from warmer to colder water sites, along with an increase in stability relating to lower altitudes of boundary layer clouds.
back
To describe the dependence of cloud properties on the two synoptic conditions, a set of composite fields are constructed based upon the daily SLP of the two airports using the upper quartile (
the lower quartile (
system) as thresholds.