Mid Latitude Flashcards
Factors affecting intensity of frontal systems and cloud/precipitation
Moisture - sea level moisture determines the cloud base when air is forcibly lifted, with a lower cloud base more latent heat will be released. Increasing intensity of frontal systems due to the destabilisation of the atmosphere.
Stability - cold fronts are typically unstable due to abrupt lifting at the frontal boundary, producing Cb’s with showers of RA/GR/SN. Weak stable layers may exist ahead of cold fronts resulting in layers of Sc/As (light rain). Warm fronts are typically stable features dominated by St/Sc/Ns/As/Cs from large scale and slow lifting, producing RA/DZ.
Slope - cold fronts tend to have a relatively steep slope often resulting in a line of embedded thunderstorms along the frontal surface, they also tend to be narrow delivering only 2-3 hours of poor weather. Warm fronts tend to have more gentle lifting which can take place over hundreds of kilometres, therefore cloud is often extensive and produces precipitation which lasts many hours.
Speed - faster moving fronts usually are more intense (30kts for cold front to be considered active) , warm fronts are slower than cold fronts.
Temperature contrast - large temp differences increase intensity, 5 degrees or more for cold front to be considered active.
Factors affecting air mass modification
Trajectory of the air w.r.t its source region
Degree of heat/moisture exchange between the airmass and the surface
Extent of mechanical mixing
Frequency that air masses occupy an area (Sahara desert vs NZ)
Describe the process of air mass modification
When a air mass with an existing set of characteristics (stability, moisture content, temperature) is advected over a surface with different characteristics, that air mass will slowly change taking on the characteristics of the underlying surface.
Air masses resist mixing so if the air mass advects to meet another airmass it will result in frontogenesis
Difference between analysis and prognosis charts
Analysis - based on observational data collected at a set time.
Prognosis - forecast weather showing predicted positions and sometimes intensities of weather at predetermined time frames into the future.
