Lecture 8 (Jan. 31) - Noboru Nakamura Natural Hazards winter quarter- \"Physics of Natural Hazards PDF

Preview

Summary

Noboru Nakamura Natural Hazards winter quarter- "Physics of Natural Hazards and Weather-Related Hazards Cont."...

Description

8: Physics of natural hazards and Weather-Related Hazards January 31, 2018 Extratropical cyclones and jet stream  Troughs and ridges in jet streams = weather systems  Travel eastward  Horizontal scale: 1000’s of kilometers  Energy source—north-south temperature gradient  Transfer heat from warm tropics to cold poles  Fronts o Warm front approaches: westward wind, increased cloudinessmodest but persistent rain o Between warm and cold fronts: a short period of warm, humid, clear sky, wind from south o Passage of cold front: severe weather, gist, sudden change in wind directionsharp decline in temperature as sky clears  Geography and statistics o Pacific and Atlantic storm tracks o Southern Ocean o Favor regions with strong temperature gradients o Active throughout the year (~100 per hemisphere) o Lifetime = a few days to a week o Predictable up to ~10 days  Metrics o Central pressure at surface (the lower the stronger) o Maximum sustained wind speed o Vorticity (spin rate)  Impacts o Heavy rain, snow, ice (potential cause of flooding) o High winds, waves, storm surge o Thunderstorms and tornadoes embedded in cyclones and fronts o Secondary precipitation: lake-effect snow, etc  “Bomb Cyclones” o More than 24 hPa drop in central pressure over 24 hours Lake effect snow  Sudden, heavy snowfalls develop in the downwind regions of the Great Lakes from November to February  Snowfall can reach 5-10 inch/hour  Geographically isolated (“snow belt”)  1-80, 1-90 in NW Indiana Tropical cyclones (hurricanes, typhoons, cyclones)  Intense, compact (200-500 km radius)  Energy source: latent heat of condensation  Eye (radius 10-50 km)  Destructive winds, copious precipitation concentrated around eyewall)



Geography and statistics: o Form over warm ocean surface (> 26 degrees Celcius) o Do not form at the equator o Lifetime: a week to 10 days o Normally less than 6 hurricanes per year are formed in the Atlantic o Once formed, predictable up to a week (steered by large-scale winds)...