Heavy rain & Low level jet
July, 2011 severe rain storm was in Umyeon mountain.
At that time, there were 11,100 victims, 18 deaths and the damage was about 25 million won. And maximum hourly precipitation was 59mm and daily precipitation was about 301.5mm.
Concepts of Heavy rain and Low level jet
Heavy rain is Strongly time concentrated, location concentrated rain. And In general, it rains over 30mm per hour, over 100mm per day, and about 10% of yearly precipitation falls in one day.
Characteristics of heavy rain
- Small region, short term
- Accompanied by typhoon, seasonal rain front, low atmospheric pressure, and
convergent zone.
Jet stream
Jet stream is fast flowing, narrow air currents found in the atmospheres. And it has Upper level jet and Low level jet.
Upper level jet
Polar jet streams are typically located near the 250hPa pressure level, or 7 to 12 kilometers above sea level, while the weaker subtropical jet streams are much higher, between 10 and 16 kilometers above sea level. In each hemisphere, both upper-level jet streams form near breaks in the tropopause, that is at a higher altitude near the equator than it is over the poles, with large changes in its height occurring near the location of the jet stream.
The northern hemisphere polar jet stream is most commonly found between latitudes 30°N and 60°N, while the northern subtropical jet stream is located close to latitude 30°N. The upper level jet stream is said to "follow the sun" as it moves northward during the warm season, or late spring and summer, and southward during the cold season, or autumn and winter.
The width of a jet stream is typically a few hundred kilometers or miles and its vertical thickness often less than five kilometers.
Low level jet
wind blows at lower levels of the atmosphere that are also referred to as jets. (about 1~3km height)
Mechanism of heavy rain
- Warm air parcel with low density goes up meeting cold air parcel.
- Water vapor of warm air parcel becomes cool and condenses, going upper.
- The potential heat is emitted and rising air getting warmer.
- Warmed air goes up faster with its density lower.
- Fast rising air draws lower warm air parcel fast.
- Fast vertical velocity of air parcel makes much clouds at once and makes severe rain storm.
1) In summer, lower pressure is formed at continent which has relatively low specific heat and high pressure is formed at continent which has relatively high specific heat.
2) At low pressure, air sucked into counterclockwise for filling the vacancy and at high pressure where occurs descending air current, air blows out clockwise.
3) When pressure trough goes strong cause of two atmospheric pressures’ development, the wind passes between two pressures speeds up. And we call this wind, 'Low level jet'