instability line

instability line

[‚in·stə′bil·əd·ē ‚līn]
(meteorology)
Any nonfrontal line or band of convective activity in the atmosphere; this is the general term and includes the developing, mature, and dissipating stages; however, when the mature stage consists of a line of active thunderstorms, it is properly termed a squall line; therefore, in practice, instability line often refers only to the less active phases.
References in periodicals archive ?
To elaborate the classification of the weather types for the rhythm analysis, the classes of atmospheric systems identified by Monteiro (1973) were used, as follows: 1) Frontal Systems--Polar Atlantic Front (FPA), Reflex Polar Front (FPR), Polar Atlantic Front in Dissipation (DIS), Occlude Polar Atlantic Front (OCL), Repercussion of Polar Atlantic Front (REP), Stationary Polar Atlantic Front (EST), and Warm Front; 2) Individualised Systems--Tropical Instability Line and Atlantic Intertropical Convergence Zone; and 3) Air Masses--Polar Atlantic mass (mPA), Old Polar mass (mPV), Continentalized Old Polar mass (PVC), Tropical Atlantic mass (mTA), Continentalized Tropical Atlantic mass (TAC), Tropical Continental mass (mTC), and Equatorial Continental mass (mEQ).
Zavattini (1990) synthesized the system according to this classification: 1) South Currents = mPA + mPV/PVC + FPA/OCL/DIS/EST + FPR; 2) East Currents = mTA + TAC + Tropical Instability Line + Warm Front + REP: 3) North Current = mEQ; and 4) West Current = mTC.
In general, the critical cyanobacterial blooms during the first trimester of 2009 were associated mainly with a mTA (80%), compared to a mTC (20%); interestingly, all of the blooms occurred after a disturbance in the water column caused by a Tropical Instability Line (20%), an EST (20%) and a FPA (60%).
The highest density in the period (29,853 cel/mL) occurred during a Tropical Atlantic mass after a conflict between an Equatorial Continental mass and a Polar Atlantic mass and continued until the appearance of a Tropical Instability Line. Similar to the rhythm in the first trimester, the blooms occurred during the warmer weather types and after a instability in the water column.