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Description:
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Variations in characteristics of tropical deep convection are examined for an association with the stratospheric quasi -biennial oscillation (QBO ) . Eight years (1998 -2005 ) of Tropical Rainfall Measuring Mission (TRMM ) Lightning Imaging Sensor (LIS ) flash densities and ten years (1998 -2007 ) of TRMM Precipitation Radar (PR ) deep convective and stratiform rainfall and convective echo top heights are analyzed . The QBO can be linked to deep convection through two hypothesized mechanisms : 1 ) modulation of tropopause height , which may affect the altitude that convection can penetrate ; and 2 ) modulation of cross -tropopause shear , which may affect the vertical development of convection via shearing of cloud tops . Tropopause height and cross -tropopause shear is measured by National Centers for Environmental Prediction (NCEP ) reanalysis 100 hPa temperatures and 50 -200 hPa zonal wind shear , respectively .
When partitioned by QBO east and west phases , zonal monthly mean anomalies and anomalous monthly mean difference maps illustrate a QBO signal in lightning flash rates , convective and stratiform rain amounts , and the number of convective echo tops > 12 km . QBO modulation of cross -tropopause shear causes 50 -200 hPa shear east (west ) phase anomalies to decrease (increase ) about the equator and increase (decrease ) in off -equator regions . QBO modulation of tropopause height induces a higher /colder (lower /warmer ) tropopause near the equator during the east (west ) phase . While the expectation was that decreases in cross -tropopause shear and tropopause temperatures at monthly time scales during the QBO would result in an increase of deep convective properties near the equator , observations suggest that deep convective properties may increase or decrease depending on the location and season . Similar to the QBO results , the increase or decrease of deep convective properties with general variations in cross -tropopause shear and tropopause temperatures depends on the location and season . |