The QBO's influence on lightning production and deep convection in the tropics
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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.
Hernandez, Celina Anne (2008). The QBO's influence on lightning production and deep convection in the tropics. Master's thesis, Texas A&M University. Available electronically from