Tropical upper tropospheric humidity variations due to potential vorticity intrusions

Abstract

Abstract. Four cases (March 2009, May 2009, April 2010 and February 2012 are presented in which the ERA-interim relative humidity (RH) shows consistent increase by more than 50 % in the upper troposphere (200-250 hPa) over tropics at the eastward side of the potential vorticity (PV) intrusion region. The increase in RH is confirmed with the spaceborne microwave limb sounder observations and radiosonde observations over Gadanki (13.5 • N, 79.2 • E) and is observed irrespective of whether the PV intrusions are accompanied by deep convection or not. It is demonstrated that the increase in RH is due to poleward advection induced by the PV intrusions in their eastward side at the upper tropospheric heights. It is suggested that the low-latitude convection, which is not necessarily triggered by the PV intrusion, might have transported water vapour to the upper tropospheric heights.

Strong downdrafts preceding rapid tropopause ascent and their potential to identify cross-tropopause stratospheric intrusions

“…Please note that the high PV and dry air have been observed intruding deep into the troposphere as low as 650 hPa (∼ 3.6 km), whereas the vertical structure of AIRS ozone has shown that the enhanced ozone intruded into the troposphere at ∼ 500 hPa. This difference in vertical scale of intrusion between ozone and PV parameters is most likely due to two reasons: (1) the local high PV value observed near ∼ 600 hPa is not a true stratospheric characterized intrusion but rather adiabatically produced high PV (e.g., Skerlak et al, 2015); (2) the relatively poor vertical resolution of AIRS ozone data may have limited the refined observation of the intrusions. From this figure, however, it is clear that stratospheric air (dry ozone-rich and high PV) intrusions have indeed occurred and were observed (at least intruded downward into ∼ 500 hPa).…”

“…Backward (forward) trajectories in given starting locations are capable to reproduce the sources (destinations) of the air parcel that will allow us to examine the intrusions of stratospheric origin in the troposphere (e.g., Elbern et al, 1997 (Rolph, 2003;Stein et al, 2016) is applied to calculate the backward and forward trajectories. The calculation method of the model is a hybrid between the Lagrangian approach and the Eulerian methodology.…”

“…This upward and poleward transport is associated with a warm conveyor belt (southerly flows dominate) that is located ahead of the COL. It contributes to the transport of the tropospheric moist and polluted air (such as aerosol) into the upper troposphere and even the lower stratosphere (e.g., Stohl et al, 2003;Sandhya et al, 2015). After the downdrafts, forward trajectories in Fig.…”