Modulation of Tropical Tropopause Layer Characteristics by the Madden-Julian Oscillation during the DYNAMO/AMIE Field Campaigns

As the transition region between the troposphere and stratosphere, the Tropical Tropopause Layer (TTL) has importance as the gateway to the stratosphere for tracers such as water vapor.  Observations in this region show time variations across multiple scales that are not fully understood.  In this study, we investigate the impacts of the Madden-Julian Oscillation (MJO) on TTL properties and their vertical structure during the DYNAMO/AMIE field campaigns (Dynamics of the Madden-Julian Oscillation/ DOE-ARM MJO Investigation Experiment) from October-December 2011.  This time period is particularly interesting in that two prominent MJO passages were seen over the tropical Indian Ocean.  We use multiple datasets, including high vertical resolution observational data from atmospheric soundings on Gan Island, Maldives [0.69S, 73.15E], to better understand the response of the TTL to MJO dynamics at the equator.  Characteristics of the broadscale structure of the MJO are analyzed, as well as higher-frequency variations of the flow near the TTL accompanying an increase in MJO-related deep convective clouds. Similar to results found in some previous studies, these observations suggest a covariation in temperature and zonal wind anomalies, with cooler temperatures co-varying with easterly anomalies. Modulation of the cold-point tropopause height is seen as a gradual lowering, followed by a sudden rise during the active phase of the MJO.