Structural evolution of the Madden‐Julian Oscillation from COSMIC radio occultation data

Abstract

The atmospheric temperature and specific humidity profiles derived from 4 years of Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation (RO) measurements during the boreal winter (November thru April in 2006–2010) were employed to study the large‐scale vertical structure of the Madden‐Julian Oscillation (MJO). In a composited MJO cycle, both RO temperature and moisture anomalies propagate eastward along with the enhanced MJO convection over the Indo‐Pacific region. In the same region, the RO temperature anomaly is positively correlated with the convection (Tropical Rainfall Measuring Mission (TRMM) rainfall) anomaly in the middle and upper troposphere (800 hPa–200 hPa) and negatively correlated in the lower troposphere and at the tropopause. A positive RO moisture anomaly has a westward tilt below 300 hPa and is well associated with the convection anomaly. RO bending angle and refractivity anomalies show vertical structure similar to that of temperature MJO anomaly above ∼300 hPa and to that of the moisture anomaly below that. These salient MJO features agree well with those revealed by global reanalysis data and meteorological satellite observations, such as the Atmospheric Infrared Sounder (AIRS), even though RO anomalies exhibit sharper structure at the tropopause region due to the higher vertical resolution of the RO. Investigation of the cold‐point tropopause anomaly indicates that the enhanced convection is preceded by cooling of the tropopause and followed by lowering of the tropopause height. The MJO moisture structures during two boreal winters, November 2007–April 2008 (La Niña) and November 2009–April 2010 (El Niño), are individually presented to demonstrate the El Niño‐Southern Oscillation (ENSO) effect on the MJO structure.