Intraseasonal isotopic variation associated with the Madden-Julian Oscillation

Abstract

[1] The Madden-Julian Oscillation (MJO) is the dominant mode of intraseasonal variability in the tropical atmosphere. This study examines the evolution of the hydrologic regime from before the onset of the MJO (pre-onset period) to the MJO onset period, using deuterated water vapor (HDO) measurements from the Tropospheric Emission Spectrometer (TES) and from ground-based stations. Ground-based observations reveal a clear transition between high HDO/H 2 O isotope ratios during the pre-onset period to a period of repeated abrupt decreases in the HDO/H 2 O isotope ratio associated with intense convection. Each observed minimum in the HDO/H 2 O ratio corresponded to a maximum in stratiform rainfall fraction, which was derived independently from radar precipitation coverage area. The ground-based observations are consistent with the satellite observations of the HDO/H 2 O ratio. In order to attribute the mechanisms that bring about the isotopic changes within the MJO convection, an isotope-enabled general circulation model (GCM) constrained by observed meteorological fields was used to simulate this MJO period. The GCM reproduced many of the observed isotopic features that accompanied the onset of an MJO. After the development of deep convection, large-scale stratiform cloud cover appears, and isotope ratios respond, as a consequence of diffusive exchange between stratiform raindrops and the surrounding vapor. In this diffusive exchange process, heavy isotopes tend to become enriched in precipitation and depleted in the surrounding vapor, and thus successive stratiform rainfall results in decreasing isotope values in the middle and lower troposphere. On the basis of these characteristics, isotope tracers can be used to partition stratiform and convective rainfall from observed isotope data and to validate the simulated proportions of convective/stratiform rainfall.

Characteristics of Seasonal Variation of Near-Surface Water Vapor D/H Isotope Ratio Revealed by Continuous in situ Measurement in Sapporo, Japan

“…Figure 6 also shows that the δD values deviated from the equilibrium vapor and changed considerably over a short period of time and were mostly affected by such organized disturbances as cloud clusters, synoptic disturbances and tropical cyclones, as reported by other researchers (e.g., Gedzelman et al 2003;Lawrence et al 2004;Kurita et al 2011). In Sapporo, short-term and large variations in δD were also observed frequently (see Fig.…”

A Tropospheric Emission Spectrometer HDO/H<sub>2</sub>O retrieval simulator for climate models

“…The focus of future comparisons between the modeled and observed δD fields will be over the tropics, following a series of recent studies Kurita et al, 2011;Berkelhammer et al, 2012;Kim et al, 2012). For broader potential application, however, we tested the performance of the TES HDO simulator outside of the tropical domain.…”

Evaluation of continuous water vapor δD and δ<sup>18</sup>O measurements by off-axis integrated cavity output spectroscopy

“…In this study, we used a custom manufactured glass trap for vapor collection. This trap has been used for water vapor sample collection in various field projects (Kurita and Yamada, 2007;Kurita, 2011;Kurita et al, 2011). Along with this, we undertook a trapping test using the WVISS/WVIA system before starting the laboratory experiment.…”