The “Year” of Tropical Convection (May 2008–April 2010): Climate Variability and Weather Highlights

Abstract

The representation of tropical convection remains a serious challenge to the skillfulness of our weather and climate prediction systems. To address this challenge, the World Climate Research Programme (WCRP) and The Observing System Research and Predictability Experiment (THORPEX) of the World Weather Research Programme (WWRP) are conducting a joint research activity consisting of a focus period approach along with an integrated research framework tailored to exploit the vast amounts of existing observations, expanding computational resources, and the development of new, high-resolution modeling frameworks. The objective of the Year of Tropical Convection (YOTC) is to use these constructs to advance the characterization, modeling, parameterization, and prediction of multiscale tropical convection, including relevant two-way interactions between tropical and extratropical systems. This article highlights the diverse array of scientifically interesting and socially important weather and climate events associated with the WCRP–WWRP/THORPEX YOTC period of interest: May 2008–April 2010. Notable during this 2-yr period was the change from cool to warm El Niño– Southern Oscillation (ENSO) states and the associated modulation of a wide range of smaller time- and space-scale tropical convection features. This period included a near-record-setting wet North American monsoon in 2008 and a very severe monsoon drought in India in 2009. There was also a plethora of tropical wave activity, including easterly waves, the Madden–Julian oscillation, and convectively coupled equatorial wave interactions. Numerous cases of high-impact rainfall events occurred along with notable features in the tropical cyclone record. The intent of this article is to highlight these features and phenomena, and in turn promote their interrogation via theory, observations, and models in concert with the YOTC program so that improved understanding and pre- dictions of tropical convection can be afforded.

Atmospheric rivers: a mini-review

“…These IWV areas match the areas of high moisture transport from the tropics to the extratropics as found by Knippertz et al (2013). Waliser et al (2012) also found that the maximum number of ARs occurred in the northeastern Pacific. In regional studies over longer periods, about 15 landfalling ARs per year were counted in California (Neiman et al, 2008), and on average about 8-10 persistent winter ARs (of at least 18 h duration) affected Great Britain (Lavers et al, 2012).…”

“…The moisture in an AR has two origins (Bao et al, 2006): (1) local moisture convergence along the cold front of the extratropical cyclone, and (2) direct poleward transport of tropical moisture. The different precipitation regimes observed in an AR event include (Matrosov, 2013) "cold" rainfall (mostly formed by ice precipitation above the freezing level for more northern latitudes); "warm" rainfall (limited amounts of ice in precipitation for temperatures above the freezing level); and regions of mixed precipitation with both warm and cold Waliser et al (2012) and Zhu and Newell (1998). White contours showed the continental areas where there are reported cases of ARs linked with extreme precipitation and floods (listed in Supplementary Table III).…”

Impact of perturbation methods in the ECMWF ensemble prediction system on tropical cyclone forecasts

“…To estimate the structure and amplitude of the model tendencies for a TC, we use the tendencies from the ECMWF Year Of Tropical Convection (YOTC) data set (Waliser et al, 2011). During the YOTC period, the tendencies from the parametrization schemes of the forecast model of ECMWF were archived every 3 h for 36 h. The resolution of the YOTC calculations is slightly higher (TL799; ≈ 25 km) than the resolution of our ensemble forecasts.…”

Microphysical properties of frozen particles inferred from Global Precipitation Measurement (GPM) Microwave Imager (GMI) polarimetric measurements

“…(Li et al, 2013). The models account for ice clouds in radiation calculations but often ignore the radiative fluxes and heating rates from frozen precipitation in the air (Waliser et al, 2012). Hence, remote sensing of microphysical properties in frozen precipitation and their connection to ice clouds above and surface precipitation, like this work, will provide a valuable surrogate for climate models in representing cloudprecipitation processes.…”