Saji N. Hameed

Nonlinear, Intraseasonal Phases of the East Asian Summer Monsoon: Extraction and Analysis Using Self-Organizing Maps

AbstractThe hypothesis that regional characteristics of the East Asian summer monsoon (EASM) result from the presence of nonlinear coupled features that modulate the seasonal circulation and rainfall at the intraseasonal time scale is advanced in this study. To examine this hypothesis, the authors undertake the analysis of daily EASM variability using a nonlinear multivariate data classifying algorithm known as self-organizing mapping (SOM).On the basis of various SOM node analyses, four major intraseasonal phases of the EASM are identified. The first node describes a circulation state corresponding to weak tropical and subtropical pressure systems, strong upper-level jets, weakened monsoonal winds, and cyclonic upper-level vorticity. This mode, related to large rainfall anomalies in southeast China and southern Japan, is identified as the mei-yu–baiu phase. The second node represents a distinct circulation state corresponding to a strengthened subtropical high, monsoonal winds, and anticyclonic upper-lev...

What caused the cool summer over northern Central Asia, East Asia and central North America during 2009?

Cool and wet weather conditions hit northern Central Asia, East Asia and central North America during the 2009 summer in concert with a strong jet stream and a prominent meandering upper-level circulation in the Northern Hemisphere mid-latitudes despite the fact that the year 2009 is the fifth warmest year globally in the modern record. It is found that the conspicuous atmospheric variability in the entire Northern Hemisphere mid-latitudes during the summer of 2009 was caused by a combination of teleconnections associated with significant tropical thermal forcings, strong polar forcing, and interaction between high-frequency weather events and climate anomalies. The strong negative circumglobal teleconnection pattern associated with the deficient Indian summer monsoon rainfall and developing El

Recent Changes in ENSO Teleconnection over the Western Pacific Impacts the Eastern China Precipitation Dipole

AbstractThe eastern China precipitation dipole (ECPD) features an out-of-phase relationship between boreal summer precipitation over the middle and lower reaches of the Yangtze River and the Hetao region to its northwest. The precipitation dipole is strongly influenced by ENSO teleconnections over the western tropical Pacific. Here it is shown that a pronounced weakening of both the rainfall variability over eastern China as well as the precipitation dipole structure occurred around the mid-1990s. The changes have been analyzed by considering two epochs: one during 1979–95 and the other during 1996–2009. The characteristic feature of the circulation anomaly during the first epoch is the well-known East Asia–Pacific/Pacific–Japan (EAP/PJ) pattern, a quasi-meridional teleconnection pattern emanating from the western tropical Pacific. On the other hand, during the latter epoch eastern China precipitation variability occurs as an integral part of the circulation anomalies over the western Pacific. In contrast...

A model for super El Niños

Super El Niños, the strongest and most powerful of El Niños, impact economies, societies, and ecosystems disproportionately. Despite their importance, we do not fully understand how super El Niños develop their intensity and unique characteristics. Here, combining observational analyses with simple numerical simulations, we suggest that eastern Pacific intensified super El Niños result from the interaction of an El Niño and a positive Indian Ocean Dipole. Further, we identify a self-limiting behavior inherent to El Niño Southern Oscillation (ENSO) dynamics. This behavior—a consequence of the atmospheric Kelvin wave response that develops to the east of ENSOs convective anomalies—dampens sea surface temperature (SST) variations in the eastern Pacific, thereby preventing super El Niños from developing through tropical Pacific dynamics alone. Our model explains the features of the large 1972, 1982, and 1997 El Niños; the large SST anomalies during the 2015 El Niño, however, were likely enhanced by strong decadal variability.Despite advances in ENSO modeling, super El Niño events remain largely unpredictable. Hameed et al. postulate that ENSO-IOD interaction is crucial for super El Niño development and identify a self-limiting factor that constrains ENSO dynamics from generating these extreme events on their own.

Accelerating Lagrangian particle dispersion in the atmosphere with OpenCL across multiple platforms

FLEXPART is a popular simulator that models the transport and diffusion of air pollutants, based on the Lagrangian approach. It is capable of regional and global simulation and supports both forward and backward runs. A complex model like this contains many calculations suitable for parallelisation. Recently, a GPU-accelerated version of the simulator (FLEXCPP) has been written in C++/CUDA. As CUDA is only supported on NVIDIA GPUs, such an implementation is tied to a single hardware vendor, and is not able to take advantage of other hardware acceleration platforms. This paper presents an OpenCL/C++ version of FLEXCPP, called FlexOcl. This simulator provides all the functionality of FLEXCPP, and has been extended to include modelling of the decay of radioactive particles. A performance comparison between the two simulators has been performed on GPU, and the performance of FlexOcl has also been evaluated on the Intel Xeon Phi, as well as a number of other hardware platforms. Our results show that the OpenCL code performs better than CUDA code on GPUs, and that equivalent performance is seen on the Xeon Phi for this type of application.