Potential effects of subduction rate in the key ocean on global warming hiatus

In this study, the possible effects of subduction rate on global warming hiatus were investigated using Simple Ocean Data Assimilation（SODA） data. This study first analyzed the characteristics of the temporal and spatial distribution of global subduction rate, which revealed that the North Atlantic meridional overturning circulation region and the Antarctic Circumpolar Current region are the two main sea areas with great subduction variations.On this basis, four key areas were selected to explore the relationship between the local subduction rate and the global mean sea surface temperature. In addition, the reason for the variations in subduction rate was preliminarily explored. The results show good correspondence of the subduction of the key areas in the North Atlantic meridional overturning the circulation region and the Antarctic Circumpolar Current region to the global warming hiatus, with the former leading by about 10 years. The subduction process may be a physical mechanism by which the North Atlantic overturning circulation and the Antarctic Circumpolar Current act on the stagnation of global warming. Advection effect plays an important role in the variations in subduction in the key regions. In the Antarctic Circumpolar Current region, the magnitude of sea surface wind stress is closely related to the local changes in subduction.

Evolution of Surface Sensible Heat over the Tibetan Plateau Under the Recent Global Warming Hiatus

Based on regular surface meteorological observations and NCEP/DOE reanalysis data, this study investigates the evolution of surface sensible heat（SH） over the central and eastern Tibetan Plateau（CE-TP） under the recent global warming hiatus. The results reveal that the SH over the CE-TP presents a recovery since the slowdown of the global warming. The restored surface wind speed together with increased difference in ground-air temperature contribute to the recovery in SH.During the global warming hiatus, the persistent weakening wind speed is alleviated due to the variation of the meridional temperature gradient. Meanwhile, the ground surface temperature and the difference in ground-air temperature show a significant increasing trend in that period caused by the increased total cloud amount, especially at night. At nighttime, the increased total cloud cover reduces the surface effective radiation via a strengthening of atmospheric counter radiation and subsequently brings about a clear upward trend in ground surface temperature and the difference in ground-air temperature.Cloud–radiation feedback plays a significant role in the evolution of the surface temperature and even SH during the global warming hiatus. Consequently, besides the surface wind speed, the difference in ground-air temperature becomes another significant factor for the variation in SH since the slowdown of global warming, particularly at night.

Attribution analysis for the failure of CMIP5 climate models to simulate the recent global warming hiatus

The Coupled Model Inter-comparison Project Phase 5 （CMIP5） contains a group of state-of-the-art climate models and represents the highest level of climate simulation thus far. However, these models significantly overestimated global mean surface temperature （GMST） during 2006-2014. Based on the ensemble empirical mode decomposition （EEMD） method, the long term change of the observed GMST time series of HadCRUT4 records during 1850-2014 was analyzed, then the simulated GMST by 33 CMIP5 climate models was assessed. The possible reason that climate models failed to project the recent global warming hiatus was revealed. Results show that during 1850-2014 the GMST on a centennial timescale rose with fluctuation, dominated by the secular trend and the multi-decadal variability （MDV）. The secular trend was relatively steady beginning in the early 20th century, with an average warming rate of 0.0883℃/decade over the last 50 years. While the MDV （with a -65-year cycle） showed 2.5 multi-decadal waves during 1850-2014, which deepened and steepened with time, the alarming warming over the last quarter of the 20th century was a result of the concurrence of the secular wanning trend and the warming phase of the MDV, both of which accounted one third of the temperature increase during 1975-1998. Recently the slowdown of global warming emerged as the MDV approached its third peak, leading to a reduction in the warming rate. A comparative analysis between the GMST time series derived from HadCRUT4 records and 33 CMIP5 model outputs reveals that the GMSTs during the historical simulation period of 1850-2005 can be reproduced well by models, especially on the accelerated global warming over the last quarter of 20th century. However, the projected GMSTs and their linear trends during 2006-2014 under the RCP4.5 scenario were significantly higher than observed. This is because the CMIP5 models confused the MDV with secular trend underlying the GMST time series, which results in a fast secular trend and an improper MDV with irregular phases and small amplitudes. This implies that the role of atmospheric CO2 in global warming may be overestimated, while the MDV which is an interior oscillation of the climate system may be underestimated, which should be related to insufficient understanding of key climatic internal dynamic processes. Our study puts forward an important criterion for the new generation of climate models： they should be able to simulate both the secular trend and the MDV of GMST.

Decadal changes of the intraseasonal oscillation during 1979–2016

The Intraseasonal Oscillation (ISO) is the cornerstone for 2–8-week subseasonal prediction. Understanding the decadal variation of the ISO is important for improving subseasonal prediction;however, there is still a gap in our knowledge of ISO dynamics. Here, we presented a method, an Empirical Orthogonal Function (EOF) analysis of 11-year-sliding ISO evolution, to objectively detect decadal variation of the ISO originated from the equatorial Indian Ocean (EIO) during 1979–2016. The results show that the properties of ISO have a notable decadal change since 1998 for both boreal summer and boreal winter seasons, mainly in its evolution rather than in its intensity at origin. During the pre-1998 epoch, the boreal summer intraseasonal oscillation (BSISO), was confined to the Indian Ocean;since 1998, however, it propagated northeastward across the Maritime Continent (MC) and the intraseasonal variability over the western North Pacific was significant enhanced. On the other hand, the boreal-winter ISO, usually known as Madden-Julian Oscillation (MJO) shows minor changes in MC ‘barrier effect’ between the two epochs, and continuously propagates eastward across the MC. The MJO only shows suppressed activity over the central equatorial Pacific in the post-1998 epoch. These decadal changes are related to the eastern Pacific cooling during the ‘global warming hiatus’ period rather than to the four-decade global warming. Results here provide a set of potential precursors for foreseeing ISO propagation under different mean states.