Four recent reanalyses—the 55-yr Japanese Reanalysis Project (JRA-55), Interim ECWMF Re-Analysis (ERA-I), NCEP Climate Forecast System Reanalysis (CFSR), and NASA Modern-Era Retrospective Analysis for Research and Applications (MERRA)—are assessed to clarify their quality in representing the diurnal cycle over East Asia. They are found to present similar patterns/structure and summer progress of the mean wind diurnal cycle, whereas they exhibit some differences in diurnal amplitude, particularly for the low-level meridional wind. An evaluation with intense soundings suggests that the amplitude difference mainly results from the diurnal variation of mean bias that differs among reanalyses. The root-mean-square (RMS) error is found to have a diurnal variation more evident in CFSR and MERRA than that in JRA-55 and ERA-I, which strongly affects the representation of the varying diurnal amplitude at the peak hours of RMS error.
Compared with satellite-derived rainfall, the four reanalyses are shown to reproduce well the rainfall diurnal cycle over East Asia in terms of large-scale terrain contrast, summer progress, and interannual variability. JRA-55 even presents a long-term increase of morning rainfall percentage over the east China plain over the past four decades, consistent with rain gauge observations. The four reanalyses exhibit some considerable discrepancies at regional scale; JRA-55 gives the best capture of the rainfall diurnal cycle over the Tibetan Plateau and the eastward propagation to the eastern lees. These results suggest that new reanalyses are potentially applicable for studying the large-scale diurnal variability over East Asia, whereas their different preferences, especially at regional scale, should be of concern in data application.
[1] Using advance satellite-derived sea surface temperature (SST), solar radiation and wind speed products, we investigate hot events (HEs) associated with very high SST of around 30°C. Amplitude of the SST diurnal variation (DSST) is obtained by an empirical formula with the downward surface shortwave radiation (DSSR) and the wind speed. The HE is defined as a connected region with SST > the time-dependent SST threshold of about 30°C having a minimum areal size greater than 3 Â 10 6 km 2 and lasting for a period longer than 10 days. Thirty-one hot events were detected from 1993 to 2003 in and around the equatorial Indo-Pacific warm pool. The HE precursor is increase of an area with SST > the time-dependent SST threshold, and the HE starts when the areal size exceeds the areal threshold. It keeps the very high SST for a while, and then its SST decreases with decrease of the HE area toward its ending phase. The HE area and the high-DSST area correspond with each other on timescales of daily and the whole one event period. In the HE period, a clear-sky and low-wind condition becomes the reason for large DSST appearance. Through statistics of the detected 31 HEs, it is indicated that the mean HE period, the mean areal size, and the means of the regional HE areal averaged SST are 24.2 days, 1.57 Â 10 7 km 2 , and 0.25°C above the time-dependent SST threshold, respectively. The HE area shifts with season though they stay within/around the SST contour of 28°C in the Indo-Pacific oceans.Citation: Qin, H., H. Kawamura, and Y. Kawai (2007), Detection of hot event in the equatorial Indo-Pacific warm pool using advanced satellite sea surface temperature, solar radiation, and wind speed,
Qin et al. have found Hot Events (HE), which are short‐term (about 20 days) large‐scale (about 15,000,000 km2) regions with very high Sea Surface Temperatures (SST > 30°C). Following their definition, an HE was identified in the tropical western Pacific in November 2006, which is named HE0611. A case study of HE is conducted by using the advanced satellite products and in‐situ measurements from the TAO/TRITON mooring array. Two parts (HE0611‐East and ‐West) with very high SST connected to form HE0611. SST in HE0611‐West increases quickly with large diurnal SST variations, which are caused by large solar radiation and suppressed latent heat loss. The increase of the mixed‐layer heat content is clearly accounted for the accumulated heat gain through the air‐sea interaction. The formation mechanism of HE0611‐East is completely different; its very high SST is supported by a subsurface high SST anomaly associated with the El Niño. Two phenomena similar to HE0611 were observed in November of the El Niño years of 1994 and 2002.
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