Four cross-coupled models were used to investigate the relative contributions of atmospheric and oceanic components to the asymmetry of the El Niño–Southern Oscillation (ENSO). Strong El Niño and La Niña events related to the negative heat flux feedbacks were found to be determined mainly by the atmospheric component, and the stronger sea surface temperature (SST) anomalies in the warm phase did not lead to an increased SST asymmetry. The skewness of the four models could be affected by both atmospheric and oceanic components; the atmospheric component determines the strength of positive and negative SST anomalies, and the oceanic component affects the strength of the negative SST anomalies in the cold phase under the same atmospheric component group. The Bjerknes stability index (BJ index) of warm and cold phases contributed to the El Niño–La Niña SSTA asymmetries in observation, but the BJ index did not necessarily explain the El Niño–La Niña SSTA asymmetries in climate model simulations. The SST asymmetries in these four models were closely associated with convective precipitation and wind stress asymmetries, which are also determined by both the atmospheric and oceanic components.

The impact of soil freezing‐thawing processes on August rainfall in Southern China (SC) during 1979–2008 and related physical mechanisms are investigated using the coupled land‐atmosphere model Grid‐Point Atmospheric Model version 2.0—Community Land Model version 2.0 (GAMIL2.0‐CLM2.0). The moisture‐budget analysis is employed to quantify the contributions of different factors to the change of precipitation in SC. The results indicate that the vertical moisture advection and its dynamic component play an essential role in the long‐term trends of August rainfall. The possible physical mechanism is that the model which includes the supercooled water simulates much higher soil/air temperature in August, especially in the north of 40°N, which is not only weakened the meridional thermal contrast but also induced an anomaly “north high–south low” circulation pattern in the middle and high latitude of Eurasia. Both resulted in the 200 hPa zonal winds weakening, and 850 hpa northerly wind southward moved. Meanwhile, a convergence anomaly cyclone is initiated in the lower troposphere over SC regions, accompanied by enhanced ascending and strong moisture flux convergence, which is beneficial to the increased precipitation. This study provides a new interpretation of the “southern flooding” during 1979–2008 from the point of frozen soil changing.

Highly convection-related short-duration heavy rainfall (SDHR), defined as rainfall greater than 20 mm h⁻¹ of a whole hour, causes severe damage every year in China. An objective forecasting method is developed to provide guidance products for the short-term probability of SDHR. Representative parameters of environmental moisture content, instability, and dynamical forcing are selected as predictors based on the ingredients-based methodology. The predictors are selected by comparing their ability to discriminate between SDHR and both no rainfall and ordinary rainfall with hourly rainfall records and the NCEP reanalysis dataset during the warm seasons of 2002 and 2009. A fuzzy logic approach is obtained for the calculation of SDHR probability. Intervals of intensities are obtained based on specific percentiles and various weight settings examined. The probabilistic SDHR forecasts during the 2015 warm seasons with the NCEP GFS dataset are obtained, and forecasts are evaluated by using an operational used spatial verification method. Results show that the reference operational SDHR forecasts are surpassed by the 00–12 h period objective SDHR forecasts measured with the maximum critical success index (CSI), and even the average CSI (CSI_ave) for the top groups is better than the reference. The guidance SDHR products are skillful within 60 h. Although the weights vary significantly, the short-term patterns of the SDHR probability are mainly determined by the environmental conditions. The objective forecasting method is ingredients-based but is combined with fuzzy logic algorithms. The new approach provides a feasible exploration of the convective weather phenomenon.

Short-duration heavy rainfall (SHR), as delineated by the National Meteorological Center of the China Meteorological Administration, is characterized by hourly rainfall amounts no less than 20.0 mm. SHR is one of the most common convective weather phenomena that can cause severe damage. Short-range forecasting of SHR is an important part of operational severe weather prediction. In the present study, an improved objective SHR forecasting scheme was developed by adopting the ingredients-based methodology and using a fuzzy logic approach. The 1.0°×1.0° National Centers for Environmental Prediction final analysis (NCEP FNL) data and the ordinary rainfall (0.1-19.9 mm h–1) and SHR observational data from 411 stations were used in the improved scheme. The best lifted index, the total precipitable water, the 925 hPa specific humidity (Q925), and the 925 hPa divergence (DIV925) were selected as predictors based on objective analysis. Continuously distributed membership functions of predictors were obtained based on relative frequency analysis. The weights were also objectively determined. Experiments with a typhoon SHR case and a spring SHR case show that the main possible areas could be captured by the improved scheme. Verification of SHR forecasts within 96 hours with NCEP global forecasts 1.0°×1.0° data initiated at 08:00 Beijing Time during the warm seasons in 2015 show the results were improved from both deterministic and probabilistic perspectives. This study provides an objectively feasible choice for short-range guidance forecasts of SHR. The scheme can be applied to other convective phenomena.

In this study, the impact of soil freezing–thawing processes on August rainfall in southern China (SC) during 1979–2008 and related physical mechanisms are investigated using the Grid-Point Atmospheric Model version 2.0 (GAMIL2.0). This model with considering the supercooled water in soil freezing-thawing scheme reproduces the climatology and trends of August precipitation in the SC region. Moisture-budget analysis is employed to quantity the contributions of different factors to the change of precipitation in SC. The results indicate that evaporation contributes significantly to the climatologically August rainfall in SC. The dynamic component of vertical moisture advection, which is related to changes in atmospheric circulation, plays an important role in August precipitation trends. The possible physical mechanism is that the GAMIL2.0 considering the supercooled water simulated much higher soil/air temperature on August especially in the north of 40°N, weakened the meridional thermal contrast, decreased the 200hpa zonal winds, strengthened 850hpa northerly wind, which is more benificial to the convergence in SC and lead to the precipitation increased. This study provides a new interpretation of the ‘southern flooding’ during 1979–2008 from the point of frozen soil changing.