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This study evaluates the ability of Earth System Models (ESMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to simulate biogeochemical variables in the southern South China Sea (SCS). The analysis focuses on chlorophyll, phytoplankton, nitrate, and oxygen at annual and seasonal scales. The models' performance is assessed against Copernicus Marine Environment Monitoring Service (CMEMS) data using statistical metrics such as the Taylor diagram and Taylor skill score. The results show that the models generally capture the observed spatial patterns of biogeochemical variables but exhibit varying degrees of overestimation or underestimation. The performance of the models is also influenced by the season, with some models showing better performance during the southwest monsoon than the northeast monsoon. Overall, the top five best-performing models for biogeochemical variables are MIROC-ES2H, GFDL-ESM4, CanESM5-CanOE, MPI-ESM1-2-LR, and NorESM2-LM. The findings of this study have implications for researchers and end-users of the datasets, providing guidance for model improvement and understanding the impacts of climate change on the SCS ecosystem. [ABSTRACT FROM AUTHOR]

We examine the change in surface ozone and its precursor behavior over 20 years at four locations in western Peninsular Malaysia which have undergone urban-commercial development. Trend and correlation analyses were carried out on ozone and oxides of nitrogen observation data over the periods of 1997–2016 as well as the decadal intervals of 1997–2006 and 2007–2016. Diurnal variation composites for decadal intervals were also plotted. Significant increasing ozone concentrations were observed at all locations for the 20-year period, with a range between 0.09 and 0.21 ppb yr−1. The most urbanized location (S3) showed the highest ozone trend. Decadal intervals show that not all stations record significant increasing trends of ozone, with S1 recording decreasing ozone at a rate of −0.44 ppb yr−1 during the latter decade. Correlation analysis showed that only oxides of nitrogen ratios (NO/NO2) had significant inverse relationships with ozone at all stations corresponding to control of ozone by photostationary state reactions. The diurnal composites show that decadal difference in NO/NO2 is mostly influenced by change in nitric oxide concentrations.

Understanding the changes in temperature extremes is important for managing and coping with the risks associated with regional climate change. However, the climatological characteristics of temperature extremes and their variabilities is still not adequately studies in Malaysia. This study evaluates the spatial and temporal variations of temperature extremes over Malaysia for the period 1985–2018. This study includes four phases: (a) collection, quality control and homogeneity analysis of temperature data; (b) general (TXmean, TNmean, TMmean and DTR), warm (TXx, TNx, TX90p and TN90p) and cool (TXn, TNn, TX10p and TN10p) temperature extreme indices calculations; (c) trend analysis of temperature extremes using the Mann‐Kendall and Sens's slope test; and (d) analyses of correlations between temperature extremes and El Niño‐Southern Oscillation (ENSO). The results indicate a warming of surface temperature across Malaysia, particularly in Peninsular Malaysia. In general, TXmean, TNmean and TMmean increased significantly at 5% significance level by 0.12°C/decade, 0.27°C/decade and 0.17°C/decade, respectively. A significant decreasing trend in DTR by 0.12°C/decade is seen, which is related to the higher increasing rate of TNmean. All of the warm extreme indices, TXx, TNx, TX90p and TN90p presents significant increasing trends by 0.19°C/decade, 0.28°C/decade, 2.86%/decade and 3.08%/decade, respectively. For the cool extreme indices, TX10p and TN10p decreased significantly by 0.95%/decade and 3.18%/decade, respectively, though the trend in TXn by 0.11°C/decade is not statistically significant. The only cool index presenting a significant increasing trend is TNn by 0.44°C/decade, indicating a reduction of cool nights. Besides that, major cities in the northern and western parts of Peninsular Malaysia generally exhibit a higher warming trend compared to rural and highland area. These are possibly related to the intensified urban heat island effect under the rapid urbanization. This study also found that the ENSO affected warm extreme indices much stronger than cool extreme indices in Malaysia. [ABSTRACT FROM AUTHOR]

This study aims to provide a basis for understanding the mechanisms of diurnal rainfall variability over Peninsular Malaysia by utilising the Non-Hydrostatic Regional Climate Model (NHRCM). The present day climate simulations at 5 km resolution over a period of 20 years, from 1st December 1989 to 31st January 2010 were conducted using the six-hourly Japanese re-analysis 55 years (JRA-55) data and monthly Centennial in situ Observation Based Estimates (COBE) of sea surface temperature as lateral and lower boundary conditions. Despite some biases, the NHRCM performed reasonably well in simulating diurnal rainfall cycles over Peninsular Malaysia. During inter-monsoon periods, the availability of atmospheric moisture played a major role in modulating afternoon rainfall maxima over the foothills of the Titiwangsa mountain range (FT sub-region). During the southwest monsoon, a lack of atmospheric moisture inhibits the occurrence of convective rainfall over the FT sub-region. The NHRCM was also able to simulate the suppression of the diurnal rainfall cycle over the east coast of Peninsular Malaysia (EC sub-region) and afternoon rainfall maximum over the Peninsular Malaysia inland-valley (IN sub-region) area during the northeast monsoon. Over the EC sub-region, daytime radiational warming of the top of clouds enhanced atmospheric stability, thus reducing afternoon rainfall. On the other hand, night-time radiational cooling from cloud tops decreases atmospheric stability and increases nocturnal rainfall. In the early morning, the rainfall maximum was confined to the EC sub-region due to the retardation of the north-easterly monsoonal wind by the land breeze and orographic blocking. However, in the afternoon, superimposition of the sea breeze on the north-easterly monsoonal wind strengthened the north-easterly wind, thus causing the zone of convection to expand further inland. [ABSTRACT FROM AUTHOR]

ABSTRACT: This study evaluates the sensitivity of precipitation in Southeast Asia (SEA) to the choice of land‐surface schemes available in RegCM4, that is BATS1e (BATS) and CLM4.5 (CLM), over the CORDEX SEA domain. Two similar simulations using different land‐surface schemes were conducted for the period 1989 to 2007, with a horizontal resolution of 25 × 25 km. Four different types of observational data were used to evaluate the performance of these simulations. It was found that both of these simulations reproduced the SEA precipitation climatology spatial patterns reasonably well. However, the BATS simulation systematically produced higher frequency and more intense precipitation over land. The CLM simulation, although overestimating the precipitation frequency, produced a lower amount of on‐land precipitation. The precipitation annual cycle and interannual variability were both insensitive to the choice of land‐surface scheme. The errors in the precipitation simulation were found to originate from the simulated convective precipitation (CPr). Large‐scale precipitation was found to be less sensitive to the choice of land‐surface scheme. The influence of the land‐surface scheme on SEA precipitation simulation took place through the interaction between soil moisture content and CPr. The soil moisture content was consistently higher in the BATS simulation, as was the CPr simulated. During December to February (DJF), the difference in the precipitation amount simulated by BATS and CLM simulations was lower over the SEA mainland, even though the soil moisture content in both simulations was very different. This difference was due to the inactivity of the convective activities over the SEA mainland during DJF. This study concludes that the simulation of SEA precipitation amount was sensitive to the choice of land‐surface scheme, and recommend the use of CLM4.5 land‐surface scheme for simulation of SEA precipitation. [ABSTRACT FROM AUTHOR]