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- Author or Editor: Biao Chen x
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Abstract
The sea surface salinity (SSS) varies largely as a result of the evaporation–precipitation difference, indicating the source or sink of regional/global water vapor. This study identifies a relationship between the spring SSS in the tropical northwest Pacific (TNWP) and the summer rainfall of the East Asian monsoon region (EAMR) during 1980–2017. Analysis suggests that the SSS–rainfall link involves the coupled ocean–atmosphere–land processes with a multifacet evolution. In spring, evaporation and water vapor flux divergence were enhanced in some years over the TNWP where an anomalous atmospheric anticyclone was established and a high SSS was well observed. As a result, the convergence of water vapor flux and soil moisture over the EAMR was strengthened. This ocean-to-land water vapor transport pattern was sustained from spring to summer and played a leading role in the EAMR rainfall. Moreover, the change in local spring soil moisture helped to amplify the summer rainfall by modifying surface thermal conditions and precipitation systems over the EAMR. As the multifacet evolution is closely related to the large-scale ocean-to-land water vapor transport, it can be well represented by the spring SSS in the TNWP. A random forest regression algorithm was used to further evaluate the relative importance of spring SSS in predicting summer rainfall compared to other climate indices. As the SSS is now monitored routinely by satellite and the global Argo float array, it can serve as a good metric for measuring the water cycle and as a precursor for predicting the EAMR rainfall.
Abstract
The sea surface salinity (SSS) varies largely as a result of the evaporation–precipitation difference, indicating the source or sink of regional/global water vapor. This study identifies a relationship between the spring SSS in the tropical northwest Pacific (TNWP) and the summer rainfall of the East Asian monsoon region (EAMR) during 1980–2017. Analysis suggests that the SSS–rainfall link involves the coupled ocean–atmosphere–land processes with a multifacet evolution. In spring, evaporation and water vapor flux divergence were enhanced in some years over the TNWP where an anomalous atmospheric anticyclone was established and a high SSS was well observed. As a result, the convergence of water vapor flux and soil moisture over the EAMR was strengthened. This ocean-to-land water vapor transport pattern was sustained from spring to summer and played a leading role in the EAMR rainfall. Moreover, the change in local spring soil moisture helped to amplify the summer rainfall by modifying surface thermal conditions and precipitation systems over the EAMR. As the multifacet evolution is closely related to the large-scale ocean-to-land water vapor transport, it can be well represented by the spring SSS in the TNWP. A random forest regression algorithm was used to further evaluate the relative importance of spring SSS in predicting summer rainfall compared to other climate indices. As the SSS is now monitored routinely by satellite and the global Argo float array, it can serve as a good metric for measuring the water cycle and as a precursor for predicting the EAMR rainfall.
Abstract
A case study investigation into the meridional and horizontal circulation over the South Pacific Ocean is presented for the 1986–89 El Niño–Southern Oscillation (ENSO) cycle. Using the European Centre for Medium-Range Weather Forecasts (ECMWF) analyses, annual average fields are created for the years before and after the 1987 minimum (warm phase) and 1989 maximum (cold phase) in the Southern Oscillation index. The analyses reveal a shift in the split jet stream over the south Pacific sector(180°–120°W)from a strong subtropical jet (STJ) and weak polar front jet (PFJ) during the warm phase to a weak STJ and strong PFJ during the cold phase.
Analysis of the momentum budget reveals how the split jet in the upper troposphere over South Pacific Ocean evolved during the 1986–89 ENSO cycle. During the warm phase, the strong STJ is associated with advection of the mean flow momentum flux from the Australian sector, which is approximately balanced by a large negative ageostrophic term; the PFJ is primarily associated with eddy momentum convergence, which is partially counterbalanced by the ageostrophic term. During the cold phase, the weakened STJ is related to an increasingly negative ageostrophic term and a less positive mean flow momentum convergence. The strengthened PFJ is associated with an increase in the convergence of eddy momentum flux that is mainly composed of 2.5–6-day poleward momentum transport from midlatitudes and 7–30-day equatorward momentum transport from high latitudes. In general, the impacts of eddy stress on the STJ and the mean momentum divergence on the PFJ in this sector are small.
The variations in the split jet may reflect the poleward propagation of the ENSO signal via the South Pacific convergence zone. The implications for the high southern latitudes are discussed as interannual variations are found in the low-level easterlies near Antarctica and the Amundsen Sea low.
Abstract
A case study investigation into the meridional and horizontal circulation over the South Pacific Ocean is presented for the 1986–89 El Niño–Southern Oscillation (ENSO) cycle. Using the European Centre for Medium-Range Weather Forecasts (ECMWF) analyses, annual average fields are created for the years before and after the 1987 minimum (warm phase) and 1989 maximum (cold phase) in the Southern Oscillation index. The analyses reveal a shift in the split jet stream over the south Pacific sector(180°–120°W)from a strong subtropical jet (STJ) and weak polar front jet (PFJ) during the warm phase to a weak STJ and strong PFJ during the cold phase.
Analysis of the momentum budget reveals how the split jet in the upper troposphere over South Pacific Ocean evolved during the 1986–89 ENSO cycle. During the warm phase, the strong STJ is associated with advection of the mean flow momentum flux from the Australian sector, which is approximately balanced by a large negative ageostrophic term; the PFJ is primarily associated with eddy momentum convergence, which is partially counterbalanced by the ageostrophic term. During the cold phase, the weakened STJ is related to an increasingly negative ageostrophic term and a less positive mean flow momentum convergence. The strengthened PFJ is associated with an increase in the convergence of eddy momentum flux that is mainly composed of 2.5–6-day poleward momentum transport from midlatitudes and 7–30-day equatorward momentum transport from high latitudes. In general, the impacts of eddy stress on the STJ and the mean momentum divergence on the PFJ in this sector are small.
The variations in the split jet may reflect the poleward propagation of the ENSO signal via the South Pacific convergence zone. The implications for the high southern latitudes are discussed as interannual variations are found in the low-level easterlies near Antarctica and the Amundsen Sea low.
Abstract
Solar radiation is one of the most important factors affecting climate and the environment. Routine measurements of irradiance are valuable for climate change research because of long time series and areal coverage. In this study, a set of quality assessment (QA) algorithms is used to test the quality of daily solar global, direct, and diffuse radiation measurements taken at 122 observatories in China during 1957–2000. The QA algorithms include a physical threshold test (QA1), a global radiation sunshine duration test (QA2), and a standard deviation test applied to time series of annually averaged solar global radiation (QA3). The results show that the percentages of global, direct, and diffuse solar radiation data that fail to pass QA1 are 3.07%, 0.01%, and 2.52%, respectively; the percentages of global solar radiation data that fail to pass the QA2 and QA3 are 0.77% and 0.49%, respectively. The method implemented by the Global Energy Balance Archive is also applied to check the data quality of solar radiation in China. Of the 84 stations with a time series longer that 20 yr, suspect data at 35 of the sites were found. Based on data that passed the QA tests, trends in ground solar radiation and the effect of the data quality assessment on the trends are analyzed. There is a decrease in ground solar global and direct radiation in China over the years under study. Although the quality assessment process has significant effects on the data from individual stations and/or time periods, it does not affect the long-term trends in the data.
Abstract
Solar radiation is one of the most important factors affecting climate and the environment. Routine measurements of irradiance are valuable for climate change research because of long time series and areal coverage. In this study, a set of quality assessment (QA) algorithms is used to test the quality of daily solar global, direct, and diffuse radiation measurements taken at 122 observatories in China during 1957–2000. The QA algorithms include a physical threshold test (QA1), a global radiation sunshine duration test (QA2), and a standard deviation test applied to time series of annually averaged solar global radiation (QA3). The results show that the percentages of global, direct, and diffuse solar radiation data that fail to pass QA1 are 3.07%, 0.01%, and 2.52%, respectively; the percentages of global solar radiation data that fail to pass the QA2 and QA3 are 0.77% and 0.49%, respectively. The method implemented by the Global Energy Balance Archive is also applied to check the data quality of solar radiation in China. Of the 84 stations with a time series longer that 20 yr, suspect data at 35 of the sites were found. Based on data that passed the QA tests, trends in ground solar radiation and the effect of the data quality assessment on the trends are analyzed. There is a decrease in ground solar global and direct radiation in China over the years under study. Although the quality assessment process has significant effects on the data from individual stations and/or time periods, it does not affect the long-term trends in the data.
Abstract
A sensitivity study to evaluate the impact upon regional and hemispheric climate caused by changing the optical properties of clouds over the Antarctic continent is conducted with the NCAR Community Model version 2 (CCM2). Sensitivity runs are performed in which radiation interacts with ice clouds with particle sizes of 10 and 40 μm rather than with the standard 10-μm water clouds. The experiments are carried out for perpetual January conditions with the diurnal cycle considered. The effects of these cloud changes on the Antarctic radiation budget are examined by considering cloud forcing at the top of the atmosphere and net radiation at the surface. Changes of the cloud radiative properties to those of 10-μm ice clouds over Antarctica have significant impacts on regional climate: temperature increases throughout the Antarctic troposphere by 1°–2°C and total cloud fraction over Antarctica is smaller than that of the control at low levels but is larger than that of the control in the mid- to upper troposphere. As a result of Antarctic warming and changes in the north–south temperature gradient, the drainage flows at the surface as well as the meridional mass circulation are weakened. Similarly, the circumpolar trough weakens significantly by 4–8 hPa and moves northward by about 4°–5° latitude. This regional mass field adjustment halves the strength of the simulated surface westerly winds. As a result of indirect thermodynamic and dynamic effects, significant changes are observed in the zonal mean circulation and eddies in the middle latitudes. In fact, the simulated impacts of the Antarctic cloud radiative alteration are not confined to the Southern Hemisphere. The meridional mean mass flux, zonal wind, and latent heat release exhibit statistically significant changes in the Tropics and even extratropics of the Northern Hemisphere. The simulation with radiative properties of 40-μm ice clouds produces colder surface temperatures over Antarctica by up to 3°C compared to the control. Otherwise, the results of the 40-μm ice cloud simulation are similar to those of the 10-μm ice cloud simulation.
Abstract
A sensitivity study to evaluate the impact upon regional and hemispheric climate caused by changing the optical properties of clouds over the Antarctic continent is conducted with the NCAR Community Model version 2 (CCM2). Sensitivity runs are performed in which radiation interacts with ice clouds with particle sizes of 10 and 40 μm rather than with the standard 10-μm water clouds. The experiments are carried out for perpetual January conditions with the diurnal cycle considered. The effects of these cloud changes on the Antarctic radiation budget are examined by considering cloud forcing at the top of the atmosphere and net radiation at the surface. Changes of the cloud radiative properties to those of 10-μm ice clouds over Antarctica have significant impacts on regional climate: temperature increases throughout the Antarctic troposphere by 1°–2°C and total cloud fraction over Antarctica is smaller than that of the control at low levels but is larger than that of the control in the mid- to upper troposphere. As a result of Antarctic warming and changes in the north–south temperature gradient, the drainage flows at the surface as well as the meridional mass circulation are weakened. Similarly, the circumpolar trough weakens significantly by 4–8 hPa and moves northward by about 4°–5° latitude. This regional mass field adjustment halves the strength of the simulated surface westerly winds. As a result of indirect thermodynamic and dynamic effects, significant changes are observed in the zonal mean circulation and eddies in the middle latitudes. In fact, the simulated impacts of the Antarctic cloud radiative alteration are not confined to the Southern Hemisphere. The meridional mean mass flux, zonal wind, and latent heat release exhibit statistically significant changes in the Tropics and even extratropics of the Northern Hemisphere. The simulation with radiative properties of 40-μm ice clouds produces colder surface temperatures over Antarctica by up to 3°C compared to the control. Otherwise, the results of the 40-μm ice cloud simulation are similar to those of the 10-μm ice cloud simulation.
