Decrease In Shortwave Radiation Research Articles

The possible impact of solar activity on the summer temperature distribution over Eurasia

The effect of solar activity on the regional temperature in winter has been widely discussed. However, whether the summer temperature of land in the northern hemisphere is sensitive to solar activity remains to be further investigated. In this study, the empirical orthogonal function (EOF) analysis, spectrum analysis, and correlation analysis are employed to reveal the possible link between the summer temperature distribution over Eurasian land (0–180°E and 20°N−80°N) and solar activity. The results show that the corresponding time series of the second pattern significantly exhibits an 11-year solar periodicity. Its tripolar temperature distribution is similar to the correlation maps between the temperature and sunspot number (SSN). Particularly, Central Asia (50°E−90°E and 30°N−60°N) is the key response region over Eurasia. The temperature of Central Asia shows a weak but significant negative correlation with SSN. Further analysis of atmospheric circulation indicates that the solar-induced cyclonic and negative geopotential height anomalies in Central Asia weaken the high-pressure ridge on the southwest side and strengthen northwesterly winds. At the same time, with the increase in the cloud cover and the decrease of shortwave radiation, the temperature is lowered. Due to the impact of solar activity, the upper atmosphere over Eurasia forms a wave train-like structure, resulting in a tripolar temperature distribution pattern. On the other hand, the 21-year sliding correlation results suggest that the connection between solar activity and the temperature in Central Asia was strong and decadal stable until 1980. Whereas the temperature and atmospheric circulations in high latitudes become more sensitive to solar activity after 1980. Anyway, solar activity still can be considered a non-negligible factor in the prediction of the summer temperature in Eurasia.

北方地区典型林草地物候时空变化特征及其对气象因子的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 北方地区典型林草地物候时空变化特征及其对气象因子的响应 DOI: 10.5846/stxb202204261156 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金(52079079);江苏省自然科学基金(BK20191129) Spatio-temporal variations of typical woodland and grassland phenology and its response to meteorological factors in Northern China Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为探究北方地区典型植被林地、草地物候特征及其对气候变化的响应,本文基于1982-2015年的GIMMS NDVI 3gv1数据集和气象资料,采用动态阈值法提取植被物候,应用线性回归和偏相关分析法分析林、草地物候时空变化特征及其与气候变化的关系。结果表明:(1)林地生长季长度(LOS)以0.32d/a的速率极显著延长,整体表现为生长季始期(SOS)以-0.18d/a极显著提前,生长季末期(EOS)以0.14d/a极显著推迟。林地SOS提前、EOS推迟和LOS延长的区域面积占比分别为93.3%、90.4%和96.3%。(2)草地LOS以-0.01d/a的速率不显著缩短,表现为SOS以-0.09d/a不显著提前,EOS以-0.10d/a不显著提前。SOS提前、EOS提前和LOS缩短的区域占比为67.5%、69.1%和50%。(3)林地SOS主要受冬末春初的气温升高和降水增加而提前,EOS受夏季气温升高、秋季以及冬末春初降水增加而推迟。(4)草地SOS主要受春季气温升高和短波辐射减少而提前,EOS受秋季气温升高和短波辐射减少而提前,草地物候与气象因子的响应时长小于林地。 Abstract:To reveal the phenological characteristics of typical vegetation woodland and grassland and its response to climate change in Northern China, adopting the GIMMS data and meteorological data from 1982 to 2015, the woodland and grassland phenology were extracted by using a dynamic threshold method, and the spatio-temporal variations of phenology and its response to climate change were identified by linear regression and partial correlation analysis methods. The results can be summarized as follows. (1) The woodland length of season (LOS) was significantly extended with a rate of 0.32d/a, while the start of season (SOS) was significantly advanced with rate at -0.18d/a and the end of season (EOS) was obviously delayed with rate at 0.14d/a. The advanced SOS, delayed EOS, and extended LOS areas covered 93.3%, 90.4%, and 96.3% of the whole woodland area, respectively. (2) The grassland LOS was insignificantly shortened with a rate of -0.01d/a, while the SOS was insignificantly advanced with rate at -0.09d/a and the EOS was insignificantly advanced with rate at -0.10d/a. The advanced SOS and EOS areas covered 67.5% and 69.1% of the whole grassland area, respectively. And, the LOS was shortened in 50% of the areas. (3) The advanced woodland SOS was mainly influenced by the increase in temperature and precipitation in late winter and early spring, and the delayed EOS was affected by the increased temperature in summer and precipitation in autumn, late winter, and early spring. (4) The advanced grassland SOS was mainly related to the increase in temperature and the decrease of short-wave radiation in spring, and the advanced EOS was affected by the increase in temperature and the decrease of short-wave radiation in autumn. The response time of grassland phenology and meteorological factors was shorter than that of woodland. 参考文献 相似文献 引证文献

Aerosol‐Radiation Interactions in China in Winter: Competing Effects of Reduced Shortwave Radiation and Cloud‐Snowfall‐Albedo Feedbacks Under Rapidly Changing Emissions

Since 2013, Chinese policies have dramatically reduced emissions of particulates and their gas‐phase precursors, but the implications of these reductions for aerosol‐radiation interactions are unknown. Using a global, coupled chemistry‐climate model, we examine how the radiative impacts of Chinese air pollution in the winter months of 2012 and 2013 affect local meteorology and how these changes may, in turn, influence surface concentrations of PM2.5, particulate matter with diameter <2.5 μm. We then investigate how decreasing emissions through 2016 and 2017 alter this impact. We find that absorbing aerosols aloft in winter 2012 and 2013 heat the middle‐ and lower troposphere by ∼0.5–1 K, reducing cloud liquid water, snowfall, and snow cover. The subsequent decline in surface albedo appears to counteract the ∼15–20 W m−2 decrease in shortwave radiation reaching the surface due to attenuation by aerosols overhead. The net result of this novel cloud‐snowfall‐albedo feedback in winters 2012–2013 is a slight increase in surface temperature of ∼0.5–1 K in some regions and little change elsewhere. The aerosol heating aloft, however, stabilizes the atmosphere and decreases the seasonal mean planetary boundary layer (PBL) height by ∼50 m. In winter 2016 and 2017, the ∼20% decrease in mean PM2.5 weakens the cloud‐snowfall‐albedo feedback, though it is still evident in western China, where the feedback again warms the surface by ∼0.5–1 K. Regardless of emissions, we find that aerosol‐radiation interactions enhance mean surface PM2.5 pollution by 10%–20% across much of China during all four winters examined, mainly though suppression of PBL heights.

Observed Extreme Air–Sea Heat Flux Variations during Three Tropical Cyclones in the Tropical Southeastern Indian Ocean

AbstractSix-month buoy-based heat flux observations from the poorly sampled tropical southeastern Indian Ocean are examined to document the extremes during three tropical cyclones (TCs) from December 2018 to May 2019. The most striking feature at the mooring site (16.9°S, 115.2°E) during the TCs is the extensively suppressed diurnal cycle of the net surface flux (Qnet), with a mean daytime (nighttime) reduction of 470 (131) W m−2, a peak decrease at approximately noon of 695 W m−2 and an extreme drop during TC Riley of 800 W m−2. The mean surface cooling in the daytime is primarily contributed by the 370 W m−2 decrease in shortwave radiation associated with the increased cloudiness. The air–sea turbulent heat fluxes increase by approximately 151 W m−2 in response to the enhanced wind speed under near-neutral boundary conditions. The daily mean rainfall-induced cooling is 8 W m−2, with a maximum magnitude of 90 W m−2. The mean values, seasonal variation, and synoptic variability of the characteristic heat fluxes are used to assess the new reanalysis data from ERA5 and MERRA2 and the analyzed OAFlux. The overall performance of the high-frequency net heat flux estimates at the synoptic scale is satisfactory, but the four flux components exhibit different quality levels. A serious error is that ERA5 and MERRA2 poorly represent TCs, and they show significant daily mean Qnet biases with opposite directions, −59 W m−2 (largely due to the overestimated latent heat with a bias of −76 W m−2) and 50 W m−2 (largely due to the overestimated shortwave radiation with a bias of 41 W m−2), respectively.

Modeling the incoming all-wave radiation in a planted trench system

Micro-catchment systems (MCs) are designed to harvest and utilize rainwater, with the aim of supporting crop growth in arid regions. While MCs were traditionally built with shallow infiltration basins, recent research indicates that MCs with deeper basins lose less water to the atmosphere than MCs with shallower basins. Consequently, we can expect more water to infiltrate the soil and be available to trees grown in deeper MCs than those grown in shallow MCs. The reduction in the direct water loss is owed, to a large extent, to the decreased flux of incoming shortwave radiation reaching the surface in deeper basins. The degree to which the incoming shortwave radiation reaching the floor of the MC is reduced, in turn, depends on the system’s dimensions and orientation, geographical location, canopy geometry, soil properties, date, and time. We present a model that calculates the incoming all-wave (short- and longwave) radiation flux densities reaching any point on the floor of a trench MC in which trees are planted. To add to previously developed models that considered direct radiation, diffuse radiation, and direct and diffuse radiation reflected downwards from the walls of the trench, the model accounts for possible shading and attenuation of the radiation caused by the presence of a canopy in the system. We have also added the component of longwave radiation, considering longwave radiation emitted from the atmosphere, from the canopy of trees planted within the system, and from the trench walls.We validated the model by comparing modeled results to field measurements inside a planted trench system. We used pyranometers to measure the incoming shortwave radiation and a 4-way net radiometer for the incoming longwave. Our results indicate that the model accurately depicts the diurnal course of shortwave and longwave radiation at different points on the floor of a N-S oriented trench MC and for different solar elevation angles. Simulations for the Negev Desert revealed that the presence of a canopy can strongly influence which trench configurations lead to the greatest decreases in incoming shortwave radiation. When a large canopy is present and the trench is wide, less radiation reaches the ground in N-S oriented trenches than in E-W oriented trenches. While the incoming longwave radiation at the bottom of the trench MC is higher than that on an equivalent horizontal surface at ground level, this increase is not enough to offset the decrease in shortwave radiation. The simulations indicate that the total incoming all-wave radiation (combined shortwave and longwave) inside trenches is less than that outside.

Sea Surface Cooling Induced by Extratropical Cyclones in the Subtropical North Pacific: Mechanism and Interannual Variability

AbstractThe influence of extratropical cyclones on the ocean is examined with a focus on the North Pacific subtropical front (STF), which is a zone of high sea surface temperature (SST) gradients located approximately 25–30°N. The STF becomes most pronounced and susceptible to frequent passages of cyclones in spring. Satellite observations reveal a significant decrease in SST concurrent with cyclone passage along the STF. The SST decreases for approximately 2 days and then gradually recovers over approximately 5 days. The magnitude of the cooling is approximately 0.4 °C. The ocean reanalysis data show a similar surface cooling with a deepening of the mixed layer. The cooling seems to reach the seasonal thermocline and persist there for more than a week. A cyclone over the STF is a subsynoptic cyclone accompanied by a larger synoptic high to the northwest of the low. The surface cooling is mainly attributable to the decrease in shortwave radiation due to the cloud band of the low and the increases in the latent heat and the ocean entrainment, which are associated with intensified northerly winds between the low‐ and high‐pressure systems. The STF varies in strength on interannual timescales in response to the western Pacific pattern, changing the baroclinicity of the overlying atmosphere and the activity of the cyclones. The intense cyclone activity weakens the seasonal SST warming in spring. It is suggested that the cyclones affect the variability of not only the mixed layer but also the seasonal thermocline.

Asymmetric Cloud‐Shortwave Radiation‐Sea Surface Temperature Feedback of Ningaloo Niño/Niña

AbstractUsing observational and reanalysis data, the cloud‐shortwave radiation‐sea surface temperature (SST) feedback in the Ningaloo Niño/Niña region off the west coast of Australia is examined. It is found that this feedback operates as a negative feedback for positive SST anomalies and as a positive feedback for negative SST anomalies. This asymmetry is due to variation in the dominant cloud amount with SST. For positive SST anomalies, a decrease in the shortwave radiation resulting from an increase in high cloud amount associated with deep convection prevails, because SSTs in this region are relatively high compared to other eastern boundary regions and close to the convective threshold. Conversely, the region is under the influence of the subtropical high, and a decrease in the surface shortwave radiation associated with an increase in low cloud amount is dominant for negative SST anomalies.

Sensitivity of glaciation in the arid subtropical Andes to changes in temperature, precipitation, and solar radiation

The subtropical Andes (18.5–27 °S) have been glaciated in the past, but are presently glacier-free. We use idealized model experiments to quantify glacier sensitivity to changes in climate in order to investigate the climatic drivers of past glaciations. We quantify the equilibrium line altitude (ELA) sensitivity (the change in ELA per change in climate) to temperature, precipitation, and shortwave radiation for three distinct climatic regions in the subtropical Andes. We find that in the western cordillera, where conditions are hyper-arid with the highest solar radiation on Earth, ELA sensitivity is as high as 34 m per % increase in precipitation, and 70 m per % decrease in shortwave radiation. This is compared with the eastern cordillera, where precipitation is the highest of the three regions, and ELA sensitivity is only 10 m per % increase in precipitation, and 25 m per % decrease in shortwave radiation. The high ELA sensitivity to shortwave radiation highlights the influence of radiation on mass balance of high elevation and low-latitude glaciers. We also consider these quantified ELA sensitivities in context of previously dated glacial deposits from the regions. Our results suggest that glaciation of the humid eastern cordillera was driven primarily by lower temperatures, while glaciations of the arid Altiplano and western cordillera were also influenced by increases in precipitation and decreases in shortwave radiation. Using paleoclimate records from the timing of glaciation, we find that glaciation of the hyper-arid western cordillera can be explained by precipitation increases of 90–160% (1.9–2.6× higher than modern), in conjunction with associated decreases in shortwave radiation of 7–12% and in temperature of 3.5 °C.

Examining the Climatology of Shortwave Radiation in the Northeastern United States

AbstractAs demand for renewable energy grows, so does the need for an improved understanding of renewable energy sources. Paradoxically, the climate change mitigation strategy of fossil fuel divestment is in itself subject to shifts in weather patterns resulting from climate change. This is particularly true with solar power, which depends on local cloud cover. However, because observed shortwave radiation data usually span a decade or less, persistent long-term trends may not be identified. A simple linear regression model is created here using diurnal temperature range (DTR) during 2002–15 as a predictor variable to estimate long-term shortwave radiation (SR) values in the northeastern United States. Using an extended DTR dataset, SR values are computed for 1956–2015. Statistically significant decreases in shortwave radiation are identified that are dominated by changes during the summer months. Because this coincides with the season of greatest insolation and the highest potential for energy production, financial implications may be large for the solar energy industry if such trends persist into the future.

Climatic response to anthropogenic sulphate aerosols versus well-mixed greenhouse gases from 1850 to 2000 AD in CLIMBER-2

The Earth system model CLIMBER-2 is extended by a scheme for calculating the climatic response to anthropogenic sulphur dioxide emissions. The scheme calculates the direct radiative forcing, the first indirect cloud albedo effect, and the second indirect cloud lifetime effect induced by geographically resolved sulphate aerosol burden. The simulated anthropogenic sulphate aerosol burden in the year 2000 amounts to 0.47 TgS. The best guesses for the radiative forcing due to the direct effect are -0.4 Wm-2 and for the decrease in short-wave radiation due to all aerosol effects -0.8 Wm-2. The simulated global warming by 1 K from 1850 to 2000 caused by anthropogenic greenhouse gases reduces to 0.6 K when the sulphate aerosol effects are included. The model’s hydrological sensitivity of 4%/K is decreased by the second indirect effect to 0.8%/K. The quality of the geographically distributed climatic response to the historic emissions of sulphur dioxide and greenhouse gases makes the extended model relevant to computational efficient investigations of future climate change scenarios.

Interactions among Cloud, Water Vapor, Radiation, and Large-Scale Circulation in the Tropical Climate. Part II: Sensitivity to Spatial Gradients of Sea Surface Temperature

Abstract The responses of the large-scale circulation, clouds, and water vapor to an imposed sea surface temperature (SST) gradient are investigated. Simulations compare reasonably to averaged observations over the Pacific, considering the simplifications applied to the model. The model responses to sinusoidal SST patterns have distinct circulations in the upper and lower troposphere. The upper circulation is sensitive to the heating from deep convection over the warmest SST. Stronger SST gradients are associated with stronger longwave cooling above stratus clouds in the subsidence region, stronger lower-tropospheric large-scale circulation, a reduction of the rain area, and larger area coverage of low clouds. A similar SST gradient with a warmer mean temperature produces slightly weaker lower-tropospheric circulation, and slightly reduced low cloud coverage. The outgoing longwave radiation (OLR) is not sensitive to the mean SST or the range of the imposed sinusoidal SST gradient. The positive feedbacks of water vapor and decreasing high cloud OLR compensate for the increase in longwave emission with increasing mean temperature in these simulations. As the SST gradient is increased keeping the mean SST constant, the positive high cloud feedback is still active, but the air temperature increases in proportion to the maximum SST in the domain, increasing the clear-sky OLR value and keeping the average OLR constant. The net absorbed shortwave radiation (SWI) is found to be extremely sensitive to the SST gradient. The stronger lower-tropospheric large-scale circulation produces a higher water content in the high and low clouds, increasing the absolute magnitude of the shortwave cloud forcing. A 25% increase in the maximum zonal mass flux of the lower circulation of the 300-K mean, 4-K SST range simulation leads to a 7.4 W m−2 decrease in SWI. Increasing the mean SST creates a positive feedback in these simulations because of the decrease in the lower-tropospheric large-scale circulation and the resultant decrease in cloud optical depth.

Simulation of high-latitude hydrological processes in the Torne–Kalix basin: PILPS Phase 2(e): 3: Equivalent model representation and sensitivity experiments

The Project for Intercomparison of Land Surface Parameterization Schemes (PILPS) Phase 2(e) showed that in cold regions the annual runoff production in Land Surface Schemes (LSSs) is closely related to the maximum snow accumulation, which in turn is controlled in large part by winter sublimation. To help further explain the relationship between snow cover, turbulent exchanges and runoff production, a simple equivalent model (SEM) was devised to reproduce the seasonal and annual fluxes simulated by 13 LSSs that participated in PILPS Phase 2(e). The design of the SEM relates the annual partitioning of precipitation and energy in the LSSs to three primary parameters: snow albedo, effective aerodynamic resistance and evaporation efficiency. Isolation of each of the parameters showed that the annual runoff production was most sensitive to the aerodynamic resistance. The SEM was somewhat successful in reproducing the observed LSS response to a decrease in shortwave radiation and changes in wind speed forcings. SEM parameters derived from the reduced shortwave forcings suggested that increased winter stability suppressed turbulent heat fluxes over snow. Because winter sensible heat fluxes were largely negative, reductions in winter shortwave radiation resulted in an increase in annual average sensible heat.