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Abstract
The present study reveals a close relation between the interannual variation of Aleutian low intensity (ALI) in March and the subsequent winter El Niño–Southern Oscillation (ENSO). When March ALI is weaker (stronger) than normal, an El Niño (a La Niña)–like sea surface temperature (SST) warming (cooling) tends to appear in the equatorial central-eastern Pacific during the subsequent winter. The physical process linking March ALI to the following winter ENSO is as follows. When March ALI is below normal, a notable atmospheric dipole pattern develops over the North Pacific, with an anticyclonic anomaly over the Aleutian region and a cyclonic anomaly over the subtropical west-central Pacific. The formation of the anomalous cyclone is attributed to feedback of the synoptic-scale eddy-to-mean-flow energy flux and associated vorticity transportation. Specifically, easterly wind anomalies over the midlatitudes related to the weakened ALI are accompanied by a decrease in synoptic-scale eddy activity, which forces an anomalous cyclone to its southern flank. The accompanying westerly wind anomalies over the tropical west-central Pacific induce SST warming in the equatorial central-eastern Pacific during the following summer–autumn via triggering eastward-propagating warm Kelvin waves, which may sustain and develop into an El Niño event during the following winter via positive air–sea feedback. The relation of March ALI with the following winter ENSO is independent of the preceding tropical Pacific SST, the preceding-winter North Pacific Oscillation, and the spring Arctic Oscillation. The results of this analysis may provide an additional source for the prediction of ENSO.
Abstract
The present study reveals a close relation between the interannual variation of Aleutian low intensity (ALI) in March and the subsequent winter El Niño–Southern Oscillation (ENSO). When March ALI is weaker (stronger) than normal, an El Niño (a La Niña)–like sea surface temperature (SST) warming (cooling) tends to appear in the equatorial central-eastern Pacific during the subsequent winter. The physical process linking March ALI to the following winter ENSO is as follows. When March ALI is below normal, a notable atmospheric dipole pattern develops over the North Pacific, with an anticyclonic anomaly over the Aleutian region and a cyclonic anomaly over the subtropical west-central Pacific. The formation of the anomalous cyclone is attributed to feedback of the synoptic-scale eddy-to-mean-flow energy flux and associated vorticity transportation. Specifically, easterly wind anomalies over the midlatitudes related to the weakened ALI are accompanied by a decrease in synoptic-scale eddy activity, which forces an anomalous cyclone to its southern flank. The accompanying westerly wind anomalies over the tropical west-central Pacific induce SST warming in the equatorial central-eastern Pacific during the following summer–autumn via triggering eastward-propagating warm Kelvin waves, which may sustain and develop into an El Niño event during the following winter via positive air–sea feedback. The relation of March ALI with the following winter ENSO is independent of the preceding tropical Pacific SST, the preceding-winter North Pacific Oscillation, and the spring Arctic Oscillation. The results of this analysis may provide an additional source for the prediction of ENSO.
Abstract
A spurious wavelike pattern in the monthly rain day statistics exists within the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis precipitation product. The anomaly, which is an artifact of the parameterization of moisture diffusion, occurs during the winter months in the Northern and Southern Hemisphere high latitudes. The anomaly is corrected by using monthly statistics from three different global precipitation products from 1) the University of Washington (UW), 2) the Global Precipitation Climate Project (GPCP), and 3) the Climatic Research Unit (CRU), resulting in three slightly different corrected precipitation products. The correction methodology, however, compromises spatial consistency (e.g., storm tracking) on a daily time scale. The effect that the precipitation correction has on the reanalysis-derived global land surface water budgets is investigated by forcing the Variable Infiltration Capacity (VIC) land surface model with all four datasets (i.e., the original reanalysis product and the three corrected datasets). The main components of the land surface water budget cycle are not affected substantially; however, the increased spatial variability in precipitation is reflected in the evaporation and runoff components but reduced in the case of soil moisture. Furthermore, the partitioning of precipitation into canopy evaporation and throughfall is sensitive to the rain day statistics of the correcting dataset, especially in the Tropics, and this has implications for the required accuracy of the correcting dataset. The output fields from these long-term land surface simulations provide a global, consistent dataset of water and energy states and fluxes that can be used for model intercomparisons, studies of annual and seasonal climate variability, and comparisons with current versions of numerical weather prediction models.
Abstract
A spurious wavelike pattern in the monthly rain day statistics exists within the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis precipitation product. The anomaly, which is an artifact of the parameterization of moisture diffusion, occurs during the winter months in the Northern and Southern Hemisphere high latitudes. The anomaly is corrected by using monthly statistics from three different global precipitation products from 1) the University of Washington (UW), 2) the Global Precipitation Climate Project (GPCP), and 3) the Climatic Research Unit (CRU), resulting in three slightly different corrected precipitation products. The correction methodology, however, compromises spatial consistency (e.g., storm tracking) on a daily time scale. The effect that the precipitation correction has on the reanalysis-derived global land surface water budgets is investigated by forcing the Variable Infiltration Capacity (VIC) land surface model with all four datasets (i.e., the original reanalysis product and the three corrected datasets). The main components of the land surface water budget cycle are not affected substantially; however, the increased spatial variability in precipitation is reflected in the evaporation and runoff components but reduced in the case of soil moisture. Furthermore, the partitioning of precipitation into canopy evaporation and throughfall is sensitive to the rain day statistics of the correcting dataset, especially in the Tropics, and this has implications for the required accuracy of the correcting dataset. The output fields from these long-term land surface simulations provide a global, consistent dataset of water and energy states and fluxes that can be used for model intercomparisons, studies of annual and seasonal climate variability, and comparisons with current versions of numerical weather prediction models.
Abstract
Kilometer-scale climate model simulations are useful tools to investigate past and future changes in extreme precipitation, particularly in mountain regions, where convection is influenced by complex topography and land–atmosphere interactions. In this study, we evaluate simulations of a flood-producing mesoscale convective system (MCS) downstream of the Tibetan Plateau (TP) in the Sichuan basin from a kilometer-scale multimodel and multiphysics ensemble. The aim is to better understand the physical processes that need to be correctly simulated for successfully capturing downstream MCS formation. We assess how the ensemble members simulate these processes and how sensitive the simulations are to different model configurations. The preceding vortex evolution over the TP, its interaction with the jet stream, and water vapor advection into the basin are identified as key processes for the MCS formation. Most modeling systems struggle to capture the interaction between the vortex and jet stream, and perturbing the model physics has little impact, while constraining the large-scale flow by spectral nudging improves the simulation. This suggests that an accurate representation of the large-scale forcing is crucial to correctly simulate the MCS and associated precipitation. To verify whether the identified shortcomings systematically affect the MCS climatology in longer-term simulations, we evaluate a 1-yr WRF simulation and find that the seasonal cycle and spatial distribution of MCSs are reasonably well captured and not improved by spectral nudging. While the simulations of the MCS case highlight challenges in extreme precipitation forecasting, we conclude that these challenges do not systematically affect simulated climatological MCS characteristics.
Significance Statement
Convective storm systems in mountain regions are not well understood, because the spatial resolution in conventional regional climate models is too coarse to resolve relevant processes. Here, we evaluate high-resolution climate model simulations of a storm system on the downwind side of the Tibetan Plateau. Understanding which models and model setups work well to represent this type of storm system is important because high-resolution models can help us understand mechanisms of storm formation in mountain regions and how climate change will affect these. A key finding is that most of the models struggle to capture the selected storm case, while a 1-yr simulation shows that the general statistics of storm systems around the Tibetan Plateau are still reasonably well captured.
Abstract
Kilometer-scale climate model simulations are useful tools to investigate past and future changes in extreme precipitation, particularly in mountain regions, where convection is influenced by complex topography and land–atmosphere interactions. In this study, we evaluate simulations of a flood-producing mesoscale convective system (MCS) downstream of the Tibetan Plateau (TP) in the Sichuan basin from a kilometer-scale multimodel and multiphysics ensemble. The aim is to better understand the physical processes that need to be correctly simulated for successfully capturing downstream MCS formation. We assess how the ensemble members simulate these processes and how sensitive the simulations are to different model configurations. The preceding vortex evolution over the TP, its interaction with the jet stream, and water vapor advection into the basin are identified as key processes for the MCS formation. Most modeling systems struggle to capture the interaction between the vortex and jet stream, and perturbing the model physics has little impact, while constraining the large-scale flow by spectral nudging improves the simulation. This suggests that an accurate representation of the large-scale forcing is crucial to correctly simulate the MCS and associated precipitation. To verify whether the identified shortcomings systematically affect the MCS climatology in longer-term simulations, we evaluate a 1-yr WRF simulation and find that the seasonal cycle and spatial distribution of MCSs are reasonably well captured and not improved by spectral nudging. While the simulations of the MCS case highlight challenges in extreme precipitation forecasting, we conclude that these challenges do not systematically affect simulated climatological MCS characteristics.
Significance Statement
Convective storm systems in mountain regions are not well understood, because the spatial resolution in conventional regional climate models is too coarse to resolve relevant processes. Here, we evaluate high-resolution climate model simulations of a storm system on the downwind side of the Tibetan Plateau. Understanding which models and model setups work well to represent this type of storm system is important because high-resolution models can help us understand mechanisms of storm formation in mountain regions and how climate change will affect these. A key finding is that most of the models struggle to capture the selected storm case, while a 1-yr simulation shows that the general statistics of storm systems around the Tibetan Plateau are still reasonably well captured.
Abstract
Combined impacts of the Pacific decadal oscillation (PDO) and two types of La Niña on climate anomalies in Europe are studied. Particularly, the conjunction of the negative PDO phase and two different types of La Niña events favors strong and significant North Atlantic Oscillation (NAO) pattern anomalies with opposite polarity. For the central Pacific (CP) La Niña, a clear positive NAO signal can be detected, which is accompanied by positive surface air temperature (SAT) anomaly and a dipolar structure of precipitation anomalies in Europe. In addition, a typical negative Pacific–North America (PNA) teleconnection pattern forms, including a high pressure anomaly over the southeastern United States, which may contribute to the development and maintenance of the NAO anomaly by strengthening the baroclinicity and the local eddy–mean flow interaction. However, for the eastern Pacific (EP) La Niña, a zonal wave train in the high latitudes can be observed, which is quite different from the typical PNA structure. Here, an anomalous anticyclone over southern Greenland supports a negative NAO pattern through the local eddy–mean flow interaction and the associated vorticity advection. Hence, reversed SAT and precipitation anomalies occur over Europe. Further analyses indicate that the wave trains emanating from the North Pacific and the synoptic eddy–mean flow interaction play essential roles in forming the anomalous NAO phases. The different wave trains for the CP and EP La Niña events may be attributed to the differences in the location and intensity of anomalous convection induced by different types of SST anomaly as well as by the corresponding background westerly wind anomalies in the upper troposphere.
Abstract
Combined impacts of the Pacific decadal oscillation (PDO) and two types of La Niña on climate anomalies in Europe are studied. Particularly, the conjunction of the negative PDO phase and two different types of La Niña events favors strong and significant North Atlantic Oscillation (NAO) pattern anomalies with opposite polarity. For the central Pacific (CP) La Niña, a clear positive NAO signal can be detected, which is accompanied by positive surface air temperature (SAT) anomaly and a dipolar structure of precipitation anomalies in Europe. In addition, a typical negative Pacific–North America (PNA) teleconnection pattern forms, including a high pressure anomaly over the southeastern United States, which may contribute to the development and maintenance of the NAO anomaly by strengthening the baroclinicity and the local eddy–mean flow interaction. However, for the eastern Pacific (EP) La Niña, a zonal wave train in the high latitudes can be observed, which is quite different from the typical PNA structure. Here, an anomalous anticyclone over southern Greenland supports a negative NAO pattern through the local eddy–mean flow interaction and the associated vorticity advection. Hence, reversed SAT and precipitation anomalies occur over Europe. Further analyses indicate that the wave trains emanating from the North Pacific and the synoptic eddy–mean flow interaction play essential roles in forming the anomalous NAO phases. The different wave trains for the CP and EP La Niña events may be attributed to the differences in the location and intensity of anomalous convection induced by different types of SST anomaly as well as by the corresponding background westerly wind anomalies in the upper troposphere.
Abstract
The Maritime Continent (MC), located in the heart of the Indo-Pacific warm pool, plays an important role in the global climate. However, the future MC climate is largely unknown, in particular the ENSO–rainfall teleconnection. ENSO induces a zonal dipole pattern of rainfall variability across the Indo-Pacific Ocean, that is, positive variability in the tropical Pacific and negative variability toward the MC. Here, new CMIP6 models robustly project that, for both land and sea rainfall, the negative ENSO teleconnection over the MC (drier during El Niño and wetter during La Niña) could intensify significantly under the Shared Socioeconomic Pathway 5–8.5 (SSP585) warming scenario. A strengthened teleconnection may cause enhanced droughts and flooding, leading to agricultural impacts and altering rainfall predictability over the region. Models also project that both the Indo-Pacific rainfall center and the zero crossing of dipole-like rainfall variability shift eastward; these adjustments are more notable during boreal summer than during winter. All these projections are robustly supported by the model agreement and scale up with the warming trend.
Abstract
The Maritime Continent (MC), located in the heart of the Indo-Pacific warm pool, plays an important role in the global climate. However, the future MC climate is largely unknown, in particular the ENSO–rainfall teleconnection. ENSO induces a zonal dipole pattern of rainfall variability across the Indo-Pacific Ocean, that is, positive variability in the tropical Pacific and negative variability toward the MC. Here, new CMIP6 models robustly project that, for both land and sea rainfall, the negative ENSO teleconnection over the MC (drier during El Niño and wetter during La Niña) could intensify significantly under the Shared Socioeconomic Pathway 5–8.5 (SSP585) warming scenario. A strengthened teleconnection may cause enhanced droughts and flooding, leading to agricultural impacts and altering rainfall predictability over the region. Models also project that both the Indo-Pacific rainfall center and the zero crossing of dipole-like rainfall variability shift eastward; these adjustments are more notable during boreal summer than during winter. All these projections are robustly supported by the model agreement and scale up with the warming trend.
Abstract
Mesoscale convective systems (MCSs) play an important role in modulating the global water cycle and energy balance and frequently generate high-impact weather events. The majority of existing literature studying MCS activity over East Asia is based on specific case studies and more climatological investigations revealing the precipitation characteristics of MCSs over eastern China are keenly needed. In this study, we use an iterative rain cell tracking method to identify and track MCS precipitation during 2008–16 to investigate regional differences and seasonal variations of MCS precipitation characteristics. Our results show that the middle-to-lower reaches of the Yangtze River basin (YRB-ML) receive the largest amount and exhibit the most pronounced seasonal cycle of MCS precipitation in eastern China. MCS precipitation over YRB-ML can exceed 2.6 mm day−1 in June, contributing over 30.0% of April–July total rainfall. Particularly long-lived MCSs occur over the eastern periphery of the Tibetan Plateau (ETP), with 25% of MCSs over the ETP persisting for more than 18 h in spring. In addition, spring MCSs feature larger rainfall areas, longer durations, and faster propagation speeds. Summer MCSs have a higher precipitation intensity and a more pronounced diurnal cycle except for southeastern China, where MCSs have similar precipitation intensity in spring and summer. There is less MCS precipitation in autumn, but an MCS precipitation center over the ETP still persists. MCSs reach peak hourly rainfall intensities during the time of maximum growth (a few hours after genesis), reach their maximum size around 5 h after genesis, and start decaying thereafter.
Abstract
Mesoscale convective systems (MCSs) play an important role in modulating the global water cycle and energy balance and frequently generate high-impact weather events. The majority of existing literature studying MCS activity over East Asia is based on specific case studies and more climatological investigations revealing the precipitation characteristics of MCSs over eastern China are keenly needed. In this study, we use an iterative rain cell tracking method to identify and track MCS precipitation during 2008–16 to investigate regional differences and seasonal variations of MCS precipitation characteristics. Our results show that the middle-to-lower reaches of the Yangtze River basin (YRB-ML) receive the largest amount and exhibit the most pronounced seasonal cycle of MCS precipitation in eastern China. MCS precipitation over YRB-ML can exceed 2.6 mm day−1 in June, contributing over 30.0% of April–July total rainfall. Particularly long-lived MCSs occur over the eastern periphery of the Tibetan Plateau (ETP), with 25% of MCSs over the ETP persisting for more than 18 h in spring. In addition, spring MCSs feature larger rainfall areas, longer durations, and faster propagation speeds. Summer MCSs have a higher precipitation intensity and a more pronounced diurnal cycle except for southeastern China, where MCSs have similar precipitation intensity in spring and summer. There is less MCS precipitation in autumn, but an MCS precipitation center over the ETP still persists. MCSs reach peak hourly rainfall intensities during the time of maximum growth (a few hours after genesis), reach their maximum size around 5 h after genesis, and start decaying thereafter.
Abstract
The present study investigates different impacts of the East Asian winter monsoon (EAWM) on surface air temperature (Ts) in North America (NA) during ENSO and neutral ENSO episodes. In neutral ENSO years, the EAWM shows a direct impact on the Ts anomalies in NA on an interannual time scale. Two Rossby wave packets appear over the Eurasian–western Pacific (upstream) and North Pacific–NA (downstream) regions associated with a strong EAWM. Further analysis suggests that the downstream wave packet is caused by reflection of the upstream wave packet over the subtropical western Pacific and amplified over the North Pacific. Also, the East Asian subtropical westerly jet stream (EAJS) is intensified in the central and downstream region over the central North Pacific. Hence, increased barotropic kinetic energy conversion and the interaction between transient eddies and the EAJS tend to maintain the circulation anomaly over the North Pacific. Therefore, a strong EAWM tends to result in warm Ts anomalies in northwestern NA via the downstream wave packet emanating from the central North Pacific toward NA. A weak EAWM tends to induce cold Ts anomalies in western-central NA with a smaller magnitude. However, in ENSO years, an anomalous EAJS is mainly confined over East Asia and does not extend into the central North Pacific. The results confirm that the EAWM has an indirect impact on the Ts anomalies in NA via a modulation of the tropical convection anomalies associated with ENSO. Our results indicate that, for seasonal prediction of Ts anomalies in NA, the influence of the EAWM should be taken into account. It produces different responses in neutral ENSO and in ENSO years.
Abstract
The present study investigates different impacts of the East Asian winter monsoon (EAWM) on surface air temperature (Ts) in North America (NA) during ENSO and neutral ENSO episodes. In neutral ENSO years, the EAWM shows a direct impact on the Ts anomalies in NA on an interannual time scale. Two Rossby wave packets appear over the Eurasian–western Pacific (upstream) and North Pacific–NA (downstream) regions associated with a strong EAWM. Further analysis suggests that the downstream wave packet is caused by reflection of the upstream wave packet over the subtropical western Pacific and amplified over the North Pacific. Also, the East Asian subtropical westerly jet stream (EAJS) is intensified in the central and downstream region over the central North Pacific. Hence, increased barotropic kinetic energy conversion and the interaction between transient eddies and the EAJS tend to maintain the circulation anomaly over the North Pacific. Therefore, a strong EAWM tends to result in warm Ts anomalies in northwestern NA via the downstream wave packet emanating from the central North Pacific toward NA. A weak EAWM tends to induce cold Ts anomalies in western-central NA with a smaller magnitude. However, in ENSO years, an anomalous EAJS is mainly confined over East Asia and does not extend into the central North Pacific. The results confirm that the EAWM has an indirect impact on the Ts anomalies in NA via a modulation of the tropical convection anomalies associated with ENSO. Our results indicate that, for seasonal prediction of Ts anomalies in NA, the influence of the EAWM should be taken into account. It produces different responses in neutral ENSO and in ENSO years.
Abstract
This study highlights the distinct modulation of May–October tropical cyclones (TCs) in the western North Pacific (WNP), eastern North Pacific (ENP), and North Atlantic (NATL) Ocean basins by tropical transbasin variability (TBV) and ENSO. The pure TBV significantly modulates total TC counts in all three basins, with more TCs in the WNP and ENP and fewer TCs in the NATL during warm TBV years and fewer TCs in the WNP and ENP and more TCs in the NATL during cold TBV years. By contrast, the pure ENSO signal shows no impact on total TC count over any of the three basins. These results are consistent with changes in large-scale factors associated with TBV and ENSO. Low-level relative vorticity (VOR) is an important driver of WNP TC genesis frequency, with broad agreement between the observed spatial distribution of TC genesis and TBV/ENSO-associated VOR anomalies. TBV significantly affects ENP TC frequency as a result of changes in basinwide vertical wind shear and sea surface temperatures, whereas the modulation in TC frequency by ENSO is primarily caused by a north–south dipole modulation of large-scale atmospheric and oceanic factors. The pure TBV-related low-level VOR changes appear to be the most important factor modulating NATL TC frequency. Changes in large-scale factors compare well with the budget of synoptic-scale eddy kinetic energy. Possible physical processes associated with pure TBV and pure ENSO that modulate TC frequency are further discussed. This study contributes to the understanding of TC interannual variability and could thus be helpful for seasonal TC forecasting.
Abstract
This study highlights the distinct modulation of May–October tropical cyclones (TCs) in the western North Pacific (WNP), eastern North Pacific (ENP), and North Atlantic (NATL) Ocean basins by tropical transbasin variability (TBV) and ENSO. The pure TBV significantly modulates total TC counts in all three basins, with more TCs in the WNP and ENP and fewer TCs in the NATL during warm TBV years and fewer TCs in the WNP and ENP and more TCs in the NATL during cold TBV years. By contrast, the pure ENSO signal shows no impact on total TC count over any of the three basins. These results are consistent with changes in large-scale factors associated with TBV and ENSO. Low-level relative vorticity (VOR) is an important driver of WNP TC genesis frequency, with broad agreement between the observed spatial distribution of TC genesis and TBV/ENSO-associated VOR anomalies. TBV significantly affects ENP TC frequency as a result of changes in basinwide vertical wind shear and sea surface temperatures, whereas the modulation in TC frequency by ENSO is primarily caused by a north–south dipole modulation of large-scale atmospheric and oceanic factors. The pure TBV-related low-level VOR changes appear to be the most important factor modulating NATL TC frequency. Changes in large-scale factors compare well with the budget of synoptic-scale eddy kinetic energy. Possible physical processes associated with pure TBV and pure ENSO that modulate TC frequency are further discussed. This study contributes to the understanding of TC interannual variability and could thus be helpful for seasonal TC forecasting.
Abstract
Variability present at a satellite instrument sampling scale (small-scale variability) has been neglected in earlier simulations of atmospheric and cloud property change retrievals using spatially and temporally averaged spectral radiances. The effects of small-scale variability in the atmospheric change detection process are evaluated in this study. To simulate realistic atmospheric variability, top-of-the-atmosphere nadir-view longwave spectral radiances are computed at a high temporal (instantaneous) resolution with a 20-km field-of-view using cloud properties retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS) measurements, along with temperature humidity profiles obtained from reanalysis. Specifically, the effects of the variability on the necessary conditions for retrieving atmospheric changes by a linear regression are tested. The percentage error in the annual 10° zonal mean spectral radiance difference obtained by assuming linear combinations of individual perturbations expressed as a root-mean-square (RMS) difference computed over wavenumbers between 200 and 2000 cm−1 is 10%–15% for most of the 10° zones. However, if cloud fraction perturbation is excluded, the RMS difference decreases to less than 2%. Monthly and annual 10° zonal mean spectral radiances change linearly with atmospheric property perturbations, which occur when atmospheric properties are perturbed by an amount approximately equal to the variability of the10° zonal monthly deseasonalized anomalies or by a climate-model-predicted decadal change. Nonlinear changes in the spectral radiances of magnitudes similar to those obtained through linear estimation can arise when cloud heights and droplet radii in water cloud change. The spectral shapes computed by perturbing different atmospheric and cloud properties are different so that linear regression can separate individual spectral radiance changes from the sum of the spectral radiance change. When the effects of small-scale variability are treated as noise, however, the error in retrieved cloud properties is large. The results suggest the importance of considering small-scale variability in inferring atmospheric and cloud property changes from the satellite-observed zonally and annually averaged spectral radiance difference.
Abstract
Variability present at a satellite instrument sampling scale (small-scale variability) has been neglected in earlier simulations of atmospheric and cloud property change retrievals using spatially and temporally averaged spectral radiances. The effects of small-scale variability in the atmospheric change detection process are evaluated in this study. To simulate realistic atmospheric variability, top-of-the-atmosphere nadir-view longwave spectral radiances are computed at a high temporal (instantaneous) resolution with a 20-km field-of-view using cloud properties retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS) measurements, along with temperature humidity profiles obtained from reanalysis. Specifically, the effects of the variability on the necessary conditions for retrieving atmospheric changes by a linear regression are tested. The percentage error in the annual 10° zonal mean spectral radiance difference obtained by assuming linear combinations of individual perturbations expressed as a root-mean-square (RMS) difference computed over wavenumbers between 200 and 2000 cm−1 is 10%–15% for most of the 10° zones. However, if cloud fraction perturbation is excluded, the RMS difference decreases to less than 2%. Monthly and annual 10° zonal mean spectral radiances change linearly with atmospheric property perturbations, which occur when atmospheric properties are perturbed by an amount approximately equal to the variability of the10° zonal monthly deseasonalized anomalies or by a climate-model-predicted decadal change. Nonlinear changes in the spectral radiances of magnitudes similar to those obtained through linear estimation can arise when cloud heights and droplet radii in water cloud change. The spectral shapes computed by perturbing different atmospheric and cloud properties are different so that linear regression can separate individual spectral radiance changes from the sum of the spectral radiance change. When the effects of small-scale variability are treated as noise, however, the error in retrieved cloud properties is large. The results suggest the importance of considering small-scale variability in inferring atmospheric and cloud property changes from the satellite-observed zonally and annually averaged spectral radiance difference.
Abstract
Sensible heat flux (H), latent heat flux (LE), and net radiation (NR) are important surface energy components that directly influence climate systems. In this study, the changes in the surface energy and their contributions from global climate change and/or land-cover change over eastern China during the past nearly 30 years were investigated and assessed using a process-based land surface model [the Ecosystem–Atmosphere Simulation Scheme (EASS)]. The modeled results show that climate change contributed more to the changes of land surface energy fluxes than land-cover change, with their contribution ratio reaching 4:1 or even higher. Annual average temperature increased before 2000 and reversed thereafter; annual total precipitation continually decreased, and incident solar radiation continually increased over the past nearly 30 years. These climatic changes could lead to increased NR, H, and LE, assuming land cover remained unchanged during the past nearly 30 years. Among these meteorological variables, at spatial distribution, the incident solar radiation has the greatest effect on land surface energy exchange. The impacts of land-cover change on the seasonal variations in land surface heat fluxes between the four periods were large, especially for H. The changes in the regional energy fluxes resulting from different land-cover type conversions varied greatly. The conversion from farmland to evergreen coniferous forests had the greatest influence on land surface energy exchange, leading to a decrease in H by 19.39% and an increase in LE and NR by 7.44% and 2.74%, respectively. The results of this study can provide a basis and reference for climate change adaptation.
Abstract
Sensible heat flux (H), latent heat flux (LE), and net radiation (NR) are important surface energy components that directly influence climate systems. In this study, the changes in the surface energy and their contributions from global climate change and/or land-cover change over eastern China during the past nearly 30 years were investigated and assessed using a process-based land surface model [the Ecosystem–Atmosphere Simulation Scheme (EASS)]. The modeled results show that climate change contributed more to the changes of land surface energy fluxes than land-cover change, with their contribution ratio reaching 4:1 or even higher. Annual average temperature increased before 2000 and reversed thereafter; annual total precipitation continually decreased, and incident solar radiation continually increased over the past nearly 30 years. These climatic changes could lead to increased NR, H, and LE, assuming land cover remained unchanged during the past nearly 30 years. Among these meteorological variables, at spatial distribution, the incident solar radiation has the greatest effect on land surface energy exchange. The impacts of land-cover change on the seasonal variations in land surface heat fluxes between the four periods were large, especially for H. The changes in the regional energy fluxes resulting from different land-cover type conversions varied greatly. The conversion from farmland to evergreen coniferous forests had the greatest influence on land surface energy exchange, leading to a decrease in H by 19.39% and an increase in LE and NR by 7.44% and 2.74%, respectively. The results of this study can provide a basis and reference for climate change adaptation.
