{"title":"Importance of ocean prediction for heavy rainfall prediction over Japan in July 2020","authors":"Yuya Baba","doi":"10.1002/asl.1099","DOIUrl":"10.1002/asl.1099","url":null,"abstract":"<p>Hindcast experiments were performed for heavy rainfall events over Japan in July 2020 using a regional atmospheric model and a regional coupled model to examine the importance of ocean prediction for predicting heavy rainfall events. Both models were able to predict the first peak of accumulated rainfall over western Japan occurring in the first half of July. However, only the coupled model predicted the second peak that occurred in the second half of July. Sea level pressure (SLP) and low-level moisture inflow originating from an existing atmospheric river (AR) were found to differ in each model. In the regional atmospheric model, the error associated with the inaccurate low-level moisture inflow grew with rising excessive latent heat flux, which enhanced convection and resulted in incorrect SLP patterns. This trend seems to be enhanced by having a prescribed sea surface temperature (SST), which affects the surface heat flux. When ocean conditions are predicted as in the coupled model, such error growth is suppressed by changes in SST that adjust surface heat flux, and it leads to generation of the correct SLP patterns. With correct SLP especially for Pacific high in this case, favorable conditions for inflow from the AR can also be predicted, thus making it possible to predict the heavy rainfall. In conclusion, considering the atmospheric feedback on SST, ocean prediction can improve the predictability of heavy rainfall over Japan, the conditions for which are influenced by the nearby AR. Ocean prediction may therefore extend the range of weather forecasting.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 9","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-05-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1099","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45699276","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Hourly rolling correction of precipitation forecast via convolutional and long short-term memory networks","authors":"Ruyi Yang, Jianli Mu, Shudong Wang, Lijuan Wang","doi":"10.1002/asl.1100","DOIUrl":"10.1002/asl.1100","url":null,"abstract":"<p>In order to improve precipitation forecast from GRAPES_Meso V4.0 in China, we propose a 1–6-h rolling correction solution, based on infrared (IR) channels from geostationary meteorological satellite and surface observation data. In particular, we design a deep learning extrapolation model to predict the evolution of cloud clusters based on convolutional neural networks and long short-term memory networks. The predicted cloud clusters, together with the relationship between the rainfall area and the cloud position, are applied to correct the 1–6-h precipitation forecast. We conduct comprehensive experiments to evaluate the proposed solution over China. Experimental results show that the deep learning model can successfully capture spatial characteristics and temporal variations between the sequences, and achieve reliable predictions of cloud clusters. The analysis further indicates that the rolling correction solution via the predicted cloud clusters has improved the precipitation forecast in China. The distribution of corrected precipitation forecast is more consistent with the observed precipitation compared to GRAPES_Meso forecast. In particular, the rolling correction model could enhance the forecast on “rain/no-rain” events, light rain, and moderate rain according to TS, ETS, BIAS, and FAR metrics.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 10","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1100","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43743564","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kai Ji, Zhongshi Zhang, Ruiqiang Ding, Jianping Li, Yurun Tian, Yongqi Gao, Jiayu Zheng
{"title":"Preceding winter Okhotsk Sea ice as a precursor to the following winter extreme precipitation in South China","authors":"Kai Ji, Zhongshi Zhang, Ruiqiang Ding, Jianping Li, Yurun Tian, Yongqi Gao, Jiayu Zheng","doi":"10.1002/asl.1095","DOIUrl":"10.1002/asl.1095","url":null,"abstract":"<p>The winter extreme precipitation over South China (SC) experiences a large year-to-year variability, causing uncertainty in its prediction. Here, we find that the boreal winter sea ice concentration (SIC) in the Okhotsk Sea can serve as a precursor to the following winter's extreme precipitation frequency (EPF) over SC, which has important implications for its prediction. Further analysis reveals that the Okhotsk Sea SIC anomalies help to reinforce North Pacific Oscillation-like atmospheric variability over the North Pacific, which induces the development of El Niño-Southern Oscillation (ENSO)-like SST anomalies in the equatorial eastern Pacific. The ENSO may act as a “power amplifier” to boost the impact of the Okhotsk Sea winter SIC anomalies on the following winter EPF over SC via a positive atmosphere–ocean feedback process. Our findings suggest that the Okhotsk Sea SIC may act as a potential precursor for the winter EPF over SC leading by about 1 year, and further improve our understanding of extratropical-tropical interactions and aid predictability of winter extreme precipitation over SC.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 8","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1095","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41341252","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Response of terrestrial net primary production to climate change associated with the quadrupling CO2 forcing in CMIP6 models","authors":"Jiawen Zhu, Xiaofei Gao, Xiaodong Zeng","doi":"10.1002/asl.1098","DOIUrl":"10.1002/asl.1098","url":null,"abstract":"<p>Terrestrial net primary production (NPP) has shown remarkable changes in response to increasing atmospheric CO<sub>2</sub> and associated climate change. Many studies have investigated and emphasized the CO<sub>2</sub> fertilization effects, while the climatic effects remain uncertain in magnitude and spatial pattern. This study investigates these climatic effects and underlying causes by using outputs of the simulation abruptly quadrupled CO<sub>2</sub> from 23 CMIP6 models. We find that tropical terrestrial NPP decreases but extratropical terrestrial NPP increases in response to the CO<sub>2</sub>-induced climate change. The decreased tropical terrestrial NPP is significantly correlated with the warmer and drier climate anomalies, while the increased extratropical terrestrial NPP is significantly correlated with the warmer and wetter climate anomalies. These results emphasize the climatic effects on terrestrial NPP and reveal the differences among different terrestrial ecosystems, which is favorable for a better understanding of the terrestrial carbon cycle and its coupling with climate.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 9","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1098","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41380231","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Michael Baidu, Juliane Schwendike, John H. Marsham, Caroline Bain
{"title":"Effects of vertical wind shear on intensities of mesoscale convective systems over West and Central Africa","authors":"Michael Baidu, Juliane Schwendike, John H. Marsham, Caroline Bain","doi":"10.1002/asl.1094","DOIUrl":"10.1002/asl.1094","url":null,"abstract":"<p>Vertical wind shear is known to play a key role in the organization and intensity of mesoscale convective systems (MCSs) in West and Central Africa. A decadal increase in vertical wind shear has recently been linked to a decadal increase in intense MCSs over the Sahel. Here, the effects of vertical wind shear on MCSs over West and Central Africa have been investigated using a 10-year (1998–2007) MCS dataset. Strong vertical shear is associated with long-lived, moderate speed, moderate size and cold (deep) storms with high rain rates. The observed cloud top heights of storms over the oceans are closer to their level of neutral buoyancies (LNBs) compared to their land counterparts on the same latitudes. We hypothesize that this is due to greater entrainment dilution over land compared to storms over the ocean. Vertical shear allows storm anvils to reach higher altitudes relative to their LNB, this is consistent with the colder top storms over the Sahel (a region with a high vertical shear) compared to the Congo, despite a higher LNB in the Congo. It is not possible to diagnose the exact mechanisms for this impact of vertical shear from the data, but it is consistent with recent work showing that shear reduces entrainment dilution of squall-line updrafts. We conclude that modelling impacts of vertical shear, which are normally missed in convection parameterizations, are not only important for predictions of high impact weather, but also for modelling the mean distribution of storm heights across Africa.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 8","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1094","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48947510","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Interannual variability of spring fire in southern Nepal","authors":"Kalpana Hamal, Shravan Kumar Ghimire, Arbindra Khadka, Binod Dawadi, Shankar Sharma","doi":"10.1002/asl.1096","DOIUrl":"10.1002/asl.1096","url":null,"abstract":"<p>Nepal is highly vulnerable to climate change with increased fire occurrences and fire burned areas in recent years; therefore, we accessed the climatic drivers for its variability using fire burned areas product of Moderate Resolution Imaging Spectroradiometer (MODIS) from 2001 and 2020. The peak fire burned areas were observed in the spring season (~91%) from March to May, especially higher in the lowlands of the western and central parts. At the interannual timescale, low precipitation, humidity, soil moisture, and high temperature supported the existence of spring fire. Combining these factors induces drought conditions, enhancing evapotranspiration from vegetation and providing more combustible fuels. Furthermore, the El Niño phase in the central-eastern Pacific Ocean is related to the weakened westerly moisture transport and moisture divergence that creates dry and warm conditions leading to increased fire activities. Thus, this study could be helpful for preparedness, management, and policy-making to limit the multi-dimensional losses in the ecosystem and society due to fire.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 9","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1096","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46045495","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Case study of the downslope wind of Japan “Rokko-oroshi”","authors":"Ieyasu Takimoto","doi":"10.1002/asl.1097","DOIUrl":"10.1002/asl.1097","url":null,"abstract":"<p>In Japan, several local strong winds that are unique to a particular region are known by names such as “oroshi,” “dashi,” and “kaze,” including Akagi-oroshi and Kiyokawa-dashi. In the area around Kobe City, northerly downslope winds from Mt. Rokko, or “Rokko-oroshi,” blow. However, there have not been many studies on Rokko-oroshi, and its nature is not yet fully known. In particular, the nature of Rokko-oroshi in the middle of Mt. Rokko (34.7321°N, 135.2539°E) and temperature changes induced by the blow of Rokko-oroshi have not been studied so far. For example, during the blowing of Rokko-oroshi, wind speeds up to 12 m/s can be recorded at the downwind while experiencing a rapid temperature decrease of between 5 and 8°C. In this study, winds and temperatures in the middle of Mt. Rokko were observed to investigate the characteristics and temperature reduction effect of Rokko-oroshi. First, characteristics of wind speed and direction in the middle of Mt. Rokko were clarified to determine the intensity and duration in which Rokko-oroshi blew. Second, hourly changes in temperature, wind speed, and wind direction were analyzed to relate variations in wind speed and direction with temperature reductions upwind and downwind of Mt. Rokko and within Kobe City. Lastly, radiosonde measurements upwind and downwind of Mt. Rokko were inspected to elucidate the physical mechanisms necessary for the generation of Rokko-oroshi.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 9","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1097","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46809736","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Influence of the urban canopy on the numerical simulation of the “720” rainstorm process in Beijing","authors":"Ming Zhang, Shanyou Zhu, Fan Ping","doi":"10.1002/asl.1092","DOIUrl":"10.1002/asl.1092","url":null,"abstract":"<p>Based on high-resolution underlying surface data and revised urban parameters, a heavy rainfall process that occurred on July 20, 2016 in Beijing was simulated using the Weather Research and Forecasting Model, version 4.0 (WRF4.0). Sensitivity experiments by changing the land-use type and terrain height, and coupling a slab urban canopy model (UCM) with modified parameters, were carried out to investigate the effects of the urban canopy on this rainstorm process in Beijing. The simulation results confirmed that the urban canopy of Beijing had significant impacts on the heavy rainfall, and its impacts on the rainfall could mainly be attributed to the internal structure and related processes of the urban canopy. The urban canopy increased the convergence of water vapor flux in the urban area, leading to strengthened rainfall in the urban area. In addition, employing the UCM also had an influence. The experiment uncoupled with the UCM suggested that the urban heat island effect of Beijing was relatively weak; its barrier effect of the urban canopy played a leading role that blocked and delayed the movement of rain bands, which divided the airflow and increased the amount of rainfall outside the urban area. The experiment coupled with the UCM took into account the parameters of building height, albedo, and anthropogenic heat, which helped improve the accuracy of rainfall simulation. Its urban heat island phenomenon was obvious, which benefited the convergence and upward movement of urban airflow and promoted the movement of the front and the total rainfall in the urban center.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 8","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1092","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45099561","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xia Qu, Gang Huang, Hongyu Hou, Zesheng Chen, Yan Du
{"title":"The opposite response of the South Asian high to increasing CO2 at different heights","authors":"Xia Qu, Gang Huang, Hongyu Hou, Zesheng Chen, Yan Du","doi":"10.1002/asl.1093","DOIUrl":"10.1002/asl.1093","url":null,"abstract":"<p>Based on the multimodel ensemble of 22 models in Coupled Model Intercomparison Project Phase 6 (CMIP6), the present manuscript found that in response to increasing CO<sub>2</sub>, the South Asian high (SAH) displays the opposite response over its southern region in the upper troposphere: an anticyclonic response at 100 hPa and a weak (insignificant) cyclonic response at 200 hPa. This opposite response is a product of tropospheric warming. In response to increasing CO<sub>2</sub>, the troposphere warms, with the potential temperatures peaking at 150–200 hPa over the northern Indian Ocean (IO). With transportation by local vertical motion (ascendance over the northeastern IO and descendance over the northwestern IO), various changes in vertical temperature advection with height form at 100 and 200 hPa. Finally, the changes contribute to a decrease in the <i>ω</i> response with pressures at 100 hPa but an increase in the <i>ω</i> response with pressures at 200 hPa over the northwestern IO. Over the northwestern IO, <i>ω</i> change is inversely related to pressure. At 100 hPa, the sign of <i>ω</i> changes with pressure, which yields distinct vorticity forcing over the northeastern and northwestern IO. This causes an anticyclonic response, which may generate zonal vorticity advection and balance the vorticity forcing. At 200 hPa, the contribution is roughly opposite to that at 100 hPa. In addition, although diabatic heating contributes to the vertical profile of <i>ω</i>, it yields the same-sign vorticity response at 100 and 200 hPa.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 8","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1093","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42272765","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Alfonso Hernanz, Juan Andrés García-Valero, Marta Domínguez, Ernesto Rodríguez-Camino
{"title":"A critical view on the suitability of machine learning techniques to downscale climate change projections: Illustration for temperature with a toy experiment","authors":"Alfonso Hernanz, Juan Andrés García-Valero, Marta Domínguez, Ernesto Rodríguez-Camino","doi":"10.1002/asl.1087","DOIUrl":"10.1002/asl.1087","url":null,"abstract":"<p>Machine learning is a growing field of research with many applications. It provides a series of techniques able to solve complex nonlinear problems, and that has promoted their application for statistical downscaling. Intercomparison exercises with other classical methods have so far shown promising results. Nevertheless, many evaluation studies of statistical downscaling methods neglect the analysis of their extrapolation capability. In this study, we aim to make a wakeup call to the community about the potential risks of using machine learning for statistical downscaling of climate change projections. We present a set of three toy experiments, applying three commonly used machine learning algorithms, two different implementations of artificial neural networks and a support vector machine, to downscale daily maximum temperature, and comparing them with the classical multiple linear regression. We have tested the four methods in and out of their calibration range, and have found how the three machine learning techniques can perform poorly under extrapolation. Additionally, we have analysed the impact of this extrapolation issue depending on the degree of overlapping between the training and testing datasets, and we have found very different sensitivities for each method and specific implementation.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 6","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1087","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46242152","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}