Atmospheric Science Letters最新文献

{"title":"Upper-level midlatitude troughs in boreal winter have an amplified low-latitude linkage over Africa","authors":"Neil Ward,&nbsp;Andreas H. Fink,&nbsp;Richard J. Keane,&nbsp;Douglas J. Parker","doi":"10.1002/asl.1129","DOIUrl":"10.1002/asl.1129","url":null,"abstract":"<p>In boreal winter, strong upper-level midlatitude troughs across the Atlantic–Africa–southwestern Asia sector generate substantial tropical–extratropical interaction and have become recognized as important factors in some extreme weather events. As such, they represent important dynamic features to understand and capture in weather forecasts, as well as in climate models for projections on longer timescales. Here, we empirically study the 20% of winter days with strongest trough signatures during 1982–2020 at each longitude across the sector, and show that the trough impact over northern Africa, most notably in central parts, is particularly strong in magnitude, low-latitude extent and persistence, leading to the characterization of a northern Africa mode of several-days weather fluctuation. Weather conditions that follow strong troughs from the eastern Atlantic to the Central Mediterranean include: (i) a warming tendency across much of northern Africa, generally of several Celsius magnitude ahead of the trough, and &gt;1°C even extending to the south of 10° N in central parts and continuing eastward until the Ethiopian Highlands; (ii) precipitation development further north than normal across northern tropical Africa, especially strong over longitudes corresponding to a northward extension of the main Congo rain belt. The intertropical discontinuity and low-level heat low are also shifted significantly north, with the complex of anomalies persisting for several days, beyond the timescale of the trough. For context, at all other trough longitudes across the sector, a warming signal does emerge (statistically significant), but with much shorter persistence (2–3 days), smaller magnitude and extending southward clearly only to 15–20° N. Mid-level tropical plumes of moisture are also typically present for strong troughs from the eastern Atlantic to southwestern Asia, and these alone can lead to weather extremes. However, low-level warming and mid-level moistening are uniquely juxtaposed at low latitudes over central Africa, where a near-equatorial signature develops.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"24 1","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1129","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45640343","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":"Progress, challenges, and future steps in data assimilation for convection-permitting numerical weather prediction: Report on the virtual meeting held on 10 and 12 November 2021","authors":"Guannan Hu,&nbsp;Sarah L. Dance,&nbsp;Ross N. Bannister,&nbsp;Hristo G. Chipilski,&nbsp;Oliver Guillet,&nbsp;Bruce Macpherson,&nbsp;Martin Weissmann,&nbsp;Nusrat Yussouf","doi":"10.1002/asl.1130","DOIUrl":"10.1002/asl.1130","url":null,"abstract":"<p>In November 2021, the Royal Meteorological Society Data Assimilation (DA) Special Interest Group and the University of Reading hosted a virtual meeting on the topic of DA for convection-permitting numerical weather prediction. The goal of the meeting was to discuss recent developments and review the challenges including methodological developments and progress in making the best use of observations. The meeting took place over two half days on the 10 and 12 November, and consisted of six talks and a panel discussion. The scientific presentations highlighted some recent work from Europe and the USA on convection-permitting DA including novel developments in the assimilation of observations such as cloud-affected satellite radiances in visible channels, ground-based profiling networks, aircraft data, and radar reflectivity data, as well as methodological advancements in background and observation error covariance modelling and progress in operational systems. The panel discussion focused on key future challenges including the handling of multiscales (synoptic-, meso-, and convective-scales), ensemble design, the specification of background and observation error covariances, and better use of observations. These will be critical issues to address in order to improve short-range forecasts and nowcasts of hazardous weather.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"24 1","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1130","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44957857","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":"Distinct response of near surface air temperature to clouds in North China","authors":"Shuyi Jiang,&nbsp;Chuanfeng Zhao,&nbsp;Yan Xia","doi":"10.1002/asl.1128","DOIUrl":"10.1002/asl.1128","url":null,"abstract":"<p>Using the daily 2 m maximum temperature (Tmax), 2 m minimum temperature (Tmin) and cloud cover data measured at ground sites of the China Meteorological Administration in North China from 2000 to 2017, this study investigates the influence of clouds on the daily temperature range (DTR) defined as the difference between Tmax and Tmin. As expected, the cloud cover shows the similar averaged spatial distribution and monthly variation with Tmin. Surprisingly, it also shows the similar average spatial distribution and monthly variation with Tmax, suggesting the more important roles of regions (latitude) and seasons associated with the variations of land surface temperature, which is further related to solar radiation absorbed and surface heat capacity. By comparing monthly variations of temperature between cloudy and clear skies, we find that clouds can weaken Tmax and increase Tmin, and thus decrease DTR. As a result, the spatial distribution of DTR is opposite to the cloud cover. The clouds have relatively stronger impact on Tmin and DTR over mountain region, which is most likely caused by the stronger longwave cloud radiative forcing associated with higher cloud tops over the mountain region.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 12","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1128","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51635894","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":"Predictability of European winter 2020/2021: Influence of a mid-winter sudden stratospheric warming","authors":"Julia F. Lockwood,&nbsp;Nicky Stringer,&nbsp;Hazel E. Thornton,&nbsp;Adam A. Scaife,&nbsp;Philip E. Bett,&nbsp;Tamara Collier,&nbsp;Ruth Comer,&nbsp;Nick Dunstone,&nbsp;Margaret Gordon,&nbsp;Leon Hermanson,&nbsp;Sarah Ineson,&nbsp;Jamie Kettleborough,&nbsp;Jeff Knight,&nbsp;Joseph Mancell,&nbsp;Peter McLean,&nbsp;Doug Smith,&nbsp;Tony Wardle,&nbsp;Prince Xavier,&nbsp;Ben Youngman","doi":"10.1002/asl.1126","DOIUrl":"10.1002/asl.1126","url":null,"abstract":"<p>Boreal winter (December–February) 2020/2021 in the North Atlantic/European region was characterised by a negative North Atlantic Oscillation (NAO) index. Although this was captured within the ensemble spread of predictions from the Met Office Global Seasonal forecast system (GloSea5), with 17% of ensemble members predicting an NAO less than zero, the forecast ensemble mean was shifted towards a positive NAO phase. The observed monthly NAO anomalies were particularly negative in January and February, following an early January sudden stratospheric warming (SSW), and a prolonged period of Phase 6 or 7 of the Madden Julian Oscillation (MJO) in late January/early February. In contrast, predictions showed the expected teleconnection from the observed La Niña, with a positive NAO signal resulting from a weakening of the Aleutian Low leading to a reduction in tropospheric wave activity, an increase in polar vortex strength and a reduced chance of an SSW. Forecasts initialised later in the winter season successfully predicted the negative NAO in January and February once the SSW and MJO were within the medium range timescale. GloSea5 likely over-predicted the strength of the La Niña which we estimate caused a small negative bias in the SSW probability. However, this error is smaller than the uncertainty in SSW probability from the finite forecast ensemble size, emphasising the need for large forecast ensembles. This case study also demonstrates the advantage of continuously updated lagged ensemble forecasts over a ‘burst’ ensemble started on a fixed date, since a change in forecast signal due to events within the season can be detected early and promptly communicated to users.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 12","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1126","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48297222","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":"Error investigation of rain retrievals from disdrometer data using triple colocation","authors":"Clizia Annella,&nbsp;Vincenzo Capozzi,&nbsp;Giannetta Fusco,&nbsp;Giorgio Budillon,&nbsp;Mario Montopoli","doi":"10.1002/asl.1127","DOIUrl":"10.1002/asl.1127","url":null,"abstract":"<p>Assessing the uncertainty of precipitation measurements is a challenging problem because precipitation estimates are inevitably influenced by various errors and environmental conditions. A way to characterize the error structure of coincident measurements is to use the triple colocation (TC) statistical method. Unlike more typical approaches, where measures are compared in pairs and one of the two is assumed error-free, TC has the enviable advantage to succeed in characterizing the uncertainties of co-located measurements being compared to each other, without requiring the knowledge of the true value which is often unknown. However, TC requires to have at least three co-located measuring systems and the compliance with several initial assumptions. In this work, for the first time, TC is applied to in-situ measurements of rain precipitation acquired by three co-located devices: a weighing rain gauge, a laser disdrometer and a bidimensional video disdrometer. Both parametric and nonparametric formulations of TC are implemented to derive the rainfall product precision associated with the three devices. While the parametric TC technique requires tighter constraints and explicit assumptions which may be violated causing some artifacts, the nonparametric formulation is more flexible and requires less strict constrains. For this reason, a comparison between the two TC formulations is also presented to investigate the impact of TC constrains and their possible violations. The results are obtained using a statistically robust dataset spanning a 1.5 year period collected in Switzerland and presented in terms of traditional metrics. According to triple colocation analysis, the two disdrometers outperform the classical weighing rain gauge and they have similar measurement error structure regardless of the integration time intervals.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 12","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1127","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49307093","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":"Recent decrease in inner-core rain rate of tropical cyclones over the western North Pacific","authors":"Na Wei,&nbsp;Jinjie Song,&nbsp;Yifei Dai,&nbsp;Sulin Jiang,&nbsp;Yihong Duan","doi":"10.1002/asl.1125","DOIUrl":"10.1002/asl.1125","url":null,"abstract":"<p>The tendency in tropical cyclone (TC) rainfall is of great concern due to its remarkable contribution to global precipitation and extreme rainfall events. This study finds a decreasing trend in TC inner-core rain rate over the western North Pacific (WNP) from 1998 to 2019. This basinwide trend is mainly induced by the decreasing TC inner-core rain rates over the region west of 150°E, while it is seldom linked to the changes in the distribution of TC occurrence. The maximum decreases in TC inner-core rain rate are observed over the offshore areas along the coastlines of East Asia. Further analysis reveals that the change in atmospheric stability, referred to as a dominant environmental contributor to basinwide TC inner-core rain rate decreases shown in previous studies, only has a primary impact over the northern South China Sea. By comparison, there is a positive correlation between the variations of the aerosol optical depth and TC inner-core rain rate over the mid-latitude regions extending from the East China Sea to Japan. Our result highlights the linkage of the recent decreasing trends in aerosol optical depth and TC inner-core rain rate over the WNP.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 12","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1125","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47444036","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":"How Asian slum emissions impact local microclimates in polluted air masses","authors":"Satyajit Ghosh,&nbsp;C. R. Sathish Kumar,&nbsp;Siddharth Gumber,&nbsp;Steven Dobbie,&nbsp;Huiyi Yang","doi":"10.1002/asl.1124","DOIUrl":"10.1002/asl.1124","url":null,"abstract":"Urban sprawl comprising densely populated slums over South Asian cities yields copious amounts of soot and black carbon from archaic cooking methods involving cow dung cakes and firewood, which remain afloat for over 10–12 h, enabling them to age in a sulphur rich environment. Not only are there toxicological concerns arising out of improper ventilation mechanisms, but there are also other concerns impacting the local microclimate. These emissions mix with other aerosol particles and, when conditions are favourable, are rendered partially soluble, enabling them to activate into cloud condensation nuclei. This study first yields a quantification of the soluble mass fraction and subsequently shows how aerosols from this local area source mix with background aerosol modes to perturb the local cloud microphysics over Chennai, a megacity in Southern India. On‐site sampling was undertaken to find the mass concentrations of the collected deposits separately from cow dung and firewood fuel. Additional micro‐physical attributes, including the morphological indentations that served as a receptacle to contain the accreted sulphate along with the particle size distribution were ascertained through Scanning Electron Microscopy. It is shown that accreted sulphate on carbonaceous particles facilitates CCN activation over the city. We show through large‐eddy simulations (LES) that extensive slum emissions over the study region contribute to the observed local cloud cover and enhanced rain amounts over a densely built‐up area housing the city's most vulnerable citizens.","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 12","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-07-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1124","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42868596","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":"Recent decrease in western North Pacific tropical cyclone rapid intensification during June","authors":"Jinjie Song,&nbsp;Philip J. Klotzbach,&nbsp;Sulin Jiang,&nbsp;Yihong Duan","doi":"10.1002/asl.1121","DOIUrl":"10.1002/asl.1121","url":null,"abstract":"<p>This study investigates the long-term tendency in the ratio of rapid intensification (RI) cases to the total number of tropical cyclone cases over the western North Pacific (WNP) during June between 1982 and 2021. There is a significant decreasing trend in RI ratio during June, which is opposite to the increasing trend in RI ratio during July–November. From 1982–2005 to 2006–2021, the June RI ratio significantly decreases over the region of 5°–20°N and 120°–150°N, while showing weak changes over other parts of the WNP. Over the region with a significant RI ratio reduction, significantly reduced 850-hPa relative vorticity and 200-hPa divergence and significantly enhanced 850 to 200-hPa vertical wind shear are the likely primary drivers. The RI-suppressing effect of the above changes in dynamical variables exceeds the RI-favoring effect of the warming ocean, for example, significantly increased sea surface temperature and tropical cyclone heat potential, over this same region. Moreover, the changes in dynamic conditions can be related to an anomalous low-level anticyclonic circulation, anomalous upper-level convergent flow and a greater enhancement of upper-level easterlies than lower-level easterlies. Our study highlights the importance of changes in dynamic variables (e.g., vertical wind shear) in modulating WNP RI activity.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 11","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1121","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43523909","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":"The relationship among summer atmospheric boundary layer height over the Taklimakan Desert, its land surface parameters and Eurasian circulation","authors":"Minzhong Wang,&nbsp;Jiantao Zhang","doi":"10.1002/asl.1122","DOIUrl":"10.1002/asl.1122","url":null,"abstract":"<p>To investigate the relationship among summer atmospheric boundary layer (ABL) over the Taklimakan Desert (TD), its land surface parameters and large scale meteorological field, the Urumqi Institute of Desert Meteorology of China Meteorological Administration conducted a comprehensive observation of boundary layer in Tazhong, the hinterland of TD from July 1 to 31, 2016. The correlations between the ABL height and surface sensible heat, latent heat, air temperature, turbulent kinetic energy (TKE) and buoyancy term are analyzed by using the observed GPS sounding data, the surface layer micro meteorological data in the hinterland of the TD and ERA5 reanalysis data so as to study the correlation of the ABL height and Eurasian circulation field. The research results indicate: (1) The height of summer ABL over the TD does not fully correspond with the variation tendency of surface sensible heat flux. In addition to surface sensible heat, large scale advection and residual mixed layer (RML) are also crucial factor influencing ABL. (2) The surface TKE over the TD is consistent with ABL height variation, with the correlation coefficient of 0.62. Hence the equation of ABL height and TKE is expressed as: <i>Y</i> = 1609.2<i>X</i>⁴ – 12,828<i>X</i>³ + 35,617<i>X</i>² –39,514<i>X</i> + 15,858. (3) When the ABL height over the TD is quite high, 500 hPa altitude in Xinjiang is mostly controlled by anticyclone circulation, and the easterly low level jet (LLJ) tends to be formed at 850 hPa the next night. (4) The high correlation areas of summer ABL height over the TD and Eurasian temperature field are Xinjiang and Balkash Lake region. Significant positive correlation is identified between the ABL height and the temperature field at 850, 700, and 500 hPa of the above regions. The maximum correlation coefficient reaches 0.7. The study deepens the understanding of the relationship among the ABL process over the TD, land surface parameters and Eurasian circulation.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 11","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1122","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43963209","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":"Moisture sources tracking of a cold vortex rainstorm over Northeast China using FLEXPART","authors":"Yuting Yang,&nbsp;Xiaopeng Cui,&nbsp;Qiangli Zou","doi":"10.1002/asl.1123","DOIUrl":"10.1002/asl.1123","url":null,"abstract":"<p>Water vapor sources and related transport processes are fundamental to the understanding of precipitation mechanisms. This study focuses on a typical Northeast Cold Vortex (NECV) rainstorm on July 25, 2016, which brought floods and huge economic losses to Northeast China. Using the Lagrangian flexible particle dispersion model (FLEXPART) and the areal source–receptor attribution method, the moisture sources and transport characteristics during this event were analyzed. The results show that this NECV rainstorm occurred under a favorable atmospheric circulation background, and particles in the rainstorm area mainly came from the Indo-China Peninsula, South China Sea, Bay of Bengal, and central China at relatively low levels. The largest water vapor uptake and release were found in central China, which was the primary moisture source of this NECV precipitation. Although the Indian Subcontinent–Bay of Bengal–Indo-China Peninsula had a higher moisture intake than the South China Sea–the Philippines, a considerable amount of moisture in the former was released during transport, making the moisture contributions of the two equivalents. Furthermore, the Northeast rainstorm area had a non-negligible precipitation recycling process. All examined sources contributed more than 90% of the moisture in the rainstorm area.</p>","PeriodicalId":50734,"journal":{"name":"Atmospheric Science Letters","volume":"23 12","pages":""},"PeriodicalIF":3.0,"publicationDate":"2022-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.1123","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47530717","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}