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A summer course developed at Purdue University leverages students' intrinsic desire to observe tornadoes as a motivator for learning severe storms forecasting. Relative to previous 'storm chasing' courses, the Students [...]

ABSTRACT Several important developments in the 1960s showed the way to using spectral analysis to identify and describe atmospheric waves predicted by theory. Among these waves were normal-mode Rossby-Haurwitz waves [...]

ABSTRACTS The 2016/17 wildfire season in Chile was the worst on record, burning more than 600,000 ha. While wildfires are an important natural process in some areas of Chile, supporting [...]

The Madden-Julian oscillation (MJO) identified by Madden and Julian in the early 1970s has been well recognized as the most prominent intraseasonal signal in the tropics. Its discovery and its [...]

New York City College of Technology has created a year-round geoscience workforce preparation and geoscience career mentoring program for nongeoscience, minority science, technology, engineering, and math (STEM) students beginning at [...]

From the authors' perspective, this means making optimal use of the comments and recommendations made by the reviewers through careful, comprehensive revisions to the paper and complete, well-reasoned responses to the reviewers and the editor. If you (the author) were the reviewer of somebody else's paper and spent 10 hours (the typical time that reviewers spend with your submitted paper; [13]) reading the paper and writing up your review, you would probably want to see that the authors acknowledged that they read and understood each comment; acknowledged that they took your comment seriously, even if they disagreed with it; and responded to the comment and revised the paper. We editors thank the authors for their continued trust in I Monthly Weather Review i , the reviewers for their essential contributions to the peer-review process, and the AMS staff for their hard work and dedication to ensuring a high-quality issue each month. If editors find that authors are not addressing the reviewers' comments, then they can send the paper back to the authors for further revision or they can reject the paper because it is not progressing toward a publishable outcome. [Extracted from the article]

10-15 January 2021, Virtual Meeting The 2021 AMS Annual Meeting theme is 'Strengthening Engagement with Communities through our Science and Services'. For the full description of the theme, please visit [...]

Anders K. Angstrom was known primarily for his contributions to the field of atmospheric radiation. However, his scientific interests encompassed many diverse topics. This paper describes the contents of two early, remarkable, and, until recently, largely unknown papers by Angstrom on probability forecasting and the use/value of weather forecasts. These papers, entitled 'Sannolikhet och Praktisk Vaderleksprognos' ('Probability and Practical Weather Forecasting') and 'On the Effectivity of Weather Warnings,' were published in 1919 and 1922, respectively. Noteworthy features of these two papers include 1) a discussion of the sources of uncertainty in weather forecasting, 2) discourses on the problems of estimating probabilities by means of empirical relative frequencies and forecasters' subjective judgments, 3) the use of a Gaussian model to describe the accuracy of minimum temperature forecasts, 4) the identification of the ratio of the protection cost a to the 'risked value' if protective action is not taken b as a characteristic of users of forecasts, 5) analytical expressions for the economic value of weather warnings, 6) quantitative analysis of the problems faced by forecasters in deciding whether or not to issue weather warnings when they are uncertain about future weather conditions, and 7) arguments concerning the need to obtain estimates of the costs and losses that may be incurred by potential users in order to assess economic effectiveness. The contents of Angstrom's two papers are reviewed and summarized, making extensive use of quotations from the texts. An effort is made to place the papers and their contents in proper historical context. Two topics of current interest, namely, ensemble forecasting and the provision of specialized weather services, are discussed briefly in light of the results presented and issues raised in these papers.

The National Oceanic and Atmospheric Administration (NOAA) has operated a network of Fischer & Porter gauges providing hourly and subhourly precipitation observations as part of the U.S. Cooperative Observer Program since the middle of the twentieth century. A transition from punched paper recording to digital recording was completed by NOAA's National Weather Service in 2013. Subsequently, NOAA's National Centers for Environmental Information (NCEI) upgraded its quality assurance and data stewardship processes to accommodate the new digital record, better assure the quality of the data, and improve the timeliness by which hourly precipitation observations are made available to the user community. Automated methods for removing noise, detecting diurnal variations, and identifying malfunctioning gauges are described along with quality control algorithms that are applied on hourly and daily time scales. The quality of the hourly observations during the digital era is verified by comparison with hourly observations from the U.S. Climate Reference Network and summary of the day precipitation totals from the Global Historical Climatology Network dataset. [ABSTRACT FROM AUTHOR]

The article discusses the process of evaluating manuscripts submitted to the American Meteorological Society. Manuscripts must meet the formatting standards prior to peer review. If it does not meet the standards, instruction are sent to the authors with a request to revise and resubmit the paper. After meeting the qualifications, papers undergo the peer-review process, wherein they are subjected to the scrutiny of experts in field to ensure high quality. Among the standards evaluated in the peer review process include originality, absence of significant errors in analysis and interpretation and scientific objectivity. After the review, the papers are returned to the editors for acceptance or rejection and one accepted, they go through copying, technical editing and publishing.

A method named BTREC, which is in fact an extension of tracking a radar echo by cross-correlation (TREC) method, is proposed based on the Barnes filter in this paper. BTREC is an efficient objective analysis method for smoothing the motion vectors of radar echo patterns. A comparative analysis of the BTREC vectors and the COTREC (another extension of TREC, which is restricted by the 2D continuity equation) vectors is conducted. The results show that the BTREC method corrects the noise and inconsistencies in TREC vectors (often induced by shielding, ground clutter, and rapid morphological changes of the radar patterns) more thoroughly than COTREC. Then the BTREC, COTREC, and TREC methods are applied to extrapolate the real radar echo pattern over Jiangxi Province in China for two cases (1900–2100 UTC 4 June and 0900–1100 UTC 30 June 2018). Results show that the BTREC method performs the best out of the three methods to forecast the radar echo patterns in the following 1 and 2 h, and has the least distortion. To further confirm that, 892 radar composite reflectivity mosaic images with precipitation in summer (June–August) over Jiangxi are collected to test the three methods. The results show that in the 1- and 2-h extrapolations, the mean differences of the threat score (TS), correlation (CORR), and probability of detection (POD) between BTREC and TREC are obviously more than 0, while that of the false alarm ratio (FAR) is remarkably less than 0 (the threshold to identify whether a grid is correctly predicted is set to 10 dBZ). Although the mean difference of TS, CORR, POD, and FAR between COTREC and TREC have similar variation, their magnitudes are obviously decreased (especially for the 2-h extrapolation). This further indicates that the BTREC method obviously improves the forecast of the radar echo pattern within the next 2 h compared to the COTREC and TREC methods. [ABSTRACT FROM AUTHOR]

The 2018 AMS Annual Meeting theme is 'Transforming communication in the weather, water, and climate enterprise--Focusing on challenges facing our sciences.' For the full description of the theme, please visit [...]

Educators can enrich their teaching with best practices, share resources, and contribute to the growing atmospheric science education research community by reading and participating in the scholarship of teaching and learning in atmospheric science. This body of scholarship has grown, particularly over the past 15 years, and is now a sizable literature base that documents and exemplifies numerous teaching innovations in undergraduate atmospheric science education. This literature base benefits the entire atmospheric science community because graduates of atmospheric science programs are better prepared to enter the workforce. This literature base has not yet been examined, however, to see how well the evidence supports education practices in the atmospheric science education literature. In this study, we characterized that evidence and show that the majority of papers we reviewed share education innovations with anecdotal or correlational evidence of effectiveness. While providing useful practitioner knowledge and preliminary evidence of the effectiveness of numerous innovative teaching practices, opportunities exist for increasing readers' confidence that the innovations caused the learning gains. Additional studies would also help move conclusions toward generalizability across academic institutions and student populations. We make recommendations for advancing atmospheric science education research and encourage atmospheric science educators to actively use the growing body of education literature as well as contribute to advancing atmospheric science education research. [ABSTRACT FROM AUTHOR]

The L-band passive microwave radiometer on board the NASA Soil Moisture Active Passive (SMAP) satellite can measure brightness temperature to retrieve sea surface wind speed under tropical cyclone (TC) conditions without being affected by rainfall or signal saturation caused by high wind speeds. Based on this advantage, this paper used the SMAP wind products for parameterizing the key decay exponent α of the Rankine vortex model (a traditional parametric model of the TC wind field) and finally developed new Rankine models. The SMAP dataset included 67 TC cases. Through data statistics, we examined the relationship between α and the maximum wind speed Um, the relationship between α and the radius of maximum wind speed (Rm), and the relationship between Rm and the averaged radius of 17 m s−1 (R17). Results showed that the three relationships were both positive correlations, indicating that α can be parameterized in three empirical ways. The first way is to calculate solely with Um. The second way is to calculate solely with Rm. The third way is to calculate Um and Rm together. The three ways correspond to three new models: the SMAP Rankine Model-1 (SRM-1), the SMAP Rankine Model-2 (SRM-2), and the SMAP Rankine Model-3 (SRM-3). Finally, comparisons were made between the new models and three existing Rankine models, according to the model simulations and the Advanced Microwave Scanning Radiometer 2 measurements of 49 TC cases. Results showed that the SRM-3 performed best overall. Significance Statement: Ocean surface wind fields are important driving factors for numerical models to guide evolution forecasting and risk assessment of tropical cyclones. The purpose of this study is to utilize the SMAP products to modify the traditional Rankine vortex model for tropical cyclone surface wind field estimation. Rankine decay exponent was found between 0.3 and 0.9 and positively dependent upon maximum wind speed and its radius. Based on these characteristics, the proposed new Rankine models could calculate the decay exponent and further the TC surface wind field symmetrically with high accuracy, simply using maximum wind and its radius. This paper shows a practical use of SMAP measurements on TC wind field monitoring, analyzing, and modeling. [ABSTRACT FROM AUTHOR]

The 95th AMS Annual Meeting in Phoenix this past January was an outstanding meeting in virtually every way. The scientific conferences were packed with great presentations, both oral and poster; [...]

The article presents updates related to climatology and weather studies in the U.S. Research reveals the significance of using the cloud-resolving model simulations in forecasting the dangers of lightning. Meanwhile, several climate scientists are searching for the best method in estimating the peak surface winds of a hurricane. Moreover, it also looks on the effectiveness of the latest multiple-Doppler tornado detection in determining the upcoming tornadoes.

The article offers news briefs in the U.S. Australian radiosondes monitor a large area of the Southern Hemisphere have experienced so many changes that unadjusted temperature trends of the bulk atmosphere computed from their soundings are suspect. Quantification of carbon exchange in forest ecosystems needs a unique sampling strategy. Strong vertical wind shear usually will weaken even mature hurricanes.

The article discusses the research which emphasizes a potential break in the tornado warning dissemination system utilized in the U.S. in 2008. The researchers measured the fatality rates caused by tornadoes that occurred between sunset and sunrise from 1880-2007 to investigate the human vulnerability to nocturnal tornadoes. Spatial analyses show that vulnerability of the nocturnal tornado is not distributed uniformly across the U.S., in which the South region is at much greater risk for nocturnal events.

The article reports developments related to meteorology. A study which examines the total lightning signatures of thunderstorm intensity over North Texas provides insight into the processes responsible for severe weather damaging straight-line winds and tornadoes. Changes in storm intensity can be predicted through the convective structure of the eyewall of a mature hurricane. Bayesian statistical models were developed for number of tropical cyclones using data from 1966-2006.

The article offers world news briefs related to meteorology. The subrotors and the internal structure of the parent rotor lifts off the surface and breakdown along the edge of the lee wave through Kelvin-Helmholtz like instability. Greenland extends one quarter of the distance between the North Pole and Equator averaging 1.5 kilometer (km) in height and reaching skyward more than 3.5 km. The Global Precipitation Climatology Project (GPCP) offers the opportunity to analyze climate variation.

The article assesses the usefulness of synthetic vortex insertion prior to the extratropical transition of hurricanes. Significant improvements in the wind and precipitation patterns within the storm at landfall were observed in the atmospheric model with vortex insertion employed in the initial conditions. The numerical hindcasts employing the technique resolved a particular forecast dilemma involving interaction of Hurricane Michael with a preexisting area of low pressure to its north. Operational forecast models at the time had incorrectly developed the northern low at the expense of the hurricane, while the opposite occurred in reality and in the numerical simulations run in hindcast mode.

The article offers news briefs related to climatology. A cold tongue which is a narrow band of cool sea surface temperature (SST) is one of the salient features in the equatorial Pacific Ocean. Two of the factors that contributed to the weather-forecasting errors increase in time are the amplification uncertainties of nonlinearities in the initial state of the atmosphere and the model deficiencies leading the model to predict the wrong rate of change for even the most certain initial conditions. INSETS: DUDE, WE'RE, LIKE, PROTESTING;PLEASED TO ZAP YOU.

Reprints of articles about meteorology research published in 2007 issues of "Weather and Forecasting", "Journal of Climate," and "Journal of Atmospheric and Oceanic Technology" are presented. They are "Performance Assessment of the World Wide Lightning Location Network (WWLLN), Using the Los Alamos Sferic Array (LASA) as Ground Truth", "How Well Do We Understand and Evaluate Climate Change Feedback Processes?," and "Developing Tools for Nowcasting Storm Severity".

Weather radars have been widely used to detect and quantify precipitation and nowcast severe weather for more than 50 years. Operational weather radars generate huge three-dimensional datasets that can accumulate to terabytes per day. So it is essential to review what can be done with existing vast amounts of data, and how we should manage the present datasets for the future climatologists. All weather radars provide the reflectivity factor, and this is the main parameter to be archived. Saving reflectivity as volumetric data in the original spherical coordinates allows for studies of the three-dimensional structure of precipitation, which can be applied to understand a number of processes, for example, analyzing hail or thunderstorm modes. Doppler velocity and polarimetric moments also have numerous applications for climate studies, for example, quality improvement of reflectivity and rain rate retrievals, and for interrogating microphysical and dynamical processes. However, observational data alone are not useful if they are not accompanied by sufficient metadata. Since the lifetime of a radar ranges between 10 and 20 years, instruments are typically replaced or upgraded during climatologically relevant time periods. As a result, present metadata often do not apply to past data. This paper outlines the work of the Radar Task Team set by the Atmospheric Observation Panel for Climate (AOPC) and summarizes results from a recent survey on the existence and availability of long time series. We also provide recommendations for archiving current and future data and examples of climatological studies in which radar data have already been used. [ABSTRACT FROM AUTHOR]

Recent measurements from cumulus clouds that are affected by paper mill effluents in Washington State do not agree with the measurements made by G.K. Mather from cumulus clouds that are affected by emissions from a Kraft paper mill in South Africa. Numerical simulation contradicts Mather's postulation that emissions induce enhance the condensation-coalescence precipitation mechanism.

The article offers information on several studies related to meteorology. One of the studies focuses on the use and performance of Weather Research and Forecting (WRF) as a regional climate model. The other study states that with the decrease in environmental temperature the ability of tropical cyclones to shed angular momentum from the core is also increased. Another study suggests a strong link between the regional heat waves observed in 2006 and the global climate change.

The article presents a study which examines the effect of synoptic-scale forcing on the stratospheric sudden warnings (SSWs) in 2006 in the U.S. The researchers used the meteorological fields from Goddard Earth Observing System (GEOS)-4 analyses in determining such effects. The study found out that stratospheric polar displaced off the pole due to earlier minor warming events. The researchers also suggest that there is a need for further investigation to determine the kind of fraction of major SSWs are initiated.

The article focuses on contribution of Yoshikazu Sasaki to the development of variational method of data assimilation. It highlights Sasaki's training in physics and the application of calculus of variations to relativity and quantum mechanics. Moreover, the author argues on fundamental difference of variational methods introduced by Sasaki as well as the meteorological community introduced by Arnt Eliassen to the stochastic approach to data assimilation. Furthermore, a study on the link between tropical cyclones and fronts is also discussed.

The article discusses the importance of peer reviewers in scholarly publishing and expresses gratitude towards those who volunteer their time to review manuscripts. The American Meteorological Society (AMS) analyzed data on peer reviews and found no trend in reviewer acceptance rates or the time taken to complete reviews over the past decade. The article also emphasizes the responsibility of authors to participate in the peer-review process by reviewing papers themselves. The authors of the article acknowledge the time and effort involved in reviewing and encourage those who have not yet embraced their responsibilities as reviewers to volunteer. [Extracted from the article]

The article discusses the importance of peer reviewers in scholarly publishing and the responsibilities of authors in the peer-review process. It highlights that editors rely on subject-matter experts to assess the suitability of manuscripts for publication and to provide guidance to authors. The American Meteorological Society (AMS) analyzed data on peer reviews and found no trend in reviewer acceptance rates or review completion time over the past decade. The article emphasizes the need for authors to participate in peer reviewing and suggests that authors should review three papers for each one they submit. The AMS expresses gratitude to reviewers and encourages others to volunteer as reviewers. [Extracted from the article]

The article discusses the importance of peer reviewers in scholarly publishing and expresses gratitude towards those who volunteer their time to review manuscripts. The American Meteorological Society (AMS) analyzed data on peer reviews and found that there is no trend of declining reviewer acceptance rates or longer review times. The article also emphasizes the responsibility of authors to participate in the peer-review process by reviewing papers themselves. The authors of the article acknowledge the time and effort involved in reviewing and encourage those who have not yet embraced their responsibilities as reviewers to volunteer. [Extracted from the article]

The article discusses the importance of peer reviewers in scholarly publishing and the responsibilities of authors in the peer-review process. Peer reviewers are subject-matter experts who provide guidance to editors on the suitability of manuscripts for publication and help authors improve the accuracy and readability of their studies. The American Meteorological Society (AMS) analyzed data on peer reviews and found that there is no trend of declining reviewer acceptance rates or longer review times. The article emphasizes the need for authors to participate in peer reviewing and suggests that authors should review three papers for each one they submit. The AMS expresses gratitude to reviewers and encourages others to volunteer as reviewers. [Extracted from the article]

The time-extended empirical orthogonal function (EEOF) patterns of error developed in a companion paper are applied in this study for model data postprocessing. Projecting forecast anomalies from the model seasonal cycle from GEFSv12 outputs onto these EEOF patterns reconstructs the error principal components (PCs) in a manner that can be applied in real time. When these reconstructed error anomalies are compared with the original GEFSv12 200-hPa geopotential height (Z200) reforecast error anomalies, the projected and validation error signals tend to align temporally. When distributed globally, projection and validation error anomalies have statistically significant positive Pearson correlation coefficients with each other at most grid points outside of the tropics. Categorical Heidke skill score (HSS) analysis reaffirms that by lead day 16 of a forecast, the algorithm skillfully predicts systematic errors for locations outside of the tropics. Hemispheric winter demonstrates that the highest magnitude HSS values are in the high latitudes, illustrating the underlying seasonality of Z200 behavior and predictability. On average, wintertime HSS values hover around 20%, with high-latitude locations exceeding mean values of 40%. Comparatively, summertime values generally exceed 10% improvement outside of the tropics. High-latitude storm-track regions, such as the North Atlantic, North Pacific, and South Pacific, contain the most Z200 variance in the globe and the highest HSS values. This algorithm will be applied to real-time forecasts and additional variables in future work, with the end goal of implementation into the NOAA-CPC subseasonal forecasts. [ABSTRACT FROM AUTHOR]

In recent years, various early warning signals of critical transition have been presented, such as autocorrelation at lag 1 [AR(1)], variance, the propagator based on detrended fluctuation analysis (DFA-propagator), and so on. Many studies have shown that the climate system has the characteristics of long-term memory (LTM). Will the LTM characteristics of the climate system change as it approaches possible critical transition points? In view of this, the present paper first studies whether the LTM of several folding (folded bifurcation) models changes consistently as they approach their critical points slowly by the rescaled range (R/S) analysis. The results of numerical experiments show that when the control parameters of the folding model are close to its critical threshold, the Hurst exponent H exhibits an almost monotonic increase (significance level α = 0.05). We compare the performance of R/S with the existing indicators, including AR(1), variance, and DFA-propagator, and find that R/S is a perfectly valid alternative. When there is no extra false noise, AR(1) and variance have good early warning effects. After the addition of extra Gaussian white noise of different intensities, the values of AR(1) and variance change significantly. As a result, the DFA-propagator based on AR(1) calibration also changed significantly. Compared with the other three indicators, the early warning effect of H has stronger ability to resist the interference of external false signals. To further verify the validity of increasing H, paleoclimate reconstruction of Cariaco Basin sediment core grayscale record with long trends filtered out is studied by R/S analysis. The other three early warning signals are calculated in the same way. The data contain a well-known abrupt climate change: the transition between the Younger Dryas (YD) and the Holocene. We find that approximately 300 years before this abrupt climate change occurred, before 11.7 kyr BP, the LTM exponents for Cariaco Basin deglacial grayscale data present an obvious increasing trend at a significant level of α = 0.05. Meanwhile, the variation trend of H and DFA-propagator is basically similar. This shows that increasing H by R/S analysis is an effective early warning signal, which indicates that a dynamic system is approaching its possible critical transition points; H is a completely valid alternative signal for AR(1) and DFA-propagator. The main conclusion of this paper is based on numerical experiments. The precise relationship between H and the stability of the underlying state approaching the transition needs to be further studied. [ABSTRACT FROM AUTHOR]

The article discusses the importance of peer reviewers in scholarly publishing and the responsibilities of authors in the peer-review process. Peer reviewers are subject-matter experts who provide guidance to editors on the suitability of manuscripts for publication and help authors improve the accuracy and readability of their studies. The American Meteorological Society (AMS) analyzed data on peer reviews and found that there is no trend of declining reviewer acceptance rates or longer review times. The article emphasizes the need for authors to participate in peer reviewing and suggests that authors should review three papers for each one they submit. The AMS expresses gratitude to reviewers and encourages others to volunteer as reviewers. [Extracted from the article]

The article discusses the importance of peer reviewers in scholarly publishing and the responsibilities of authors in the peer-review process. Peer reviewers are subject-matter experts who provide guidance to editors on the suitability of manuscripts for publication and help authors improve the accuracy and readability of their studies. The American Meteorological Society (AMS) analyzed data on peer reviews and found that there is no trend of declining reviewer acceptance rates or longer review times. The article emphasizes the need for authors to participate in peer reviewing and suggests that authors should review three papers for each one they submit. The AMS expresses gratitude to reviewers and encourages others to volunteer as reviewers. [Extracted from the article]

Humidity sounder radiances are currently thinned to 110-km spacing prior to assimilation at ECMWF and used with no averaging applied. In this paper, the thinning scale and possible averaging of all-sky humidity sounder observations into "superobs" are considered. The short- and medium-range forecast impacts of changing the thinning and averaging scales of humidity sounder radiances prior to the data assimilation are investigated separately and then together. Superobbing acts as a low-pass filter and provides smoother images of departures, decreasing the effective sensor noise and thus the standard deviation of background departures, marginally for 183-GHz channels (5%–15%) and significantly for 118-GHz channels (5%–55%). Observations are thus more representative of the model effective resolution, with a better utilization of total information content than thinning native-resolution radiances, as less information is discarded. Whether changed in isolation or combination, the additions of data via superobbing and finer thinning are both shown to markedly improve background fits to independent observations, indicative of better short-range forecasts of humidity and improved winds via the 4D-Var tracer effect. Wind forecasts in the Southern Hemisphere are slightly improved in the medium range. A final configuration is tested at the resolution of the current operational model, with humidity sounder radiances averaged into 50-km superobs with 70-km spacing. This provides about 140% more radiances for assimilation and more finely detailed maps to analyze mesoscale features. The forecast impact of this change is larger in testing with higher model and data assimilation resolutions, showing the scale dependence of such decisions and the expected performance in an operational configuration. Significance Statement: This paper investigates thinning and averaging scales for humidity-sounding microwave observations in the ECMWF data assimilation system. The introduction of spatial averaging shows a positive impact, as does the assimilation of observations with finer spacing. These changes permit more total information on humidity into the system, and both are beneficial for short-range forecasts of humidity and winds in the mid- to upper troposphere. The results highlight the interplay between spatial scales of observations and those of the analysis system, with possibilities for improved utilization in this particular case. This is expected to remain a key consideration in assimilation systems going forward, given the continued increases in the resolution of assimilation systems and forecast models. [ABSTRACT FROM AUTHOR]

This paper examines ice particle reorganization by three-dimensional horizontal kinematic flows within the comma head regions of two U.S. East Coast winter storms and the effect of reorganization on particle concentrations within snowbands in each storm. In these simplified experiments, the kinematic flows are from the initialization of the HRRR model. Ice particles falling through the comma head were started from either 9-, 8-, or 7-km altitude, spaced every 200 m, and were transported north or northwest, arriving within the north or northwest half of the primary snowband in each storm. The greatest particle concentration enhancement within each band was a factor of 2.32–3.84 for the 16–17 December 2020 storm and 1.76–2.32 for the 29–30 January 2022 storm. Trajectory analyses for particles originating at 4 km on the southeast side of the comma head beneath the dry slot showed that this region supplied particles to the south side of the band with particle enhancements of factor of 1.36–2.08 for the 16–17 December 2020 storm and 1.04–2.16 for the 29–30 January 2022 storm. Snowfall within the bands had two source regions: 1) on the north/northwestern side, from ice particles falling from the comma head, and 2) on the southeastern side, from particles forming at or below 4-km altitude and transported northwestward by low-level flow off the Atlantic. While the findings give information on the source of particles in the bands, they do not definitively determine the cause of precipitation banding since other factors, such as large-scale ascent and embedded convection, also contribute to snow growth. Significance Statement: Wintertime storms along the east coast of North America can produce heavy snowfall, high winds, coastal flooding, and cold temperatures, resulting in major economic impacts within the northeast U.S. urban corridor. The heaviest snowfall typically occurs within snowbands, elongated narrow regions identifiable by high reflectivity on radar. This paper examines the potential sources of the ice particles contributing to the snowbands and how the flow fields throughout the storm can contribute to enhanced particle concentrations within the bands. [ABSTRACT FROM AUTHOR]

On 8 August 2023, a wind-driven wildfire pushed across the city of Lahaina, located in West Maui, Hawaii, resulting in at least 100 deaths and an estimated economic loss of 4–6 billion dollars. The Lahaina wildfire was associated with strong, dry downslope winds gusting to 31–41 m s−1 (60–80 kt; 1 kt ≈ 0.51 m s−1) that initiated the fire by damaging power infrastructure. The fire spread rapidly in invasive grasses growing in abandoned agricultural land upslope from Lahaina. This paper describes the synoptic and mesoscale meteorology associated with this event, as well as its predictability. Stronger-than-normal northeast trade winds, accompanied by a stable layer near the crest level of the West Maui Mountains, resulted in a high-amplitude mountain-wave response and a strong downslope windstorm. Mesoscale model predictions were highly accurate regarding the location, strength, and timing of the strong winds. Hurricane Dora, which passed approximately 1300 km to the south of Maui, does not appear to have had a significant impact on the occurrence and intensity of the winds associated with the wildfire event. The Maui wildfire was preceded by a wetter-than-normal winter and near-normal summer conditions. Significance Statement: The 2023 Maui wildfire was one of the most damaging of the past century, with at least 100 fatalities. This paper describes the meteorological conditions associated with the event and demonstrates that excellent model forecasts made the threat foreseeable. [ABSTRACT FROM AUTHOR]

Numerical simulations of turbulent moist Rayleigh–Bénard convection driving CCN activation and droplet growth in the laboratory Pi chamber are discussed. Supersaturation fluctuations come from isobaric mixing of warm and humid air rising from the lower boundary with colder air featuring lower water vapor concentrations descending from the upper boundary. Lagrangian particle–based microphysics is used to represent the growth of haze CCN and cloud droplets with kinetic, solute, and surface tension effects included. Dry CCN spectra in the range between 2- and 200-nm radii from field observations are considered. Increasing the total CCN concentration from pristine to polluted conditions results in an increase in the droplet concentration and reduction in the mean droplet radius and spectral width. These are in agreement with Pi chamber observations and numerical simulations, as well as with numerous past studies of CCN cloud-base activation in natural clouds. The key result is that a relatively small fraction of the available CCN is activated in the Pi chamber fluctuating supersaturations, from about a half in the pristine case to only a 10th in the polluted case. The activation fraction as a function of the dry CCN radius is similar in all simulations, close to zero at the CCN small end, increasing to a maximum at CCN radius around 50 nm, and decreasing to close to zero at the large CCN end. This is explained as too small supersaturations to activate small CCN as in natural clouds and insufficient time to allow large CCN reaching the critical radius. Significance Statement: Impact of turbulence on the formation and growth of cloud droplets is an important cloud physics problem. Laboratory experiments in the Michigan Technological University cloud chamber provide key insights into this problem. Numerical simulations of cloud chamber processes discussed in this paper complement laboratory experiments by providing insights difficult or impossible to obtain in the laboratory. The study contrasts the formation and growth of cloud droplets in the laboratory cloud chamber with processes taking place in natural clouds. The differences documented in this paper pose questions concerning the impact of turbulence on the formation and growth of cloud droplets as a result of interactions of clouds with their environment. [ABSTRACT FROM AUTHOR]

This study evaluates the performance of the area-based, district heatwave forecasts that drive the Australian heatwave warning service. The analysis involves using a recently developed approach of scoring multicategorical forecasts using the fixed risk multicategorical (FIRM) scoring framework. Additionally, we quantify the stability of the district forecasts between forecast updates. Notably, at longer lead times, a discernible overforecast bias exists that leads to issuing severe and extreme heatwave district forecasts too frequently. Consequently, at shorter lead times, forecast heatwave categories are frequently downgraded with subsequent revisions. To address these issues, we demonstrate how isotonic regression can be used to conditionally bias correct the district forecasts. Finally, using synthetic experiments, we illustrate that even if an area warning is derived from a perfectly calibrated gridded forecast, the area warning will be biased in most situations. We show how these biases can also be corrected using isotonic regression which could lead to a better warning service. Importantly, the evaluation and bias correction approaches demonstrated in this paper are relevant to forecast parameters other than heat indices. Significance Statement: Heatwaves have terrible impacts on society. Understanding the performance of heatwave forecasts and warnings is important so that we can understand how they can be improved to reduce negative health impacts. We demonstrate techniques to evaluate the performance, biases, and stability of area-based forecasts that are used by a warning service. We illustrate how area-based forecasts can be improved through conditional bias correction. Additionally, we conduct a synthetic experiment that shows that deriving an area-based warning from a perfectly calibrated gridded forecast may lead to biased warnings. [ABSTRACT FROM AUTHOR]

During routine analyses of the calibration stability of ocean surface wind retrievals from satellites, we identified a significant bias between satellite measurements and wind observations from the Tropical Atmosphere Ocean (TAO) buoy array, starting in mid-2020 until the present. After extensive investigation, we determined that the bias did not arise from anomalies in the satellites' calibration or coding errors, as it appeared regardless of which satellite these buoys were compared to. A sudden increase of about 10% (0.5–0.8 m s−1) in wind speed observations was first identified in over 40 TAO buoys that were serviced between March and September 2020. Our concerns were shared with scientists at the National Data Buoy Center (NDBC), who confirmed our estimates. The exact source of this sudden change is still under investigation, but it appears to be related to changes in the calibration of buoy anemometers installed during recent service trips. By 2024, all currently operating TAO buoys under NDBC management have been serviced since 2020, and they all manifest a sudden wind speed increase postservice in the public-facing buoy data. This change is a source of concern because the stability of the integrated satellite–buoy system is vital for international ocean observation programs. The aim of this paper is to inform the research community about this spurious wind signal in the TAO array, discuss the impact it could have on the research community, and prevent it from being misinterpreted as climate variability, impacting the calibration of other observing systems, or affecting derived data products such as ocean surface fluxes. SIGNIFICANCE STATEMENT: The Tropical Atmosphere Ocean (TAO) buoys are used for both monitoring and predicting El Niño–Southern Oscillation (ENSO) events and for tropical climate variability studies. Buoy data are also routinely assimilated into numerical prediction models, and they are used for precise (0.1 m s−1) calibration of satellite wind retrievals. It is important that sudden calibration changes are shared with the research community to avoid either having them misinterpreted as climate signals or propagating them to derived datasets such as ocean surface fluxes. Additionally, the misalignment between the calibration of one buoy array (e.g., TAO) versus the others [e.g., PIRATA, Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction (RAMA), or the National Data Buoy Center (NDBC) meteorological/ocean extratropical buoys] poses a dilemma for the users interested in ground truth, e.g., when using buoys for satellite calibration. [ABSTRACT FROM AUTHOR]

The variability of daytime–nighttime compound heat waves (CHWs) is a highly concerning issue due to severe impacts on human and natural systems. Although several studies surveyed physical processes for the CHW occurrence, its interannual variability and associated mechanisms have not been well understood. Focusing on CHWs in the Yangtze River valley (YRV, a hotspot across China), this paper indicates an emergence of enlarged interannual variability after entering into the twenty-first century, before which the interannual variability was quite small. The possible mechanism underlying the high interannual variability is further explored in terms of atmospheric and oceanic backgrounds. The results show that the atmospheric background associated with higher-than-normal CHWs over the YRV features anticyclonic circulation anomalies tilting southeastward from the north of the YRV in the upper troposphere to the western Pacific in the lower troposphere. Accordingly, the upper-tropospheric easterly and lower-tropospheric southwesterly anomalies dominate the YRV, causing anomalous subsidence and increased humidity in situ, respectively, which benefit the increase in CHWs. The tripole (positive–negative–positive) sea surface temperature (SST) anomalies in the North Atlantic (NA) and the positive SST anomalies in the Maritime Continent (MC) also play roles in increasing the YRV CHWs by influencing the above atmospheric circulations. The NA tripole SST anomalies tend to affect the upper- and midtropospheric anticyclonic anomalies through the eastward-propagating wave train across Eurasia. The warming of the MC SSTs can impact the lower-tropospheric anticyclonic anomaly over the western Pacific via local meridional circulation. The opposite situations are applicable for decreased CHWs over the YRV. Significance Statement: Daytime–nighttime compound heat waves (CHWs) refer to persistent processes with abnormally high temperatures occurring both in daytime and nighttime. Compared with heat waves (HWs) occurring only at daytime or nighttime, the CHWs exert more severe damage to natural ecosystems and human society. Thus, understanding the physical mechanisms of CHWs is urgently needed. This study examines the interannual variability of Yangtze River valley (YRV) CHWs and finds that it exhibits a pronounced enlargement after 2000. During this period, an anomalous anticyclone tilting southeastward from the north of the YRV in the upper level to the western Pacific in the lower level is a favorable atmospheric circulation background for the increase in CHWs over the YRV, and vice versa. Sea surface temperatures (SSTs) in the North Atlantic (NA) and the Maritime Continent (MC) also play important roles. The positive–negative–positive SST anomalies in the NA and the warming SSTs in the MC tend to increase the YRV CHWs, through their influences on CHW-related atmospheric circulations in the upper troposphere and lower troposphere, respectively. These findings are expected to deepen our understanding of CHW variability, which are of great importance for disaster prevention and mitigation. [ABSTRACT FROM AUTHOR]

We derive, at leading order in the thin-shell parameter, a consistent set of nonlinear governing equations for the dynamics of flows confined to a zonal cloud band such as those on Jupiter, in a thin layer near the top of the planetary troposphere. Some exact solutions are provided in the material (Lagrangian) framework. The explicit specification of the individual particle paths enables a detailed study of these flows that model oscillations superimposed on a mean current. This approach is applied to Jupiter's Great Red Spot and to the filamentary zonal flow at its southern boundary. Significance Statement: We propose a new approach to the study of some flow patterns visible in zonal cloud bands on Jupiter. Motivated by observations showing that the dominant motions in the cloud bands on Jupiter are zonal and rotational, we provide some exact solutions to the governing equations for the leading-order dynamics. These solutions model rotating particle paths interacting with a straight-line flow. The approach offers detailed insight into basic features of the flow, highlighting the interplay between density variations and wind forcing. The exact solutions presented here are a useful starting point for a perturbation analysis. Current advances in computing methods enhance the feasibility of numerical simulations of perturbed flows that are designed to capture a wider range of effects, whose relevance can be ascertained by comparison with the exact solutions presented in this paper. [ABSTRACT FROM AUTHOR]

Scientific interest in Mount Everest has been largely focused on the physiology of hypoxia caused by the summit's low barometric pressure. Although weather is recognized as a significant risk for climbers on the mountain, it has not been extensively studied. In this paper, we reconstruct the meteorological conditions associated with the deadly outbreak of high-impact weather on Mount Everest that occurred in May 1996 and was the subject of the best-selling book Into Thin Air. The authors show that during this event, two jet streaks—an upper-level short-wave trough and an intrusion of stratospheric air into the upper troposphere—were present in the vicinity of Mount Everest. Meanwhile, in the lower troposphere, there was convergence of water vapor transport from both the Arabian Sea and the Bay of Bengal into the region to the south of Mount Everest. The authors propose that the ageostrophic circulation associated with the upper-level features resulted in a region of large-scale ascent near Mount Everest that, in combination with the anomalous availability of moisture in the region, triggered convective activity. The resulting high-impact weather trapped over 20 climbers on Mount Everest's exposed upper slopes leading to the deaths of 8. These synoptic-scale characteristics provide some expectation of predicting life-threatening high-altitude storms in the Himalayas. In addition, the authors argue that the falling barometric pressure and the presence of ozone-rich stratospheric air that occurred near the summit of Mount Everest during this event could have shifted a coping climber from a state of brittle tolerance to physiological distress. [ABSTRACT FROM AUTHOR]

Climate changepoint (homogenization) methods abound today, with a myriad of techniques existing in both the climate and statistics literature. Unfortunately, the appropriate changepoint technique to use remains unclear to many. Further complicating issues, changepoint conclusions are not robust to perturbations in assumptions; for example, allowing for a trend or correlation in the series can drastically change changepoint conclusions. This paper is a review of the topic, with an emphasis on illuminating the models and techniques that allow the scientist to make reliable conclusions. Pitfalls to avoid are demonstrated via actual applications. The discourse begins by narrating the salient statistical features of most climate time series. Thereafter, single- and multiple-changepoint problems are considered. Several pitfalls are discussed en route and good practices are recommended. While most of our applications involve temperatures, a sea ice series is also considered. Significance Statement: This paper reviews the methods used to identify and analyze the changepoints in climate data, with a focus on helping scientists make reliable conclusions. The paper discusses common mistakes and pitfalls to avoid in changepoint analysis and provides recommendations for best practices. The paper also provides examples of how these methods have been applied to temperature and sea ice data. The main goal of the paper is to provide guidance on how to effectively identify the changepoints in climate time series and homogenize the series. [ABSTRACT FROM AUTHOR]

In this paper, a data-driven transfer learning (TL) model for locating tropical cyclone (TC) centers from satellite infrared images in the northwest Pacific is developed. A total of 2450 satellite infrared TC images derived from 97 TCs between 2015 and 2018 were used for this paper. The TC center location model (ResNet-TCL) with added residual fully connected modules is built for the TC center location. The MAE of the ResNet-TCL model is 34.8 km. Then TL is used to improve the model performance, including obtaining a pretrained model based on the ImageNet dataset, transferring the pretrained model parameters to the ResNet-TCL model, and using TC satellite infrared imagery to fine-train the ResNet-TCL model. The results show that the TL-based model improves the location accuracy by 14.1% (29.3 km) over the no-TL model. The model performance increases logarithmically with the amount of training data. When the training data are large, the benefit of increasing the training samples is smaller than the benefit of using TL. The comparison of model results with the best track data of TCs shows that the MAEs of TCs center is 29.3 km for all samples and less than 20 km for H2–H5 TCs. In addition, the visualization of the TL-based TC center location model shows that the TL model can accurately extract the most important features related to TC center location, including TC eye, TC texture, and contour. On the other hand, the no-TL model does not accurately extract these features. [ABSTRACT FROM AUTHOR]