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Dongxue Mo
,
Po Hu
,
Jian Li
,
Yijun Hou
, and
Shuiqing Li

Abstract

The wave effect is crucial to coastal ocean dynamics, but the roles of the associated wave-dependent mechanisms, such as the wave-enhanced surface stress, wave-enhanced bottom stress, and three-dimensional wave force, are not yet fully understood. In addition, the parameterizations of each mechanism vary and need to be assessed. In this study, a coupled wave-current model based on the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) model system was established to identify the effect of the wave-dependent mechanism on storm surges and currents during three typical extreme weather systems, i.e., cold wave, extratropical cyclone, and typhoon systems, in a semi-enclosed sea. The effects of the three coupled mechanisms on the surface or bottom stress, in terms of both the magnitude and direction, were investigated and quantified separately based on numerical sensitive analysis. A total of seven parameterizations is used to evaluate these mechanisms, resulting in significant variations in the storm surge and current vectors. The similarities and differences of the wave-induced surge and wave-induced current among the various mechanisms were summarized. The change in the surface stress and bottom stress and the excessive momentum flux due to waves were found to mainly occur in shallow nearshore regions. Optimal choice of the combination of parameterization schemes was obtained through comparison with measured data. The wave-induced current in the open waters with a deep-water depth and complex terrain could generate cyclonic or anticyclonic current vorticities, the number and intensity of which always increased with the enhanced strength and rotation of the wind field increased.

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Megan Porter
,
Rodolfo Hernández
,
Blake Checkoway
,
Erik R. Nielsen
,
Castle Williamsberg
,
Gina Eosco
,
Katy Christian
,
Ashley Morris
,
Erica Grow Cei
,
Keely Patelski
, and
Jen Henderson
Open access
J. Anselin
,
P. R. Holland
,
A. Jenkins
, and
J. R. Taylor

Abstract

Efforts to parameterize ice shelf basal melting within climate models are limited by an incomplete understanding of the influence of ice base slope on the turbulent ice shelf-ocean boundary current (ISOBC). Here we examine the relationship between ice base slope, boundary current dynamics, and melt rate using 3-D, turbulence-permitting large-eddy simulations (LES) of an idealized ice shelf-ocean boundary current forced solely by melt-induced buoyancy. The range of simulated slopes (3-10%) is appropriate to the grounding zone of small Antarctic ice shelves and to the flanks of relatively wide ice base channels, and the initial conditions are representative of warm-cavity ocean conditions. In line with previous studies, the simulations feature the development of an Ekman boundary layer adjacent to the ice, overlaying a broad pycnocline. The time-averaged flow within the pycnocline is in thermal wind balance, with a mean shear that is only weakly dependent on the ice base slope angle α, resulting in a mean gradient Richardson number 〈Rig〉 that decreases approximately linearly with sinα. Combining this inverse relationship with a linear approximation to the density profile, we derive formulations for the friction velocity, thermal forcing, and melt rate in terms of slope angle and total buoyancy input. This theory predicts that melt rate varies like the square root of slope, which is consistent with the LES results and differs from a previously proposed linear trend. The derived scalings provide a potential framework for incorporating slope-dependence into parameterizations of mixing and melting at the base of ice shelves.

Open access
Matthew C. Wheeler
,
Hanh Nguyen
,
Chris Lucas
,
Zhi-Weng Chua
,
Simon Grainger
,
David A. Jones
,
Michelle L. L'Heureux
,
Ben Noll
,
Tristan Meyers
,
Nicolas C. Fauchereau
,
Alexandre Peltier
,
Thea Turkington
,
Hyung-Jin Kim
, and
Takafumi Umeda
Open access
Erica Bower
,
Michael J. Erickson
,
James A. Nelson
,
Mark Klein
, and
Andrew Orrison

Abstract

The Weather Prediction Center (WPC) issues Mesoscale Precipitation Discussions (MPDs) to highlight regions where heavy rainfall is expected to pose a threat for flash flooding. Issued as short-term guidance, the MPD consists of a graphical depiction of the threat area and a technical discussion of the forecasted meteorological and hydrological conditions conducive to heavy rainfall and the potential for a flash flood event. MPDs can be issued either during or in anticipation of an event and typically are valid for up to 6 hours. This study presents an objective verification of WPC’s MPDs issued between 2016 and 2022, complete with a climatology, false alarm analysis, and contingency table-based skill scores (e.g. critical success index, fractional coverage, etc). Regional and seasonal differences become evident when MPDs are assessed based on these groupings. MPDs improved in basic skill scores between 2016 and 2020, with slight decline in scores for 2021 and 2022. The false alarm ratio of MPDs has decreased between 2016 and 2021. The most dramatic improvement over the period occurs in the MPDs in the winter season (December, January, and February) and along theWest Coast (primarily atmospheric river events). The accuracy of MPDs in this group has quadrupled when measured by fractional coverage, and the false alarm rate is approximately one fifth of the 2016 value. Skill during active monsoon seasons tends to decrease, partially due to the large size of MPDs issued for monsoon-related flash flooding events.

Restricted access
Mitchell Bushuk
,
Sahara Ali
,
David A. Bailey
,
Qing Bao
,
Lauriane Batté
,
Uma S. Bhatt
,
Edward Blanchard-Wrigglesworth
,
Ed Blockley
,
Gavin Cawley
,
Junhwa Chi
,
François Counillon
,
Philippe Goulet Coulombe
,
Richard I. Cullather
,
Francis X. Diebold
,
Arlan Dirkson
,
Eleftheria Exarchou
,
Maximilian Göbel
,
William Gregory
,
Virginie Guemas
,
Lawrence Hamilton
,
Bian He
,
Sean Horvath
,
Monica Ionita
,
Jennifer E. Kay
,
Eliot Kim
,
Noriaki Kimura
,
Dmitri Kondrashov
,
Zachary M. Labe
,
WooSung Lee
,
Younjoo J. Lee
,
Cuihua Li
,
Xuewei Li
,
Yongcheng Lin
,
Yanyun Liu
,
Wieslaw Maslowski
,
François Massonnet
,
Walter N. Meier
,
William J. Merryfield
,
Hannah Myint
,
Juan C. Acosta Navarro
,
Alek Petty
,
Fangli Qiao
,
David Schröder
,
Axel Schweiger
,
Qi Shu
,
Michael Sigmond
,
Michael Steele
,
Julienne Stroeve
,
Nico Sun
,
Steffen Tietsche
,
Michel Tsamados
,
Keguang Wang
,
Jianwu Wang
,
Wanqiu Wang
,
Yiguo Wang
,
Yun Wang
,
James Williams
,
Qinghua Yang
,
Xiaojun Yuan
,
Jinlun Zhang
, and
Yongfei Zhang

Abstract

This study quantifies the state-of-the-art in the rapidly growing field of seasonal Arctic sea ice prediction. A novel multi-model dataset of retrospective seasonal predictions of September Arctic sea ice is created and analyzed, consisting of community contributions from 17 statistical models and 17 dynamical models. Prediction skill is compared over the period 2001–2020 for predictions of Pan-Arctic sea ice extent (SIE), regional SIE, and local sea ice concentration (SIC) initialized on June 1, July 1, August 1, and September 1. This diverse set of statistical and dynamical models can individually predict linearly detrended Pan-Arctic SIE anomalies with skill, and a multi-model median prediction has correlation coefficients of 0.79, 0.86, 0.92, and 0.99 at these respective initialization times. Regional SIE predictions have similar skill to Pan-Arctic predictions in the Alaskan and Siberian regions, whereas regional skill is lower in the Canadian, Atlantic, and Central Arctic sectors. The skill of dynamical and statistical models is generally comparable for Pan-Arctic SIE, whereas dynamical models outperform their statistical counterparts for regional and local predictions. The prediction systems are found to provide the most value added relative to basic reference forecasts in the extreme SIE years of 1996, 2007, and 2012. SIE prediction errors do not show clear trends over time, suggesting that there has been minimal change in inherent sea ice predictability over the satellite era. Overall, this study demonstrates that there are bright prospects for skillful operational predictions of September sea ice at least three months in advance.

Open access
Malcolm Maas
,
Timothy Supinie
,
Andrew Berrington
,
Samuel Emmerson
,
Ava Aidala
, and
Michael Gavan

Abstract

Given inconsistencies in reporting methods and general lack of documentation, the creation of a unified tornado database across the world has been an elusive target for severe weather climatology purposes and historical interest. Previous online tornado documentation has also often been inconsistent or is now defunct. Many individual countries or continents maintain tornado information through either government-sponsored or independent organizations. The Tornado Archive was developed to create a first-of-its-kind digitized synthesis of worldwide tornado documentation, using the most complete sources of information available for regions known to be tornadically active. Spatial and temporal trends in tornado occurrence and reporting can be visualized through an interactive user interface with a variety of filtering methods and environmental reanalysis datasets, such as ERA5. The additional data introduced using Thomas Grazulis’ Significant Tornadoes may be beneficial for tornado climatology studies over the United States. The Tornado Archive is also intended to be a collaborative exercise, with clear data attribution and open avenues for augmentation, and the creation of a common data model to store the tornado information will assist in maintaining and updating the database. In this work, we document the methods necessary for creating the Tornado Archive database, provide broader climatological analysis of spatiotemporal patterns in tornado occurrence, and outline potential use cases for the data. We also highlight its key limitations, and emphasize the need for further international standardization of tornado documentation.

Open access
Shoobhangi Tyagi
,
Sandeep Sahany
,
Dharmendra Saraswat
,
Saroj Kanta Mishra
,
Amlendu Dubey
, and
Dev Niyogi

Abstract

The 2015 Paris Agreement outlined limiting global warming to 1.5°C relative to the preindustrial levels, necessitating the development of regional climate adaptation strategies. This requires a comprehensive understanding of how the 1.5°C rise in global temperature would translate across different regions. However, its implications on critical agricultural components, particularly blue and green water, remains understudied. This study investigates these changes using a rice-growing semiarid region in central India. The aim of this study is to initiate a discussion on the regional response of blue–green water at specific warming levels. Using different global climate models (GCMs) and shared socioeconomic pathways (SSPs), the study estimated the time frame for reaching the 1.5°C warming level and subsequently investigated changes in regional precipitation, temperature, surface runoff, and blue–green water. The results reveal projected reductions in precipitation and surface runoff by approximately 5%–15% and 10%–35%, respectively, along with decrease in green and blue water by approximately 12%–1% and 40%–10%, respectively, across different GCMs and SSPs. These findings highlight 1) the susceptibility of blue–green water to the 1.5°C global warming level, 2) the narrow time frame available for the region to develop the adaptive strategies, 3) the influence of warm semiarid climate on the blue–green water dynamics, and 4) the uncertainty associated with regional assessment of a specific warming level. This study provides new insights for shaping food security strategies over highly vulnerable semiarid regions and is expected to serve as a reference for other regional blue/green water assessment studies.

Significance Statement

This study helps to drive home the message that a global agreement to limit the warming level to 1.5°C does not mean local-scale temperature (and associated hydrological) impacts would be limited to those levels. The regional changes can be more exaggerated and uncertain, and they also depend on the choice of the climate model and region. Therefore, local-scale vulnerability assessments must focus on the multidimensional assessment of a 1.5°C warmer world involving different climate models, climate-sensitive components, and regions. This information is relevant for managing vulnerable agricultural systems. This study is among the first to investigate the critical agricultural components such as the blue–green water over a semiarid Indian region, and the findings and methodology are expected to be transferable for performing regional-scale assessments elsewhere.

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Martin P. Hoerling
,
Jon K. Eischeid
,
Henry F. Diaz
,
Balaji Rajagopolan
, and
Eric Kuhn

Abstract

Of concern to Colorado River management, as operating guidelines post-2026 are being considered, is whether water resource recovery from low flows during 2000–2020 is possible. Here we analyze new simulations from the sixth generation of the Coupled Model Intercomparison Project (CMIP6) to determine plausible climate impacts on Colorado River flows for 2026–2050 when revised guidelines would operate. We constrain projected flows for Lee Ferry, the gauge through which 85% of the river flow passes, using its estimated sensitivity to meteorological variability together with CMIP6 projected precipitation and temperature changes. The critical importance of precipitation, especially its natural variability, is emphasized. Model projections indicate increased precipitation in the Upper Colorado River basin due to climate change, which alone increases river flows 5%–7% (relative to a 2000–2020 climatology). Depending on the river’s temperature sensitivity, this wet signal compensates some, if not all, of the depleting effects from basin warming. Considerable internal decadal precipitation variability (~5% of the climatological mean) is demonstrated, driving a greater range of plausible Colorado River flow changes for 2026–2050 than previously surmised from treatment of temperature impacts alone: the overall precipitation-induced Lee Ferry flow changes span −25% to +40% contrasting with a −30% to −5% range from expected warming effects only. Consequently, extreme low and high flows are more likely. Lee Ferry flow projections, conditioned on initial drought states akin to 2000–2020, reveal substantial recovery odds for water resources, albeit with elevated risks of even further flow declines than in recent decades.

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Arshdeep Singh
,
Sanjiv Kumar
,
Liang Chen
,
Montasir Maruf
,
Peter Lawrence
, and
Min-Hui Lo

Abstract

This study examines the effects of land use (LU) change on regional climate, comparing historical and future scenarios using seven climate models from Coupled Model Intercomparison Phase 6 – Land Use Model Intercomparison Project experiments. LU changes are evaluated relative to land use conditions during the pre-industrial climate. Using the Community Earth System Model version 2 Large Ensemble (CESM2-LE) experiment, we distinguish LU impacts from natural climate variability. We assess LU impact locally by comparing the impacts of climate change in neighboring areas with and without LU changes. Further, we conduct CESM2 experiments with and without LU changes to investigate LU-related climate processes.

A multi-model analysis reveals a shift in LU-induced climate impacts, from cooling in the past to warming in the future climate across mid-latitude regions. For instance, in North America, LU's effect on air temperature changes from −0.24±0.18°C historically to 0.62±0.27°C in the future during the boreal summer. The CESM2-LE shows a decrease in LU-driven cooling from −0.92±0.09°C in the past to −0.09±0.09°C in future boreal summers in North America.

A hydroclimatic perspective linking LU and climate feedback indicates LU changes causing soil moisture drying in the mid-latitude regions. This contrasts with hydrology-only views showing wetter soil conditions due to LU changes. Furthermore, global warming causes widespread drying of soil moisture across various regions. Mid-latitude regions shift from a historically wet regime to a water limited transitional regime in the future climate. This results in reduced evapotranspiration, weakening LU-driven cooling in future climate projections. A strong linear relationship exists between soil moisture and evaporative fraction in mid-latitudes.

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