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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
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
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.

Restricted access
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.

Restricted access
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.

Restricted access
Gong Shang
,
Zhiwei Zhang
,
Shoude Guan
,
Xiaodong Huang
,
Chun Zhou
,
Wei Zhao
, and
Jiwei Tian

Abstract

Diapycnal mixing in the South China Sea (SCS) is commonly attributed to the vertical shear variance (S2) of horizontal ocean current velocity, but the seasonal modulation of the S2 is still poorly understood due to the scarcity of long-term velocity observations. Here, this issue is explored in detail based on nearly 10-year-long ADCP velocity data from a mooring in the northern SCS. We find that the S2 in the northern SCS exhibits significant seasonal variations at both the near-surface (90–180 m) and sub-surface (180–400 m) layers, but their seasonal cycles and modulation mechanisms are quite different. For the near-surface layer, the S2 is stronger in late summer, autumn, and winter but weaker in spring and early summer, while in the sub-surface layer, it is much stronger in winter than other seasons. Further analysis suggests that in the near-surface layer, the stronger S2 in autumn and winter is primarily caused by typhoons-induced near-inertial internal waves (NIWs) and the large sub-inertial velocity shear of the baroclinic mesoscale eddies, respectively. With respect to the sub-surface layer, the enhanced wintertime S2 is primarily associated with the “inertial chimney” effect of anticyclonic eddies, trapping wind-forced downward-propagating NIWs and significantly increasing the near-inertial shear at the critical layer. The findings in this study highlight the potentially important roles of mesoscale eddies and NIWs in modulating the seasonality of upper-ocean mixing in the northern SCS. This modulation is attributed not only to the strong shear of these features but also to their interactions.

Restricted access
Matthew H. Hitchman
and
Shellie M. Rowe

Abstract

On 10 August 2020, a derecho caused widespread damage across Iowa and Illinois. Des Moines station data show that the arrival of the gust front was characterized by an abrupt shift to northerly flow, exceeding 22 m/s for ~ 20 min. To test the hypothesis that this northerly jet is associated with a horizontal potential vorticity (PV) dipole in the lower troposphere, we investigated the structure of PV in the University of Wisconsin Nonhydrostratic Modeling System (UWNMS) and of absolute vorticity in High Resolution Rapid Refresh (HRRR) forecast analyses.

This structure is described here for the first time. The negative PV member coincides with the downdraft, while the positive PV member coincides with the updraft, with a northerly jet between. The westerly inflow jet descends anticyclonically in the downdraft, joining with northerly flow from the surface anticyclone. The resulting northerly outflow jet creates the trailing comma-shaped radar echo.

The speed of propagation of the derecho is similar to the westerly wind maximum in the 3-5 km layer associated with the approaching synoptic cyclone, which acts as a steering level for resonant amplification. Idealized diagrams and 3D isosurfaces illustrate the commonality of the PV dipole / northerly jet structure. Differences in this structure among three model states are related to low-level wind shear theory. The PV dipole coincides with the pattern of diabatic stretching tendency, which shifts westward and downward relative to the updraft/downdraft with increasing tilt. The PV dipole can contribute toward dynamical stability in a derecho.

Restricted access
Anand Gnanadesikan
,
Gianluca Fabiani
,
Jingwen Liu
,
Renske Gelderloos
,
G. Jay Brett
,
Yannis Kevrekidis
,
Thomas Haine
,
Marie-Aude Pradal
,
Constaninos Siettos
, and
Jennifer Sleeman

Abstract

In the modern ocean, transformation of light surface waters to dense deep waters primarily occurs in the Atlantic basin rather than in the North Pacific or Southern Oceans. The reasons for this remain unclear, as both models and paleoclimatic observations suggest that sinking can sometimes occur in the Pacific. We present a six-box model of the overturning that combines insights from a number of previous studies. A key determinant of the overturning configuration in our model is whether the Antarctic Intermediate Waters are denser than northern subpolar waters, something that depends on the magnitude and configuration of atmospheric freshwater transport. For the modern ocean, we find that although the interbasin atmospheric freshwater flux suppresses Pacific sinking, the poleward atmospheric freshwater flux out of the subtropics enhances it. When atmospheric temperatures are held fixed, North Pacific overturning can strengthen with either increases or decreases in the hydrological cycle, as well as under reversal of the interbasin freshwater flux. Tipping-point behavior, where small changes in the hydrological cycle may cause the dominant location of densification of light waters to switch between basins and the magnitude of overturning within a basin to exhibit large jumps, is seen in both transient and equilibrium states. This behavior is modulated by parameters such as the poorly constrained lateral diffusive mixing coefficient. If hydrological cycle amplitude is varied consistently with global temperature, northern polar amplification is necessary for the Atlantic overturning to collapse. Certain qualitative insights incorporated in the model can be validated using a fully-coupled climate model.

Restricted access