Browse

Louise Crochemore
,
Stefano Materia
,
Elisa Delpiazzo
,
Stefano Bagli
,
Andrea Borrelli
,
Francesco Bosello
,
Eva Contreras
,
Francesco Dalla Valle
,
Silvio Gualdi
,
Javier Herrero
,
Francesca Larosa
,
Rafael Lopez
,
Valerio Luzzi
,
Paolo Mazzoli
,
Andrea Montani
,
Isabel Moreno
,
Valentina Pavan
,
Ilias Pechlivanidis
,
Fausto Tomei
,
Giulia Villani
,
Christiana Photiadou
,
María José Polo
, and
Jaroslav Mysiak

Abstract

Assessing the information provided by co-produced climate services is a timely challenge given the continuously evolving scientific knowledge and its increasing translation to address societal needs. Here we propose a joint evaluation and verification framework to assess prototype services that provide seasonal forecast information based on the experience from the H2020 CLARA project. The quality and value of the forecasts generated by CLARA services were firstly assessed for five climate services utilizing the Copernicus Climate Change Service seasonal forecasts and responding to knowledge needs from the water resources management, agriculture, and energy production sectors. This joint forecast verification and service evaluation highlights various skills and values across physical variables, services and sectors, as well as a need to brigde the gap between verification and user-oriented evaluation. We provide lessons learnt based on the service developers’ and users’ experience, and recommendations to consortia that may want to deploy such verification and evaluation exercises. Lastly, we formalize a framework for joint verification and evaluation in service development, following a transdisciplinary (from data purveyors to service users) and interdisciplinary chain (climate, hydrology, economics, decision analysis).

Open access
Beiyao Liu
,
Ying Li
,
Zhehong Wu
, and
Jialu Lin

Abstract

Early summer is a peak time for tropical cyclone (TC) activities over the Bay of Bengal (BoB) and a period of South Asian monsoon onset, and the TCs during this time have a significant impact on the water vapor transport associated with monsoons. This study investigates the anomalous characteristics of the dynamic–thermal atmospheric circulation structure and water vapor budget over the Tibetan Plateau (TP) under the influence of BoB TCs generated in May from 1979 to 2020 with JTWC best track data and ERA5 data. Results reveal that a significant southerly water vapor channel forms from the BoB to the southeastern TP with a water vapor convergence near the Yarlung Zangbo Grand Canyon. A part of the water vapor is transported directly to the TP by deep southerly jet, while the other part is lifted by TCs and then climbs upward to the TP by two uplift processes occurring on the southern slope of the TP and over the TP respectively, which makes the whole troposphere over the southeastern TP warmer and wetter. It is found that anomalous southeasterly airflow in the northeast of TC circulation turns to anomalous southwesterly airflow forming an abnormal anticyclonic circulation over the southern TP in the middle and upper troposphere due to the diabatic heating effect. In this process, the TP acts as an anomalous water vapor sink with remarkable water vapor inflow through its southern boundary, with the main water vapor outflow through the eastern boundary, but a weak easterly water vapor backflow to the eastern TP in the lower troposphere.

Significance Statement

This study attempts to investigate the anomalous features of the water vapor budget over the Tibetan Plateau (TP) under the influence of the Bay of Bengal (BoB) tropical cyclones (TCs) during early summer. Results show that a significant southerly water vapor channel forms from the BoB to the southeastern TP with a water vapor convergence near the Yarlung Zangbo Grand Canyon. The TP acts as an anomalous water vapor sink with more and higher water vapor inflows through the southern boundary of the TP. A positive temperature and humidity anomaly can be found over the southeastern TP extending upward into the middle and upper troposphere. The results are helpful to understand how the BoB TCs affect the weather process over the TP.

Restricted access
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.

Restricted access
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
Free access
Free 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