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CW3E Publication Notice: A long short-term memory neural network-based error estimator for three-dimensional dynamically adaptive mesh generation

CW3E Publication Notice

A long short-term memory neural network-based error estimator for three-dimensional dynamically adaptive mesh generation

November 20, 2023

A new paper titled “A long short-term memory neural network-based error estimator for three-dimensional dynamically adaptive mesh generation” by Xiaofei Wu (CUIT, China), Pu Gan (CUIT, China), Jinxi Li (IAP, CAS), Fangxin Fang (ICL, UK), Jerry Zou (CW3E), Christopher Pain (ICL, UK), Xiao Tang (IAP, CAS), Jinyuan Xin (IAP, CAS), Zifa Wang (IAP, CAS), and Jiang Zhu (IAP, CAS) was recently published in the Physics of Fluids. This study introduces a LSTM neural network for guiding mesh adaptation in atmospheric modeling. The LSTM neural network model is integrated into the existing unstructured mesh atmosphere model to generate adaptive meshes in both time and space for 2D/3D scenarios. This constitutes an initial phase toward establishing a comprehensive neural network for 3D unstructured adaptive mesh generation. This work supports the Modeling Capabilities for the Western United States priority area in CW3E’s 2019–2024 Strategic Plan.

In this study, we harness the innovative power of a long short-term memory (LSTM) neural network as an error estimator for adapting unstructured meshes in both 2D and 3D scenarios. This LSTM network predicts the evolution of the adaptive grid based on specified variables, presenting itself as an artificial intelligence-driven architecture to optimize the adaptive criterion for the target variable. Our findings reveal that the mesh patterns generated by the LSTM error estimator within 3D adaptive atmospheric model Fluidity-Atmosphere closely resemble those produced by traditional error estimators, highlighting superior performance in enhancing simulation accuracy. Notably, with an increase in the number of nodes, the LSTM mesh generator significantly reduces CPU time requirements by up to 50% in 3D cases compared to the conventional mesh generator within Fluidity-Atmos, showcasing its remarkable computational efficiency.

Adaptive meshes play a pivotal role in numerical weather modeling, providing an efficient, precise, and flexible representation of intricate physical phenomena. The potential application of adaptive meshes holds promise for improving predictions of high-impact weather systems that require high-resolution simulations at a reasonable cost.

Figure 1: The proposed LSTM neural network for mesh adaptivity (a), the LSTM memory cell in this architecture (b), and the schematic of input data selection criteria (c).

Wu, X., Gan, P., Li, J., Fang, F., Zou, X., Pain, C. C., Tang, X., Xin, J., Wang, Z., & Zhu, J. (2023). A long short-term memory neural network-based error estimator for three-dimensional dynamically adaptive mesh generation. Physics of Fluids, 35(10), 106610. https://doi.org/10.1063/5.0172020

CW3E Publication Notice: Mesoscale and Synoptic Scale Analysis of Narrow Cold Frontal Rainband During a Landfalling Atmospheric River in California During January 2021

CW3E Publication Notice

Mesoscale and Synoptic Scale Analysis of Narrow Cold Frontal Rainband During a Landfalling Atmospheric River in California During January 2021

November 20, 2023

A new paper titled “Mesoscale and Synoptic Scale Analysis of Narrow Cold Frontal Rainband During a Landfalling Atmospheric River in California During January 2021” by a group of CW3E scientists (Jerry Zou, Jay Cordeira, Sam Bartlett, Brian Kawzenuk, Shawn Roj, Chris Castellano, Chad Hecht, and Marty Ralph) was recently published in the American Geophysical Union’s Journal of Geophysical Research: Atmospheres. On 27 January 2021, an atmospheric river (AR) associated with an intense surface cyclone made landfall over coastal northern California. The landfalling AR featured both synoptic-scale and mesoscale precipitation processes related to quasi-geostrophic (QG) forcing for ascent, upslope flow, a narrow cold-frontal rainband (NCFR), potential instability and a moist absolutely unstable layer (MAUL), and likely the seeder-feeder mechanism. This particular case involved a distinctive combination of short-duration, high-impact rainfall, and moderate stratiform precipitation along the coastal regions of California, attributed to the stalling and pivoting of the NCFR. Additionally, it offers valuable insights into non-typical orographic forcing of extreme precipitation, serving as a useful addition to prior studies. This work supports the AR Research and
Applications and Modeling Capabilities for the Western United States Priority Areas in CW3E’s 2019–2024 Strategic Plan.

Our study employs high-resolution West-WRF simulations to accurately characterize the gap and core structure of the NCFR, offering reliable precipitation estimations that address the limitations of radar and satellite observations. The NCFR was supported by robust synoptic-scale QG forcing for ascent and frontogenesis. It propagated southward from Cape Mendocino to Big Sur in 12 hr before stalling and rotating counter-clockwise in central/southern California due to upstream Rossby wave breaking and an amplifying upper-tropospheric trough. With the lower to middle tropospheric flow backed considerably to the south-southwest over the NCFR, the increase of the vertical wind shear caused the transition from parallel to trailing stratiform precipitation. The stall and pivot of the AR and NCFR led to intense rainfall with a 2-day precipitation accumulation greater than 300 mm over central California. In addition, under the potential instability and frontogenesis, a MAUL between 850 and 700 hPa was captured at the leading edge of the NCFR, which indicated slantwise deep layer lifting and high precipitation efficiency.

The results of this study complement previous studies on AR-related NCFR events in California by Cannon et al. (2018, 2020) and reaffirm the importance of developing West-WRF as a cutting-edge high-resolution numerical weather prediction system with a focus on extreme precipitation and related natural hazards. High-resolution simulations offer improved insights into the physical mechanisms driving efficient air lifting, leading to intense precipitation. Furthermore, we highlight the necessity for improved observational coverage along the U.S. West Coast to capture the shallow convective structure in NCFRs, essential for monitoring and forecasting extreme precipitation events.

Figure 1: (Figure 4 from Zou et al. 2023) Parallel stratiform (PS) precipitation and trailing stratiform (TS) precipitation during the 2021 January narrow cold-frontal rain event. (a, b) 2-m temperature and 10-m wind from West-WWRF D03 (1 km) at 0600 UTC 27 January (PS) and 0000 UTC 28 January (TS), respectively. Blue arrow represents cold air advection, and white arrow represents warm air advection. (c, d) 850-hPa geopotential height (contour line), temperature (contour fill), and wind field (vector) from West-WRF D01 (9 km) at 0600 UTC 27 January and 0000 UTC 28 January, respectively. (e, f) Composite reflectivity from West-WRF D03 (1 km) at 0600 UTC 27 January and 0000 UTC 28 January, respectively. The subplot at the right corner in (c, d) are NEXRAD observations at San Francisco station (KMUX). Black boxes in (c, d) represent the domain of the subplots.

Zou, X., Cordeira, J. M., Bartlett, S. M., Kawzenuk, B., Roj, S., Castellano, C., Hecht, C., & Ralph, F. M. (2023). Mesoscale and synoptic scale analysis of narrow cold frontal rainband during a landfalling atmospheric river in California during January 2021. Journal of Geophysical Research: Atmospheres, 128(20), e2023JD039426. https://doi.org/10.1029/2023JD039426

CW3E’s Mike Dettinger reviews National Climate Assessment released November 14, 2023

November, 20 2023

On November 14, 2023, the Biden-Harris administration took several bold steps towards addressing the problems of human-caused climate change at national and international levels. First, it announced more than $6 billion in investments in climate action (the largest ever), with the aim of putting the US on a part towards cutting carbon emissions in half by 2023. Second, together with Chinese President Xi Jinping, Biden pledged to accelerate both nation’s efforts to address climate change and steps to reduce emissions of methane and other greenhouse gases besides CO2.

Thirdly, the administration released the Fifth National Climate Assessment on this momentous day. The Global Change Research Act of 1990 mandates that the US Global Change Research Program deliver a report to Congress and the President every 4 or 5 years that integrates, evaluates, interprets and discusses current scientific findings and uncertainties associated with global change; effects of global change on the Nation’s environment, agriculture, energy production and use, land and water resources, transportation, human health and welfare, social systems, and biological diversity; and current trends in global change, both human-induced and natural, projecting those trends for the next 25 to 100 years. The Fifth National Climate Assessment (NCA5) is the latest to fulfill that mandate. Much of NCA5 built upon the approaches, processes, and results of the Fourth National Climate Assessment (NCA4), and is the result of arduous assessments and contributions from nearly 500 authors from every State and territory, led by 14 federal agencies but including authors from many academic disciplines and all sectors. These National Climate Assessments provide scientific foundations to support informed climate-change decisions and actions across the United States, and thus are the official “word” and guidance on the topic at national level.

Such a large and comprehensive document on such an often-contentious topic requires close review and scrutiny before its release, which in this case included extensive public engagements and comments and a peer review conducted by the National Academies of Sciences, Engineering and Medicine which included extensive inputs from CW3E’s Dr. Michael Dettinger. In broadest terms, the NCA5 concludes that, even as US population and GDP have risen in the past decade, its greenhouse gas emissions have declined because the US is finally taking action. It also finds that Americans are experiencing increasing risks from extreme weather events including heavy precipitation, droughts, floods, wildfires, and heat waves, more in some settings than others. California was one such setting with atmospheric-river extremes, where CW3E has lead the science and projections of future changes. And this assessment focused more than previous ones of the fact that climate change exacerbates social inequities so that climate actions provide generally opportunities for a more resilient and just society. As chastening as such assessments are, NCA5 is an opportunity for at least some renewed optimism; we have the science, technologies and resources to address climate change, we just need the political will to do so.

Bar chart showing city- and state-level adaptation plans and actions and mitigation activities by state and territory. Notice that California is far and away the leader in adaptation activities at city and state levels, and far and away the leader in mitigation actions at the city level. Research and contributions from Scripps Institution of Oceanography, and more recently from CW3E, have helped to motivate many of these actions over the past couple of decades.

CW3E Subseasonal Outlook: 17 November 2023

November 17, 2023

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Summary provided by Z. Yang, J. Wang, C. Castellano, M. DeFlorio, and J. Kalansky; 17 November 2023

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*Outlook products are considered experimental

CW3E Seasonal Outlook: 17 November 2023

November 17, 2023

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Summary provided by J. Wang, Z. Yang, C. Castellano, M. DeFlorio, and J. Kalansky; 17 November 2023

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*Outlook products are considered experimental

CW3E Atmospheric River Outlook: 9 Nov 2023

CW3E AR Update: 9 November 2023 Outlook

November 9, 2023

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Potential Atmospheric River to Impact the West Coast Next Week

Several low pressure systems will interact across the Northeast Pacific Ocean this weekend.
As they do, they will evolve into a deep storm system off the California coast.
Significant amounts of moisture will be drawn northward into the system.
As the system advances onshore, at least one atmospheric river will develop and very likely bring widespread rain and snow to the West Coast and inland areas.
The Atmospheric River Reconnaissance field campaign has been tracking these systems and is planning sampling flights coming up.
Watch for updates from CW3E in the days ahead and follow local NOAA/NWS offices for official forecast updates.

Click images to see loops of GFS IVT and 500 hPa Vorticity forecasts Valid 0000 UTC 12 November – 0000 UTC 17 November 2023

Summary provided by P. Iniguez, C. Castellano, M. Steen, and S. Bartlett; 9 November 2023

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*Outlook products are considered experimental

CW3E Subseasonal Outlook: 3 November 2023

November 3, 2023

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Summary provided by C. Castellano, J. Wang, Z. Yang, M. DeFlorio, and J. Kalansky; 3 November 2023

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*Outlook products are considered experimental

CW3E delivers guest lecture and field laboratory session for the Watershed Protection and Restoration class at Feather River College

Nov 1, 2023

Center for Western Weather and Water Extremes (CW3E) hydrologists Garrett McGurk and Gabe Lewis recently visited Feather River College (FRC) in Quincy, California, to deliver a paired guest lecture and field laboratory session for the Watershed Protection and Restoration class. The class, taught by FRC Assistant Professor Dana Flett, is designed to provide students with essential concepts, techniques, and tools to comprehend the structure and function of watersheds and how to apply this knowledge to stream corridor restoration.

During their lecture, Garrett and Gabe shared their personal journeys to becoming hydrologists, the mission of CW3E, FIRO, AR Recon, CW3E research and operations partnerships, the importance of both high-quality meteorological and hydrological measurements, and the principles of streamflow monitoring. The students were highly engaged and actively participated by asking numerous questions during and after the presentation.

Before the visit, the students had already gathered manual discharge measurements and conducted a stream channel survey on a section of Spanish Creek situated on FRC-owned property near a CW3E hydrometeorological monitoring station installed in 2019 as part of Yuba-Feather FIRO. To supplement this data, Garrett and Gabe’s lab focused on streamgaging techniques, ultimately leading to the installation of a new streamgage on Spanish Creek. This streamgage comprises a stilling well that houses a pressure transducer for continuous level measurements and a staff gage to facilitate visual level observations.

During the lab, students took turns operating power tools and installing concrete anchors to secure the stilling well and staff gage to concrete blocks previously positioned to stabilize the channel bank. Students were also instructed on conducting discharge measurements using various flow monitoring equipment, the importance of minimizing error during high flow events, and field safety protocols. Fortunately, the water temperature allowed students to comfortably wade in the stream while engaging Garrett and Gabe in discussions related to hydrology and pertinent western water issues.

The recently installed streamgage on Spanish Creek is designed to capture continuous level measurements and will play a pivotal role in establishing a stage-discharge relationship, also known as a rating curve, in conjunction with manual discharge measurements. Developing a rating curve is a key element of FRC’s long-term objectives for stream channel restoration on Spanish Creek. The streamgage will serve to characterize baseline conditions prior to any restoration activities, providing valuable insights into the current state of the waterway. Spanish Creek is an important tributary of the Feather River, which is part of the Yuba-Feather FIRO project.

While the streamgage is not currently equipped with telemetry, FRC has plans to upgrade the station with telemetered equipment in the near future. This upgrade will enhance the accessibility and real-time monitoring capabilities of the streamgage, further advancing their ability to track and respond to changing conditions on Spanish Creek.

Students from Feather River College learn about the equipment used to monitor streamflow and the importance of hydrologic measurements from CW3E hydrologist Garrett Mcgurk.

Students from Feather River College take turns helping to install a staff gage to measure stream level during a field laboratory session for the Watershed Protection and Restoration class.

CW3E Publication Notice: Impacts of Dropsonde Observations on Forecasts of Atmospheric Rivers and Associated Precipitation in the NCEP GFS and ECMWF IFS models

CW3E Publication Notice

Impacts of Dropsonde Observations on Forecasts of Atmospheric Rivers and Associated Precipitation in the NCEP GFS and ECMWF IFS models

October 31, 2023

A paper titled “Impacts of Dropsonde Observations on Forecasts of Atmospheric Rivers and Associated Precipitation in the NCEP GFS and ECMWF IFS models” by Laurel DeHaan (CW3E), Anna Wilson (CW3E), Brian Kawzenuk (CW3E), Minghua Zheng (CW3E), Luca Delle Monache (CW3E), Xingren Wu (NOAA/NCEP and Axiom Consultants), David A. Lavers (ECMWF), Bruce Ingleby (ECMWF), Vijay Tallapragada (NOAA/NCEP, AR Recon Co-PI), Florian Pappenberger (ECMWF), and F. Martin Ralph (CW3E Director and AR Recon PI) was recently accepted in Weather and Forecasting. This paper investigates the differences in skill between forecasts that assimilated dropsonde data from Atmospheric River Reconnaissance (AR Recon) and forecasts that did not assimilate the dropsonde data, and illustrates improvements in the forecasts that do include the additional dropsonde data. This work supports the Atmospheric Rivers (AR) Research and Applications Priority Areas in CW3E’s 2019-2024 Strategic Plan, and represents an important international, interagency collaboration, in the framework of a Research And Operations Partnership, to diagnose the impact of AR Recon data. Forecast comparison is made in terms of both precipitation and integrated vapor transport (IVT) at multiple thresholds (13, 25, and 50 mm for precipitation, and 250 and 500 kg m-1 s-1 for IVT) for two global numerical prediction models: the Integrated Forecast System (IFS) from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the Global Forecast System (GFS) from the National Centers for Environmental Prediction (NCEP). The comparison was made for 22 different Intensive Observation Periods (IOPs) in 2019 and 2020 at lead times from one to five days.

Differences between the control and denial forecasts were measured in terms of mean absolute error (MAE) and spatial correlation for both IVT and precipitation skill. In addition, the difference in precipitation was also measured using Fractions Skill Score (FSS) and a watershed intensity metric. Figure 1 shows an example of the comparison between the control and denial forecasts in terms of MAE and spatial correlation averaged over multiple thresholds. In this example, both models show generally modest improvement with the inclusion of dropsondes in IVT MAE and show larger improvements in IVT using the correlation metric. The NCEP model shows significant improvement at all three lead times for IVT correlation (Fig. 1f). For precipitation, the ECMWF model has significant improvements in MAE with the control forecasts at three lead times (Fig. 1c) and the NCEP model has significant improvements at two lead times (Fig. 1g). The correlation of precipitation has mixed results, with the only significant improvements with the control forecasts occurring at 48 and 72-hour lead times for the NCEP model (Figs. 1 d, h).

Combining this example with the other comparisons in the publication, this work illustrates that, more often than not, forecasts were improved when dropsonde data were assimilated. Both the ECMWF IFS and the NCEP GFS models show many improvements in forecast skill with the added information from the dropsondes. In particular, significant improvements in the control forecast IVT generally occur in both models, especially at a higher threshold. Significant improvements in the control forecast precipitation also generally occur in both models, but the two models are not consistent in the lead times and metrics that demonstrate the improvements.

Figure 1: (Figure 6 from DeHaan et al 2023): Averages of differences (control – denial) in error or correlation across all thresholds. Boxes are the interquartile range; the middle line is the median and the asterisk shows the mean. Blue colors indicate the control has less MAE or higher correlation in the mean; red colors indicate the denial has less MAE or higher correlation in the mean. Darker shades indicate significant differences in the mean based on a 90% confidence interval computed with bootstrapping.

DeHaan, L. L., and Coauthors, 2023: Impacts of Dropsonde Observations on Forecasts of Atmospheric Rivers and Associated Precipitation in the NCEP GFS and ECMWF IFS models. Wea. Forecasting, https://doi.org/10.1175/WAF-D-23-0025.1, in press.

Corresponding author: Laurel Dehaan

CW3E AR Update: 30 October 2023 Outlook

October 30, 2023

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Multiple Atmospheric Rivers Forecast to Impact Pacific Northwest and Northern California

Multiple atmospheric rivers (AR) are forecast to make landfall in the Pacific Northwest over the next 7 days, the first late Wed 1 Nov
AR2 conditions (based on Ralph et al. scale) are forecast during the first AR, with a ~24 hour period of IVT >800 kg m-1 s-1 forecast for Washington to Northern California in both the GFS and ECMWF
There is disagreement in the timing, strength and duration of the ARs that follow between the models
The GFS is forecasting AR1 conditions during the second AR along the coast of Central Oregon into Northern California early Sat 4 Nov, with a ~15 hour period of IVT >700 kg m-1 s-1 forecast in this region
The second AR is forecast to make landfall late Fri 3 Nov in the ECMWF, where EPS ensemble members are forecasting the second AR to be stronger and for AR conditions to persist longer than the GEFS, resulting in significant differences in precipitation forecasts
GEFS ensemble members show uncertainty of the forecast conditions for the third AR to register on the Ralph et al. scale, while the EPS shows many members forecasting AR conditions persisting from the second AR through to the third with the arrival of the next moisture corridor
The NWS Weather Prediction Center (WPC) is forecasting precipitation totals >1.5 inches during the first AR for the Olympic Peninsula, Cascade Range and Washington and Oregon Coasts
Precipitation associated with these ARs are forecast to be primarily beneficial to the Pacific Northwest where widespread drought conditions are present, with no river levels forecast to rise above action stage within the boundaries of the NWS Northwest River Forecast center
Most of the precipitation is expected to fall as rain, with freezing levels forecast to stay above 6000 feet throughout these events