CW3E Publication Notice: Atmospheric River Tracking Method Intercomparison Project (ARTMIP): Project Goals and Experimental Design

CW3E Publication Notice

Atmospheric River Tracking Method Intercomparison Project (ARTMIP): Project Goals and Experimental Design

July 9, 2018

As research has expanded on ARs, new detection algorithms have been developed, and yet no detailed intercomparison has been made. To fill this gap, a grass roots “community” effort was organized to develop an approach to perform such a comparison, which is described in the recently published paper by Shields et al (2018). The community effort is called the Atmospheric River Tracking Method Intercomparison Project “ARTMIP.” It has been organized by a small, ad-hoc, planning committee, co-chaired by Christine Shields (NCAR) and Jon Rutz (NWS and CW3E), with Mike Wehner (DOE/LBNL), Ruby Leung (DOE/PNNL) and F. Martin Ralph (UCSD/SIO/CW3E) as its members. This team organized its first meeting with interested parties in May 2017, which was hosted and sponsored by CW3E at Scripps Institution of Oceanography (SIO).

The paper was published in Geoscientific Model Development and titled Atmospheric River Tracking Method Intercomparison Project (ARTMIP): Project Goals and Experimental Design (https://www.geosci-model-dev-discuss.net/gmd-2017-295/). This paper describes ARTMIP, an international community effort to understand and quantify the uncertainties in atmospheric river (AR) science due to the differences in detection algorithms. The goal of ARTMIP is to provide the weather forecasting and climate community with a deeper understanding of AR tracking, mechanisms, and impacts, through providing a framework with which to objectively compare detection schemes that can be fundamentally different. The paper describes the experimental design and timeline, and includes preliminary results that use the key metrics of frequency, intensity, duration, and precipitation attribution (For an example of preliminary results, see figure 1).

The project is divided into two tiers with different science objectives. The first tier consists of applying all participating algorithms to a common dataset, the MERRA-2 reanalysis, from 1980-2017. The second tier will be divided into subtopics and consist of sensitivity studies to different reanalysis datasets and to climate model data. A variety of precipitation datasets will also be used to assess uncertainties in AR impacts.

The ARTMIP project has been positively received by the AR community and has the potential to shape much of how AR science and detection is conducted. The project has steadily increased participation since the paper was first presented in the open-forum GMD Discussions. Participation in ARTMIP is open to any researchers with an AR detection algorithm or with interest in evaluating the data. If you are interested in participating, please contact Christine Shields (shields@ucar.edu) or Jon Rutz (jonathan.rutz@noaa.gov).

Figure 1. Composite MERRA-2 IVT (kg m-1s-1) for landfalling ARs along North American west coast for 14 different algorithms. Time instances where an AR was detected along the coastline were composited for the entire region. Composite data is plotted for February 2017. To test the ARTMIP framework, a 1-month proof-of-concept trial was designed and performed for February 2017. This month was chosen due to large number of landfalling ARs that impacted western North America during this period.

Shields, C. A., Rutz, J. J., Leung, L.-Y., Ralph, F. M., Wehner, M., Kawzenuk, B., Lora, J. M., McClenny, E., Osborne, T., Payne, A. E., Ullrich, P., Gershunov, A., Goldenson, N., Guan, B., Qian, Y., Ramos, A. M., Sarangi, C., Sellars, S., Gorodetskaya, I., Kashinath, K., Kurlin, V., Mahoney, K., Muszynski, G., Pierce, R., Subramanian, A. C., Tome, R., Waliser, D., Walton, D., Wick, G., Wilson, A., Lavers, D., Prabhat, Collow, A., Krishnan, H., Magnusdottir, G., and Nguyen, P., 2018: Atmospheric River Tracking Method Intercomparison Project (ARTMIP): Project Goals and Experimental Design, Geosci. Model Dev., https://doi.org/10.5194/gmd-2017-295

CW3E Publication Notice: Global Analysis of Climate Change Projection Effects on Atmospheric Rivers

CW3E Publication Notice

Global Analysis of Climate Change Projection Effects on Atmospheric Rivers

May 24, 2018

Vicky Espinoza (UC Merced) and CW3E collaborators Bin Guan (UCLA), Duane Waliser (NASA/JPL), along with CW3E director Marty Ralph and David Lavers European Centre for Medium‐Range Weather Forecast, recently published a paper in Geophysical Research Letters, titled Global Analysis of Climate Change Projection Effects on Atmospheric Rivers.

Atmospheric rivers (ARs) are elongated strands of horizontal water vapor transport, accounting for over 90% of the poleward water vapor transport across midlatitudes. ARs have important implications for extreme precipitation when they make landfall, particularly along the west coasts of many midlatitude continents (e.g., North America, South America, and West Europe) due to orographic lifting. ARs are important contributors to extreme weather and precipitation events, and while their presence can contribute to beneficial rainfall and snowfall, which can mitigate droughts, they can also lead to flooding and extreme winds. This study takes a uniform, global approach that is used to quantify how ARs change between Coupled Model Intercomparison Project Phase 5 (CMIP5) historical simulations and future projections under the Representative Concentration Pathway (RCP) 4.5 and RCP8.5 warming scenarios globally. The projections indicate that while there will be ~10% fewer ARs in the future, the ARs will be ~25% longer, ~25% wider, and exhibit stronger integrated water vapor transports under RCP8.5 (Figure 1). These changes result in pronounced increases in the frequency (integrated water vapor transport strength) of AR conditions under RCP8.5: ~50% (25%) globally, ~50% (20%) in the northern midlatitudes, and ~60% (20%) in the southern midlatitudes (Figure 2).

Figure 2 from Espinoza et al., 2018. AR frequency (shading; percent of time steps) and IVT (vectors; kg · m−1 · s−1) for (a) ERA‐Interim reanalysis for the historical period (1979–2002) with six green boxes depicting regions analyzed in Figures S2 and S3, (b) the MMM for the 21 CMIP5 models analyzed in this study for the historical period (1979–2002), (c) RCP4.5 warming scenario (2073–2096), and (d) RCP8.5 warming scenario (2073–2096).

This research was supported by the NASA Energy and Water cycle Study (NEWS) program. Vicky Espinoza’s contribution to this study was made possible by NASA Jet Propulsion Laboratory’s Year-Round Internship Program during her graduate studies at the University of Southern California. Please contact Duane Waliser at duane.waliser@jpl.nasa.gov with inquiries. More information can be found from the NASA website https://www.jpl.nasa.gov/news/news.php?feature=7141.

Espinoza, V., Waliser, D. E., Guan, B., Lavers, D. A., & Ralph, F. M. 2018: Global Analysis of Climate Change Projection Effects on Atmospheric Rivers. Geophysical Research Letters. 45. https://doi.org/10.1029/2017GL076968

CW3E Undergraduate Student Presents Research at Conference

CW3E Undergraduate Student Presents Research at Conference

May 8, 2018

Cody Poulsen, is a soon to be graduate student with CW3E at Scripps Institution of Oceanography, UC San Diego. During his undergraduate career at UCSD he collaborated on a research project with ex-CW3E post-doc Scott Sellars. The project began during the summer of 2016 and was focused on using a program created by the Monterey Bay Aquarium Research Institute (MBARI) named Video Annotation Reference Systems (VARS) to produce useable meteorological metadata. VARS was created by MBARI to aid researchers in cataloguing the occurrences of biological species and geological formations in the large amounts of underwater footage collected by their ROVs. The research continued as part of Cody’s senior thesis during which he created an Atmospheric River metadata set with VARS. During the process, he learned more about the system and its capabilities. The metadata set is comprised of annotations for the location of AR landfall and center of AR events during the Water Years (WYs) 2001 and 2011. In addition, annotations for ARs with an associated Lower Level Jet (LLJ) structure where produced for both WYs. In the case study of WYs 2001 and 2011, the metadata depicted an anomalously high amount of landfalling AR events in California/Oregon for December 2010 juxtaposed to zero landfalling events along the North American West Coast excluding Alaska for December 2000. 500-hPa average wind speeds, heights, & direction plots for the two months where created to discern the general first principal flow that might explain the different AR trajectories. With these plots, it was found that a high-pressure ridge at 180° and low pressure trough at 140°W funneled ARs onto the California/Oregon coast for December 2010. Where December 2000 had a slight high pressure ridge along the coast to produce an insignificant blocking action leading to the assumption that some other synoptic features must be at play to produce the zero-event period.

Cody produced a poster on the VARS research project and presented it at the Association for Environmental Health and Sciences Foundation (AEHS), 28th Annual International Conference on Soil, Water, Energy, & Air, held in San Diego, CA. His research was presented at the conference’s 14th Annual Student Competition and was selected by the competition committee to receive the second-place award. In addition, to receiving the award Cody was invited to the AEHS appreciation dinner where he met with several industry professionals and researchers to network and discuss the future of the environmental field. Overall, the conference was a great experience for Cody to gain more presentation experience. In addition, he received valuable feedback from a wide range of individuals in the environmental field all with diverse backgrounds.

The VARS program is currently being used by Cody and CW3E post-doc Rachel Weihs to further study Atmospheric Rivers and their impacts on the western coast of the United States of America.

Odds of Reaching 100% Water Year Precipitation – May Update

Odds of Reaching 100% of Normal Precipitation for Water Year 2018 (May Update)

May 2, 2018

Contribution from Dr. M.D. Dettinger, USGS

Here is how we usually tend to see the water-year precip-drought to-date or last month’s contributions represented:

Figure 1: Total precipitation anomaly (large map) and total precipitation (smaller map) during water 2018 (September 2017-April 2018). Images courtesy PRISM Climate Group.

A somewhat different viewpoint on the development of drought considers how much precipitation has fallen (or not) AND how much is likely to fall in coming months, based on climatology. April 2018 produced precipitation over much of northern California and improved odds of reaching normal in some locales, but overall did little to undo the deficits of the previous months in a majority of the state. The following are maps of this year’s drought development that explicitly takes both of these aspects into account.

Here is how the drought has evolved so far this water year in terms of the odds of reaching 100% of normal precipitation by end of water-year 2018.

Figure 2: Odds of reaching 100% of water-year normal precipitation totals throughout water-year 2018.

  • Drought conditions have continued to develop across the Southwest, as odds of reaching normal have progressively dwindled month by month. Although April was wet over parts of northern California, it was—arguably—too little too late to set us up for reaching 100% of normal this year, in all but a few locales.

Figure 3 shows the current odds of reaching various fractions (including but not limited to 100%) of water-year-total this year (top row), as well as the corresponding odds prior to April (bottom row).
This approach offers a far different view than the precipitation anomalies of figure 1, emphasizing different “hot spots” of hope & despair.

Figure 3: Odds of water-year 2018 reaching various fractions of water year normal precipitation totals based on water year precipitation through April (top row) and prior to April (bottom row).

Finally, figure 4 is the “flipped” version of the analysis, asking-at each pixel-how large a water-year total precipitation has a 50% (and other exceedances) chance of being equaled or exceeded this year, as of May 1, 2018.

Figure 4: Chance of water-year total precipitation being equaled or exceeded this year.

  • A different color bar is used here to emphasize that the shades now are illustrating something quite different from the previous maps

How the probabilities above were estimated:
At the end of a given month, if we know how much precipitation has fallen to date (in the water year), the amount of precipitation that will be required to close out the water year (on Sept 30) with a water-year total equal to the long-term normal is just that normal amount minus the amount received to date. Thus the odds of reaching normal by the end of the water year are just the odds of precipitation during the remaining of the year equaling or exceeding that remaining amount.

To arrive at the probabilities shown, the precipitation totals for the remaining months of the water year were tabulated in the long-term historical record (WY1948-2017 in these figures) and the number of years in which that precipitation total equaled or exceeded the amount still needed to reach normal were counted. The fraction of years that at least reached that threshold is the probability estimate. The calculation was also made for the probabilities of reaching 75% of normal by end of water year, 125%, etc., for these figures.

[One key simplifying assumption goes into estimating the probabilities this way: The assumption that the amount of precipitation that will fall in the remainder of a water year does not depend on the amount that has already fallen in that water year to date. This assumption was tested (across all climate divisions in California, so far) for each month of the year by correlating historical year-to-date amounts with the remainder-of-the-year amounts, and the resulting correlations were never statistically significantly different from zero.]

Contact: Michael Dettinger (USGS)

CW3E Participates in Second ARTMIP Workshop

CW3E Participates in 2nd ARTMIP Workshop

April 26, 2018

The 2nd Atmospheric River Tracking Method Intercomparison Project (ARTMIP) Workshop was recently held in Gaithersburg, Maryland. The ARTMIP, started in 2017, is an effort to quantify the uncertainty in AR climatology, precipitation, and related impacts that arise because of different AR tracking methods, and how these AR-related metrics may change in the future. It also aims to provide guidance regarding the advantages and disadvantages of these different AR tracking methods, and which of these methods are best suited to answer certain scientific questions. Several members of CW3E are actively participating in ARTMIP and attended the workshop, including, Director Marty Ralph, Brian Kawzenuk, Aneesh Subramanian, Tamara Shulgina, and Anna Wilson.

The purpose and goals of the workshop were:

  • Discuss Tier 1 catalogues in context of science questions defined in the 1st ARTMIP workshop
  • Discuss Tier 1 analysis for the science overview paper
  • Discuss metrics, and adjust if necessary, and begin to formulate guidance on algorithmic choices based on Tier 1 results
  • Discuss and organize Tier 2 catalogue details and future studies

A main outcome from the workshop included the discussion of Tier 1 analysis and two publications from Tier 1. The first, an outline on the experimental design led by Christine Shields (NCAR), is currently under review with GMD. The second, led by Jon Rutz (NOAA), will provide overviews of the results from Tier 1. Another main outcome from the workshop was the discussion and planning of three publications from Tier 2 datasets: high-resolution climate change model runs, CMIP5 climate runs, and historical reanalyses comparison to the MERRA-2. At least eight other additional publications were discussed as well, including topics such as extreme precipitation, ENSO, ARs in polar regions, measures of internal variability, data resolution sensitivity, and more. Next steps for the ARTMIP include completion of the Tier 1 overview paper and beginning of Tier 2 catalog generation and analyses.

Workshop Participants (left to right): Jon Rutz (NOAA), Roger Pierce (NOAA), Ruby Leung (PNNL), Phu Nguyen (UC Irvine), Irina Gorodetskaya (Univ. Aveiro), Helen Griffith (Univ. Reading), Christine Shields (NCAR), Brian Kawzenuk (UCSD), Alexandre Ramos (Univ. Lisbon), Marty Ralph (UCSD), Juan Lora (UCLA), Gary Geernaert (DOE), Ashley Payne (Univ. Michigan), Elizabeth McClenny (UC Davis), Travis O’Brien (LBNL), Naomi Goldenson (UCLA), Daniel Walton (UCLA), Vitaliy Kurlin (LBNL), Aneesh Subramanian (UCSD), Tamara Shulgina (UCSD), Yang Zhou (Stony Brook Univ.), Bin Guan (UCLA), Renu Joesph (DOE), Michael Wehner (LBNL), Maximilliano Viale (Univ. Chile), Paul Ullrich (UC Davis; not pictured), Swen Brands (Meteogalicia; not pictured), Anna Wilson (UCSD; not pictured).

For more information on ARTMIP, visit the ARTMIP website.

CW3E Publication Notice: Evaluation of Atmospheric River Predictions by the WRF Model Using Aircraft and Regional Mesonet Observations of Orographic Precipitation and Its Forcing

CW3E Publication Notice

Evaluation of Atmospheric River Predictions by the WRF Model Using Aircraft and Regional Mesonet Observations of Orographic Precipitation and Its Forcing

April 16, 2018

CW3E project scientist Andrew Martin and co-authors have published a study characterizing predictability limits in Atmospheric River (AR) forecasts and apportioning Russian River precipitation forecast errors among vapor transport and orographic precipitation components. The article, titled Evaluation of Atmospheric River Predictions by the WRF Model Using Aircraft and Regional Mesonet Observations of Orographic Precipitation and its Forcing, is now in early online release at the Journal of Hydrometeorology.

This study leveraged airborne dropsonde observations of offshore Atmospheric Rivers completed during the CalWater experiment and the Atmospheric River Observatory at Bodega Bay and Cazadero, CA to verify forecasts of AR properties and their resulting precipitation. Forecasts were created by CW3E’s numerical weather prediction model, West-WRF, and compared to Global Forecast System reforecasts (GFSRe) valid for the same events. Forecast skill in AR properties and precipitation was evaluated at lead times up to 7 days ahead. Notably, the study found that deterministic skill in integrated vapor transport and other related fields degrades (meaning that forecasts created from climatology perform just as well or better) more than 4 days ahead for both models. However, West-WRF improves upon GFSRe skill in IVT at days 1, 2 and 3 ahead (see Fig. 1c).

Figure 1. a) Value added by GFSRe over GFSRe climatology validated against 145 CalWater dropsondes for the variables z500 (blue), IVT (black), IWV (green) and e925 (red). b) as in a, except for West-WRF value added over GFSRe climatology. c) as in b, except reference forecast is GFSRe.

The study also employed a novel forecast error separation technique to apportion precipitation forecast errors among the component caused by vapor transport simulation and orographic precipitation process simulation. Data from the Atmospheric River Observatory was used to demonstrate that West-WRF forecasts of orographic precipitation during landfalling AR are more accurate in simulating both components; but also that West-WRF forecasts of precipitation can be improved by improving the vapor transport component because its orographic precipitation process is accurate. This lends confidence that CW3E’s effort to improve west coast precipitation forecasts by assimilating offshore observations into West-WRF analyses can yield successful results.

Co-authors include Dr. F Martin Ralph, Reuben Demirdjian, Laurel DeHaan, and Dr. Rachel Weihs of CW3E with Dr. David Reynolds of the Cooperative Institute for Research in Environmental Sciences and Dr. Sam Iacobellis of Scripps Institution of Oceanography. The study was funded by the US Army Corps of Engineers, the California Department of Water Resources, and the National Science Foundation XSEDE program.

Odds of Reaching 100% Water Year Precipitation – April Update

Odds of Reaching 100% of Normal Precipitation for Water Year 2018 (April Update)

April 10, 2018

Contribution from Dr. M.D. Dettinger, USGS

Here is how we usually tend to see the water-year precip-drought to-date or last month’s contributions represented:

Figure 1: Total precipitation anomaly (large map) and total precipitation (smaller map) during water 2018 (September 2017-March 2018). Images courtesy PRISM Climate Group.

A somewhat different viewpoint on the development of precipitation drought considers that development to be a matter of both how much precipitation has fallen (or not) already AND how much more is realistically likely to fall in coming months. E.g., March 2018 simultaneously produced helpful additions to this year’s precipitation totals in California AND was disappointingly far from completely undoing the deficits of the preceding months in most of the State. The following are maps of this year’s drought development that explicitly take both of these aspects into account.

Here is how the drought has evolved so far this water year in terms of the odds of reaching 100% of normal precipitation by end of water-year 2018.

Figure 2: Odds of reaching 100% of water-year normal precipitation totals throughout water-year 2018.

  • Notice how drought conditions have developed across the Southwest, as odds of reaching normal have progressively dwindled month by month. Also notice that, although March was wet in California/Nevada, it was—arguably—too little too late to set us up well for reaching 100% of normal this year, in all but a few locales.

The top row in figure 3 shows the current odds of reaching various fractions (including but not limited to 100%) of water-year-total this year.
Also shown are the corresponding odds prior to March (middle row), and the amount that March precip changed the odds (bottom). This approach offers a far different view than the precipitation anomalies of figure 1, emphasizing different “hot spots” of hope & despair.

Figure 3: Odds of water-year 2018 reaching various fractions of water year normal precipitation totals and the change in these odds during March 2018.

Finally, figure 4 is the “flipped” version of the analysis, asking-at each pixel-how large a water-year total precipitation has a 50% (and other exceedances) chance of being equaled or exceeded this year, as of April 1, 2018.

Figure 4: Chance of water-year total precipitation being equaled or exceeded this year.

  • A different color bar is used here to emphasize that the shades now are illustrating something quite different from the previous maps

How the probabilities above were estimated:
At the end of a given month, if we know how much precipitation has fallen to date (in the water year), the amount of precipitation that will be required to close out the water year (on Sept 30) with a water-year total equal to the long-term normal is just that normal amount minus the amount received to date. Thus the odds of reaching normal by the end of the water year are just the odds of precipitation during the remaining of the year equaling or exceeding that remaining amount.

To arrive at the probabilities shown, the precipitation totals for the remaining months of the water year were tabulated in the long-term historical record (WY1948-2017 in these figures) and the number of years in which that precipitation total equaled or exceeded the amount still needed to reach normal were counted. The fraction of years that at least reached that threshold is the probability estimate. The calculation was also made for the probabilities of reaching 75% of normal by end of water year, 125%, etc., for these figures.

[One key simplifying assumption goes into estimating the probabilities this way: The assumption that the amount of precipitation that will fall in the remainder of a water year does not depend on the amount that has already fallen in that water year to date. This assumption was tested (across all climate divisions in California, so far) for each month of the year by correlating historical year-to-date amounts with the remainder-of-the-year amounts, and the resulting correlations were never statistically significantly different from zero.]

Contact: Michael Dettinger (USGS)

CW3E AR Update: 03 April 2018 Outlook

CW3E AR Update: 03 April Outlook

April 03, 2018

Click here for a pdf of this information.

Atmospheric river forecast to impact Northern California later this week

  • GFS Ensemble members are currently forecasting a potentially strong to extreme AR over northern and central California later this week
  • Forecast certainty has increased since yesterday but there is still some uncertainty in the onset, duration, and strength of the AR
  • Up to 7 inches of precipitation is forecasted to fall over the Coastal and Sierra Nevada Mtns in CA, OR, and WA
  • The GEFS is currently suggesting high freezing levels for most of this event, which may lead to most of the precipitation falling as rain

Click IVT or IWV image to see loop of 0-126 hour GFS forecast

Valid 0600 UTC 03 April – 1200 UTC 08 April 2018

 

 

 

 

 

 

 

Summary provided by B. Kawzenuk, F.M. Ralph, and C. Hecht; 11 AM PT Tuesday 03 April 2018

*Outlook products are considered experimental

CW3E AR Update: 22 March 2018 Outlook

CW3E AR Update: 22 March Outlook

March 22, 2018

Click here for a pdf of this information.

Update on Atmospheric River Currently Impacting California

  • Precipitation continues to fall across portions of California
  • The AR will begin to propagate southward bringing moderate AR conditions to Orange and San Diego Counties
  • As much as 9.5 inches of precipitation has fallen over the Coastal Mountains of California during the last 48 hours
  • ~3.75 inches of precipitation has fallen over the high elevations of Santa Barbara and Ventura Counties and 3.5 more inches could fall during the remainder of the storm
  • AR conditions are expected to end at ~11 pm PDT (+/– 3 hours) tonight over Southern California

SSMI/SSMIS/AMSR2-derived Integrated Water Vapor (IWV)

Valid 0000 UTC 19 March – 1600 UTC 22 March 2018

Images from CIMSS/Univ. of Wisconsin

Click IVT or IWV image to see loop of 0-48 hour GFS forecast

Valid 1200 UTC 22 March – 1200 UTC 24 March 2018

 

 

 

 

 

 

 

 

Summary provided by C. Hecht, F.M. Ralph, and B. Kawzenuk; 3 PM PT Thursday 22 March 2018

*Outlook products are considered experimental