| NSF Org: |
AGS Division of Atmospheric and Geospace Sciences |
| Recipient: |
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| Initial Amendment Date: | June 11, 2019 |
| Latest Amendment Date: | April 9, 2024 |
| Award Number: | 1849654 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Yolande L. Serra
yserra@nsf.gov (703)292-2651 AGS Division of Atmospheric and Geospace Sciences GEO Directorate for Geosciences |
| Start Date: | June 15, 2019 |
| End Date: | November 30, 2024 (Estimated) |
| Total Intended Award Amount: | $688,165.00 |
| Total Awarded Amount to Date: | $753,002.00 |
| Funds Obligated to Date: |
FY 2024 = $64,837.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
10889 WILSHIRE BLVD STE 700 LOS ANGELES CA US 90024-4200 (310)794-0102 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
Box 951524, 1255 Bunche Hall Los Angeles CA US 90095-1524 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Climate & Large-Scale Dynamics |
| Primary Program Source: |
01002425DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): | |
| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Episodes of extreme events, such as droughts and floods, can have serious societal, agricultural, economic, and ecological impacts. Basin-wide tropical sea surface temperature anomalies are known to play a major role in causing these extreme events. The linkage of these extreme hydrological events to tropical sea surface temperature anomalies allows us to predict them with useful skill at a long lead time in advance ranging from few months to few years.
This project aims to explore the idea for the first time to utilize the information of spring land surface temperature/subsurface temperature anomalies over the western high elevation areas in North America and East Asia for the prediction of late spring/summer droughts or floods over the eastern part of the continents. The results from this research would be useful for the sub-seasonal to seasonal prediction community. This project is a direct response to the new initiative "Impact of initialized land temperature and snowpack on sub-seasonal to seasonal prediction" recently developed by the Global Energy and Water Exchanges (GEWEX) Program, which involves more than 30 institutions worldwide. Findings of this NSF project should provide valuable information to the GEWEX community. Knowledge gained in this research will be disseminated through classroom teaching, short course training classes as well as the GEWEX initiative.
Unlike predictions using sea surface temperature, which uses sea surface temperature as a lower boundary condition for atmospheric models, the PI will use the information of spring land surface temperature (LST) and subsurface temperature (SUBT) anomalies as initial conditions in the land component of coupled climate models. The main hypothesis is that LST and SUBT anomalies in early Spring hold the information about the abundance of water locked in frozen ground (i.e., the amount of snow/ice on the ground and in the frozen surface layer below) to be melted in later Spring and early Summer. The more snow/ice on the ground and in the frozen surface layer below is, the longer the seasonal transition from Spring to Summer is. The timing of such seasonal transition over high elevation areas in the west plays an important role in setting up the circulation pattern downstream over the low elevation areas in the east. The strength as well as length of its interactions with the circulation pattern over the low elevation areas controlled by land-ocean temperature contrast would affect the occurrence of droughts or floods in late spring/summer over the eastern part of the continents.
The research will run various numerical simulations using global and regional models under different climate and weather conditions (i) to understand the mechanisms for the downstream influences of LST/SUBT anomalies, (ii) to compare their effects with SST anomalies, (iii) to identify and distinguish roles of snow and soil moisture in contributing to soil memory and preserving the LST/SUBT anomalies, and (iv) to explore characteristics of soil layer memory and LST/SUBT anomalies and the causes of the spring LST/SUBT anomalies. The project will also develop a new SUBT initialization methodology for operational models to better utilize SUBT information for sub-seasonal/seasonal forecasts in spring/summer seasons.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Extreme hydroclimate events, such as droughts and floods, can have widespread impacts. The role of basin-wide tropical sea surface temperature (SST) anomalies has been extensively investigated since the 1970s and is known to play a key role in causing these extreme events. The linkage of these extreme hydrological events to tropical SST anomalies allows us to predict them with useful skill months to years in advance. However, accurate sub-seasonal to seasonal (S2S) prediction remains a major challenge. The Sub-seasonal to Seasonal Prediction Project of the World Weather Research Programme and the World Climate Research Programme acknowledges that much of the S2S research is still in its early stages.
Our NSF project aims to explore a novel approach by utilizing spring land surface temperature/subsurface temperature (LST/SUBT) anomalies over the western high-elevation areas of North America and East Asia to predict late spring/summer droughts or floods over the eastern parts of the continents. Land surface temperature has global and long-term observations with the highest quality among measured land variables. Its role in climate prediction has long been underappreciated.
This NSF research has attracted significant attention from the global climate modeling community. The Global Energy and Water Exchange (GEWEX) project supported us in organizing the initiative “Impact of Initialized Land Surface Temperature and Snowpack on Subseasonal to Seasonal Prediction Project (LS4P)” to encourage a community effort to test our hypothesis and disseminate findings. More than 40 institutions worldwide, including many major climate centers, are actively participating.
Since every LS4P Earth System Model (ESM) has large errors in simulating high mountain surface temperatures, this project leverages observed spring LST anomalies to improve initial LST/SUBT conditions over high mountains in the land component of coupled climate models to produce the observed LST anomalies over high mountains. The main hypothesis is that through eastward propagation of disturbance, LST and SUBT anomalies over high elevation areas in the west play a significant role in setting up the summer circulation pattern downstream over the low elevation areas in the east triggering droughts/floods.
Using the newly developed LST/SUBT initialization method, the observed surface temperature anomaly over the Tibetan Plateau has been partially reproduced by the LS4P ESM ensemble mean and Eight (8) global hotspot regions have been identified by the LS4P ESMs, where June precipitation is significantly associated with May Tibetan Plateau land temperature anomalies. These hotspot regions are (1) the southern Yangtze River Basin, (2) northeast Asia, (3) northwest North America, (4) Southern Great Plains, (5) Central America, (6) northern South America, (7) western Sahel, and (8) East Africa. The Tibetan Plateau LST/SUBT effect accounts for about 25%-50% of observed precipitation anomalies in most hotspot regions.
The influence of Tibetan Plateau Spring temperature is underscored by an out-of-phase oscillation between Tibetan Plateau and Rocky Mountain surface temperatures. A Tibetan Plateau-Rocky Mountain Circumglobal (TRC) wave train, spanning from the Tibetan Plateau, northeast Asia, the Bering Strait, and western North America, has been identified using observational data and LS4P ESM ensemble analysis. This wave train intrinsically exists in the midlatitude atmosphere along the westerly jet, likely due to the presence of two major high-elevation mountain regions. Changes in heating over the Tibetan Plateau modify the phase, strength, and structure of the TRC wave train, affecting downstream atmospheric circulation, including over the West Coast of North America.
Global SST effects were also analyzed in the LS4P experiment. Results indicate that Tibetan Plateau LST/SUBT and SST effects are largely non-overlapping, with Tibetan Plateau ST/SUBT impacts potentially comparable in magnitude to SST effects. Our study identifies a missing link in extreme climate event prediction and reveals that Tibetan Plateau LST/SUBT is a first-order source and key driver of S2S precipitation predictability worldwide. Through barotropic instability and Rossby wave dispersion aligned with seasonal variations of the westerly jet, the Tibetan Plateau LST/SUBT effect plays a significant role in S2S prediction of midlatitude hydroclimate events.
The project has resulted in about 30 peer-reviewed papers, including (1) An LS4P paper in Geoscientific Model Development (GMD), presenting the LS4P project organization and protocol; (2) A paper in Bulletin of the American Meteorological Society (BAMS), highlighting major LS4P Phase 1 results, including the global hotspots of June precipitation anomalies due to Tibetan Plateau May LST/SUBT effects; (3) A special issue in Climate Dynamics, titled “Sub-seasonal to Seasonal (S2S) predictability and Land-induced Forcing”, featuring 17 papers and a prelude; (4) A recent publication in Science Bulletin (January 2025), which identifies the causes and mechanisms behind the catastrophic summer 2024 heavy rainfall and flooding in China and Bangladesh. Publishing a paper on such extreme hydroclimate events within a short time frame (normally a process that takes several years) underscores the robustness of our hypothesis. In addition, numerous presentations based on this NSF project research have been delivered at professional conferences.
Last Modified: 02/11/2025
Modified by: Yongkang Xue
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