Liu et al. (2025) Rapid Shrinking of the Warming Hole Over the United States in ERA5 and SPEAR

⚠️ Warning: This summary was generated from the abstract only, as the full text was not available.

Identification

• Journal: Journal of Geophysical Research Atmospheres
• Year: 2025
• Date: 2025-11-26
• Authors: Ping Liu, Kevin A. Reed, Ming Zhao, Steve Garner, Minghua Zhang
• DOI: 10.1029/2025jd044627

Research Groups

Not explicitly stated in the provided abstract.

Short Summary

This study reveals that the U.S. "warming hole," a summer cooling anomaly, has significantly shrunk and weakened in recent decades, with accelerated contraction during 2021–2024, driven by changes in atmospheric circulation and precipitation. It projects the warming hole's disappearance around 2050 under strong external forcing, emphasizing the role of both external forcing and internal variability.

Objective

• To analyze the recent evolution and future trajectory of the U.S. "warming hole" (a long-term summer cooling anomaly in near-surface maximum temperatures) and identify the underlying atmospheric circulation and hydrologic mechanisms driving these changes.

Study Configuration

• Spatial Scale: United States, specifically the central and northern regions.
• Temporal Scale: Mid-20th century to mid-21st century (historical analysis and future projection).

Methodology and Data

• Models used: Seamless System for Prediction and Earth System Research (SPEAR) model (30-member large ensemble).
• Data sources: European Centre for Medium‐Range Weather Forecasts ERA5 reanalysis.

Main Results

• The "warming hole" over the U.S. has shrunk and weakened in recent decades, with its contraction accelerating during 2021–2024.
• Changes are seasonally asymmetric, with June exhibiting the strongest weakening, while May retains negative anomalies.
• A well-known mechanism involving a strengthened southerly low-level jet enhancing precipitation and suppressing maximum temperature is confirmed.
• An additional process is identified: enhanced northerly winds from Canada advect cooler air and increase convergence and rainfall, reinforcing the cooling.
• Opposite circulation and precipitation anomalies, which previously reduced cooling effects, have recently strengthened in step with the warming trend, contributing to the rapid shrinkage.
• The SPEAR model reasonably captures the detrended variability and spatial pattern of anomalies but overestimates the warming trend relative to ERA5.
• Combining SPEAR's detrended variability with the ERA5 trend, the warming hole is projected to vanish around 2050 under a strong external forcing.

Contributions

• Demonstrates the recent rapid shrinkage and weakening of the U.S. warming hole, particularly its accelerated contraction during 2021–2024.
• Identifies an additional mechanism for cooling involving enhanced northerly winds, complementing the established role of the southerly low-level jet.
• Provides a projection for the warming hole's disappearance around 2050 under strong external forcing, contrasting with previous studies that emphasized seasonal persistence and southerly winds alone.
• Underscores the critical importance of both externally forced and internal variability associated with hydrologic cycle changes in shaping the future trajectory of the U.S. warming hole.

Funding

Not available in the provided abstract.

Citation

@article{Liu2025Rapid,
  author = {Liu, Ping and Reed, Kevin A. and Zhao, Ming and Garner, Steve and Zhang, Minghua},
  title = {Rapid Shrinking of the Warming Hole Over the United States in ERA5 and SPEAR},
  journal = {Journal of Geophysical Research Atmospheres},
  year = {2025},
  doi = {10.1029/2025jd044627},
  url = {https://doi.org/10.1029/2025jd044627}
}