Zhang et al. (2025) Thermodynamic and dynamic features of summer extreme heat events in the southwestern region of the Mongolian Plateau

Identification

• Journal: Climate Dynamics
• Year: 2025
• Date: 2025-11-01
• Authors: Jing Zhang, Ning Shi, Yu Chen
• DOI: 10.1007/s00382-025-07917-z

Research Groups

• State Key Laboratory of Climate System Prediction and Risk Management/Key Laboratory of Meteorological Disaster, Ministry of Education/Collaborative Innovation Center On Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, Nanjing, China
• School of Atmospheric Sciences, Nanjing University of Information Science and Technology, Nanjing, China

Short Summary

This study investigates the thermodynamic and dynamic mechanisms of summer extreme heat waves in the southwestern Mongolian Plateau using JRA-55 reanalysis data, revealing a unique vertically tilted anticyclonic anomaly structure with dual-stratified wave activity peaks and distinct layer-specific heating pathways compared to Eastern China.

Objective

• What are the basic thermodynamic characteristics of extreme Southwestern Mongolian Plateau (SWM) heat waves (HWs)?
• What are the internal dynamic causes of abnormal atmospheric circulation in extreme HWs?
• Are there thermodynamic and/or dynamic differences in extreme HWs between the SWM and eastern China?

Study Configuration

• Spatial Scale: Southwestern region of the Mongolian Plateau (SWM) [40°–47.5°N, 92.5°–102.5°E], covering 23 isobaric surfaces from 1000 hPa to 100 hPa.
• Temporal Scale: Summer (June–August) from 1958 to 2022 (65 years) using daily data. Extreme HWs are defined by a 95th percentile regionally averaged surface air temperature anomaly threshold, persistence for ≥ 3 consecutive days, and ≥ 8-day separation between peak days.

Methodology and Data

• Models used:
  • Thermodynamic budget equation.
  • Local finite-amplitude wave activity (LWA) and its budget equation (Huang and Nakamura, 2016).
  • Composite analysis of 63 extreme HW events.
  • Lanczos low-pass filter (period > 8 days) for anomaly fields.
• Data sources:
  • Japanese 55-year Reanalysis dataset (JRA-55, Kobayashi et al., 2015) daily data (1958–2022) at 1.25° × 1.25° horizontal resolution, including three-dimensional wind (u, v, ω), geopotential height (hgt), air temperature (T), surface pressure (pres), and surface air temperature (SAT).
  • ERA5 monthly dataset (Hersbach et al., 2020) for planetary boundary height field (for context).

Main Results

• Circulation and Temperature Structure: Extreme SWM HWs are characterized by significant positive air temperature anomalies throughout the troposphere, with distinct centers in the upper troposphere (350 hPa) and near-surface (850 hPa). A vertically tilted anticyclonic height anomaly is observed from the troposphere to the lower stratosphere, tilting westward with height, accompanied by significant subsidence motion.
• Layer-Specific Thermodynamics:
  • Free Atmosphere (e.g., 350 hPa): Adiabatic heating, primarily from horizontal advection and vertical motion, dominates the warming process. Diabatic heating plays a destructive role.
  • Planetary Boundary Layer (e.g., 800 hPa): Warming is initiated by diabatic heating (days -7 to -2) and sustained by meridional advection (days -2 to 1). Diabatic heating is mainly driven by longwave radiation flux from the ground, following dynamically-reduced cloud cover and enhanced shortwave radiation, with suppressed sensible heat flux.
• Local Finite-Amplitude Wave Activity (LWA) Dynamics:
  • Dual-Stratified LWA Peaks: Two significant positive LWA anomaly centers are identified: one in the lower stratosphere/upper troposphere (approximately 12 km) and another in the mid-lower troposphere (approximately 3.5 km).
  • Upper-Level LWA (8-15 km): Formation is initiated by the injection of Rossby wave packets from upstream regions and transport by the basic flow. Nonlinear processes (Stokes drift flux, dF2) become the most important contributor to the maintenance of positive LWA anomalies around the peak day. Decay is attributed to downstream dispersion of Rossby wave energy.
  • Mid-Lower-Level LWA (2-5 km): The generation of positive LWA anomalies is primarily dominated by diabatic heating, with Rossby wave propagation playing a secondary role.
• Differentiation from Eastern China HWs: SWM HWs exhibit shorter thermal cycles, a greater dominance of diabatic heating in the boundary layer, higher anomaly mobility, and feedbacks constrained by arid soil conditions, distinguishing them as a distinct category of continental-interior HWs.

Contributions

• First identification of a novel vertically tilted anticyclonic anomaly structure with dual-stratified peaks in local finite-amplitude wave activity (lower stratosphere/upper troposphere and mid-lower troposphere), revealing a new dynamical type for heat waves.
• Discovery of distinct layer-specific thermodynamic and dynamic pathways for SWM HWs, highlighting a sharp contrast between the free atmosphere (adiabatic warming, remote wave forcing) and the planetary boundary layer (local diabatic heating, reduced clouds, longwave radiation, suppressed sensible heat flux).
• Establishes a paradigm-shifting differentiation of SWM HWs from Eastern China HWs, attributing mechanistic differences to higher anomaly mobility and arid soil-constrained feedbacks, thereby defining a distinct category of continental-interior heat waves.
• Redefines the genesis framework for dryland heat waves, offering direct implications for improving regional climate predictability.
• Utilizes the local finite-amplitude wave activity (LWA) framework to analyze large-amplitude atmospheric disturbances, providing a suitable theoretical framework for extreme events.

Funding

• National Key R&D Program of China (No. 2022YFF0801601)
• Jiangsu Innovation & Entrepreneurship Team
• Qing Lan Project

Citation

@article{Zhang2025Thermodynamic,
  author = {Zhang, Jing and Shi, Ning and Chen, Yu},
  title = {Thermodynamic and dynamic features of summer extreme heat events in the southwestern region of the Mongolian Plateau},
  journal = {Climate Dynamics},
  year = {2025},
  doi = {10.1007/s00382-025-07917-z},
  url = {https://doi.org/10.1007/s00382-025-07917-z}
}