Iranian Journal of Geophysics

Iranian Journal of Geophysics

Study of convection-producing instabilities in an ideal simulation of baroclinic waves

Articles in Press

Document Type : Research Article

Authors
Elahe Bohlouli 1
Mohammad Mirzaei 2
Farhang Ahmadi-Givi 3
Ali Reza Mohebalhojeh 3
1 M.Sc. of Meteorology, Institute of Geophysics, University of Tehran, , Tehran, Iran
2 Associate Professor, Department of Space Physics, Institute of Geophysics, University of Tehran, , Tehran, Iran
3 Professor, Department of Space Physics, Institute of Geophysics, University of Tehran, , Tehran, Iran
10.30499/ijg.2026.568501.1744
Abstract
Baroclinic instability is the primary mechanism for the development of synoptic-scale cyclonic systems in the midlatitudes, often accompanied by mesoscale convective systems. Understanding the instabilities contributing to the formation of mesoscale convective features, such as cloud and precipitation bands that can lead to extreme weather events, is of great importance. The instabilities responsible for convection during the development of mesoscale precipitation can be investigated using idealized simulations of baroclinic waves. In this study, the life cycle of idealized baroclinic waves was simulated using the WRF model under initial conditions consisting of a balanced moist jet in a channel with dimensions of 4000 km (zonal), 10,000 km (meridional), and 30 km (vertical), on an f-plane, with horizontal (vertical) resolution of 25 km (250 m), over a period of 15 days. The model configuration included the Kessler and WSM6 microphysics schemes, the Kain–Fritsch convection scheme, and excluded land surface and planetary boundary layer schemes. Model outputs were used to compute the potential temperature (), equivalent potential temperature (), saturated equivalent potential temperature (), potential vorticity (PV), equivalent potential vorticity (EPV), saturated equivalent potential vorticity (SEPV), absolute vorticity, and frontogenesis function. These quantities were used to assess the absolute instability (AI), symmetric instability (SI), potential instability (PI), potential symmetric instability (PSI), conditional instability (CI), conditional symmetric instability (CSI), and inertial instability (II).
Results from the evolution of the baroclinic wave show that its formation on day 5 of the simulation was accompanied by a strong horizontal temperature gradient, the development of a surface front, and an upper-tropospheric jet. The wave reaches its maximum growth on day 8 and begins to decay by day 12. On day 5, when precipitation intensity and amount peak, SI, PI, PSI, CSI, and II occur with similar patterns in both the Kessler and WSM6 schemes. Additionally, CI is released in the WSM6 scheme, suggesting that the more intense precipitation in WSM6 compared to Kessler on day 5 is due to the release of CI in conjunction with CSI and a tilted pattern of II. By day 8, SI, PSI, CI, CSI, and II are still present for both schemes, but precipitation intensities and amounts are reduced compared to day 5. On day 12, when the wave is clearly decaying, the presence of CI and CSI with reduced intensity and the absence of II result in much less precipitation. Furthermore, the evolution of convection, the maximum precipitation intensity, and the peak negative values of EPV and SEPV aligned with the comma head of the baroclinic wave are clearly identifiable on day 5 for both the Kessler and WSM6 schemes. Finally, it can be concluded that the low-resolution (25 km) simulation is unable to adequately capture the rainbands, which are often on the meso-gamma scale. This finding is also consistent with previous studies.
Keywords
Baroclinic waves
inertial instability
conditional instability
conditional symmetric instability
WRF

Subjects

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Iranian Journal of Geophysics

Articles in Press, Accepted Manuscript
Available Online from 11 April 2026