DOI: 10.5281/zenodo.15829234
title: Tracks of South Asian monsoon low pressure systems in CMIP6 model output

description: This dataset contains tracked locations and characteristics of monsoon low-pressure systems (LPSs). The data are derived from Coupled Model Intercomparison Project Phase 6 (CMIP6) model outputs and ERA5/MERRA-2 reanalysis, spanning the period from 1850 to 2100. It includes metrics such as LPS location, intensity, and precipitation. The dataset also provides global and regional warming levels, allowing for the analysis of how climate change may impact the characteristics of LPSs.

Further details are given in the associated paper (preprint here: http://dx.doi.org/10.13140/RG.2.2.34860.17287).

 

Methods

The data were generated by applying a vorticity-based tracking algorithm to identify and follow monsoon low-pressure systems (LPSs) within CMIP6 climate model simulations and ERA5 reanalysis data.

The primary steps in the methodology were as follows:





LPS tracking: An algorithm was used to identify LPSs using six-hourly 850 hPa relative vorticity from June to September. To eliminate transient features, and ensure resolution invariance, we applied a T63 spectral truncation. The algorithm identified the centroids of positive vorticity and linked them over time to construct tracks. To ensure that only robust LPS tracks were included, a series of constraints were applied. These include a minimum track duration of 48 hours, a genesis location south of 25°N, and a minimum travel distance of 100 km.




Warming levels: The dataset also provides calculations for both global and regional warming levels. These are determined by calculating the 30-year rolling mean temperature anomalies relative to a pre-industrial baseline period (1850–1900 for the CMIP6 models and 1995–2014 for the reanalysis data). The regional warming is specifically calculated for the Bay of Bengal and monsoon core zone, defined here as 74°–92°E, 16°–26°N.



 

File Description

The dataset is provided as CSV files. In these files, each row corresponds to a single time point for a distinct LPS track. The columns are defined as follows:





x, y: The longitude and latitude of the centre of the LPS.




frame: A unique identifier for each six-hourly time step in the dataset.




year, month, day, hour: The date and time of the observation.




radius: The radius, measured in degrees, that was used to calculate the spatial statistics around the centre of the LPS.




max_vort, mean_vort: The maximum and mean 850 hPa relative vorticity, expressed in units of 10^−5 s^−1, within the specified radius.




mean_vort_850, mean_vort_700, mean_vort_500: The mean relative vorticity, in units of 10^−5 s^−1, at the 850, 700, and 500 hPa pressure levels.




max_trunc_vort: The maximum T63 spectrally-truncated 850 hPa relative vorticity, also in units of 10^−5 s^−1.




mean_prcp: The mean rate of precipitation, in m s^-1, within the given radius.




track_id: A unique numerical identifier assigned to each individual LPS track. Use these as unique identifiers when computing broader LPS statistics.




over_land: A boolean value that indicates whether the centre of the LPS is located over land.




global_warming: The 30-year rolling mean global warming level (°C) for the corresponding year.




bob_warming: The 30-year rolling mean regional warming level (°C) over the Bay of Bengal region for that season (Jun-Sep).