[Paper Review] On the predictability of springtime ozone depletion events using the ECCC Global Deterministic Prediction System

J. de Grandpré, И. Н. Иванова+3 more|arXiv (Cornell University)|Oct 15, 2024

Atmospheric Ozone and ClimateEarth and Planetary Sciences3 citations

TL;DR

This study evaluates the medium-range predictability of springtime polar ozone depletion events using Environment and Climate Change Canada’s Global Deterministic Prediction System (ECCC GDPS) with ozone assimilation and a simplified photochemical scheme. It demonstrates that including ozone radiative coupling improves stratospheric temperature and wind forecasts, particularly over Antarctica, where it reduces cold biases and strengthens the polar vortex, enhancing predictability beyond 10 days.

ABSTRACT

Ozone depletion events are recurring phenomena in both polar regions, characterized by significant interannual variability. In this study, the Environment and Climate Change Canada (ECCC) Global Deterministic Prediction System is used to investigate the medium-range predictability of ozone and weather throughout the anomalous polar ozone depletion events of 2020. The system includes ozone assimilation and makes use of a prognostic ozone field for the computation of heating rates. The ozone scheme uses simplified photochemical modules to represent the impact of both gas-phase and heterogeneous reactions throughout polar ozone depletion events. The study shows that during the Boreal and Austral spring seasons, the predictability of the total ozone column exceeds 10 days and is comparable to the predictability of large-scale weather variables. It also demonstrates that over both polar regions, the inclusion of ozone radiative coupling has a significant impact on the temperature and wind distributions throughout the stratosphere. Over Antarctica, the ozone coupled forecasts are systematically colder at all lead times, which helps eliminate a temperature bias present in the model using climatological ozone. The strength of the polar vortex also increases significantly throughout the lower stratosphere, in better agreement with zonal wind analyses. Over the Arctic the use of an ozone-interactive model also produces significant changes in the temperature and wind forecasts, but the impact on the quality of the weather forecasts is generally neutral. The study shows the overall benefits of using ozone coupled models in the highly perturbed springtime conditions of the polar regions.

Motivation & Objective

• To assess the medium-range predictability of springtime ozone depletion events in the Arctic and Antarctic using a high-top NWP system.
• To evaluate the impact of ozone radiative coupling on stratospheric temperature and wind forecasts during extreme depletion events.
• To quantify improvements in total column ozone (TOC) and meteorological variable forecasts when using prognostic ozone and simplified chemistry.
• To determine the role of initial ozone analysis quality and ozone transport representation in forecast accuracy.
• To investigate the timescale at which ozone radiative feedback becomes significant for weather predictability in polar regions.

Proposed method

• Utilizes the ECCC Global Deterministic Prediction System (GDPS) with a high-top model extending above the stratopause to resolve stratospheric dynamics.
• Incorporates ozone assimilation to provide accurate initial conditions for ozone fields during extreme depletion events in 2020.
• Employs a simplified photochemical module to represent gas-phase and heterogeneous reactions (e.g., on PSCs) during ozone depletion.
• Uses a prognostic ozone field to compute radiative heating rates, enabling feedback between ozone and temperature fields.
• Compares forecasts from ozone-coupled and ozone-climatological configurations to isolate the impact of radiative coupling.
• Validates results against GDPS analyses, OMI satellite observations, and in-situ ozonesonde data at Ny-Alesund.

Experimental results

Research questions

• RQ1 Can medium-range NWP forecasts reliably predict springtime ozone depletion events in both polar regions?
• RQ2 How does including ozone radiative coupling affect the accuracy of stratospheric temperature and wind forecasts during extreme ozone loss?
• RQ3 To what extent does the use of prognostic ozone and simplified chemistry reduce biases in total column ozone and meteorological variables?
• RQ4 What is the relative contribution of initial ozone analysis quality versus ozone transport representation to forecast skill?
• RQ5 At what timescale does the radiative feedback from ozone loss become significant for weather predictability in the polar stratosphere?

Key findings

• The predictability of total column ozone (TOC) exceeds 10 days during springtime ozone depletion events in both the Arctic and Antarctic, comparable to large-scale weather variables.
• In the Southern Hemisphere, the use of the heterogeneous chemistry parameterization reduced TOC biases by about 75% in August and September and improved TOC predictability by approximately 8 hours.
• In the Northern Hemisphere, the same scheme reduced TOC biases by about 40% in February and March, with minor reductions in standard deviation.
• Ozone radiative coupling significantly improved temperature and zonal wind forecasts in the lower stratosphere: temperature biases decreased by ~0.5 K at 5-day lead times, and zonal winds increased by ~0.5 m/s in Antarctica.
• The inclusion of ozone coupling increased temperature forecast predictability by about 12 hours at 70 hPa in the Southern Hemisphere, indicating improved resolution of radiative-photochemical feedbacks.
• Over the Arctic, the radiative impact of ozone was weaker due to dynamical variability, but ozone-coupled forecasts still reduced short-lead-time temperature biases compared to climatological ozone.