Experiments

Coordinated model experiments of the HEPPA and SOLARIS working groups

Ongoing: evaluation experiments for the CMIP7 solar forcing recommendations. A description and due dates are given here. The decadal runs w/o particle precipitation will form the core of the HEPPA V experiment.

The HEPPA community has carried out a number of dedicated model-measurement intercomparison experiments to evaluate our understanding of the impact of High-Energy Particle Precipitation into the Atmosphere.

SOLARIS has defined model experiments to assess the impact of solar radiation (TSI and SSI) variability on atmospheric dynamics and surface climate in the context of large coordinated projects like CCMVal or CMIP.

HEPPA model-measurement intercomparison experiments

Thermospheric nitric oxide NO during solar minimum modulated by O/O2 ratio and thermospheric transport and mixing (HEPPA IV)

In this follow-up experiment of HEPPA-III, the large spread of NO between models particularly in the lower thermosphere was analyzed further with a focus on the formation and loss of NO in the lower thermosphere. It was shown that order-of-magnitude differences between models in the winter-time lower thermosphere arise due to differences in the models thermospheric O/O2 ratio and treatment of gravity waves. A preprint can be found here: (Sinnhuber et al., ACP, preprint)

HEPPA-III Intercomparison Experiment on Electron Precipitation Impacts

The HEPPA-III experiment focussed on the direct effects of energetic electron precipitation on atmospheric ionization rates and NO during a geomagnetically active period in April 2010. The aim was to investigate the impact of medium-energy electrons (MEE, 30-300 keV) which directly affect the upper mesosphere. However, large discrepancies were also found in lower thermospheric NO at mid-and high latitudes, indicating possible problems with EUV photoionization or NO photochemistry. Results were published in two companion papers, Nesse et al., JGR., 2022 focussing on the ionization, and Sinnhuber et al., JGR, 2022, focussing on atmospheric composition.

HEPPA-II: EEP indirect effects during the unusual 2009 NH polar winter

The HEPPA-II exercise focuses on Energetic Particle Precipitation indirect effects (i.e., polar winter NOx descent) during and after an unusually strong sudden stratospheric warming. Results show that all models morphologically reproduce the indirect effect, but particularly models with their top in the lower thermosphere struggle to quantifically reproduce the indirect effect, while models with their top around the mesopause using upper boundary conditions of NOy perform better. Results are published in Funke et al., ACP, 2017.

HEPPA-I: Composition changes after the “Halloween” solar proton event

The HEPPA-I exercise has focused on the intercomparison of MIPAS/Envisat data obtained in the aftermath of the “Halloween” Solar Proton Event (SPE, 26 October – 30 November 2003) with state of the art GCMs and CTMs. The large number of models participating in this exercise allowed for an evaluation of the overall ability of atmospheric models to reproduce observed atmospheric perturbations generated by SPEs, particularly with respect to NOy and ozone changes. Results are published in Funke et al., ACP, 2011

SOLARIS coordinated experiments

A) Coordinated Model Runs to Investigate Aliasing of Different Factors in the Tropical Lower Stratosphere

Recently, the discrepancy between modelling studies and observations regarding the vertical structure in the tropical solar signal, as shown by the WMO (2007), has been reduced in both CCMVal-1 reference simulations (Austin et al., 2008) and CCMVal-2 simulations (SPARC CCMVal, 2010, chapter 8). Similarly, other recent simulations with CCMs reproduce the observed vertical structure in the tropical stratosphere, but only with a (prescribed) QBO, time-varying solar cycle conditions and constant SSTs (Matthes et al., 2007; Matthes et al., 2010), or in a CCM with fixed solar cycle conditions, with or without an internally-generated QBO (Schmidt et al., 2010). It is still unclear why a vertical structure in the solar signal appears, and whether it is related to non-linear interactions or arises from contamination by other signals (QBO, tropical SSTs). To eliminate possible aliasing between the solar cycle and the QBO, as well as between the solar cycle and the SSTs, and/or the QBO and the SSTs, the REF-B1 CCMVal experiments (Eyring et al., 2008, SPARC CCMVal 2010) were repeated with filtered SST and/or QBO data:

  • Filtered SST data:
    The QBO signal (2-3 years) and solar cycle signals (larger than 10 years) have been filtered out of the SST data set used as a lower boundary for the REF-B1 simulations.
  • Filtered QBO data:
    Similarly, the QBO data were filtered to retain only periods between 9-48 months and exclude signals related to ENSO or the solar cycle.

Currently, two CCMs with a prescribed QBO (EMAC, WACCM), and one with internally generated QBO (MRI) have finished one ensemble of the modified REF-B1 experiments.

B) Coordinated Model Runs to Study the Uncertainty in Solar Forcing

Uncertainties in the solar irradiance could have a large impact on the simulation of the climate system. The solar irradiance data compiled by J. Lean (Lean, 2000) are most frequently used for model simulations. However, in the wavelength range important for ozone chemistry (200-400 nm), there are differences of up to 20% to the estimate of Krivova et al. (2006). Further uncertainties arise from new measurements from the SIM instrument onboard the SORCE satellite, which shows a completely different spectral distribution than expected, with possible implications for solar heating and ozone chemistry (e.g., Haigh et al., 2010).
The proposed coordinated CCM experiments include:

  1. A control (time slice) experiment with either Lean (standard) or SIM solar irradiance data,
  2. Idealized experiments with enhanced solar UV forcing in certain spectral ranges, i.e. an increase of 5% between 200 and 300 nm, and an increase of 1% between 300 and 400nm.

It is important to investigate the reliability of current SOLARIS irradiance data recommendations for CMIP5 and SPARC-CCMVal, and test the sensitivity of different radiation and photochemistry models to different spectral irradiance data sets.

SolarMIP

The Solar Model Inter-comparison Project (SolarMIP) is a SPARC/SOLARIS initiative to compare the coupled ocean-atmosphere model response to variability in solar irradiance in the CMIP5 (Coupled Model Intercomparison Project phase 5) model simulations. SolarMIP aims at examining the model responses to the 11-year solar cycle variations with special care on (a) the stratospheric response, which is dominated by ozone absorption of incoming UV-radiation and (b) the surface response, which is believed to be a combination of direct heating of the tropical SSTs and indirect effects via the stratosphere. The scope of this international activity falls directly under the aims of WG4 of the European COST Action TOSCA (ES 1005) regarding the investigation of solar influence on the vertical coupling between atmospheric layers, the role of the ocean influence on the solar impact on the troposphere and the intercomparison of solar cycle effects in climate models simulations.