Reply on RC1

Question

1. What is the significance of HO2 catalytic cycles in the lower stratosphere?

2. How are ionisation rates obtained for Halloween SPE?

3. What is the 1D model ExoTIC based on?

4. How are primary positive charges distributed in full-ion chemistry?

Accepted Answer

Catalytic cycles involving HO2 are crucial in the lower stratosphere (10-30 km) due to their role in ozone destruction. The fastest of these cycles, shown in Reactions R14, R15, and R16, involve the reaction of OH with O3 to produce HO2, O2, and O. This process contributes to the net loss of ozone (O3 + O + O2). Another important HOx catalytic destruction cycle occurs in the middle and upper mesosphere (above 60 km), as demonstrated by Reactions R17 and R18. In these reactions, one molecule of O3, O(3P), or O(1D) is lost while reforming H and OH, resulting in the production of a net ozone loss (Reaction R19). Overall, these catalytic cycles play a significant role in the depletion of ozone in different atmospheric layers.

Accepted Answer

Ionisation rates for Halloween SPE are obtained from the Atmospheric Ionization during Substorm (AISstorm) model, an enhanced version of the Atmospheric Ionization Module Osnabruck (AIMOS) model. The AIMOS model computes ionization rates by precipitating electrons, protons, and alpha particles for the whole atmosphere based on particle flux measurements from Polar Operational Environmental Satellites (POES), the Meteorological Operational satellites (Metop), and the Geostationary Operational Environmental Satellites (GOES). The treatment of electron fluxes is in the energy range of 0.154-300 keV, while protons have an energy range of 0.154 eV to 500 MeV. The AIMOS v2.0-AISstorm model has improved time resolution (0.5 hr) and spatial resolution compared to AIMOS. Integrated ionization rates for the extreme event were taken from an extreme SPE of 23 February 1956 (SPE 56) and scaled by a factor of 70 to represent a one in a 1000 year event. The profiles for the Halloween SPE show average ionization rates for October 27 and 28 before the SPE, and the average ionization rates for October 28 and 29 during the main SPE phase. The ionization rates for the extreme event are about 1-2 orders of magnitude higher compared to the Halloween SPE main phase due to the presence of protons with energies up to a few GeV.

Accepted Answer

The 1D model ExoTIC is based on the UBIC model developed by Winkler et al. (2009) for terrestrial middle atmosphere ion-chemistry and the SLIMCAT model by Chipperfield (1999) for neutral chemistry. It simulates a neutral atmosphere with 106 charged and 58 neutral species interacting through various reactions. The model uses 2.7 km boxes in height and is calculated iteratively with the neutral chemistry model feeding volume mixing ratios to the ion-chemistry model. The ion-chemistry is calculated in equilibrium state, with the highest level being 1 (207.4 km) and the lowest level being 53 (25.4 km). The model also computes net effective production or loss rates of neutral species due to primary ionization and ion-chemistry, which can be used as a parameterization for global chemistry-climate models.

Accepted Answer

In full-ion chemistry, primary positive charges are distributed onto N2, N, O2, and O, balanced with electrons. This distribution is driven by prescribed ionization rates and photo-ionization of NO, as described by Sinnhuber et al. (2012). The ionization cross-sections used for calculating these rates are based on research by Rusch et al. (1981) and Jones and Rees (1973). Additionally, dissociation and dissociative ionization of O2 and N2, as well as ionization of O2, N2, and O, contribute to the formation of excited states of N, O, N+2, N+, and NO+. These processes and their reaction rates are detailed in Sinnhuber et al. (2012) and updated in Herbst et al. (2022).

Accepted Answer

O(1 D) formation significantly impacts neutral chemistry due to its short-lived nature and large rate of production. In the ion-chemistry model, O(1 D) is not considered to go into photo-chemical equilibrium, leading to an excessive rate of formation being passed to neutral chemistry. This results in a higher concentration of O(1 D) in the lower stratosphere, where it can react with species like H2O, H2, and CH4, as well as HCl to produce OH. Consequently, setting the formation rates of O(1 D) to zero or calculating it in photo-chemical equilibrium can significantly alter the full ion-chemistry through reactions R40, R41, R42, and R43. This highlights the importance of accurately accounting for O(1 D) in ion-chemistry models to ensure precise predictions of atmospheric chemistry.

Accepted Answer

In parameterised NO x, 1.25 N atoms are produced per ion pair when electrically charged particles collide and dissociate N2. This process results in the formation of N+2 and NO+ ions, as well as atomic nitrogen. The atomic nitrogen is produced in its ground state N(4S) (45% or 0.55 per ion pair) and the excited state N(2D) (55% or 0.7 per ion pair). These values are commonly used in stratospheric and mesospheric models. Understanding the production rate of N atoms per ion pair is crucial for accurately modeling atmospheric chemistry and predicting the behavior of nitrogen compounds in the atmosphere.

Accepted Answer

The spectral range of MIPAS on ENVISAT was 4.15 um to 14.6 um. This range allowed for the detection of a wide variety of trace gases, as their absorption lines and signals are generally higher in this part of the spectrum. The Planck function maximizes at around 10 um for atmospheric temperatures, making this range particularly suitable for atmospheric observations. MIPAS's high spectral resolution enabled the identification of trace gases with their unique 'fingerprints' based on their characteristic emission and absorption lines.

Accepted Answer

Averaging kernels are used to adjust model profiles by convolving and adjusting the original model profiles to match the MIPAS altitude resolution. The adjustment procedure involves using the averaging kernel matrix (A) and the original model profile (x orig) to calculate the adjusted model profile (x new) using the formula x new = Ax orig + (I - A)x a. The averaging kernel matrix represents the contribution of true values to the retrieved values and the response of delta peak perturbations at each altitude. The adjusted model profiles are then used to compare with MIPAS observations, ensuring a meaningful comparison between the model and MIPAS data.

Accepted Answer

During SPEs, ClO can react with HO x species, particularly HO 2, to produce HOCl (R8), a short-lived species. This leads to a short-term enhancement of HOCl during both events. However, for the extreme scenario, loss of ClO continues even after the event stops due to excess HO x. ClO can react with OH to form ClO (R9), and then ClO can react back with HO 2, resulting in the loss of both species due to excess HO x. This catalytic cycle contributes to the loss of ClO during SPEs.

Accepted Answer

The impact of chlorine ions on ozone loss varies depending on the event. For the Halloween SPE and the extreme event in 775 A.D., a small impact of 10-20% was observed on the event day. Qualitatively, the impact was slightly higher for the extreme event. After the event stops, an increase of around 5% in ozone was seen for the extreme scenario. The comparison of the Halloween SPE and the extreme event showed long-lasting stratospheric ozone loss for the extreme scenario. Additionally, a long-lasting impact was found for chlorine species like HOCl and HCl in the extreme scenario. The parameterised model showed a much higher NO y enhancements and HO x enhancements during the extreme event. Ozone formation was observed after the event, attributed to the impact of chlorine ion-chemistry. ExoTIC simulations reproduced the impacts of the Halloween SPE well, mainly for HOCl and NO y, but the initial state of the atmosphere could influence the results. Future work will focus on including D-region ion-chemistry into the global 3D chemistry climate model EMAC and evaluating the chemistry with MIPAS observations considering atmospheric dynamics.

Reply on RC1

Chat with Paper

AI Agents for this Paper

Most frequently asked questions

1. What is the significance of HO2 catalytic cycles in the lower stratosphere?

2. How are ionisation rates obtained for Halloween SPE?

3. What is the 1D model ExoTIC based on?

4. How are primary positive charges distributed in full-ion chemistry?

5. How does O(1 D) formation affect neutral chemistry?

6. What is the production rate of N atoms per ion pair in parameterised NO x?

7. What was the spectral range of MIPAS on ENVISAT?

8. How are averaging kernels used to adjust model profiles?

9. What happens to ClO during SPEs?

10. What is the impact of chlorine ions on ozone loss?

Related Papers (5)

Use of coupled ozone fields in a 3-D circulation model of the middle atmosphere

The impact of the chlorocarbon industry on the ozone layer

Enhancement of heavy ozone in the Earth's atmosphere?

Implications of Satellite OH Observations for Middle Atmospheric H2O and Ozone

Photochemistry of ozone in a moist atmosphere