On the climatological probability of the vertical propagation of stationary planetary waves

We introduce a diagnostic tool to assess a climatological framework of the optimal propagation conditions for stationary planetary waves. Analyzing 50 winters using NCEP/NCAR (National Center for Environmental Prediction/National Center for Atmospheric Research) reanalysis data we derive probability density functions (PDFs) of positive vertical wave number as a function of zonal and meridional wave numbers. We contrast this quantity with classical climatological means of the vertical wave number. Introducing a membership value function (MVF) based on fuzzy logic, we objectively generate a modified set of PDFs (mPDFs) and demonstrate their superior performance compared to the climatological mean of vertical wave number and the original PDFs. We argue that mPDFs allow an even better understanding of how background conditions impact wave propagation in a climatological sense. As expected, probabilities are decreasing with increasing zonal wave numbers. In addition we discuss the meridional wave number dependency of the PDFs which is usually neglected, highlighting the contribution of meridional wave numbers 2 and 3 in the stratosphere. We also describe how mPDFs change in response to strong vortex regime (SVR) and weak vortex regime (WVR) conditions, with increased probabilities of the wave propagation during WVR than SVR in the stratosphere. We conclude that the mPDFs are a convenient way to summarize climatological information about planetary wave propagation in reanalysis and climate model data

On the climatological probability of the vertical propagation of stationary planetary waves

We introduce a diagnostic tool to assess a climatological framework of the optimal propagation conditions for stationary planetary waves. Analyzing 50 winters using NCEP/NCAR (National Center for Environmental Prediction/National Center for Atmospheric Research) reanalysis data we derive probability density functions (PDFs) of positive vertical wave number as a function of zonal and meridional wave numbers. We contrast this quantity with classical climatological means of the vertical wave number. Introducing a membership value function (MVF) based on fuzzy logic, we objectively generate a modified set of PDFs (mPDFs) and demonstrate their superior performance compared to the climatological mean of vertical wave number and the original PDFs. We argue that mPDFs allow an even better understanding of how background conditions impact wave propagation in a climatological sense. As expected, probabilities are decreasing with increasing zonal wave numbers. In addition we discuss the meridional wave number dependency of the PDFs which is usually neglected, highlighting the contribution of meridional wave numbers 2 and 3 in the stratosphere. We also describe how mPDFs change in response to strong vortex regime (SVR) and weak vortex regime (WVR) conditions, with increased probabilities of the wave propagation during WVR than SVR in the stratosphere. We conclude that the mPDFs are a convenient way to summarize climatological information about planetary wave propagation in reanalysis and climate model data

A semi-empirical model for mesospheric and stratospheric NOy produced by energetic particle precipitation

The MIPAS Fourier transform spectrometer on board Envisat has measured global distributions of the six principal reactive nitrogen (NO$_{γ}$) compounds (HNO$_{3}$, NO$_{2}$, NO, N$_{2}$O$_{5}$, ClONO$_{2}$, and HNO$_{4}$) during 2002–2012. These observations were used previously to detect regular polar winter descent of reactive nitrogen produced by energetic particle precipitation (EPP) down to the lower stratosphere, often called the EPP indirect effect. It has further been shown that the observed fraction of NO$_{γ}$ produced by EPP (EPP-NO$_{γ}$ ) has a nearly linear relationship with the geomagnetic A$_{ρ}$ index when taking into account the time lag introduced by transport. Here we exploit these results in a semiempirical model for computation of EPP-modulated NO$_{γ}$ densities and wintertime downward fluxes through stratospheric and mesospheric pressure levels. Since the A$_{ρ}$ dependence of EPP-NO$_{γ}$ is distorted during episodes of strong descent in Arctic winters associated with elevated stratopause events, a specific parameterization has been developed for these episodes. This model accurately reproduces the observations from MIPAS and is also consistent with estimates from other satellite instruments. Since stratospheric EPP-NO$_{γ}$ depositions lead to changes in stratospheric ozone with possible implications for climate, the model presented here can be utilized in climate simulations without the need to incorporate many thermospheric and upper mesospheric processes. By employing historical geomagnetic indices, the model also allows for reconstruction of the EPP indirect effect since 1850. We found secular variations of solar cycleaveraged stratospheric EPP-NO$_{γ}$ depositions on the order of 1 GM. In particular, we model a reduction of the EPP-NO$_{γ}$ deposition rate during the last 3 decades, related to the coincident decline of geomagnetic activity that corresponds to 1.8% of the NO$_{γ}$ production rate by N$_{2}$O oxidation. As the decline of the geomagnetic activity level is expected to continue in the coming decades, this is likely to affect the long-term NO$_{γ}$ trend by counteracting the expected increase caused by growing N$_{2}$O emissions

Modelled thermal and dynamical responses of the middle atmosphere to EPP-induced ozone changes

Energetic particles including protons, electrons and heavier ions, enter the Earth\u27s atmosphere over the polar regions of both hemispheres, where they can greatly disturb the chemical composition of the upper and middle atmosphere and contribute to ozone depletion in the stratosphere and mesosphere. The chemistry–climate general circulation model EMAC is used to investigate the impact of changed ozone concentration due to Energetic Particle Precipitation (EPP) on temperature and wind fields. The results of our simulations show that ozone perturbation is a starting point for a chain of processes resulting in temperature and circulation changes over a wide range of latitudes and altitudes. In both hemispheres, as winter progresses the temperature and wind anomalies move downward with time from the mesosphere/upper stratosphere to the lower stratosphere. In the Northern Hemisphere (NH), once anomalies of temperature and zonal wind reach the lower stratosphere, another signal develops in mesospheric heights and moves downward. Analyses of Eliassen and Palm (EP) flux divergence show that accelerating or decelerating of the stratospheric zonal flow is in harmony with positive and negative anomalies of the EP flux divergences, respectively. This results suggest that the oscillatory mode in the downwelling signal of temperature and zonal wind in our simulations are the consequence of interaction between the resolved waves in the model and the mean stratospheric flow. Therefore, any changes in the EP flux divergence lead to anomalies in the zonal mean zonal wind which in turn feed back on the propagation of Rossby waves from the troposphere to higher altitudes. The analyses of Rossby waves refractive index show that the EPP-induced ozone anomalies are capable of altering the propagation condition of the planetary-scale Rossby waves in both hemispheres. It is also found that while ozone depletion was confined to mesospheric and stratospheric heights, but it is capable to alter Rossby wave propagation down to tropospheric heights. In response to an accelerated polar vortex in the Southern Hemisphere (SH) late wintertime, we found almost two weeks delay in the occurrence of mean dates of Stratospheric Final Warming (SFW). These results suggest that the stratosphere is not merely a passive sink of wave activity from below, but it plays an active role in determining its own budget of wave activity

On the climatological probability of the vertical propagation of stationary planetary waves

We introduce a diagnostic tool to assess in a climatological framework the optimal propagation conditions for stationary planetary waves. Analyzing 50 winters using NCEP/NCAR reanalysis data we derive probability density functions (PDFs) of positive refractive indices as a function of zonal and meridional wave numbers. We contrast this quantity with classical climatological means of the refractive index. Introducing a Membership Value Function (MVF) based on fuzzy logic, we objectively generate a modified set of PDFs (mPDFs) and demonstrate their superior performance compared to the climatological mean of refractive indices and the original PDFs. We argue that mPDFs allow an even better understanding of how background conditions impact wave propagation in a climatological sense. As expected, probabilities are decreasing with increasing zonal wave numbers. In addition we discuss the meridional wave number dependency of the PDFs which is usually neglected, highlighting the contribution of meridional wave numbers 2 and 3 in the stratosphere. We also describe how mPDFs change in response to strong vortex regime (SVR) and weak vortex regime (WVR) conditions, with increased probabilities during WVR than SVR in the stratosphere. We conclude that the mPDFs are a convenient way to summarize climatological information about planetary wave propagation in reanalysis and climate model data

Retrieval of temperature, H₂O, O₃, HNO₃, CH₄, N₂O, ClONO₂ and ClO from MIPAS reduced resolution nominal mode limb emission measurements

Retrievals of temperature, H2O, O3, HNO3, CH4, N2O, ClONO2 and ClO from MIPAS reduced spectral resolution nominal mode limb emission measurements outperform retrievals from respective full spectral resolution measurements both in terms of altitude resolution and precision. The estimated precision (including measurement noise and propagation of uncertain parameters randomly varying in the time domain) and altitude resolution are typically 0.5–1.4K and 2–3.5 km for temperature between 10 and 50 km altitude, and 5–6%, 2–4 km for H2O below 30 km altitude, 4– 5%, 2.5–4.5 km for O3 between 15 and 40 km altitude, 3– 8%, 3–5 km for HNO3 between 10 and 35 km altitude, 5– 8%, 2–3 km for CH4 between 15 and 35 km altitude, 5–10%, 3 km for N2O between 15 and 35 km altitude, 8–14%, 2.5– 9 km for ClONO2 below 40 km, and larger than 35%, 3– 7 km for ClO in the lower stratosphere. As for the full spectral resolution measurements, the reduced spectral resolution nominal mode horizontal sampling (410 km) is coarser than the horizontal smoothing (often below 400 km), depending on species, altitude and number of tangent altitudes actually used for the retrieval. Thus, aliasing might be an issue even in the along-track domain. In order to prevent failure of convergence, it was found to be essential to consider horizontal temperature gradients during the retrieval

Global stratospheric hydrogen peroxide distribution from MIPAS-Envisat full resolution spectra compared to KASIMA model results

MIPAS-ENVISAT full resolution spectra were analyzed to obtain a global distribution of hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) in the stratosphere. H<sub>2</sub>O<sub>2</sub> acts as reservoir gas for the HO<sub>x</sub> family (= H+OH+HO<sub>2</sub>) and thus, observations of H<sub>2</sub>O<sub>2</sub> provide a better understanding of the HO<sub>x</sub> chemistry in the atmosphere. A retrieval approach based on constrained least squares fitting was developed and applied to small dedicated spectral analysis windows with maximum H<sub>2</sub>O<sub>2</sub> information and minimum contribution of interfering gases. Due to a low signal to noise ratio in the measured spectra single profiles cannot be used for scientific interpretation and about 100 profiles have to be averaged temporally or spatially. Our retrievals of H<sub>2</sub>O<sub>2</sub> from MIPAS measurements provide meaningful results between approximately 20 and 60 km. A possible impact by the high uncertainty of the reaction rate constant for HO<sub>2</sub> + HO<sub>2</sub>→H<sub>2</sub>O<sub>2</sub> + O<sub>2</sub> in our 3D-CTM KASIMA is discussed. We find best agreement between model and observations for applying rate constants according to Christensen et al. (2002) however, a mismatch in vertical profile shape remains. The observations were compared to the model results of KASIMA focusing on low to mid latitudes. Good agreement in spatial distribution and in temporal evolution was found. Highest vmr of H<sub>2</sub>O<sub>2</sub> in the stratosphere were observed and modeled in low latitudes shortly after equinox at about 30 km. The modelled diurnal cycle with lowest vmr shortly after sunrise and highest vmr in the afternoon is confirmed by the MIPAS observations

Northern Hemisphere Atmospheric Influence of the Solar Proton Events and Ground Level Enhancement in January 2005

Solar eruptions in early 2005 led substantial barrage of charged particles on the Earth's atmosphere during the January 16-21 period. Proton fluxes were greatly increased during these several days and led to the production ofHO(x)(H, OH, BO2)and NO(x)(N, NO, NO2), which then caused the destruction of ozone. We focus on the Northern polar region, where satellite measurements and simulations with the Whole Atmosphere Community Climate Model (WACCM3) showed large enhancements in mesospheric HO(x) and NO(x) constituents, and associated ozone reductions, due 10 these solar proton events (SPEs). The WACCM3 simulations show enhanced short-lived OH throughout the mesosphere in the 60-82.5degN latitude band due to the SPEs for most days in the Jan.16-2l,2005 period, in reasonable agreement with the Aura Microwave Limb Sounder (MLS) measurements. Mesospheric HO2 is also predicted to be increased by the SPEs, however, the modeled HO2 results are somewhat larger than the MLS measurements. These HO(x) enhancements led to huge predicted and MLS-measured ozone decreases of greater than 40% throughout most of the Northern polar mesosphere during the SPE period. Envisat Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) measurements of hydrogen peroxide (H2O2) show increases throughout the stratosphere with highest enhancements of about 60 ppt y in the lowermost mesosphere over the Jan. 16-18, 2005 period due to the solar protons. WACCM3 predictions indicate H2O2 enhancements over the same time period of more than twice that amount. Measurements of nitric acid (HNO3) by both MLS and MIPAS show an increase of about 1 ppbv above background levels in the upper stratosphere during January 16-29, 2005. WACCM3 simulations show only minuscule HNO3 changes in the upper stratosphere during this time period. However due to the small loss rates during winter, polar mesospheric enhancements of NO(x) are computed to be greater than 50 ppbv during the SPE period. Computed NO(x)increases, which were statistically significant at the 95% level, lasted about a month past the SPEs. The SCISAT-I Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) NO(x) measurements and MIPAS NO, measurements for the polar Northern Hemisphere are in reasonable agreement with these predictions. An extremely large ground level enhancement (GLE) occurred during the SPE period on January 20, 2005. We find that protons of energies 300 to 20,000 MeV, not normally included in our computations, led to enhanced lower stratospheric odd nitrogen concentrations of less than 0.1% as a result of this GLE