Precipitation of energetic particles into the atmosphere greatly disturbs the chemical composition from the upper stratosphere to the lower thermosphere. Most important are changes to the budget of atmospheric nitric oxides (NOx = N, NO, NO2) and to atmospheric reactive hydrogen oxides (HOx = H, OH, HO2), which both contribute to ozone loss in the stratosphere and mesosphere. The impact of energetic particle precipitation on the chemical composition of the atmosphere has been studied since the 1960s, and there are a number of observations as well as model studies concerning especially the auroral impact and large solar particle events. Changes to the NOx budget due to energetic particle precipitation can be quite long-lived during polar winter and can then be transported down into the lower mesosphere and stratosphere, where NOx is one of the main participants in catalytic ozone destruction. Energetic particle precipitation can also affect temperatures and dynamics of the atmosphere from the source region down to the stratosphere and possibly even down to the surface, due to a coupling of chemical composition changes affecting atmospheric heating and cooling rates, the mean circulation, and wave propagation and breaking. Thus, energetic particle precipitation impacts have been implemented in chemistry-climate models reaching from the surface up to the mesosphere or lower thermosphere. However, there are still a number of open questions in the theoretical description of the energetic particle precipitation impact; the most important are uncertainties in the formation rate of different NOx species due to energetic particle precipitation, and the complex coupling between chemical changes, atmospheric heating and cooling rates, and atmospheric dynamics.

/pdf/energetic-particle-precipitation-and-the-chemistry-of-the-fitpttl7l5.pdf

Energetic Particle Precipitation and the Chemistry of the Mesosphere/Lower Thermosphere

This study analyzes a new high-resolution general circulation model with regard to secondary gravity waves in the mesosphere during austral winter. The model resolves gravity waves down to horizontal and vertical wavelengths of 165 and 1.5 km, respectively. The resolved mean wave drag agrees well with that from a conventional model with parameterized gravity waves up to the midmesosphere in winter and up to the upper mesosphere in summer. About half of the zonal-mean vertical flux of westward momentum in the southern winter stratosphere is due to orographic gravity waves. The high intermittency of the primary orographic gravity waves gives rise to secondary waves that result in a substantial eastward drag in the winter mesopause region. This induces an additional eastward maximum of the mean zonal wind at z ∼ 100 km. Radar and lidar measurements at polar latitudes and results from other high-resolution global models are consistent with this finding. Hence, secondary gravity waves may play a significant role in the general circulation of the winter mesopause region. Plain Language Summary We present a new gravity-resolving general circulation model that extends into the lower thermosphere. The simulated summer-to-winter-pole circulation in the upper mesosphere is nearly realistic and driven by resolved waves. We find a new phenomenon that results from the generation of secondary gravity waves in the stratosphere and lower mesosphere. The effect is characterized by an eastward gravity drag that causes a secondary eastward wind maximum around the polar winter mesopause. Analysis of the simulated gravity waves shows consistence with other gravity wave resolving models and with observational studies of the austral winter middle atmosphere, including the mesopause region.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2017JD027460

Secondary Gravity Waves in the Winter Mesosphere: Results From a High-Resolution Global Circulation Model

This review recapitulates the concept of the wave-driven residual circulation in the stratosphere and mesosphere. The residual circulation is defined as the conventional mean meridional circulation corrected by the quasi-linear Stokes drift due to atmospheric waves. Only when the zonal-mean primitive equations are transformed using the residual circulation, they reflect the causality arising from the Eliassen-Palm (EP) theorem. The EP theorem states that the proper wave-mean flow interaction, defined as the EP flux divergence, vanishes for waves that are linear, conservative, and steady. In the real atmosphere, this theorem is violated mainly due to wave breaking and turbulence. The resulting EP flux divergence then drives a residual circulation which causes the observed substantial deviations from some hypothetical radiatively determined state. With regard to this dynamical control we discuss the different contributions of Rossby waves and gravity waves. Recapitulation of Lindzen’s theory of gravity-wave saturation allows us to interpret various phenomena in the upper mesosphere such as interhemispheric coupling or modulations of the gravity-wave driven branch of the residual circulation by solar proton effects and thermal tides. In addition we discuss the relative importance of changes in radiative transfer and tropospheric gravity-wave sources on the long-term temperature trends in the summer mesosphere.

Dynamical Control of the Middle Atmosphere

We present a new version of the high‐resolution Kühlungsborn Mechanistic general Circulation Model (KMCM) extended to z∼ 450 km. This model is called HIAMCM (HI Altitude Mechanistic general Circulation Model) and explicitly simulates gravity waves (GWs) down to horizontal wavelengths of λh ∼ 165 km. We find predominant tertiary GWs in the winter thermosphere at middle/high latitudes. These GWs typically have horizontal wavelengths λh∼ 300–1,100 km, ground‐based periods ∼ 25–90 min, and intrinsic horizontal phase speeds cIh∼ 250–350m s . Above z ∼ 200 km, the predominant GW horizontal propagation directions are roughly against the background winds from the diurnal tide; the GWs propagate mainly poleward at midnight, eastward at 6 local time (LT), equatorward at noon, and westward at 18 LT. Wintertime GWs at z ∼ 300 km having 165 km ≤ λh ≤ 330 km create a large hot spot over the Southern Andes/Antarctic Peninsula that agrees well with quiet time satellite measurements. Due to cancelation effects, the time‐averaged zonal mean Eliassen‐Palm flux divergence from the resolved GWs in the thermosphere is negligible compared to that of the tides and compared to the zonal component of the time‐averaged zonal mean ion drag. We also find that the thermospheric GWs dissipate mainly from macroturbulent diffusion and, above z ∼ 200 km, from molecular diffusion, whereas the tides dissipate mainly from ion drag. The averaged dissipative heating in the thermosphere due to tides is much stronger than that due to GWs.

Explicit global simulation of gravity waves in the thermosphere

[1] We use atmospheric ozone density profiles between 35 and 65 km altitude derived from SCIAMACHY limb measurements to quantify the ozone changes caused by the solar proton events from 26 October to 6 November 2003, known as the Halloween storm. Detailed maps and daily resolved time series up to 5 weeks after the first event are compared with the results from a chemistry, transport, and photolysis model of the middle atmosphere that includes NO x and HO x production due to energetic particle precipitation. The general features of the ozone loss are captured by the model fairly well. A strong ozone depletion of more than 50% even deep into the stratosphere is observed at high geomagnetic latitudes in the Northern Hemisphere, whereas the observed ozone depletion in the more sunlit Southern Hemisphere is much weaker. Reasons for these interhemispheric differences are given. Two regimes can be distinguished, one above about 50 km dominated by HO x (H, OH, HO 2 ) driven ozone loss, one below about 50 km, dominated by NO x (NO, NO 2 ) driven ozone loss. The regimes display a different temporal evolution of ozone depletion and recovery. We observe for the first time an establishment of two contemporaneous maxima of ozone depletion at different altitudes, which solely can be explained by these regimes.

Ozone depletion during the solar proton events of October/November 2003 as seen by SCIAMACHY : Violent sun-earth connection events of october-November 2003

[1] The observed heating of the polar summer mesopause during and after a solar proton event (SPE) is interpreted as a large-scale dynamical response to the temporary diabatic cooling in the lower mesosphere above the summer pole that results from the temporary ozone depletion during an SPE. Our method is based on time slice sensitivity experiments performed with a mechanistic general circulation model. The model response shows that according to the gradient wind balance, the polar lower mesospheric cooling induces an anomalous eastward wind component. As a result, the drag exerted by eastward propagating gravity waves (GWs) shifts to lower altitudes in tandem with a balancing downward shift of the residual circulation. Around the extratropical summer mesopause, this is accompanied by an anomalous large-scale dynamic heating which qualitatively explains the positive temperature response in this region. A quantitative inspection of the zonal momentum and sensible heat budgets reveals that the GW drag response is partly compensated by a downshift of planetary Rossby waves and that about two thirds of the anomalous large-scale dynamic heating around the mesopause is balanced by changes of the direct thermal effects due to GWs, diffusion, and dissipation.

/pdf/dynamical-heating-of-the-polar-summer-mesopause-induced-by-n65tp5w6an.pdf

Dynamical heating of the polar summer mesopause induced by solar proton events

[1] The dynamical fields of a high-resolution mechanistic general circulation model (GCM) with resolved gravity waves (GWs) are used to drive a chemistry-transport model (CTM) of the mesosphere-lower thermosphere (MLT). Both models have been used in previous studies and are coupled in off-line mode in order to study the explicit effects of GWs on the transport and photochemistry of minor constituents of the MLT. This is done on the basis of a sensitivity experiment. In our control simulation the CTM is driven with the full dynamical fields from an annual cycle simulated with the GCM, where mid-frequency GWs down to horizontal wavelengths of 350 km are resolved and their wave-mean flow interaction is self-consistently induced by an advanced turbulence model. A perturbation simulation with the CTM is defined by eliminating all meso-scale variations with horizontal wavelengths shorter than 1000 km from the dynamical fields by means of spectral filtering before running the CTM. The response of the CTM to GWs perturbations reveals strong effects on the trace-gas concentrations. In particular, minor chemical constituents with large photochemical life-time are strongly affected by vertical wave mixing, while constituents with short life-time reflect the dependence of their reaction rates on meso-scale temperature perturbations and on the changed distributions of long-lived constituents. The mean model response is strongest around the mesopause. We present detailed discussions of the simulated gravity-wave mixing effects on the photochemistry and highlight the consequences for our understanding of the general circulation of the MLT.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2010JD015518

Wave mixing effects on minor chemical constituents in the MLT region: Results from a global CTM driven by high‐resolution dynamics

A new scheme that solves the advection-diffusion equation for tracers in a spectral General Circulation Model (GCM) is presented. The main ideas are (1) using a monotonic and smooth functional of the tracer as prognostic variable to ensure positive definite concentrations and continuity of all derivatives and (2) defining an adjustable tracer-mass correction as a multiplication of the tracer in grid space, giving rise to an efficient correction in spectral space. Common standard benchmark tests for two-dimensional horizontal advection using deformational wind fields show that the new scheme is accurate and essentially not diffusive. A three-dimensional test is proposed in order to validate vertical transport. Additionally to standard error norms and global tracer mass, the entropy of mixing is introduced as another conservation constraint and utilized to determine the strength of the mass correction which is a free parameter. The transport scheme is applied in a mechanistic spectral GCM from the surface to the lower thermosphere. It is extended such that the mass correction takes the diffusion and other nonconservative effects explicitly into account. By this method we estimate the mean age of air along with its dependence on the turbulent horizontal Schmidt number.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014JD021661

Positive definite and mass conserving tracer transport in spectral GCMs

The Earth’s middle atmosphere is affected by short-term solar variability in a variety of ways. This chapter focuses on the investigation of two different short-term solar effects on the polar summer mesopause region and on noctilucent clouds (NLCs). First, the effect of solar proton events (SPEs) on the thermal conditions near the polar summer mesopause and consequently on NLCs is discussed. An analysis of the SBUV(/2) time series to identify examples of NLC depletion due to SPEs shows that NLCs are probably frequently affected during strong SPEs. As part of this study a physical mechanism explaining a dynamically induced warming at the polar summer mesopause during and after SPEs is investigated using model simulations with the Kuhlungsborn Mechanistic General Circulation Model (KMCM). A second aspect related to the effect of SPEs on NLCs is on the SPE-induced ion-chemical conversion of H2O to HO x , leading to a possible sublimation of NLCs. However, this effect was found to be of minor importance compared to the dynamically induced temperature effect. Second, we discuss the recently discovered 27-day solar cycle signature in NLCs, which was identified in SCIAMACHY as well as SBUV satellite observations of NLCs using cross correlation analysis and the superposed epoch method. NLC occurrence rate and albedo anomalies are anti-correlated with Lyman-α anomalies with a time-lag of 1 day at most. The sensitivities of the NLC albedo anomalies to Lyman-α forcing in terms of the 27-day and the 11-year solar cycle were found to agree within their uncertainties. This finding suggests that the same underlying physical mechanism drives the 27-day as well as the 11-year solar cycle signature in NLCs. The exact mechanism is still unknown, however.

Impact of Short-Term Solar Variability on the Polar Summer Mesopause and Noctilucent Clouds

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

E. Becker

Author Tools

Chat about Author

Papers

Dynamical heating of the polar summer mesopause induced by solar proton events

Wave mixing effects on minor chemical constituents in the MLT region: Results from a global CTM driven by high‐resolution dynamics

Positive definite and mass conserving tracer transport in spectral GCMs

Impact of Short-Term Solar Variability on the Polar Summer Mesopause and Noctilucent Clouds