M. Sinnhuber

A model study of the impact of magnetic field structure on atmospheric composition during solar proton events

[1] During a polarity transition of the Earth’s magnetic field, the structure and strength of the field change significantly from their present values. This will alter the global pattern of charged particle precipitation into the atmosphere. Thus, particle precipitation is possible into regions that are at the moment effectively shielded by the Earth’s magnetic field. A two-dimensional global chemistry, photolysis and transport model of the atmosphere has been used to investigate how the increased particle precipitation affects the chemical composition of the middle and lower atmosphere. Ozone losses resulting from large energetic particle events are found to increase significantly, with resultant losses similar to those observed in the Antarctic ozone hole of the 1990s. This results in significant increases in surface UV-B radiation as well as changes in stratospheric temperature and circulation over a period of several months after large particle events. INDEXTERMS:0340Atmospheric Composition and Structure: Middle atmosphere—composition and chemistry; 0341 Atmospheric Composition and Structure: Middle atmosphere—constituent transport and chemistry (3334); 1535 Geomagnetism and Paleomagnetism: Reversals (process, timescale, magnetostratigraphy); 1650 Global Change: Solar variability; 2716 Magnetospheric Physics: Energetic particles, precipitating. Citation: Sinnhuber, M., J. P. Burrows, M. P. Chipperfield,

Modeling impacts of geomagnetic field variations on middle atmospheric ozone responses to solar proton events on long timescales

[1] Strength and structure of the Earth’s magnetic field control the deflection of energetic charged particles of solar and cosmic origin. Therefore variations of the geomagnetic field occurring on geological timescales affect the penetration of charged particles into the atmosphere. During solar proton events (SPEs) the flux of high-energy protons from the Sun is markedly increased. In order to investigate the impact of SPEs on the middle atmospheric ozone on longer timescales, two-dimensional atmospheric chemistry and transport simulations have been performed using simulated time series of SPEs covering 200 years. Monte Carlo calculations were used to obtain ionization rates, which were then applied to the atmosphere under the consideration of different shielding properties of the geomagnetic field. The present-day magnetic field configuration and four other scenarios were analyzed. For the first time, field configurations representing possible realistic situations during reversals have been investigated with respect to SPE-caused ozone losses. With decreasing magnetic field strength the impacts on the ozone are found to significantly increase especially in the Southern Hemisphere, and subsequently, the flux of harmful ultraviolet radiation increases at the Earth’s surface. The ozone destructions are most pronounced in the polar regions, and for some field configurations they exceed the values of ozone hole situations after large SPEs. In contrast to ozone holes the depletions due to SPEs are not restricted to winter and spring times but persist into polar summer.

NOx production due to energetic particle precipitation in the MLT region: Results from ion chemistry model studies

Production of neutral species such as NOx(N, NO, and NO2) during particle-induced ionization events plays an important role in the chemistry of the mesosphere and lower thermosphere (MLT) region, especially in high latitudes. The effective production rate of NOx is composed of the direct production in reactions associated with the ionization or dissociation process and of indirect production during subsequent ionic reactions and recombination. A state of the art ion chemistry model is used to study the dependence of the effective production rate of NOx on several atmospheric parameters such as density, temperature, and abundance of atmospheric constituents and trace gases. The resulting effective production rates vary significantly, depending on the atmospheric state, and reach values between 1.2 NOx per ion pair in the lower mesosphere and 1.9 NOx per ion pair in the lower thermosphere. In this paper, an alternative approach to obtain realistic NOx production rates without running a full ion chemistry model is discussed; a database setup and readout system is used to replace ion chemistry calculations. It is compared to the full ion chemistry model and to a thermospheric reduced ion chemistry model combined with constant rate estimation below the mesopause. Database readout performs better than the constant estimate at all altitudes, where above 100km reduced ion chemistry better reproduces full ion chemistry, but database readout performs better in terms of numerical cost.

The 27 day solar rotational effect on mesospheric nighttime OH and O3 observations induced by geomagnetic activity.

Abstract Observations performed by the Earth Observing System Microwave Limb Sounder instrument on board the Aura satellite from 2004 to 2009 (2004 to 2014) were used to investigate the 27 day solar rotational cycle in mesospheric OH (O3) and the physical connection to geomagnetic activity. Data analysis was focused on nighttime measurements at geomagnetic latitudes connected to the outer radiation belts (55°N/S–75°N/S). The applied superposed epoch analysis reveals a distinct 27 day solar rotational signal in OH and O3 during winter in both hemispheres at altitudes >70 km. The OH response is positive and in‐phase with the respective geomagnetic activity signal, lasting for 1–2 days. In contrast, the O3 feedback is negative, delayed by 1 day, and is present up to 4 days afterward. Largest OH (O3) peaks are found at ~75 km, exceeding the 95% significance level and the measurement noise of <2% (<0.5%), while reaching variations of +14% (−7%) with respect to their corresponding background. OH at 75 km is observed to respond to particle precipitation only after a certain threshold of geomagnetic activity is exceeded, depending on the respective OH background. The relation between OH and O3 at 75 km in both hemispheres is found to be nonlinear. In particular, OH has a strong impact on O3 for relatively weak geomagnetic disturbances and accompanying small absolute OH variations (<0.04 ppb). In contrast, catalytic O3 depletion is seen to slow down for stronger geomagnetic variations and OH anomalies (0.04–0.13 ppb), revealing small variations around −0.11 ppm.

Retrieval of nitric oxide in the mesosphere and lower thermosphere from SCIAMACHY limb spectra

Abstract. We use the ultra-violet (UV) spectra in the range 230–300 nm from the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) to retrieve the nitric oxide (NO) number densities from atmospheric emissions in the gamma-bands in the mesosphere and lower thermosphere. Using 3-D ray tracing, a 2-D retrieval grid, and regularisation with respect to altitude and latitude, we retrieve a whole semi-orbit simultaneously for the altitude range from 60 to 160 km. We present details of the retrieval algorithm, first results, and initial comparisons to data from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). Our results agree on average well with MIPAS data and are in line with previously published measurements from other instruments. For the time of available measurements in 2008–2011, we achieve a vertical resolution of 5–10 km in the altitude range 70–140 km and a horizontal resolution of about 9° from 60° S–60° N. With this we have independent measurements of the NO densities in the mesosphere and lower thermosphere with approximately global coverage. This data can be further used to validate climate models or as input for them.

The response of mesospheric NO to geomagnetic forcing in 2002–2012 as seen by SCIAMACHY

Daily NO number density, retrieved from measurements of the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) from 2002 to 2012 for polar summer in the mesosphere, is used to investigate the response of NO to geomagnetic activity, as expressed by the auroral electrojet (AE) index. Applying the superposed epoch analysis, we observe a clear response of NO to strong geomagnetic forcing at geomagnetic latitudes 55–75 ∘ N/S and altitudes above 66 km. The 27 day solar rotation cycle is observed, indicating that some of the observed geomagnetic events are related to solar coronal holes. We find a linear relationship between anomalies of AE and NO at geomagnetic latitudes 55–70 ∘ N/S and 70–74 km altitude. A clear auroral oval-like structure is observed on days of strong geomagnetic forcing in both hemispheres, with small longitudinal inhomogeneities, which might be related to the South Atlantic Anomaly or the magnetic local time. The NO lifetime and production rate per AE anomaly has been derived from a least squares fit to the observations. Comparisons of results from a simple model using this empirical NO production and a lifetime varying from 1.2 days in summer to 10 days in winter to SCIAMACHY observations show good agreement. In particular, the strength and interannual variability of the wintertime maximum is well captured. This suggests that direct production of NO in the upper mesosphere above 72 km contributes substantially to the so-called energetic particle precipitation indirect effect.

Intercomparison of ozone profile measurements from ASUR, SCIAMACHY, MIPAS, OSIRIS, and SMR

The airborne submillimeter radiometer ( ASUR) was deployed onboard the Falcon research aircraft during the scanning imaging absorption spectrometer for atmospheric cartography ( SCIAMACHY) validation and utilization experiment ( SCIAVALUE) and the European polar stratospheric cloud and lee wave experiment ( EuPLEx) campaigns. A large number of ozone profile measurements were performed over a latitude band spanning from 5 degrees S to 80 degrees N in September 2002 and February/March 2003 during the SCIAVALUE and around the northern polar latitudes in January/February 2003 during the EuPLEx. Both missions amassed an ample microwave ozone profile data set that is used to make quantitative comparisons with satellite measurements in order to assess the quality of the satellite retrievals. In this paper, the ASUR ozone profile measurements are compared with measurements from SCIAMACHY and Michelson interferometer for passive atmospheric sounding ( MIPAS) on Environmental Satellite and optical spectrograph and infrared imager system ( OSIRIS) and submillimeter radiometer ( SMR) on the Odin satellite. The cross comparisons with the criterion that the ASUR measurements are performed within +/- 1000 km and +/- 6 hrs of the satellite observations show a good agreement with all the four satellite sensors. The differences in data values are the following: -4 to +8% for ASUR-SCIAMACHY ( operational product, v2.1), within +/- 15% for ASUR-SCIAMACHY ( scientific product, v1.62), up to +6% for ASUR-MIPAS ( operational product v4.61) and ASUR- MIPAS ( scientific product v1-O(3)-1), up to 17% for ASUR- OSIRIS ( v012), and -6 to 17% for ASUR- SMR ( v222) between the 20- and 40- km altitude range depending on latitude. Thus, the intercomparisons provide important quantitative information about the quality of the satellite ozone profiles, which has to be considered when using the data for scientific analyses.

Model studies of short-term variations induced in trace gases by particle precipitation in the mesosphere and lower thermosphere

The 3-dimensional global chemistry and transport model (3dCTM) was used to investigate NO, OH, and O3 from January 2002 to May 2010 between 60 km and 133 km. Their daytime and nighttime mean zonal means (55°-75° geomagnetic latitude) were analyzed with respect to short-term variations associated with particle precipitation. The corresponding ionization rates were derived from the 3-dimensional atmospheric ionization module Osnabruck (AIMOS), which is based on particle flux measurements. The trace gas variations with respect to their background were investigated by using a superposed epoch analysis. The 27 day signature associated with particle precipitation is found in NO, while it is only indicated in OH and O3 during winter. A varying solar spectrum associated with the 11 year solar cycle causes modifications of this signal up to 10% while the main patterns are conserved. Published observations show a clear 27 day signal, qualitatively agreeing with the model results at altitudes >70 km except for O3 in Northern Hemisphere winter. Further differences occur with respect to the magnitude of the trace gas variations, primarily attributed to the different trace gas background and dynamical variations of the background atmosphere. Absolute OH variations are overestimated by the 3dCTM during winter, while the opposite is true for O3. These differences might originate from an unknown offset in AIMOS, incorrect chemical reaction rates, a different background of H2O and O3, and the model dynamics. However, their non-linear relationship and their altitude of largest response are qualitatively captured in Southern Hemisphere winter.

SCIAMACHY’s View of the Changing Earth’s Environment

Since August 2002 SCIAMACHY delivers a wealth of high-quality data permitting to study the status of the Earth’s atmosphere. Enhanced concentrations of greenhouse gases are identified as the major source of global warming and their atmospheric concentrations are increasing. SCIAMACHY monitors the most prominent species such as CO2, CH4 and water vapour, the latter including isotope variants. Further anthropogenic impacts on the troposphere occur by emission of reactive trace gases contributing to pollution and affecting air quality. With SCIAMACHY their global, regional and even local signatures can be detected. Long-term analyses document how the emissions of NO2, SO2, HCHO, CHOCHO and CO evolve with time. In addition, the halogen cycle of polar BrO and IO, both of natural origin, is studied. The stratosphere is the layer where public interest in the Earth’s atmosphere has begun to grow with the detection of the ozone hole in the mid-1980s. Until the mid-1990s a steady decrease has been observed in the ozone abundance. The most striking feature is the massive loss of stratospheric ozone over Antarctica during each southern spring. In order to detect possible signs of recovery, SCIAMACHY contributes to the continuous monitoring of the ozone layer, the ozone hole, Polar Stratospheric Clouds (PSC) and species impacting the ozone chemistry such as NO2, OClO and BrO. A much more poorly explored region is the mesosphere and lower thermosphere, which forms the transition between interplanetary space and the terrestrial atmosphere. This region is dominated by extraterrestrial impacts as well as couplings to the lower atmosphere. With SCIAMACHY’s limb viewing capabilities Noctilucent Clouds (NLC) are studied providing insight into generation and depletion mechanisms. At times of strong solar activity, SCIAMACHY measurements reveal how the chemistry of the upper atmosphere is disturbed. By analysis of emission lines in SCIAMACHY spectra the composition of the thermosphere above 100 km can be studied. SCIAMACHY is the first instrument to globally observe the metal layers in the upper mesosphere/lower thermosphere (MLT) region. When applying appropriate retrieval techniques it is meanwhile possible to derive vegetation information over land and phytoplankton characteristics in the oceans from SCIAMACHY data. Finally SCIAMACHY even has proven useful in planetary science by measuring spectra of our solar system neighbour Venus.

Arctic ozone depletion in 2002–2003 measured by ASUR and comparison with POAM observations

We present ozone loss estimated from airborne measurements taken during January-February and March in the Arctic winter 2002/2003. The first half of the winter was characterized by unusually cold temperatures and the second half by a major stratospheric sudden warming around 15-18 January 2003. The potential vorticity maps show a vortex split in the lower stratosphere during the major warming (MW) in late January and during the minor warming in mid-February due to wave 1 amplification. However, the warming can be termed as a vortex displacement event as there was no vortex split during the MW period at 10 hPa. Very low temperatures, large areas of polar stratospheric clouds (PSCs), and high chlorine activation triggered significant ozone loss in the early winter, as the vortex moved to the midlatitude regions. The ozone depletion derived from the ASUR measurements sampled inside the vortex, in conjunction with the Mimosa-Chim model tracer, shows a maximum of 1.3 +/- 0.2 ppmv at 450-500 K by late March. The partial column loss derived from the ASUR ozone profiles reaches up to 61 +/- 4 DU in 400-550 K in the same period. The evolution of ozone and ozone loss assessed from the ASUR measurements is in very good agreement with POAM observations. The reduction in ozone estimated from the POAM measurements shows a similar maximum of 1.3 +/- 0.2 ppmv at 400-500 K or 63 +/- 4 DU in 400-550 K in late March. Our study reveals that the Arctic winter 2002/2003 was unique as it had three minor warmings and a MW, yet showed large loss in ozone. No such feature was observed in any other Arctic winter in the 1989-2010 period. In addition, an unusually large ozone loss in December, around 0.5 +/- 0.2 ppmv at 450-500 K or 12 +/- 1 DU in 400-550 K, was estimated for the first time in the Arctic. A careful and detailed diagnosis with all available published results for this winter exhibits an average ozone loss of 1.5 +/- 0.3 ppmv at 450-500 K or 65 +/- 5 DU in 400-550 K by the end of March, which exactly matches the ozone depletion derived from the ASUR, POAM and model data. The early ozone loss together with considerable loss afterwards put the warm Arctic winter 2002/2003 amongst the moderately cold winters in terms of the significance of the ozone loss.