Impact of Solar Proton Events and Planetary Wave Activity on Noctilucent Clouds

Noctilucent clouds (NLCs), also known as Polar Mesospheric Clouds (PMCs) are a rare phenomenon observed at polar latitudes during the summer season. These optically thin clouds are situated in the mesopause region at about 83 km altitude. We study the possible impact of solar proton precipitation in the Earth's atmosphere and the behaviour of the noctilucent clouds during the solar proton event. For this purpose we use SBUV/2 (Solar Backscatter Ultraviolet) NLC observations that cover the last 30 years. The proton fluxes measured by GOES (Geostationary Operational Environmental Satellite) cover the same time period. A statistical investigation between solar proton events (SPEs) and a possible depletion of NLCs is aimed at in this work. This is done for both hemispheres separately. It is shown that solar proton events are well correlated with the depletion of NLCs. The majority of SPEs lead to significant reductions in the observed NLC residual albedo and occurrence rate time series. The extraction of the SPE forcing on the NLCs is disturbed by other forcings such as planetary wave activity, causing large scale perturbations in meridional wind circulation which can occur simultaneously. We assume, that therefore the reduction of NLCs albedo and occurrence rate during SPEs due to an increase of temperature in the mesopause region is a combination of several forcings and effects which contribute to the total variation in NLC signal. The last part of the work is dedicated to the possible influence of planetary waves such as the 2-day wave and 5-day wave on the mesopause temperatures at mid and polar latitudes. The planetary wave (PW) signatures retrieved from the SBUV/2 and SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) NLC data are in good agreement with the observed PW signatures in temperature data from MLS (Microwave Limb Sounder). Moreover, since the NLC perturbation is mainly triggered by temperature in the mesopause region, temperature increases at polar latitudes are compared with the peak amplitudes of the PWs activity at mid-latitudes. The 2-day wave activity at mid-latitudes coincides with the temperature pulses at polar latitudes for the seasons 2004/05, 2005/06 and 2006/07. For the seasons 2007/08 and 2008/09 the 5-day wave activity at mid-latitudes is responsible for the temperature pulses at polar latitudes. Peak 2-day wave amplitudes are anti-correlated with the peak 5-day wave amplitudes at mid-latitudes. Comparison of peak amplitudes at polar latitudes show that the peak 5-day wave amplitudes are higher at polar latitudes in comparison to the 2-day wave peak amplitudes at these latitudes except for the January 2005 in the southern hemisphere. A combined forcing on temperature due to the SPE and 2-day wave activity in the summer polar mesopause region can be assumed to be responsible for the warming and massive depletion of NLCs for mid January 2005 in the southern hemisphere

An update on ozone profile trends for the period 2000 to 2016

Ozone profile trends over the period 2000 to 2016 from several merged satellite ozone data sets and from ground-based data measured by four techniques at stations of the Network for the Detection of Atmospheric Composition Change indicate significant ozone increases in the upper stratosphere, between 35 and 48 km altitude (5 and 1 hPa). Near 2 hPa (42 km), ozone has been increasing by about 1.5 % per decade in the tropics (20° S to 20° N), and by 2 to 2.5 % per decade in the 35 to 60° latitude bands of both hemispheres. At levels below 35 km (5 hPa), 2000 to 2016 ozone trends are smaller and not statistically significant. The observed trend profiles are consistent with expectations from chemistry climate model simulations. This study confirms positive trends of upper stratospheric ozone already reported, e.g., in the WMO/UNEP Ozone Assessment 2014 or by Harris et al. (2015). Compared to those studies, three to four additional years of observations, updated and improved data sets with reduced drift, and the fact that nearly all individual data sets indicate ozone increase in the upper stratosphere, all give enhanced confidence. Uncertainties have been reduced, for example for the trend near 2 hPa in the 35 to 60° latitude bands from about ±5 % (2σ) in Harris et al. (2015) to less than ±2 % (2σ). Nevertheless, a thorough analysis of possible drifts and differences between various data sources is still required, as is a detailed attribution of the observed increases to declining ozone-depleting substances and to stratospheric cooling. Ongoing quality observations from multiple independent platforms are key for verifying that recovery of the ozone layer continues as expected

Tropospheric Ozone Assessment Report: Present-day distribution and trends of tropospheric ozone relevant to climate and global atmospheric chemistry model evaluation

The Tropospheric Ozone Assessment Report (TOAR) is an activity of the International Global Atmospheric Chemistry Project. This paper is a component of the report, focusing on the present-day distribution and trends of tropospheric ozone relevant to climate and global atmospheric chemistry model evaluation. Utilizing the TOAR surface ozone database, several figures present the global distribution and trends of daytime average ozone at 2702 non-urban monitoring sites, highlighting the regions and seasons of the world with the greatest ozone levels. Similarly, ozonesonde and commercial aircraft observations reveal ozone’s distribution throughout the depth of the free troposphere. Long-term surface observations are limited in their global spatial coverage, but data from remote locations indicate that ozone in the 21st century is greater than during the 1970s and 1980s. While some remote sites and many sites in the heavily polluted regions of East Asia show ozone increases since 2000, many others show decreases and there is no clear global pattern for surface ozone changes since 2000. Two new satellite products provide detailed views of ozone in the lower troposphere across East Asia and Europe, revealing the full spatial extent of the spring and summer ozone enhancements across eastern China that cannot be assessed from limited surface observations. Sufficient data are now available (ozonesondes, satellite, aircraft) across the tropics from South America eastwards to the western Pacific Ocean, to indicate a likely tropospheric column ozone increase since the 1990s. The 2014–2016 mean tropospheric ozone burden (TOB) between 60˚N–60˚S from five satellite products is 300 Tg ± 4%. While this agreement is excellent, the products differ in their quantification of TOB trends and further work is required to reconcile the differences. Satellites can now estimate ozone’s global long-wave radiative effect, but evaluation is difficult due to limited in situ observations where the radiative effect is greatest

Tropospheric column ozone variability from space: results from the first multi-instrument intercomparison .

International audienceTropospheric ozone is a pollutant detrimental to human health and crop and ecosystem productivity. Tropospheric ozone is also the third most important greenhouse gas (after CO2 and methane), responsible for ~17% of global radiative forcing since 1750. However, the lack of a comprehensive global ozone monitoring network means that ozone’s radiative forcing must be estimated by chemistry-climate models with a large error barsof ± 50% due to model uncertainties (0.40 ± 0.20 W m-2, according to the fifth IPCC assessment report). Improvements to this estimate require an accurate observation- based quantification of the present-day tropospheric ozone burden (TOB), and greater confidence in chemistry-climate model estimates of TOB in pre-industrial times. TOB is the total mass (Tg) of ozone in the troposphere, calculated by summing all of the tropospheric column ozone (TCO) values at every point on Earth. Presently there is one published observation-based estimate of TOB, which comes from the OMI/MLS satellite instruments on NASA’s Aura satellite. Recently, four new satellite products have been developed for measuring TCO and TOB, with two based on the OMI satellite instrument and two based on the IASI satellite instrument. The first intercomparison of these products will soon be published as a component of the Tropospheric Ozone Assessment Report (TOAR). While all five products show the same general tropospheric ozone features across the globe, they differ in absolute TCO quantities and they also differ in terms of decadal trends. The next step is to evaluate all products against the exact same set of in situ ozone observations to gauge the performance of each product in different regions of the world. We will present preliminary results from this evaluation which relies on daily IAGOS commercial aircraft profiles above Frankfurt, Germany and weekly NOAA GMD ozonesonde profiles above Hilo, Hawaii; Trinidad Head, California; and Boulder, Colorado

Overview of the main achievements of the Ozone Climate Change Initiative Project

International audienceAtmospheric ozone is an Essential Climate Variable which impacts the radiation budget of the Earth, interacts with atmospheric dynamics and climate, and influences chemically other radiatively active species. As part of the Ozone Climate Change Initiative (Ozone_cci) project, a large number of ozone data sets have been generated from a full suite of atmospheric chemistry satellite missions. Following a first phase of 3 years during which new and improved algorithms and data products have been demonstrated and assessed against well-defined user requirements, the ongoing second phase of the Ozone_cci concentrates on extending and further improving these data sets with the ambition to realize the full potential of the existing archive of satellite ozone sensors. We present an overview of the main realizations of the project. This covers long-series of consistent ozone columns and profiles derived from nadir UV sensors and the thermal infrared IASI instrument. Also addressed is the generation of a large scale coherent data base of vertically resolved ozone measurements derived from a full suite of limb and occultation sensors, optimised for accuracy in a broad range of altitudes extending from the UT/LS to the mesosphere