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The Tibetan Plateau (TP) contains the largest amount of snow outside the polar regions and is the source of many major rivers in Asia. An accurate long-range (i.e. seasonal) meteorological forecast is of great importance for this region. SEAS5 provides global long-range meteorological forecasts including over the TP. However, SEAS5 assimilating IMS snow data only below 1500m altitude may affect its forecast skill for this region. To investigate the impacts of snow assimilation and dynamical downscaling on temperature and precipitation forecasts, twin ensemble reforecasts initialized with and without snow assimilation above 1500m altitude over the TP for spring and summer 2018 are conducted, and are further downscaled by WRF. The results show that the reforecasts without snow assimilation underestimate daily temperature over the TP, which are consistently improved after snow assimilation in the spring. However, the positive biases between the precipitation reforecasts and satellite observations worsen in the east TP. Compared to the experiment without snow assimilation, the snow assimilation experiment significantly increases temperature and precipitation for the east TP and around the longitude 95ºE. The higher temperature after snow assimilation, in particular the cold bias reduction after initialization, can be attributed to the effects of a more realistic, decreased snowpack, providing favourable conditions for generating more precipitation. Overall, snow assimilation can improve seasonal forecasts through the interaction between land surface and atmosphere. Moreover, the convection-permitting dynamical downscaling further decreases the biases of seasonal forecasts, as more accurate physical processes can be resolved at this scale., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The Tibetan Plateau (TP) has recently been polluted by strong anthropogenic emissions from South Asia. However, the mechanisms controlling the atmospheric circulations conducive to the aerosol transport to the TP are poorly understood. Here we show that winter loss of Arctic sea-ice over the sub-polar North Atlantic boosts the aerosol delivery toward the TP in April, when the aerosol loading is at its climatological maximum, preceding the Indian summer monsoon onset. Low sea-ice in February weakens the polar jet, which leads to the decreased Ural snowpack through a lessened transport of oceanic air. The decreased snowpack persisting to April reinforces the Ural pressure ridge and the East Asian trough, parts of a quasi-stationary Rossby wavetrain extending across Eurasia. These conditions facilitate the enhanced subtropical westerly jet at the southern edge of the TP, invigorating upslope wind combined with mesoscale updrafts wafting upstream emissions over the Himalayas onto the TP., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Nitric oxide (NO) is produced by energetic particle precipitation (EPP) in the mesosphere-lower thermosphere (MLT) region, and during the polar winter, NO can descend to stratospheric altitudes where it destroys ozone. In this paper, we study the general scenario, as opposed to a case study, of NO production in the thermosphere due to energetic particles in the auroral region. We first investigate the relationship between NO production and two geomagnetic indices. The analysis indicates that the auroral electrojet index is a more suitable proxy for EPP-produced NO than the typically used midlatitude Ap index. In order to study the production and downward transport of NO from the lower thermosphere to the mesosphere, we perform superposed epoch analyses on NO observations made by the Solar Occultation For Ice Experiment instrument on board the Aeronomy of Ice in the Mesosphere satellite. The epoch analysis clearly shows the impact of the 27 day solar cycle on NO production. The effect is observed down to an altitude range of about 50 km to 65 km, depending on the hemisphere and the occurrence of stratospheric warmings. Initially, a rapid downward transport is noted during the first 10 days after EPP onset to an altitude of about 80–85 km, which is then followed by a slower downward transport of approximately 1–1.2 km/d to lower mesospheric altitudes in the order of 30 days.

Ozone and methane are chemically active climate-forcing agents affected by climate-chemistry interactions in the atmosphere. Key chemical reactions and processes affecting ozone and methane are presented. It is shown that climate-chemistry interactions have a significant impact on the two compounds. Ozone, which is a secondary compound in the atmosphere, produced and broken down mainly in the troposphere and stratosphre through chemical reactions involving atomic oxygen (O), NOx compounds (NO, NO2), CO, hydrogen radicals (OH, HO2), volatile organic compounds (VOC) and chlorine (Cl, ClO) and bromine (Br, BrO). Ozone is broken down through changes in the atmospheric distribution of the afore mentioned compounds. Methane is a primary compound emitted from different sources (wetlands, rice production, livestock, mining, oil and gas production and landfills).Methane is broken down by the hydroxyl radical (OH). OH is significantly affected by methane emissions, defined by the feedback factor, currently estimated to be in the range 1.3 to 1.5, and increasing with increasing methane emission. Ozone and methane changes are affected by NOx emissions. While ozone in general increase with increases in NOx emission, methane is reduced, due to increases in OH. Several processes where current and future changes have implications for climate-chemistry interactions are identified. It is also shown that climatic changes through dynamic processes could have significant impact on the atmospheric chemical distribution of ozone and methane, as we can see through the impact of Quasi Biennial Oscillation (QBO). Modeling studies indicate that increases in ozone could be more pronounced toward the end of this century. Thawing permafrost could lead to important positive feedbacks in the climate system. Large amounts of organic material are stored in the upper layers of the permafrost in the yedoma deposits in Siberia, where 2 to 5% of the deposits could be organic material. During thawing of permafrost, parts of the organic material that is deposited could be converted to methane. Furthermore, methane stored in deposits under shallow waters in the Arctic have the potential to be released in a future warmer climate with enhanced climate impact on methane, ozone and stratospheric water vapor. Studies performed by several groups show that the transport sectors have the potential for significant impacts on climate-chemistry interactions. There are large uncertainties connected to ozone and methane changes from the transport sector, and to methane release and climate impact during permafrost thawing. © 2014 by the authors.

International audience; During springtime, after the final stratospheric warming, the breakdown of the polar vortex occurs and the summer circulation starts to develop. Air mass intrusions from the tropics can be trapped into the polar latitudes in ananticyclone which can persist until August, advected by summer easterlies. These structures, named “Frozen In Anticyclones” (FrIACs), have already been observed in 2003, 2005 and 2007 by MIPAS-ENVISAT and MLS-AURAinstruments [Lahoz et al., 2007, Manney et al., 2006, Thiéblemont et al., 2011]. These FrIACs lead to an irreversible ozone loss in the tropics.Here, we present a new case of FrIAC occurring in 2011. It is the major one in term of spatial extent since 1960 (see poster #6072). Using MIPAS, MLS tracer species and ozone measurements, we characterize in detail its durationand location in comparison with the previous FrIAC event in 2007. We compared simulations using several CTM models, and evaluated them against measurements. Then we examined the specific chemistry in the core of theFrIAC.

This is an annual report describing the activities and main results of the monitoring programme 'Monitoring of the atmospheric ozone layer and natural ultraviolet radiation' for 2011. 2011 was a year with generally low ozone values above Norway. A clear decrease in the ozone layer above Norway during the period 1979-1997 stopped after 1998 and the ozone layer above Norway seems now to have stabilized.

International audience

International audience; The polar stratosphere in the summertime remains largely unexplored. Dynamical conditions are characterizedby large scale transport and mixing between air masses of higher and lower latitude origins. Understanding theseexchanges is crucial since they have a large impact on the distribution of trace gases and aerosols at polar latitudes,and thus on the stratospheric ozone budget. Ozone change affects the radiative balance, the coupling betweentroposphere and stratosphere, and therefore the climate.In the framework of the International Polar Year, the STRAPOLETE project starts on January 2009. It is associatedwith a successful balloon borne campaign which took place close to Kiruna (Sweeden) from 2 August 2009 to12 September 2009 with eight balloon flights. During this campaign the main characteristics of the summertimearctic stratosphere have been captured. The data set obtained using UV-visible and infrared instruments, remoteand in situ sensing embarked spectrometers provided detailed information on vertical distributions of more thanfifteen chemical tracers and reactive species from the upper troposphere to the middle stratosphere. A number of insitu optical aerosol counters, a UV-visible remote spectrometer for the aerosol extinction and a photopolarimeterprovided information on the nature and size distribution of the stratospheric aerosols. These balloon measurementswith high precision and high vertical resolution are relevant to qualify the dynamical processes occurring in thisregion during summertime, the aerosols variability, the bromine abundance and establish a reference state of thepolar summer stratosphere. The data set is completed by satellite data offering large spatial coverage of the regionof interest. Data analysis is made using relevant dynamical (trajectory calculations, contour advection model) andchemistry-transport models (CTM) to highlight major mechanisms that control the distribution of tracers, aerosolsand bromine.An overview of the project, its scientific issues, the measurement campaign and some balloon measurementsobtained will be presented, as well as preliminary comparisons between measurements and models outputs.

International audience; The polar stratosphere in the summertime remains largely unexplored. Dynamical conditions are characterized by large scale transport and mixing between air masses of higher and lower latitude origins. Understanding these exchanges is crucial since they have a large impact on the distribution of trace gases and aerosols at polar latitudes, and thus on the stratospheric ozone budget. Ozone change affects the radiative balance, the coupling between troposphere and stratosphere, and therefore the climate. In the framework of the International Polar Year, the STRAPOLETE project starts on January 2009. It is associated with a successful balloon borne campaign which took place close to Kiruna (Sweeden) from 2 August 2009 to 12 September 2009 with eight balloon flights. During this campaign the main characteristics of the summertime arctic stratosphere have been captured. The data set obtained using UV-visible and infrared instruments, remote and in situ sensing embarked spectrometers will provide detailed information on vertical distributions of more than fifteen chemical tracers and reactive species from the upper troposphere to the middle stratosphere. A number of in situ optical aerosol counters, a UV-visible remote spectrometer for the aerosol extinction and a photopolarimeter will provide information on the nature and size distribution of the stratospheric aerosols. These balloon measurements with high precision and high vertical resolution are relevant to qualify the dynamical processes occuring in this region during summertime, the aerosols variability, the bromine abundance and establish a reference state of the polar summer stratosphere. The data set is "complete" by satellite data offering large spatial coverage of the region of interest. Data analysis is made using relevant dynamical (trajectory calculations, contour advection model) and chemistry-transport models (CTM) to highlight major mechanisms that controlled the distribution of tracers, aerosols and bromine. An overview of the project, its scientific issues, the measurements obtained will be presented, as well as preliminary results and comparisons between measurements and models outputs.

International audience; The Sub-Millimetre Radiometer (SMR) on board the Odin satellite, launched in February 2001, observes thermal emissions of stratospheric nitric acid (HNO3) originating from the Earth limb in a band centred at 544.6 GHz. Height-resolved measurements of the global distribution of nitric acid in the stratosphere between ~18?45 km (~1.5?60 hPa) were performed approximately on two observation days per week. An HNO3 climatology based on roughly 6 years of observations from August 2001 to December 2007 was created. The study highlights the spatial and seasonal variation of nitric acid in the stratosphere, characterised by a pronounced seasonal cycle at middle and high latitudes with maxima during late fall and minima during spring, strong denitrification in the lower stratosphere of the Antarctic polar vortex during winter (the irreversible removal of NOy by the sedimentation of cloud particles containing HNO3), as well as high quantities of HNO3 formed every winter at high-latitudes in the middle and upper stratosphere. A strong inter-annual variability is observed in particular at high latitudes. A comparison with a stratospheric HNO3 climatology based on UARS/MLS measurements from the 1990s shows a good consistency and agreement of the main morphological features in the potential temperature range ~465 to ~960 K, if the different characteristics of the data sets such as altitude range and resolution are considered.

The EU CANDIDOZ project investigated the chemical and dynamical influences on decadal ozone trends focusing on the Northern Hemisphere. High quality long-term ozone data sets, satellite-based as well as ground-based, and the long-term meteorological reanalyses from ECMWF and NCEP are used together with advanced multiple regression models and atmospheric models to assess the relative roles of chemistry and transport in stratospheric ozone changes. This overall synthesis of the individual analyses in CANDIDOZ shows clearly one common feature in the NH mid latitudes and in the Arctic: an almost monotonic negative trend from the late 1970s to the mid 1990s followed by an increase. In most trend studies, the Equivalent Effective Stratospheric Chlorine (EESC) which peaked in 1997 as a consequence of the Montreal Protocol was observed to describe ozone loss better than a simple linear trend. Furthermore, all individual analyses point to changes in dynamical drivers, such as the residual circulation (responsible for the meridional transport of ozone into middle and high latitudes) playing a key role in the observed turnaround. The changes in ozone transport are associated with variations in polar chemical ozone loss via heterogeneous ozone chemistry on PSCs (polar stratospheric clouds). Synoptic scale processes as represented by the new equivalent latitude proxy, by conventional tropopause altitude or by 250 hPa geopotential height have also been successfully linked to the recent ozone increases in the lowermost stratosphere. These show significant regional variation with a large impact over Europe and seem to be linked to changes in tropospheric climate patterns such as the North Atlantic Oscillation. Some influence in recent ozone increases was also attributed to the rise in solar cycle number 23. Changes from the late 1970s to the mid 1990s were found in a number of characteristics of the Arctic vortex. However, only one trend was found when more recent years are also considered, namely the tendency for cold winters to become colder.

The EU CANDIDOZ project investigated the chemical and dynamical influences on decadal ozone trends focusing on the Northern Hemisphere. High quality long-term ozone data sets, satellite-based as well as ground-based, and the long-term meteorological reanalyses from ECMWF and NCEP are used together with advanced multiple regression models and atmospheric models to assess the relative roles of chemistry and transport in stratospheric ozone changes. This overall synthesis of the individual analyses in CANDIDOZ shows clearly one common feature in the NH mid latitudes and in the Arctic: an almost monotonic negative trend from the late 1970s to the mid 1990s followed by an increase. In most trend studies, the Equivalent Effective Stratospheric Chlorine (EESC) which peaked in 1997 as a consequence of the Montreal Protocol was observed to describe ozone loss better than a simple linear trend. Furthermore, all individual analyses point to changes in dynamical drivers, such as the residual circulation (responsible for the meridional transport of ozone into middle and high latitudes) playing a key role in the observed turnaround. The changes in ozone transport are associated with variations in polar chemical ozone loss via heterogeneous ozone chemistry on PSCs (polar stratospheric clouds). Synoptic scale processes as represented by the new equivalent latitude proxy, by conventional tropopause altitude or by 250 hPa geopotential height have also been successfully linked to the recent ozone increases in the lowermost stratosphere. These show significant regional variation with a large impact over Europe and seem to be linked to changes in tropospheric climate patterns such as the North Atlantic Oscillation. Some influence in recent ozone increases was also attributed to the rise in solar cycle number 23. Changes from the late 1970s to the mid 1990s were found in a number of characteristics of the Arctic vortex. However, only one trend was found when more recent years are also considered, namely the tendency for cold winters to become colder. ISSN:0992-7689 ISSN:0939-4176 ISSN:1432-0576

Årsliste 2002 Bakgrunnen for dette arbeidet er sjøsaltepisoders betydning for vannkvaliteten (surhet og giftighet for fisk) i Vestlandsvassdrag og den sammenhengen det er mellom sjøsaltdeposisjon og uvær. Værforholdene i Europa og Nord-Amerika og dermed en rekke ulike effekter er koplet til den nordatlantiske svingning (NAO). Det var derfor av interesse å undersøke om det også var en sammenheng mellom dette klimatiske mønsteret og vannkvaliteten i vassdrag. Lange vannkjemiske dataserier for både nedbør og vassdrag er tilgjengelige takket være overvåkingsprogrammet for langtransportert forurenset luft og nedbør og effektene i vann og vassdrag. NAO-indekser er tilgjengelige helt tilbake til 1800-tallet. Det er påvist en klar sammenheng mellom sjøsaltdeposisjon, sjøsaltepisoder i vassdrag på Vestlandet og i Nord-Trøndelag og NAO-indeksen. Betydningen av dette for historiske episoder med fiskedød og forsuringsutviklingen framover er diskutert. Direktoratet for naturforvaltning (DN)