Rigel Kivi

Dehydration and sedimentation of ice particles in the Arctic stratospheric vortex

Balloon borne frost-point hygrometers and backscatter sondes were launched at Sodankyla, Finland in January and February of 1996. These instruments measure water vapor and the backscatter ratio of light due to polar stratospheric clouds in the Arctic stratospheric vortex. Here we report the results of a hygrometer sonde and a backscatter sonde launched within 3.5 hours of each other on January 22/23. Together these soundings show a strong loss of water vapor due to the formation of ice clouds as a result of record cold temperatures in the Arctic stratosphere. The separation of the upper edge of the layer showing water vapor loss and the upper edge of the PSC layer indicates sedimentation of the ice particle layer, possibly leading to a permanent dehydration in the upper part of the layer exhibiting water vapor loss.

Polar stratospheric cloud threshold temperatures in the 1995-1996 arctic vortex

Balloon-borne backscattersondes have been used to study the relationship between particle scattering and ambient temperature near the vertical edge of arctic polar stratospheric clouds (PSCs) as well as to delineate the cloud type occurrence probability as a function of temperature. The observed typical threshold temperatures as a function of altitude are about1°K warmer than the temperature TSTS expected for rapid growth of supercooled ternary solution aerosols. A more descriptive analysis shows that the threshold temperatures occur over a definable range of temperatures and tend to cluster near, but somewhat warmer than, TSTS. Considering the experimental and theoretical uncertainties, this difference may not be significant. The probability of type Ib PSC occurrence shows a dramatic increase at TSTS±1°K, while for type Ia PSCs the probability is roughly constant at 10% for temperatures below the formation point of nitric acid trihydrate (TNAT).

Middle Atmospheric Water Vapour Radiometer (MIAWARA): Validation and first results of the LAPBIAT Upper Tropospheric Lower Stratospheric Water Vapour Validation Project (LAUTLOS‐WAVVAP) campaign

[1] We present a validation study for the ground-based Middle Atmospheric Water Vapour Radiometer (MIAWARA) operating at 22 GHz. MIAWARA measures the water vapor profile in the range of 20–80 km. The validation was conducted in two phases at different geographical locations. During the first operational period the radiometer was operated at middle latitudes in Bern, Switzerland, and the measured water vapor profiles were compared with the HALOE satellite instrument. The agreement between HALOE and MIAWARA was for most altitudes better than 10%. In the second comparison phase, MIAWARA took part in the Lapland Atmosphere-Biosphere Facility (LAPBIAT) Upper Tropospheric Lower Stratospheric Water Vapour Validation Project (LAUTLOSWAVVAP) campaign in early 2004 in the subarctic region of northern Finland. During this campaign, different balloon sondes probed the water vapor content in the upper troposphere and lower stratosphere. The stratospheric water vapor profiles of the fluorescent hygrometer FLASH-B and the NOAA frost point hygrometer mirror in the range of 20–26 km were compared with the lowermost retrieval points of MIAWARA. The agreement between the balloon instruments and MIAWARA was better than 2% for a total number of 10 comparable flights. This showed the potential of MIAWARA in water vapor retrieval down to 20 km. In addition, the northern Finland MIAWARA profiles were compared with POAM III water vapor profiles. This comparison confirmed the good agreement with the other instruments, and the difference between MIAWARA and POAM was generally less than 8%. Finally, the tipping curve calibration was validated with tipping curve measurements of the All-Sky Multi Wavelength Radiometer (ASMUWARA) which was operated 10 months side by side with MIAWARA. The agreement of the tropospheric opacity derived from these tipping curves agree within 1%.

Climatology of UTLS ozone and the ratio of ozone and potential vorticity over northern Europe

Annual and interannual variations of ozone in the upper troposphere and lower stratosphere (UTLS) region have been studied using ozonesonde data collected between 1994 and 2001 at several northern European stations. The climatology of ozone exhibits a prominent annual cycle in the UTLS region. The observed change in the phase of the annual cycle from late spring-early summer at 500 hPa to spring at 200 hPa and to winter-early spring at 100 hPa shows the switching of the ozone control from photochemical to dynamical. Traces of interannual variation in the lower stratosphere are seen not only in the upper troposphere but also in the middle troposphere (not necessarily always) indicating the dynamical influence on tropospheric ozone budget. Further, the correlation between ozone mixing ratio and potential vorticity (PV) is studied at three northern high-latitude stations. As expected, a good correlation is found in the lower stratosphere, while the correlation is fair in the middle troposphere, except during summer over the European Arctic. This weak correlation at high latitudes indicates the dominance of photochemistry over dynamics in the presence of prolonged hours of solar illumination. The correlation coefficients derived at high latitudes are smaller than those reported at midlatitudes. This could be due to the greater number of tropopause folds at midlatitudes than at high latitudes and this eventually leads to the conclusion that the downward cross-tropopause flux is greater at midlatitudes than at high latitudes. Absence of a significant north-south gradient in the ozone/PV ratio in the lower stratosphere suggests that a single ozone/PV ratio (however, the ratio varies with month) can be used to convert global PV fluxes to ozone fluxes. A few cases of tropopause folds (only one case study is reported in the present study) are selected and studied in detail with the help of a very high frequency radar and meteorological analysis. The ratio between ozone and PV for these case studies agrees reasonably well with the climatological ratios.

Yearly cycle of lower tropospheric ozone at the Arctic Circle

Abstract Measurements of tropospheric ozone at three sites at the Arctic Circle in the Finnish Lapland are presented. The variability of ground-level ozone over the diurnal and seasonal cycles in 1992–1993 is discussed for the sites of Oulanka and Pallas. The variability with height and over the annual cycle in 1989–1994 is discussed for the Sodankyld aerological Observatory, which has the longest record on the vertical distribution of ozone in the Nordic region. Seasonally resolved ozone statistics and the differences between the sites are accounted for. At the surface, ozone levels peak in the spring, but they decline rapidly in the early summer (remote area feature) with a 15–30% seasonal difference. The seasonal difference between spring and summer decreases with height in the lower troposphere and at 850 and 700 hPa, the spring maximum continues as high ozone levels in the summer (an anthropogenic feature). At these two levels, the relative differences in ozone between spring and summer were 4% and −1.3 %, respectively. The summertime high ozone levels in the lower troposphere highlight the importance of transport of anthropogenic precursors of ozone for the regional lower troposphere. A three-dimensional trajectory climatology is used for assessing tropospheric transport patterns. Air mass transport occurs from both remote and polluted source regions. The Arctic is the most important source region at the 950 hPa level. With increasing altitude, the contributions of the European and the Atlantic regions become comparable. The evolution of snow cover and surface-based inversions affect the variability of ozone, through variations in the deposition sink strength and the boundary layer stability.

International Arctic Systems for Observing the Atmosphere: An International Polar Year Legacy Consortium

AbstractInternational Arctic Systems for Observing the Atmosphere (IASOA) activities and partnerships were initiated as a part of the 2007–09 International Polar Year (IPY) and are expected to continue for many decades as a legacy program. The IASOA focus is on coordinating intensive measurements of the Arctic atmosphere collected in the United States, Canada, Russia, Norway, Finland, and Greenland to create synthesis science that leads to an understanding of why and not just how the Arctic atmosphere is evolving. The IASOA premise is that there are limitations with Arctic modeling and satellite observations that can only be addressed with boots-on-the-ground, in situ observations and that the potential of combining individual station and network measurements into an integrated observing system is tremendous. The IASOA vision is that by further integrating with other network observing programs focusing on hydrology, glaciology, oceanography, terrestrial, and biological systems it will be possible to under...

Non‐uniform PSC occurrence within the Arctic Polar Vortex

A multi-year dataset of lidar measurements of polar stratospheric clouds (PSCs) from two sites in the Arctic (Sodankyla, 67°N, 27°E, and Ny-Alesund, 79°N, 12°E) has been analyzed with respect to the existence temperature of different PSC types. Due to the location of the measurement sites relative to the polar vortex, their observations are most of the time representative of vortex edge and vortex center conditions, respectively. The comparison of the aerosol lidar measurements with local and trajectory temperatures reveals that PSC occurrence is favored at the edge of the Arctic polar vortex. One possibility discussed here is a differential distribution of water vapor that could be responsible for the non-uniform threshold temperatures and thus differential PSC occurrence within the polar vortex.

Global land mapping of satellite-observed CO2 total columns using spatio-temporal geostatistics

ABSTRACT This study presents an approach for generating a global land mapping dataset of the satellite measurements of CO2 total column (XCO2) using spatio-temporal geostatistics, which makes full use of the joint spatial and temporal dependencies between observations. The mapping approach considers the latitude-zonal seasonal cycles and spatio-temporal correlation structure of XCO2, and obtains global land maps of XCO2, with a spatial grid resolution of 1° latitude by 1° longitude and temporal resolution of 3 days. We evaluate the accuracy and uncertainty of the mapping dataset in the following three ways: (1) in cross-validation, the mapping approach results in a high correlation coefficient of 0.94 between the predictions and observations, (2) in comparison with ground truth provided by the Total Carbon Column Observing Network (TCCON), the predicted XCO2 time series and those from TCCON sites are in good agreement, with an overall bias of 0.01 ppm and a standard deviation of the difference of 1.22 ppm and (3) in comparison with model simulations, the spatio-temporal variability of XCO2 between the mapping dataset and simulations from the CT2013 and GEOS-Chem are generally consistent. The generated mapping XCO2 data in this study provides a new global geospatial dataset in global understanding of greenhouse gases dynamics and global warming.

Thin Film Capacitive Sensors

Achievements in microtechnology have encouraged the development of a large variety of very small humidity sensors for miscellaneous applications to measure the water vapour content in gaseous systems. Today, more than 75 % of these miniaturised humidity sensors in the market use a capacitive technique (Rittersma 2002). Most of these capacitive sensors are based on dielectric changes of thin films upon water vapour uptake as a measure of the water vapour content. The porous polymer material acts as a hydroactive sponge whereby the water molecules within the polymer material are in thermodynamic equilibrium with the gas phase, i.e. the rate of adsorption of molecules onto the surface is exactly counterbalanced by the rate of desorption of molecules into the gas phase (Anderson 1995). The water adhesion is characterized by physical hydrogen bonds through the “weak” Van der Waals interaction of water molecules with the hydrophilic groups of the polymer molecules (Matsuguchi et al. 1998, e.g.). The capacitive thin-film moisture sensor responds to changes of relative, rather than absolute humidity in the surrounding air as well as to changes of temperature. It is, therefore, commonly calibrated in terms of relative humidity (RH). The response time of the humidity sensor is dependent on the polymer’s ability to adsorb and desorb water vapour and on the sensor design, whereby it is strongly dependent on the temperature of the sensor. The sensor is sensitive to chemical contamination by either additional bonding of the non-water molecules or reducing the ability of the polymer to adsorb water molecules, which may cause either a dry bias or reduce the sensitivity of the sensor. The best known meteorological application is the Humicap sensing element developed by Vaisala (Finland) in 1970’s (Salasmaa and Kostamo1975), which is being used on their radiosondes since 1980. Based on thin-film technology the sensor consists of a hydroactive polymer film as dielectric between two electrodes applied on a

Evolution of the Arctic stratospheric aerosol mixing ratio measured with balloon-borne aerosol backscatter sondes for years 1988–2000

Balloon-borne aerosol backscatter measurements were made at 12 Arctic stations as part of a polar stratospheric cloud study. The record starts in 1988, which is well before the eruption of Mount Pinatubo in the beginning of June 1991, and continues to 2000. These measurements provide absolutely calibrated in situ detection of atmospheric aerosols with simultaneous measurements of pressure, temperature, relative humidity, and O3 partial pressure. The instrument is also capable of operating during cloudy conditions, which may be considered as an advantage compared with lidar measurements. Even though backscatter soundings represent the state of the atmosphere at the sounding time and site, we demonstrate here that with a limited, homogeneous set of measurements it is possible to effectively study the time development of atmospheric aerosol loading. The initial aim of the study has been to define the general features of aerosol distribution in the Arctic winter troposphere and stratosphere and then to document the perturbation in the lower stratospheric aerosols caused by the eruption of Mount Pinatubo and, in addition, to infer the background state of lower stratospheric aerosol loading during the pre- and post-Pinatubo conditions. Our measurements suggest that the e-folding time for the decaying volcanic aerosol intrusion was ∼0.7 year and the full recovery of the Arctic lower stratosphere from the Mount Pinatubo perturbation was roughly 5 years.