scholarly journals Spatio-temporal variations of HNO<sub>3</sub> total column from 9 years of IASI measurements – A driver study

2017 ◽  
Author(s):  
Gaétane Ronsmans ◽  
Catherine Wespes ◽  
Daniel Hurtmans ◽  
Cathy Clerbaux ◽  
Pierre-François Coheur
Keyword(s):  
Time Series ◽  
Polar Vortex ◽  
Temporal Variations ◽  
P Value ◽  
Spatial And Temporal Variability ◽  
Quasi Biennial Oscillation ◽  
Explanatory Variables ◽  
Multivariate Enso Index ◽  
Spatio Temporal ◽  
Stratospheric Clouds

Abstract. This study aims at understanding the spatial and temporal variability of HNO3 total columns in terms of explanatory variables. To achieve this, multiple linear regressions are used to fit satellite-derived time series of HNO3 daily averaged total columns. First, an analysis of the IASI 9-year time series (2008–2016) is conducted based on various equivalent latitude bands. The strong and systematic denitrification of the southern polar stratosphere is observed very clearly. It is also possible to distinguish, within the polar vortex, three regions wich are differently affected by the denitrification. Three exceptional denitrification episodes in 2011, 2014 and 2016 are also observed in the northern hemisphere, due to unusually low arctic temperatures. The time series are then fitted by multivariate regressions to identify what variables are responsible for HNO3 variability in global distributions and time series, and to quantify their respective influence. Out of an ensemble of proxies (annual cycle, solar flux, quasi-biennial oscillation, multivariate ENSO index, Arctic and Antarctic oscillations and volume of polar stratospheric clouds), only the ones defined as significant (p-value 

scholarly journals Spatio-temporal variations of nitric acid total columns from 9 years of IASI measurements – a driver study

2018 ◽  
Vol 18 (7) ◽  
pp. 4403-4423 ◽  
Author(s):  
Gaétane Ronsmans ◽  
Catherine Wespes ◽  
Daniel Hurtmans ◽  
Cathy Clerbaux ◽  
Pierre-François Coheur
Keyword(s):  
Time Series ◽  
Temporal Variations ◽  
Major Influence ◽  
P Value ◽  
Spatial And Temporal Variability ◽  
Good Representation ◽  
Polar Regions ◽  
Polar Stratospheric Clouds ◽  
Quasi Biennial Oscillation ◽  
Stratospheric Clouds

Abstract. This study aims to understand the spatial and temporal variability of HNO3 total columns in terms of explanatory variables. To achieve this, multiple linear regressions are used to fit satellite-derived time series of HNO3 daily averaged total columns. First, an analysis of the IASI 9-year time series (2008–2016) is conducted based on various equivalent latitude bands. The strong and systematic denitrification of the southern polar stratosphere is observed very clearly. It is also possible to distinguish, within the polar vortex, three regions which are differently affected by the denitrification. Three exceptional denitrification episodes in 2011, 2014 and 2016 are also observed in the Northern Hemisphere, due to unusually low arctic temperatures. The time series are then fitted by multivariate regressions to identify what variables are responsible for HNO3 variability in global distributions and time series, and to quantify their respective influence. Out of an ensemble of proxies (annual cycle, solar flux, quasi-biennial oscillation, multivariate ENSO index, Arctic and Antarctic oscillations and volume of polar stratospheric clouds), only the those defined as significant (p value < 0.05) by a selection algorithm are retained for each equivalent latitude band. Overall, the regression gives a good representation of HNO3 variability, with especially good results at high latitudes (60–80 % of the observed variability explained by the model). The regressions show the dominance of annual variability in all latitudinal bands, which is related to specific chemistry and dynamics depending on the latitudes. We find that the polar stratospheric clouds (PSCs) also have a major influence in the polar regions, and that their inclusion in the model improves the correlation coefficients and the residuals. However, there is still a relatively large portion of HNO3 variability that remains unexplained by the model, especially in the intertropical regions, where factors not included in the regression model (such as vegetation fires or lightning) may be at play.

scholarly journals Spatial Variability and Detection Levels for Chlorophyll-a Estimates in High Latitude Lakes Using Landsat Imagery

2020 ◽  
Vol 12 (18) ◽  
pp. 2898
Author(s):  
Filipe Lisboa ◽  
Vanda Brotas ◽  
Filipe Duarte Santos ◽  
Sakari Kuikka ◽  
Laura Kaikkonen ◽  
...  
Keyword(s):  
Time Series ◽  
Chlorophyll A ◽  
Spatial Resolution ◽  
High Latitude ◽  
Trophic State ◽  
Linear Models ◽  
P Value ◽  
Spatial And Temporal Variability ◽  
Eutrophic Lakes ◽  
Long Time

Monitoring lakes in high-latitude areas can provide a better understanding of freshwater systems sensitivity and accrete knowledge on climate change impacts. Phytoplankton are sensitive to various conditions: warmer temperatures, earlier ice-melt and changing nutrient sources. While satellite imagery can monitor phytoplankton biomass using chlorophyll a (Chl) as a proxy over large areas, detection of Chl in small lakes is hindered by the low spatial resolution of conventional ocean color satellites. The short time-series of the newest generation of space-borne sensors (e.g., Sentinel-2) is a bottleneck for assessing long-term trends. Although previous studies have evaluated the use of high-resolution sensors for assessing lakes’ Chl, it is still unclear how the spatial and temporal variability of Chl concentration affect the performance of satellite estimates. We discuss the suitability of Landsat (LT) 30 m resolution imagery to assess lakes’ Chl concentrations under varying trophic conditions, across extensive high-latitude areas in Finland. We use in situ data obtained from field campaigns in 19 lakes and generate remote sensing estimates of Chl, taking advantage of the long-time span of the LT-5 and LT-7 archives, from 1984 to 2017. Our results show that linear models based on LT data can explain approximately 50% of the Chl interannual variability. However, we demonstrate that the accuracy of the estimates is dependent on the lake’s trophic state, with models performing in average twice as better in lakes with higher Chl concentration (>20 µg/L) in comparison with less eutrophic lakes. Finally, we demonstrate that linear models based on LT data can achieve high accuracy (R2 = 0.9; p-value < 0.05) in determining lakes’ mean Chl concentration, allowing the mapping of the trophic state of lakes across large regions. Given the long time-series and high spatial resolution, LT-based estimates of Chl provide a tool for assessing the impacts of environmental change.

scholarly journals Large Scale Solar Magnetic Fields: Temporal Variations

2004 ◽  
Vol 219 ◽  
pp. 552-556 ◽  
Author(s):  
R. Knaack ◽  
J. O. Stenflo
Keyword(s):  
Magnetic Field ◽  
Time Series ◽  
Large Scale ◽  
Solar Magnetic Field ◽  
Temporal Variations ◽  
Solar Photosphere ◽  
Solar Cycles ◽  
Radial Magnetic Field ◽  
Quasi Biennial Oscillation ◽  
Harmonic Decomposition

We have investigated the temporal evolution of the solar magnetic field during solar cycles 20, 21 and 22 by means of spherical harmonic decomposition and subsequent time series analysis. A 33 yr and a 25 yr time series of daily magnetic maps of the solar photosphere, recorded at the Mt. Wilson and NSO/Kitt Peak observatories respectively, were used to calculate the spherical coefficients of the radial magnetic field. Fourier and wavelet analysis were then applied to deduce the temporal variations. We compare the results of the two datasets and present examples of zonal modes which show significant variations, e. g. with a period of approx. 2.0—2.5 years. We provide evidence that this quasi-biennial oscillation originates mainly from the southern hemisphere. Furthermore, we show that low degree modes with odd l — m exhibit periods of 29.2 and 28.1 days while modes with even l — m show a dominant period of 26.9 days. A resonant modal structure of the solar magnetic field (apart from the 22 yr cycle) has not been found.

scholarly journals Spatio-temporal variations in soil hydrology of a typical semiarid sand-meadow-desert landscape

2011 ◽  
Vol 8 (1) ◽  
pp. 1895-1928 ◽  
Author(s):  
L. Duan ◽  
T. Liu ◽  
X. Wang ◽  
G. Wang ◽  
L. Ma ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Land Cover ◽  
Physicochemical Properties ◽  
Fine Particles ◽  
Temporal Variations ◽  
P Value ◽  
Horqin Sandy Land ◽  
Sandy Land ◽  
Spatio Temporal ◽  
Semiarid Land

Abstract. A good understanding of the interrelations between land cover alteration and changes in hydrologic conditions (e.g., soil moisture) as well as soil physicochemical properties (e.g., fine particles and nutrients) is crucial for maintaining the fragile hydrologic and environmental conditions of semiarid land, such as the Horqin Sandy Land in China, but is lacking in existing literature. The objectives of this study were to examine: (1) spatio-temporal variations of soil moisture and physicochemical properties in semiarid land; and (2) how those variations are influenced by land cover alteration. Using the data collected in a 9.71 km2 well-instrumented area of the Horqin Sandy Land, this study examined by visual examination and statistical analyses the spatio-temporal variations of soil moisture and physicochemical properties. The results indicated that for the study area, the soil moisture and physicochemical properties were dependent on local topography, soil texture, vegetation density, and human activity. Long-term reclamation for agriculture was found to reduce soil moisture by over 23% and significantly (p-value < 0.05) lower the contents of soil organic matter, fine particles, and nutrients.

scholarly journals Multidecadal variations of the effects of the Quasi-Biennial Oscillation on the climate system

2016 ◽  
Vol 16 (24) ◽  
pp. 15529-15543 ◽  
Author(s):  
Stefan Brönnimann ◽  
Abdul Malik ◽  
Alexander Stickler ◽  
Martin Wegmann ◽  
Christoph C. Raible ◽  
...  
Keyword(s):  
Time Series ◽  
Climate Model ◽  
Surface Air Temperature ◽  
Polar Vortex ◽  
Boreal Winter ◽  
Mean Flow ◽  
Quasi Biennial Oscillation ◽  
Large Variability ◽  
Model Simulations ◽  
Biennial Oscillation

Abstract. Effects of the Quasi-Biennial Oscillation (QBO) on tropospheric climate are not always strong or they appear only intermittently. Studying them requires long time series of both the QBO and climate variables, which has restricted previous studies to the past 30–50 years. Here we use the benefits of an existing QBO reconstruction back to 1908. We first investigate additional, newly digitized historical observations of stratospheric winds to test the reconstruction. Then we use the QBO time series to analyse atmospheric data sets (reconstructions and reanalyses) as well as the results of coupled ocean–atmosphere–chemistry climate model simulations that were forced with the reconstructed QBO. We investigate effects related to (1) tropical–extratropical interaction in the stratosphere, wave–mean flow interaction and subsequent downward propagation, and (2) interaction between deep tropical convection and stratospheric flow. We generally find weak connections, though some are statistically significant over the 100-year period and consistent with model results. Apparent multidecadal variations in the connection between the QBO and the investigated climate responses are consistent with a small effect in the presence of large variability, with one exception: the imprint on the northern polar vortex, which is seen in recent reanalysis data, is not found in the period 1908–1957. Conversely, an imprint in Berlin surface air temperature is only found in 1908–1957 but not in the recent period. Likewise, in the model simulations both links tend to appear alternatingly, suggesting a more systematic modulation due to a shift in the circulation, for example. Over the Pacific warm pool, we find increased convection during easterly QBO, mainly in boreal winter in observation-based data as well as in the model simulations, with large variability. No QBO effects were found in the Indian monsoon strength or Atlantic hurricane frequency.

scholarly journals Spatio-temporal variations of NO<sub>y</sub> species in the northern latitudes stratosphere measured with the balloon-borne MIPAS instrument

2009 ◽  
Vol 9 (4) ◽  
pp. 1151-1163 ◽  
Author(s):  
A. Wiegele ◽  
A. Kleinert ◽  
H. Oelhaf ◽  
R. Ruhnke ◽  
G. Wetzel ◽  
...  
Keyword(s):  
Continuous Measurement ◽  
Temporal Distribution ◽  
Polar Vortex ◽  
Temporal Variations ◽  
Model Calculations ◽  
Mixing Ratios ◽  
Northern Latitudes ◽  
Photolysis Rates ◽  
Spatio Temporal ◽  
Good Agreement

Abstract. This paper presents the spatio-temporal distribution of NOy species at altitudes between 14 and 31 km as measured with the MIPAS-B instrument on the morning of 21 March 2003 in northern Scandinavia. At lower altitudes (below about 22 km), temperature variations, the distribution of ClONO2, and the tracer N2O reveal the dynamics through the edge of the late arctic polar vortex. At higher altitudes, continuous measurement before, during, and after sunrise provides information about photochemistry illustrating the evolution of the photochemically active gases NO2 and N2O5 around sunrise. The measured temporal evolution of NO2 and N2O5 is compared to box modelling that is run along backward calculated trajectories. While the comparison of measured and modelled N2O5 reveals significant differences, there is a good agreement between the model and observations for NO2 in terms of volume mixing ratios but the simulated decrease shortly after sunrise is underestimated compared to the measurements. The differences are attributed to the photolysis rates used in the box model calculations.

scholarly journals Multidecadal Variations of the Effects of the Quasi-Biennial Oscillation on the Climate System

2016 ◽  
Author(s):  
Stefan Brönnimann ◽  
Abdul Malik ◽  
Alexander Stickler ◽  
Martin Wegmann ◽  
Christoph C. Raible ◽  
...  
Keyword(s):  
Time Series ◽  
Climate Model ◽  
Surface Air Temperature ◽  
Polar Vortex ◽  
Boreal Winter ◽  
Mean Flow ◽  
Quasi Biennial Oscillation ◽  
Large Variability ◽  
Model Simulations ◽  
Biennial Oscillation

Abstract. Effects of the Quasi-Biennial Oscillation (QBO) on tropospheric climate are relatively small or appear only intermittently. Studying them requires long time series of both the QBO and climate variables, which has restricted previous studies to the past 30–50 years. Here we use the benefits of an existing QBO reconstruction back to 1908. We first investigate additional, newly digitized historical observations of stratospheric winds to test the reconstruction. Then we use the QBO time series to analyze atmospheric data sets (reconstructions and reanalyses) as well as the results of coupled ocean-atmosphere-chemistry climate model simulations that were forced with the reconstructed QBO. We investigate effects related to (1) tropical-extratropical interaction in the stratosphere, wave-mean flow interaction, and subsequent downward propagation and (2) interaction between deep tropical convection and stratospheric flow. We generally find weak connections, though some are statistically significant over the 100-year period and consistent with model results. Apparent multidecadal variations in the connection between the QBO and the investigated climate responses are consistent with a small effect in the presence of large variability, with one exception: the imprint on the northern polar vortex, which is seen in recent reanalysis data, is not found in the period 1908–1957. Conversely, an imprint in Berlin surface air temperature is only found in 1908–1957, but not in the recent period. In the model simulations, likewise, both links tend to appear alternatingly, suggesting a more systematic modulation. Over the Pacific warm pool, we find increased convection during easterly QBO mainly in boreal winter in observation-based data as well as in the model simulations, with large variability. No QBO effects were found in the Indian monsoon strength or Atlantic hurricane frequency.

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