Variations of the global sea level pressure (SLP) field reflect atmospheric and oceanic influences and have a profound influence on temperature, precipitation and the global carbon cycle. The impact of various forcing factors on this field was investigated mainly based on numerical simulations. Alternatively, here we identify and quantify the influences of various forcing factors on observational, reanalysis and simulated SLP fields. By applying canonical correlation analysis (CCA) on the aforementioned data sets, we separated and quantified the impact of increase CO 2 concentration, El Niño-Southern Oscillation (ENSO), Atlantic Multidecadal Oscillation (AMO), Arctic Oscillation (AO) and solar forcing on the global SLP field, based on their associations with known footprints on the sea surface temperature (SST). Together, their corresponding SLP spatial structures explain ~ 60% of the observed variance. Whereas the atmospheric CO 2 concentration has the most prominent impact on the global SLP field, explaining 28% of variance, ENSO and AO account for 9% each. The solar forcing and AMO explain 7%, respectively 6% of global SLP variance. Similar spatial structures corresponding to the same forcing factors are identified based on the reanalysis SLP data. CCA applied on simulated SLP fields derived from six CMIP5 model simulations captures only the spatial structures of atmospheric CO 2 concentration, ENSO, AAO and AO. Such a decomposition of the global pressure field based on a linear combination of coupled SST-SLP pairs provide a reference against which one could validate the performance of general circulation models in simulating the lower atmosphere dynamics. KeywordsSea level pressure • Ocean temperature • CO 2 • Internal modes of variability • Solar influence Electronic supplementary material The online version of this article (
We investigate the connections of the North Atlantic and Indian Ocean sectors with Iraq winter/summer temperature and precipitation. Canonical Correlation Analyses (CCAs) are performed in order to identify potential links between Iraq climate and the atmospheric circulation over these two regions. Regression maps of 200 hPa and 500 hPa geopotential height and sea level pressure fields on the time series derived through CCAs are constructed in order to infer the physical mechanisms connecting the North Atlantic and Indian Ocean regions with Iraq climate. The winter temperature in this country is linked with the North Atlantic Scandinavian pattern, whereas the winter precipitation is associated with the North Atlantic Oscillation. In the free atmosphere, the connection with Iraq temperature is provided by Rossby waves, while the winter precipitation is linked to a more zonal structure. At surface, the air advection is a relevant mechanism through which North Atlantic modes appear to affect Iraq climate.
Abstract. Global cloud cover represents a critical component of the climate system, with a considerable impact on the Earth's radiation budget. Small changes in clouds properties have a significant climatological impact because of the feedbacks that they generate, thus it is difficult to simulate the global cloud cover evolution in general circulation models. Observational investigations of cloud processes are constrained either by limited temporal and spatial extension of ground-based measurements or by imperfections in satellite data, like changes in geostationary satellite zenith angle, equatorial crossing time, or calibration. In this study, we used the Empirical Orthogonal Functions method to separate global patterns of total cloud cover variability in two satellite datasets from the International Satellite Cloud Climatology Project and the Pathfinder Atmospheres–Extended projects, each corrected for specific errors, and in the ERA5 Reanalysis. The first two modes explain most of the variance from what could be considered “signal” in both satellite data. Through Canonical Correlation Analysis, they are associated in a physically consistent manner with two different types of El Niño-Southern Oscillation (ENSO), namely the canonical ENSO which manifests itself in the eastern tropical Pacific and the El-Niño Modiki which manifest itself in the central Pacific. This work provides a comprehensive picture of the relationship between global total cloud cover and the tropical Pacific processes and indicates that cloud cover in the Indo-Pacific sector plays a significant role in the Earth radiative budget at interannual to decadal time scales. The similarity of the results across satellite and reanalysis data indicate that the both the observed and reanalysis cloud data sets contain consistent and valuable information related to global climate variability.
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