5 research outputs found
Interannual variability in the gravity wave drag – vertical coupling and possible climate links
Gravity wave drag (GWD) is an important driver of the middle
atmospheric dynamics. However, there are almost no observational
constraints on its strength and distribution (especially
horizontal). In this study we analyze orographic GWD (OGWD) output
from Canadian Middle Atmosphere Model simulation with specified
dynamics (CMAM-sd) to illustrate the interannual variability in the
OGWD distribution at particular pressure levels in the stratosphere
and its relation to major climate oscillations. We have found
significant changes in the OGWD distribution and strength depending
on the phase of the North Atlantic Oscillation (NAO), quasi-biennial
oscillation (QBO) and El Niño–Southern Oscillation. The
OGWD variability is shown to be induced by lower-tropospheric wind
variations to a large extent, and there is also significant
variability detected in near-surface momentum fluxes. We argue
that the orographic gravity waves (OGWs) and gravity waves (GWs) in general can be
a quick mediator of the tropospheric variability into the
stratosphere as the modifications of the OGWD distribution can
result in different impacts on the stratospheric dynamics during
different phases of the studied climate oscillations.Grantová Agentura České Republiky | Ref. 16-01562JSecretaría de Estado de Investigación, Desarrollo e Innovación | Ref. CGL2015-71575-PGrantová Agentura České Republiky | Ref. 18-01625
Revisiting internal gravity waves analysis using GPS RO density profiles: comparison with temperature profiles and application for wave field stability study
We revise selected findings regarding the utilization of Global
Positioning System radio occultation (GPS RO) density profiles for
the analysis of internal gravity waves (IGW), introduced by
Sacha et al. (2014). Using various GPS RO datasets, we show that the
differences in the IGW spectra between the dry-temperature and
dry-density profiles that were described in the previous study as
a general issue are in fact present in one specific data version
only. The differences between perturbations in the temperature and
density GPS RO profiles do not have any physical origin, and there is
not the information loss of IGW activity that was suggested in
Sacha et al. (2014). We investigate the previously discussed question
of the temperature perturbations character when utilizing GPS RO
dry-temperature profiles, derived by integration of the hydrostatic
balance. Using radiosonde profiles as a proxy for GPS RO, we provide
strong evidence that the differences in IGW perturbations between
the real and retrieved temperature profiles (which are based on the
assumption of hydrostatic balance) include a significant
nonhydrostatic component that is present sporadically and might be
either positive or negative. The detected differences in related
spectra of IGW temperature perturbations are found to be mostly
about ±10 %. The paper also presents a detailed study on the utilization of GPS
RO density profiles for the characterization of the wave field
stability. We have analyzed selected stability parameters derived
from the density profiles together with a study of the vertical
rotation of the wind direction. Regarding the Northern Hemisphere
the results point to the western border of the Aleutian high, where
potential IGW breaking is detected. These findings are also
supported by an analysis of temperature and wind velocity
profiles. Our results confirm advantages of the utilization of the
density profiles for IGW analysis.Grantová Agentura České Republiky | Ref. 16-01562JMinisterstvo Školství, Mládeže a Tělovýchovy | Ref. 7AMB16AT021OeAD-GmbH | Ref. CZ 06/2016Ministerio de Ciencia e Innovación | Ref. CGL2015-71575-
Stratospheric contraction caused by increasing greenhouse gases
Rising emissions of anthropogenic greenhouse gases (GHG) have led to tropospheric warming and stratospheric cooling over recent decades. As a thermodynamic consequence, the troposphere has expanded and the rise of the tropopause, the boundary between the troposphere and stratosphere, has been suggested as one of the most robust fingerprints of anthropogenic climate change. Conversely, at altitudes above ∼55 km (in the mesosphere and thermosphere) observational and modeling evidence indicates a downward shift of the height of pressure levels or decreasing density at fixed altitudes. The layer in between, the stratosphere, has not been studied extensively with respect to changes of its global structure. Here we show that this atmospheric layer has contracted substantially over the last decades, and that the main driver for this are increasing concentrations of GHG. Using data from coupled chemistry-climate models we show that this trend will continue and the mean climatological thickness of the stratosphere will decrease by 1.3 km following representative concentration pathway 6.0 by 2080. We also demonstrate that the stratospheric contraction is not only a response to cooling, as changes in both tropopause and stratopause pressure contribute. Moreover, its short emergence time (less than 15 years) makes it a novel and independent indicator of GHG induced climate change
KDD in Telecommunications
We present an application of some KDD methods in the telecommunication domain. This paper extends the results from our earlier work [8] where a first-order logic rule was discovered that identified the origin of redirected calls and this rule was used to discover some typical transferring schemes suitable for automation. Here we use this redirection-rule for data visualization which provides a useful insight into the data that allows us to formulate a refined ILP discovery task which is solved more effectively and uses richer expressive means than in [8]. We also show a simple propositionallearning experiment for a comparison with the ILP results. 1
Predictive Model of Heart Operation Result-Built on Merged National Registry on Cardiovascular Interventions of MEDICON Center.
Available from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi