Petr Šácha

Petr Šácha
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Petr verified their affiliation via an institutional email.
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Petr verified their affiliation via an institutional email.
Charles University in Prague | CUNI · Faculty of Mathematics and Physics

RNDr., Ph.D.
Working on a paper analyzing kinematic mechanisms responsible for the increasing BDC.

About

53
Publications
6,087
Reads
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409
Citations
Introduction
My main research focus is on orographic gravity waves (OGWs) and their representation in global models, on the Brewer-Dobson circulation and stratospheric dynamics and on structural changes of the atmosphere in the course of the climate change. I am leading a GW research group and supervise four students along these research topics. Regarding teaching, I am a guarantor and lecturer of courses at Charles University - Fluid Dynamics and Wave processes in the neutral atmosphere.
Additional affiliations
April 2016 - December 2018
Charles University in Prague
Position
  • PostDoc Position
January 2015 - present
Charles University in Prague
Position
  • PhD Student

Publications

Publications (53)
Article
Full-text available
The Brewer‐Dobson circulation (BDC) characterizes the large‐scale meridional overturning mass circulation influencing the composition of the whole middle atmosphere. The BDC consists of two separate parts—a shallow branch in the lower stratosphere and a deep branch higher in the middle atmosphere. Climate models robustly project the advective BDC p...
Article
Full-text available
A 30-year (1980–2010) climatology of the major variables and terms of the transformed Eulerian-mean (TEM) momentum and thermodynamic equations is constructed by using four global atmospheric reanalyses: the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2); the Japanese 55-year Reanalysis (JRA-55); the European Ce...
Article
Full-text available
Climate models robustly project acceleration of the Brewer‐Dobson circulation (BDC) in response to climate change. However, the BDC trends simulated by comprehensive models are poorly constrained by observations, which cannot even determine the sign of potential trends. Additionally, the changing structure of the troposphere and stratosphere has re...
Article
Full-text available
Orographic gravity waves (OGWs) are an important mechanism for coupling of the free atmosphere with the surface, mediating the momentum and energy transport and influencing the dynamics and circulation especially in the middle-atmosphere. Current global climate models are not able to resolve a large part of the OGW spectrum and hence, OGW effects h...
Preprint
Full-text available
A 30-year (1980–2010) climatology of the major variables and terms of the transformed Eulerian-mean (TEM) momentum and thermodynamic equations is constructed by using four global atmospheric reanalyses, MERRA-2, JRA-55, ERA-Interim, and CFSR. Both the reanalysis ensemble mean (REM) and the differences of each reanalysis from the REM are investigate...
Preprint
Full-text available
Climate models robustly project acceleration of the Brewer-Dobson circulation (BDC) in response to climate change. However, the BDC trends derived from comprehensive models do not fully match observations. Additionally, the changing structure of the troposphere and stratosphere has received increasing attention in recent years and to which extent v...
Article
Full-text available
The climatologies of the stratopause height and temperature in the UA‐ICON model are examined by comparing them to 17‐years (2005–2021) of Microwave Limb Sounder (MLS) observations. In addition, the elevated stratopause (ES) event occurrence, their main characteristics, and driving mechanisms in the UA‐ICON model are examined using three 30‐year ti...
Article
Internal gravity waves (GWs) are ubiquitous in the atmosphere, making significant contributions to the mesoscale motions. Since the majority of their spectrum is unresolved in global circulation models, their effects need to be parameterized. In recent decades GWs have been increasingly studied in high-resolution simulations, which, unlike direct o...
Conference Paper
Full-text available
The gravity waves play a crucial role in driving and shaping the middle atmospheric circulation. The Upper-Atmospheric extension of the ICOsahedral Non-hydrostatic (UA-ICON) general circulation model was recently developed with satisfying performances in both idealized test cases and climate simulations, however the sensitivity of the circulation t...
Preprint
Full-text available
The instability of the Northern Hemisphere polar vortex is mainly caused by the breaking of planetary-scale (Rossby) waves (RWs). However, gravity waves (GWs) may also play an important role in polar vortex preconditioning before breakdown events. Moreover, GWs affect dynamics in the stratosphere by altering the upward propagation of RWs at short t...
Article
Full-text available
Sudden stratospheric warmings (SSWs) are a major mode of variability of the winter stratosphere. In recent years, climate models have improved their ability to simulate SSWs. However, the representation of the frequency and temporal distribution of SSWs in models depends on many factors and remains challenging. The vertical resolution of a model mi...
Article
Full-text available
Plain Language Summary The majority of atmospheric waves are generated near the surface and propagate subsequently upward in the atmosphere. This includes Rossby waves that are resolved in climate models and small‐scale gravity waves (GWs) that commonly have to be parameterized. In the middle atmosphere, the waves eventually break, thereby dissipat...
Article
Full-text available
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 anth...
Article
Four state-of-the-science numerical weather prediction (NWP) models were used to perform mountain wave (MW)-resolving hindcasts over the Drake Passage of a 10-day period in 2010 with numerous observed MW cases. The Integrated Forecast System (IFS) and the Icosahedral Nonhydrostatic (ICON) model were run at Δ x ≈ 9 and 13 km globally. The Weather Re...
Article
Full-text available
Gravity wave (GW) breaking and associated GW drag is not uniformly distributed among latitudes and longitudes. In particular, regions of enhanced GW breaking, so-called GW hotspots, have been identified, major Northern Hemisphere examples being located above the Rocky Mountains, the Himalayas and the East Asian region. These hotspots influence the...
Article
Full-text available
When orographic gravity waves (OGWs) break, they dissipate their momentum and energy and thereby influence the thermal and dynamical structure of the atmosphere. This OGW forcing mainly takes place in the middle atmosphere. It is zonally asymmetric and strongly intermittent. So-called “OGW hotspot regions” have been shown to exert a large impact on...
Article
Full-text available
Tropospheric warming and stratospheric cooling influence the vertical structure of the atmosphere. Numerous studies have analysed the thermal expansion of the troposphere, however, stratospheric cooling reverses the sign of this shift in the middle stratosphere, causing a downward shift in the upper stratosphere and mesosphere. This is a robust fea...
Preprint
Full-text available
Abstract. When orographic gravity waves (OGWs) break, they dissipate their momentum and energy and thereby influence the thermal and dynamical structure of the atmosphere. This OGW forcing mainly takes place in the middle atmosphere. It is zonally asymmetric and strongly intermittent. So-called OGW hotspot regions have been shown to exert a large i...
Article
Full-text available
Energy and momentum deposition from planetary-scale Rossby waves as well as from small-scale gravity waves (GWs) largely control stratospheric dynamics. Interactions between these different wave types, however, complicate the quantification of their individual contribution to the overall dynamical state of the middle atmosphere. In state-of-the-art...
Article
Full-text available
The effects of gravity wave (GW) breaking hotspots in the lower stratosphere, especially the role of their longitudinal distribution, are evaluated through a sensitivity study by using a simplified middle atmosphere circulation model. For the position of the local GW hotspot, we first selected a fixed latitude range between 37.5 and 62.5∘ N and a l...
Article
Full-text available
The effects of gravity wave (GW) breaking hotspots in the lower stratosphere, especially the role of their longitudinal distribution, are evaluated through a sensitivity study by using a simplified middle atmosphere circulation model. For the position of the local GW hotspot, we first selected a fixed latitude range between 37.5 and 62.5° N and a l...
Article
Full-text available
In order to investigate the impact of a locally confined gravity wave (GW) hotspot, a sensitivity study based on simulations of the middle atmosphere circulation during northern winter was performed with a nonlinear, mechanistic, general circulation model. To this end, we selected a fixed longitude range in the East Asian region (120–170∘ E) and a...
Article
Full-text available
Climate model simulations show an acceleration of the Brewer–Dobson circulation (BDC) in response to climate change. While the general mechanisms for the BDC strengthening are widely understood, there are still open questions concerning the influence of the details of the wave driving. Mean age of stratospheric air (AoA) is a useful transport diagn...
Article
Full-text available
In order to investigate the impact of a locally confined gravity wave (GW) hotspot, a sensitivity study based on simulations of the middle atmosphere circulation during northern winter was performed with a nonlinear, mechanistic, global circulation model. To this end, for the hotspot region we selected a fixed longitude range in the East Asian regi...
Article
Full-text available
Climate models consistently predict an acceleration of the Brewer–Dobson circulation (BDC) due to climate change in the 21st century. However, the strength of this acceleration varies considerably among individual models, which constitutes a notable source of uncertainty for future climate projections. To shed more light upon the magnitude of this...
Article
Full-text available
Climate model simulations show a Brewer-Dobson circulation (BDC) acceleration in the course of climate change. While the mechanisms for the BDC strengthening are well understood, there are still open questions concerning its dynamical driving. Mean age of stratospheric air (AoA) is a useful transport diagnostic for accessing changes of the BDC. Ana...
Article
Full-text available
Climate models consistently predict an acceleration of the Brewer-Dobson circulation (BDC) due to climate change in the 21st century. However, the strength of this acceleration varies considerably among individual models, which constitutes a notable source of uncertainty for future climate projections. To shed more light upon the magnitude of this...
Article
Full-text available
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...
Article
Full-text available
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 . 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 th...
Article
Full-text available
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 an...
Conference Paper
Through analysis of mean age of air (AoA), we study the capabilities of the Chemistry Climate Models (CCMs) from the CCMI (Chemistry-Climate Model Initiative) project to simulate transport along the Brewer-Dobson circulation. The reason for the well-known large model spread in stratospheric AoA can be investigated by untangling the effects of the d...
Article
Full-text available
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 previously detected differences in the IGW spectra between dry temperature and density pro...
Article
Full-text available
Analysing GPS radio occultation density profiles, we have recently pointed out a localised area of enhanced gravity wave (GW) activity and breaking in the lower stratosphere of the east Asian–northwestern Pacific (EA/NP) region. With a mechanistic model of the middle and upper atmosphere, experiments are performed to study the possible effect of su...
Article
Full-text available
Analyzing GPS radio occultation density profiles, we have recently pointed out a localized area of enhanced gravity wave (GW) activity and breaking in the lower stratosphere of the Eastern Asia/North-western Pacific (EA/NP) region. With a mechanistic model for the middle and upper atmosphere (MUAM), experiments are performed to study a possible eff...
Poster
Full-text available
With a mechanistic circulation model for the middle atmosphere we performed experimental runs to study the effect of a localized gravity wave (GW) breaking region above the Eastern Asia/North-western Pacific (EA/NP) region on the large-scale circulation and transport. Our results demonstrate an important role of the spatial distribution of GW activ...
Article
Full-text available
We have found a stratospheric area of anomalously low annual cycle amplitude and specific dynamics in the stratosphere over the northeastern Pacific–eastern Asia coastal region. Using GPS radio occultation density profiles from the Formosat Satellite Mission 3/Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMI...
Article
Full-text available
We have found a stratospheric area of anomalously low annual cycle amplitude and specific dynamics in the stratosphere over the Northeastern Pacific/Eastern Asia coastal region. Using GPS radio occultation density profiles from FORMOSAT-3/COSMIC, we have discovered an internal gravity wave activity and breaking hotspot in this region. Conditions su...
Article
Full-text available
This study focusses on the variability of temperature , ozone and circulation characteristics in the stratosphere and lower mesosphere with regard to the influence of the 11-year solar cycle. It is based on attribution analysis using multiple nonlinear techniques (support vector regression , neural networks) besides the multiple linear regression a...
Article
Full-text available
This study focusses on the variability of temperature, ozone and circulation characteristics in the stratosphere and lower mesosphere with regard to the influence of the 11-year solar cycle. It is based on attribution analysis using multiple nonlinear techniques (support vector regression, neural networks) besides the multiple linear regression app...
Poster
Full-text available
We analyse the effect of lower atmosphere gravity wave (GW) regional distributions in the Middle and Upper Atmosphere Model (MUAM). To this end, we compare an artificial GW distribution with more realistic ones obtained from GPS RO measurements as zonal means and horizontal 2D fields. Model results are: • larger differences between the reference ru...
Article
This study focusses on the variability of temperature, ozone and circulation characteristics in the stratosphere and lower mesosphere with regard to the influence of the 11 year solar cycle. It is based on attribution analysis using multiple nonlinear techniques (Support Vector Regression, Neural Networks) besides the traditional linear approach. T...
Article
Full-text available
GPS radio occultation (RO) data have proved to be a great tool for atmospheric monitoring and studies. In the past decade, they were frequently used for analyses of the internal gravity waves in the upper troposphere and lower stratosphere region. Atmospheric density is the first quantity of state gained in the retrieval process and is not burdened...
Article
Full-text available
GPS (Global Positioning System) radio occultation (RO) data proved to be a great tool for atmospheric monitoring and studies. In the recent decade, they were frequently used for analyses of the internal gravity waves in the upper troposphere lower stratosphere region. Atmospheric density is the first quantity of state gained in the retrieval 5 proc...
Article
Full-text available
GPS (Global Positioning System) radio occultation (RO) data proved to be a great tool for atmospheric monitoring and studies. In the recent decade, they were frequently used for analyses of the internal gravity waves in the upper troposphere lower stratosphere region. Atmospheric density is the first quantity of state gained in the retrieval proces...
Article
The cloudiness represents one of the basic climate elements. It plays an important role in the global energy and water cycle, dominates the planetary albedo and takes part in many climate feedback processes. Its traditional man-made observation provides usually high-quality data. But it is partly influenced by the observer capabilities to see vario...
Conference Paper
Full-text available
The large-scale dynamics of the stratosphere and its interaction and coupling with troposphere are reviewed. Geophysical fluid dynamics methods, quantities suitable for the description of the middle atmosphere circulation and general patterns of the stratospheric circulation are described. Emphasis is placed on the important effects of two-way inte...

Questions

Questions (3)
Question
I am looking for some (preferentially recent) observational evidences of mountain wave breaking in the upper troposphere - lower stratosphere region. It is to be expected from a simple consideration of increasing GW amplitudes with height that the largest amplitude modes will break lower and the smaller ones propagate higher and I think that I have read a similar conclusion from some papers related to DEEPWAVE campaign..Geographically less localized papers would be welcomed as well..
Question
Dear all,
I am currently involved in more research projects, where we would need 3D information on orographic GWD at least on daily basis. Right now we are using accelogw output from CMAM, but it would be desirable to have similar data from other models with different GW parametrizations..
E.g. some models participating at CCMI community simulations have 3D GWD on monthly basis. Possible to find daily 3D GWD data anywhere?
Thanks in advance,
Petr.
Question
I would like to compute my diagnostics using this "full" EPflux not just using the ordinary quasi-geostrophic one. The results seem quite different so far.

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