Alexander Pogoreltsev

Simulating influences of QBO phases and orographic gravity wave forcing on planetary waves in the middle atmosphere

Recently developed parameterization of stationary orographic gravity waves (OGWs) generated by the Earth’s topography was implemented into a general circulation model of the middle and upper atmosphere. We performed numerical simulations of the zonal mean wind and amplitudes of stationary planetary waves and normal atmospheric modes with periods of 4–16 days at altitudes from the troposphere to the lower thermosphere in January for easterly and westerly phases of the quasi-biennial oscillation (QBO) including and excluding the stationary OGW parameterization. Simulations show that accounting dynamical and thermal effects of stationary OGWs can lead to substantial changes (up to 50–90 %) in the amplitudes of stationary planetary waves. Amplitudes of westward travelling normal atmospheric modes change (up to 50–90 %) at different altitudes and latitudes of the northern hemisphere due to OGW effects. Transitions from the easterly to westerly QBO phases can change planetary wave amplitudes up to ±30–90 % at middle and high latitudes. These changes in PW amplitudes are consistent with distributions of EP-flux and refractive index under different QBO phases simulated including our parameterization of stationary OGWs.

Dynamics of 2013 Sudden Stratospheric Warming event and its impact on cold weather over Eurasia: Role of planetary wave reflection.

In the present study, we investigate the impact of stratospheric planetary wave reflection on tropospheric weather over Central Eurasia during the 2013 Sudden Stratospheric Warming (SSW) event. We analyze EP fluxes and Plumb wave activity fluxes to study the two and three dimensional aspects of wave propagation, respectively. The 2013 SSW event is excited by the combined influence of wavenumber 1 (WN1) and wavenumber 2 (WN2) planetary waves, which makes the event an unusual one and seems to have significant impact on tropospheric weather regime. We observe an extraordinary development of a ridge over the Siberian Tundra and the North Pacific during first development stage (last week of December 2012) and later from the North Atlantic in the second development stage (first week of January 2013), and these waves appear to be responsible for the excitation of the WN2 pattern during the SSW. The wave packets propagated upward and were then reflected back down to central Eurasia due to strong negative wind shear in the upper stratospheric polar jet, caused by the SSW event. Waves that propagated downward led to the formation of a deep trough over Eurasia and brought extreme cold weather over Kazakhstan, the Southern part of Russia and the Northwestern part of China during mid-January 2013.

Numerical simulation of the influence of stationary mesoscale orographic waves on the meridional circulation and ozone fluxes in the middle atmosphere

The authors’ parameterization of the dynamic and thermal action of stationary orographic waves generated by the Earth’s surface relief is included into the model of general circulation of the middle and upper atmosphere. Numerical simulation of the general circulation in the troposphere and stratosphere was performed and the influence of stationary orographic waves propagating upward from the Earth’s surface on the meridional and vertical velocity was studied. It is shown that the allowance for the dynamic and thermal action of these waves in the numerical model leads to changes by up to 20–30% in the meridional circulation and ozone fluxes associated with it at heights of the ozone layer maximum.

Influence of wave activity on the composition of the polar stratosphere

The planetary wave impact on the polar vortex stability, polar stratosphere temperature, and content of ozone and other gases was simulated with the global chemical–climatic model of the lower and middle atmosphere. It was found that the planetary waves propagating from the troposphere into the stratosphere differently affect the gas content of the Arctic and Antarctic stratosphere. In the Arctic region, the degree of wave activity critically affects the polar vortex formation, the appearance of polar stratospheric clouds, the halogen activation on their surface, and ozone anomaly formation. Ozone anomalies in the Arctic region as a rule are not formed at high wave activity and can be registered at low activity. In the Antarctic Regions, wave activity affects the stability of polar vortex and the depth of ozone holes, which are formed at almost any wave activity, and the minimal ozone values depend on the strong or weak wave activity that is registered in specific years.

An abrupt rainfall decrease over the Asian inland plateau region around 1999 and the possible underlying mechanism

A decadal change in summer rainfall in the Asian inland plateau (AIP) region is identified around 1999. This decadal change is characterized by an abrupt decrease in summer rainfall of about 15.7% of the climatological average amount, leading to prolonged drought in the Asian inland plateau region. Both the surface air temperature and potential evapotranspiration in the AIP show a significant increase, while the soil moisture exhibits a decrease, after the late 1990s. Furthermore, the normalized difference vegetation index shows an apparent decreasing trend during 1999–2007. Three different drought indices—the standardized precipitation index, the standardized precipitation evapotranspiration index, and the self-calibrating Palmer drought severity index—present pronounced climate anomalies during 1999–2007, indicating dramatic drought exacerbation in the region after the late 1990s. This decadal change in the summer rainfall may be attributable to a wave-like teleconnection pattern from Western Europe to Asia. A set of model sensitivity experiments suggests that the summer warming sea surface temperature in the North Atlantic could induce this teleconnection pattern over Eurasia, resulting in recent drought in the AIP region.

Three-dimensional semi-empirical climate model of water vapor distribution and its implementation to the radiation module of the middle and upper atmosphere model

To provide the more accurate simulation of stationary planetary waves and atmospheric tides using the middle and upper atmosphere model (MUAM), the three-dimensional (longitude-latitude-height) semi-empirical climate model of water vapor distribution in the troposphere was developed which takes into account seasonal variations. The modules of radiation heating and cooling in the MUAM model were modified taking into account the dependence of water vapor concentration on longitude. The simulations performed using the modified version of MUAM revealed that the consideration of water vapor concentration variability along the circle of latitude leads to the substantial dependence of solar heating on longitude that affects the amplitudes of stationary planetary waves in the stratosphere.

Statistical inhomogeneity of dates of sudden stratospheric warmings in the wintertime northern hemisphere

Using the data of meteorological information reanalysis, a statistical analysis of dates of the main sudden stratospheric warmings observed in 1958–2014 has been performed and their inhomogeneous distribution in winter months with maximums in the beginning of January, from the end of January to the beginning of February, and in the end of February has been shown. To explain these regularities, a climatological analysis of variations in the amplitudes and vertical components of Eliassen–Palm fluxes created by large-scale planetary waves (PWs), as well as of zonal-mean winds and deviations of temperature from their winter-average values in high northern latitudes at heights of up to 50 km from the surface has been carried out using the 20-year (1995–2014) collection of daily meteorological information from the UK Met Office database. During the aforementioned intervals of observing more frequent sudden stratospheric warmings, climatological maximums of temperature perturbations, local minimums of eastward winds, and local maximums of the amplitude and Eliassen–Palm fluxes of PWs with a zonal wavenumber of 1 in the high-latitude northern stratosphere were found. Distinctions between atmospheric characteristics averaged over two last decades have been revealed.

Numerical simulation of wave interactions during sudden stratospheric warming

Parameterizations of normal atmospheric modes (NAMs) and orographic gravity waves (OGWs) are implemented into the mechanistic general circulation model of the middle and upper atmosphere (MUA). Numerical experiments of sudden stratospheric warming (SSW) events are performed for climatological conditions typical for January and February using meteorological reanalysis data from the UK MET Office in the MUA model averaged over the years 1992–2011 with the easterly phase of quasi-biennial oscillation (QBO). The simulation shows that an increase in the OGW amplitudes occurs at altitudes higher than 30 km in the Northern Hemisphere after SSW. The OGW amplitudes have maximums at altitudes of about 50 km over the North American and European mountain systems before and during SSW, as well as over the Himalayas after SSW. At high latitudes of the Northern Hemisphere, significant (up to 50–70%) variations in the amplitudes of stationary planetary waves (SPWs) are observed during and after the SSW. Westward travelling NAMs have local amplitude maximums not only in the Northern Hemisphere, but also in the Southern Hemisphere, where there are waveguides for the propagation of these modes. Calculated variations of SPW and NAM amplitudes correspond to changes in the mean temperature and wind fields, as well as the Eliassen-Palm flux and atmospheric refractive index for the planetary waves, during SSW. Including OGW thermal and dynamical effects leads to an increase in amplitude (by 30–70%) of almost all SPWs before and during SSW and to a decrease (up to 20–100%) after the SSW at middle and high latitudes of the Northern Hemisphere.

The influence of orographic waves and quasi-biennial oscillations on vertical ozone flux in the model of general atmospheric circulation

A parameterization of the dynamical and thermal effects of orographic gravity waves (OGWs) and assimilation quasibiennial oscillations (QBOs) of the zonal wind in the equatorial lower atmosphere are implemented into the numerical model of the general circulation of the middle and upper atmosphere MUAM. The sensitivity of vertical ozone fluxes to the effects of stationary OGWs at different QBO phases at altitudes up to 100 km for January is investigated. The simulated changes in vertical velocities produce respective changes in vertical ozone fluxes caused by the effects of the OGW parameterization and the transition from the easterly to the westerly QBO phase. These changes can reach 40 - 60% in the Northern Hemisphere at altitudes of the middle atmosphere.

Improving capabilities of broadband differential satellite navigation systems via radio occultation technology

The existent satellite system for radio occultation monitoring the Earth’s neutral atmosphere and ionosphere (COSMIC) provides data to consumers in the regions with limited possibilities of constructing dense measurement networks (e.g., in the World Ocean area). A forthcoming increase of LEO small spacecrafts and the deployment of new satellite radio navigation systems will result in a pronounced increase in the efficiency of radio occultation method and its space resolution. As a result, the Space-Based Augmentation Systems (SBAS) broadband differential system will become global, or the quality of corrections delivered to single-frequency consumers of individual systems, e.g., the Augmentation and Monitoring System, will be improved. Therefore, the methods for processing and analyzing obtained radio occultation data should be improved. A simple method to reconstruct the electron density profile at radio occultation points, based on the total electron content measurement on the satellite–satellite path and the IRI-type ionospheric model has been proposed. The method needs initial information, it does not require refraction measurements, and it is free of the assumption that the ionosphere is spherically stratified in the occultation region. Verification of the proposed method based on data for 121 radio occultation cases across Europe in May 2013 demonstrated good agreement with the vertical sounding data.