scholarly journals Transient Extratropical Response to Solar Ultraviolet Radiation in the Northern Hemisphere Winter

2021 ◽  
pp. 1-51
Author(s):  
Yonatan Givon ◽  
Chaim I. Garfinkel ◽  
Ian White
Keyword(s):  
Uv Radiation ◽  
Zonal Wind ◽  
General Circulation ◽  
Solar Rotation ◽  
Rotation Period ◽  
Circulation Model ◽  
Solar Variability ◽  
Solar Ultraviolet Radiation ◽  
Hemisphere Winter ◽  
Solar Ultraviolet

AbstractAn intermediate complexity General Circulation Model is used to investigate the transient response of the NH winter stratosphere to modulated ultraviolet (UV) radiation by imposing a step-wise, deliberately exaggerated UV perturbation and analyzing the lagged response. Enhanced UV radiation is accompanied by an immediate warming of the tropical upper stratosphere. The warming then spreads into the winter subtropics due to an accelerated Brewer Dobson Circulation in the tropical upper stratosphere. The poleward meridional velocity in the subtropics leads to an increase in zonal wind in midlatitudes between 20N and 50N due to Coriolis torque. The increase in mid-latitude zonal wind is accompanied by a dipole in Eliassen-Palm flux convergence, with decreased convergence near the winter pole and increased convergence in mid-latitudes (where winds are strengthening due to the Coriolis torque); this dipole subsequently extends the anomalous westerlies to subpolar latitudes within the first ten days. The initial radiatively-driven acceleration of the Brewer-Dobson circulation due to enhanced shortwave absorption is replaced in the subpolar winter stratosphere by a wave-driven deceleration of the Brewer-Dobson circulation, and after a month the wave-driven deceleration of the Brewer-Dobson circulation encompasses most of the winter stratosphere. Approximately a month after UV is first modified, a significant poleward jet shift is evident in the troposphere. The results of this study may have implications for the observed stratospheric and tropospheric responses to solar variability associated with the 27-day solar rotation period, and also to solar variability on longer timescales.

scholarly journals Axisymmetric Constraints on Cross-Equatorial Hadley Cell Extent

2019 ◽  
Vol 76 (6) ◽  
pp. 1547-1564 ◽  
Author(s):  
Spencer A. Hill ◽  
Simona Bordoni ◽  
Jonathan L. Mitchell
Keyword(s):  
Angular Momentum ◽  
Zonal Wind ◽  
General Circulation ◽  
Potential Temperature ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Hadley Cell ◽  
Equal Area ◽  
Area Model ◽  
Hadley Cells

Abstract We consider the relevance of known constraints from each of Hide’s theorem, the angular momentum–conserving (AMC) model, and the equal-area model on the extent of cross-equatorial Hadley cells. These theories respectively posit that a Hadley circulation must span all latitudes where the radiative–convective equilibrium (RCE) absolute angular momentum satisfies or or where the RCE absolute vorticity satisfies ; all latitudes where the RCE zonal wind exceeds the AMC zonal wind; and over a range such that depth-averaged potential temperature is continuous and that energy is conserved. The AMC model requires knowledge of the ascent latitude , which needs not equal the RCE forcing maximum latitude . Whatever the value of , we demonstrate that an AMC cell must extend at least as far into the winter hemisphere as the summer hemisphere. The equal-area model predicts , always placing it poleward of . As is moved poleward (at a given thermal Rossby number), the equal-area-predicted Hadley circulation becomes implausibly large, while both and become increasingly displaced poleward of the minimal cell extent based on Hide’s theorem (i.e., of supercritical forcing). In an idealized dry general circulation model, cross-equatorial Hadley cells are generated, some spanning nearly pole to pole. All homogenize angular momentum imperfectly, are roughly symmetric in extent about the equator, and appear in extent controlled by the span of supercritical forcing.

Influence of gravity wave drag parametrisations on the stratospheric circulation of seasonal ICON-NWP experiments

2020 ◽  
Author(s):  
Raphael Köhler ◽  
Dörthe Handorf ◽  
Ralf Jaiser ◽  
Klaus Dethloff ◽  
Günther Zängl ◽  
...  
Keyword(s):  
Gravity Wave ◽  
General Circulation ◽  
Weather Prediction ◽  
Polar Vortex ◽  
Circulation Model ◽  
Seasonal Prediction ◽  
Wave Drag ◽  
Stratospheric Polar Vortex ◽  
Sensitivity Experiments ◽  
Hemisphere Winter

<p>The stratospheric polar vortex is highly variable in winter and thus, models often struggle to capture its variability and strength. Yet, the influence of the stratosphere on the tropospheric circulation becomes highly important in Northern Hemisphere winter and is one of the main potential sources for subseasonal to seasonal prediction skill in mid latitudes. Mid-latitude extreme weather patterns in winter are often preceded by sudden stratospheric warmings (SSWs), which are the strongest manifestation of the coupling between stratosphere and troposphere. Misrepresentation of the SSW-frequency and stratospheric biases in models can therefore also cause biases in the troposphere.</p><p>In this context this work comprises the analysis of four seasonal ensemble experiments with a high-resolution, nonhydrostatic global atmospheric general circulation model in numerical weather prediction mode (ICON-NWP). The main focus thereby lies on the variability and strength of the stratospheric polar vortex. We identified the gravity wave drag parametrisations as one important factor influencing stratospheric dynamics. As the control experiment with default gravity wave drag settings exhibits an overestimated amount of SSWs and a weak stratospheric polar vortex, three sensitivity experiments with adjusted drag parametrisations were generated. Hence, the parametrisations for the non-orographic gravity wave drag and the subgrid‐scale orographic (SSO) drag were chosen with the goal of strengthening the stratospheric polar vortex. Biases to ERA-Interim are reduced with both adjustments, especially in high latitudes. Whereas the positive effect of the reduced non-orographic gravity wave drag is strongest in the mid-stratosphere in winter, the adjusted SSO-scheme primarily affects the troposphere by reducing mean sea level pressure biases in all months. A fourth experiment using both adjustments exhibits improvements in the troposphere and stratosphere. Although the stratospheric polar vortex in winter is strengthened in all sensitivity experiments, it is still simulated too weak compared to ERA-Interim. Further mechanisms causing this weakness are also investigated in this study.</p>

scholarly journals Role of Nonlinear Atmospheric Response to SST on the Asymmetric Transition Process of ENSO

2009 ◽  
Vol 22 (1) ◽  
pp. 177-192 ◽  
Author(s):  
Masamichi Ohba ◽  
Hiroaki Ueda
Keyword(s):  
Observational Data ◽  
Zonal Wind ◽  
General Circulation ◽  
Circulation Model ◽  
La Niña ◽  
Atmospheric Response ◽  
Cold Event ◽  
Transition Processes ◽  
La Nina ◽  
Sst Anomalies

Abstract Physical processes that are responsible for the asymmetric transition processes between El Niño and La Niña events are investigated by using observational data and physical models to examine the nonlinear atmospheric response to SST. The air–sea coupled system of ENSO is able to remain in a weak, cold event for up to 2 yr, while the system of a relatively warm event turns into a cold phase. Through analysis of the oceanic observational data, it is found that there is a strong difference in thermocline variations in relation to surface zonal wind anomalies in the equatorial Pacific (EP) during the mature-to-decaying phase of ENSO. The atmospheric response for the warm phase of ENSO causes a rapid reduction of the EP westerlies in boreal winter, which play a role in hastening the following ENSO transition through the generation of upwelling oceanic Kelvin waves. However, the anomalous EP easterlies in the cold phase persist to the subsequent spring, which tends to counteract the turnabout from the cold to warm phase of ENSO. A suite of idealized atmospheric general circulation model (AGCM) experiments are performed by imposing two different ENSO-related SST anomalies, which have equal amplitudes but opposite signs. The nonlinear climate response in the AGCM is found at the mature-to-decaying phase of ENSO that closely resembles the observations, including a zonal and meridional shift in the equatorial positions of the atmospheric wind. By using a simple ocean model, it is determined that the asymmetric responses of the equatorial zonal wind result in different recovery times of the thermocline in the eastern Pacific. Thus, the differences in transition processes between the warm and cold ENSO event are fundamentally due to the nonlinear atmospheric response to SST, which originates from the distribution of climatological SST and its seasonal changes. By including the asymmetric wind responses the intermediate air–sea coupled model herein demonstrates that the essential elements of the redevelopment of La Niña arise from the nonlinear atmospheric response to SST anomalies.

scholarly journals Episode of unusual high solar ultraviolet radiation in central Europe due to dynamical reduced stratospheric ozone in May 2005

2005 ◽  
Vol 5 (5) ◽  
pp. 10409-10420 ◽  
Author(s):  
C. Stick ◽  
K. Krüger ◽  
N. H. Schade ◽  
H. Sandmann ◽  
A. Macke
Keyword(s):  
Ultraviolet Radiation ◽  
Uv Radiation ◽  
Stratospheric Ozone ◽  
Solar Ultraviolet Radiation ◽  
Solar Uv ◽  
Resultant Increase ◽  
The Tropics ◽  
Effective Radiation ◽  
Ozone Episodes ◽  
Solar Ultraviolet

Abstract. In late May this year unusual high levels of solar ultraviolet radiation were observed in Europe. In Northern Germany the measured irradiance of erythemally effective radiation exceeded the climatological mean by more than about 20%. An extreme low ozone event for the season coincided with the high solar elevation angles during late spring leading to the highest value of erythemal UV-radiation ever observed at this location in May. This ''ozone mini-hole'' was caused by an elevation of tropopause height accompanied with a poleward advection of natural low total ozone from the tropics. The resultant increase in UV-radiation is of particular significance for human health. Dynamically induced low ozone episodes that happen around the summer solstice can considerably enhance the solar UV-radiation in the mid latitudes and therefore contribute to the UV-burden of people living in the mid latitudes.

scholarly journals EFSO at different geographical locations verified with observing-system experiments

2021 ◽  
Author(s):  
Akira Yamazaki ◽  
Takemasa Miyoshi ◽  
Jun Inoue ◽  
Takeshi Enomoto ◽  
Nobumasa Komori
Keyword(s):  
Northern Hemisphere ◽  
General Circulation ◽  
Short Range ◽  
Geographical Location ◽  
Circulation Model ◽  
The Arctic ◽  
Tropical Regions ◽  
Arctic Regions ◽  
Hemisphere Winter ◽  
Geographical Locations

AbstractAn ensemble-based forecast sensitivity to observations (EFSO) diagnosis has been implemented in an atmospheric general circulation model–ensemble Kalman filter data assimilation system to estimate the impacts of specific observations from the quasi-operational global observing system on weekly short-range forecasts. It was examined whether EFSO reasonably approximates the impacts of a subset of observations from specific geographical locations for 6-hour forecasts, and how long the 6-hour observation impacts can be retained during the 7-day forecast period. The reference for these forecasts was obtained from 12 data denial experiments in each of which a subset of three radiosonde observations launched from a geographical location was excluded. The 12 locations were selected from three latitudinal bands comprising (i) four Arctic regions, (ii) four midlatitude regions in the Northern Hemisphere, and (iii) four tropical regions during the Northern Hemisphere winter of 2015/16. The estimated winter-averaged EFSO-derived observation impacts well corresponded to the 6-hour observation impacts obtained by the data denials and EFSO could reasonably estimate the observation impacts by the data denials on short-range (6-hour to 2-day) forecasts. Furthermore, during the medium-range (4-day to 7-day) forecasts, it was found that the Arctic observations tend to seed the broadest impacts and their short-range observation impacts could be projected to beneficial impacts in Arctic and midlatitude North American areas. The midlatitude area located just downstream of dynamical propagation from the Arctic toward the midlatitudes. Results obtained by repeated Arctic data-denial experiments were found to be generally common to those from the non-repeated experiments.

scholarly journals On the influence of zonal gravity wave distributions on the Southern Hemisphere winter circulation

2017 ◽  
Vol 35 (4) ◽  
pp. 785-798 ◽  
Author(s):  
Friederike Lilienthal ◽  
Christoph Jacobi ◽  
Torsten Schmidt ◽  
Alejandro de la Torre ◽  
Peter Alexander
Keyword(s):  
Gravity Wave ◽  
Southern Hemisphere ◽  
Zonal Wind ◽  
Middle Atmosphere ◽  
Lower Boundary ◽  
Circulation Model ◽  
Global Circulation Model ◽  
Global Circulation ◽  
The Andes ◽  
Hemisphere Winter

Abstract. A mechanistic global circulation model is used to simulate the Southern Hemisphere stratospheric, mesospheric, and lower thermospheric circulation during austral winter. The model includes a gravity wave (GW) parameterization that is initiated by prescribed 2-D fields of GW parameters in the troposphere. These are based on observations of GW potential energy calculated using GPS radio occultations and show enhanced GW activity east of the Andes and around the Antarctic. In order to detect the influence of an observation-based and thus realistic 2-D GW distribution on the middle atmosphere circulation, we perform model experiments with zonal mean and 2-D GW initialization, and additionally with and without forcing of stationary planetary waves (SPWs) at the lower boundary of the model. As a result, we find additional forcing of SPWs in the stratosphere, a weaker zonal wind jet in the mesosphere, cooling of the mesosphere and warming near the mesopause above the jet. SPW wavenumber 1 (SPW1) amplitudes are generally increased by about 10 % when GWs are introduced being longitudinally dependent. However, at the upper part of the zonal wind jet, SPW1 in zonal wind and GW acceleration are out of phase, which reduces the amplitudes there.

scholarly journals Sensitivity of an atmospheric general circulation model to the parameterization of leads in sea ice

1997 ◽  
Vol 25 ◽  
pp. 96-101 ◽  
Author(s):  
Gregory M. Flato ◽  
David Ramsden
Keyword(s):  
Sea Ice ◽  
General Circulation Model ◽  
General Circulation ◽  
Climate Models ◽  
Atmospheric General Circulation Model ◽  
Circulation Model ◽  
Open Water ◽  
Arctic Sea Ice ◽  
Atmospheric General Circulation ◽  
Hemisphere Winter

Open-water leads in sea ice dominate the exchange of heat between the ocean and atmosphere in ice-covered regions, and so must be included in climate models. A parameterization of leads used in one such model is compared to observations and the results of a detailed Arctic sea-ice model. Such comparisons, however, are hampered by the errors in observed lead fraction, but the parameterization appears to compare better in winter than in summer. Simulations with an atmospheric general circulation model (AGCM), using prescribed sea-surface temperatures and ice extent, are used to illustrate the effect of parameterized lead fraction on atmospheric climate, and so provide some insight into the importance of improved lead-fraction parameterizations and observations. The effect of leads in the AGCM is largest in Northern Hemisphere winter, with zonal mean surface-air temperatures over ice increasing by up to 5 K when lead fraction is increased from 1% to near 5%. The effect of leads on sensible heat loss in winter is more important than the effect on radiative heat gain in summer. No significant effect on sea-level pressure, and hence on atmospheric circulation, is found, however. Indirect effects, due to feedbacks between the atmosphere and ice thickness and extent, were not included in these simulations, but could amplify the response.

scholarly journals Rectification Feedback of High-Frequency Atmospheric Variability into Low-Frequency Zonal Flows in the Tropical Pacific

2012 ◽  
Vol 25 (14) ◽  
pp. 5088-5101 ◽  
Author(s):  
Yoo-Geun Ham ◽  
Jong-Seong Kug ◽  
Mi-Jung Lim
Keyword(s):  
Zonal Wind ◽  
High Frequency ◽  
General Circulation ◽  
Low Frequency ◽  
Circulation Model ◽  
Atmospheric Variability ◽  
Easterly Wind ◽  
Zonal Winds ◽  
Wind Variability ◽  
Wind Events

Abstract In this study, the rectification process of high-frequency (HF) zonal-wind variability on the low-frequency (LF) zonal wind is investigated through an idealized experiment using an atmospheric general circulation model (AGCM). Through an idealized AGCM experiment with a fixed SST boundary forcing, it is shown that there is positive (negative) correlation between HF (2–90-day period) zonal-wind variance and LF (3-month average) zonal wind where the HF zonal-wind variance is positively (negatively) skewed because the stronger HF westerly (easterly) wind events than HF easterly (westerly) wind events induce a residual westerly (easterly), and it results in an additional rectified LF westerly (easterly) anomaly. This means that, over regions with positively skewed HF zonal winds, LF westerly anomalies are generated due to the residuals of the HF zonal winds. It implies that the LF zonal wind can be generated through internal processes of the atmosphere without external forcing and the interaction between LF and HF is not a one-way process from LF to HF but, rather, a two-way interaction process.

scholarly journals The Antarctic Oscillation Structure in an AOGCM with Interactive Stratospheric Ozone

2012 ◽  
Vol 2012 ◽  
pp. 1-12
Author(s):  
S. Brand ◽  
K. Dethloff ◽  
D. Handorf
Keyword(s):  
General Circulation ◽  
Planetary Wave ◽  
Middle Atmosphere ◽  
Stratospheric Ozone ◽  
Circulation Model ◽  
Wave Activity ◽  
Antarctic Oscillation ◽  
Wave Dynamics ◽  
Hemisphere Winter ◽  
The Antarctic

Based on 150-year equilibrium simulations using the atmosphere-ocean-sea ice general circulation model (AOGCM) ECHO-GiSP, the southern hemisphere winter circulation is examined focusing on tropo-stratosphere coupling and wave dynamics. The model covers the troposphere and strato-mesosphere up to 80 km height and includes an interactive stratospheric chemistry. Compared to the reference simulation without interactive chemistry, the interactive simulation shows a weaker polar vortex in the middle atmosphere and is shifted towards the negative phase of the Antarctic Oscillation (AAO) in the troposphere. Differing from the northern hemisphere winter situation, the tropospheric planetary wave activity is weakened. A detailed analysis shows, that the modelled AAO zonal mean signal behaves antisymmetrically between troposphere and strato-mesosphere. This conclusion is supported by reanalysis data and a discussion of planetary wave dynamics in terms of Eliassen-Palm fluxes. Thereby, the tropospheric planetary wave activity appears to be controlled from the middle atmosphere.

Sign in / Sign up

Export Citation Format

Share Document