A deeper insight into the dynamics and effects of the Hiccup of the fall transition

2021 ◽  
Author(s):  
Vivien Matthias ◽  
Daniela Banys ◽  
Marc Hansen
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Zonal Wind ◽  
Middle Atmosphere ◽  
3D Structure ◽  
Reanalysis Data ◽  
Wind Regime ◽  
Altitudinal Shift ◽  
D Region ◽  
Insight Into

<p>In autumn the prevailing wind in the middle atmosphere at mid and high latitudes changes from summer easterly to winter westerly.  This process is not smooth but interrupted by the Hiccup of the fall transition with characteristics similar to a mini sudden stratospheric warming (SSW) which occurs in fall even though the zonal mean zonal wind does not reverse to easterly again. Combining global reanalysis data and satellite observations we improve our knowledge and understanding of the dynamics of the Hiccup of the fall transition in the middle atmosphere. The introduction of a new definition for the onset of the Hiccup focusing now on its core region in the lower mesosphere allows us the automatic detection of a Hiccup in almost every year and thus a deeper insight into its dynamics. For example, we found a latitudinal and altitudinal shift in the zonal wind regime during the Hiccup. We also investigate its 3D-structure and compare the characteristics of the Hiccup in the Northern hemisphere with those in the Southern hemisphere. We found that the latitudinal and altitudinal shift of the zonal wind regime occurs in both hemispheres but is more pronounced in the Northern hemisphere and smoother in the Southern hemisphere.  Additionally, we discuss the possible impact of the Hiccup on the D-region.</p>

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 Recent Developments in Calibration for Archaeological and Environmental Samples

Radiocarbon ◽  
2020 ◽  
Vol 62 (4) ◽  
pp. 1095-1117 ◽  
Author(s):  
J van der Plicht ◽  
C Bronk Ramsey ◽  
T J Heaton ◽  
E M Scott ◽  
S Talamo
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Tree Rings ◽  
Environmental Samples ◽  
Varved Sediments ◽  
Companion Article ◽  
Recent Developments ◽  
General Readership ◽  
Paleolithic Archaeology ◽  
Insight Into

ABSTRACTThe curves recommended for calibrating radiocarbon (14C) dates into absolute dates have been updated. For calibrating atmospheric samples from the Northern Hemisphere, the new curve is called IntCal20. This is accompanied by associated curves SHCal20 for the Southern Hemisphere, and Marine20 for marine samples. In this “companion article” we discuss advances and developments that have led to improvements in the updated curves and highlight some issues of relevance for the general readership. In particular the dendrochronological based part of the curve has seen a significant increase in data, with single-year resolution for certain time ranges, extending back to 13,910 calBP. Beyond the tree rings, the new curve is based upon an updated combination of marine corals, speleothems, macrofossils, and varved sediments and now reaches back to 55,000 calBP. Alongside these data advances, we have developed a new, bespoke statistical curve construction methodology to allow better incorporation of the diverse constituent records and produce a more robust curve with uncertainties. Combined, these data and methodological advances offer the potential for significant new insight into our past. We discuss some implications for the user, such as the dating of the Santorini eruption and also some consequences of the new curve for Paleolithic archaeology.

scholarly journals Northern Hemisphere stratospheric winds in higher midlatitudes: longitudinal distribution and long-term trends

2015 ◽  
Vol 15 (4) ◽  
pp. 2203-2213 ◽  
Author(s):  
M. Kozubek ◽  
P. Krizan ◽  
J. Lastovicka
Keyword(s):  
Northern Hemisphere ◽  
Zonal Wind ◽  
Meridional Circulation ◽  
Meridional Wind ◽  
Reanalysis Data ◽  
Core Structure ◽  
Middle Latitudes ◽  
Meridional Winds ◽  
Long Term Trends

Abstract. The Brewer–Dobson circulation (mainly meridional circulation) is very important for stratospheric ozone dynamics and thus for the overall state of the stratosphere. There are some indications that the meridional circulation in the stratosphere could be longitudinally dependent, which would have an impact on the ozone distribution. Therefore, we analyse here the meridional component of the stratospheric wind at northern middle latitudes to study its longitudinal dependence. The analysis is based on the NCEP/NCAR-1 (National Centers for Environmental Prediction and the National Center for Atmospheric Research), MERRA (Modern Era-Retrospective Analysis) and ERA-Interim (European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis Interim) reanalysis data. The well-developed two-core structure of strong but opposite meridional winds, one in each hemisphere at 10 hPa at higher northern middle latitudes, and a less pronounced five-core structure at 100 hPa are identified. In the central areas of the two-core structure the meridional and zonal wind magnitudes are comparable. The two-core structure at 10 hPa is almost identical for all three different reanalysis data sets in spite of the different time periods covered. The two-core structure is not associated with tides. However, the two-core structure at the 10 hPa level is related to the Aleutian pressure high at 10 hPa. Zonal wind, temperature and the ozone mixing ratio at 10 hPa also exhibit the effect of the Aleutian high, which thus affects all parameters of the Northern Hemisphere middle stratosphere. Long-term trends in the meridional wind in the "core" areas are significant at the 99% level. Trends of meridional winds are negative during the period of ozone depletion development (1970–1995), while they are positive after the ozone trend turnaround (1996–2012). Meridional wind trends are independent of the sudden stratospheric warming (SSW) occurrence and the quasi-biennial oscillation (QBO) phase. The influence of the 11-year solar cycle on stratospheric winds has been identified only during the west phase of QBO. The well-developed two-core structure in the meridional wind illustrates the limitations of application of the zonal mean concept in studying stratospheric circulation.

scholarly journals Methane as a diagnostic tracer of changes in the Brewer–Dobson circulation of the stratosphere

2015 ◽  
Vol 15 (7) ◽  
pp. 3739-3754 ◽  
Author(s):  
E. E. Remsberg
Keyword(s):  
Time Series ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Lower Stratosphere ◽  
Middle Atmosphere ◽  
Wave Activity ◽  
Mixing Ratio ◽  
Use Of Time ◽  
Wave Induced ◽  
Middle Stratosphere

Abstract. This study makes use of time series of methane (CH4) data from the Halogen Occultation Experiment (HALOE) to detect whether there were any statistically significant changes of the Brewer–Dobson circulation (BDC) within the stratosphere during 1992–2005. The HALOE CH4 profiles are in terms of mixing ratio versus pressure altitude and are binned into latitude zones within the Southern Hemisphere and the Northern Hemisphere. Their separate time series are then analyzed using multiple linear regression (MLR) techniques. The CH4 trend terms for the Northern Hemisphere are significant and positive at 10° N from 50 to 7 hPa and larger than the tropospheric CH4 trends of about 3% decade−1 from 20 to 7 hPa. At 60° N the trends are clearly negative from 20 to 7 hPa. Their combined trends indicate an acceleration of the BDC in the middle stratosphere of the Northern Hemisphere during those years, most likely due to changes from the effects of wave activity. No similar significant BDC acceleration is found for the Southern Hemisphere. Trends from HALOE H2O are analyzed for consistency. Their mutual trends with CH4 are anti-correlated qualitatively in the middle and upper stratosphere, where CH4 is chemically oxidized to H2O. Conversely, their mutual trends in the lower stratosphere are dominated by their trends upon entry to the tropical stratosphere. Time series residuals for CH4 in the lower mesosphere also exhibit structures that are anti-correlated in some instances with those of the tracer-like species HCl. Their occasional aperiodic structures indicate the effects of transport following episodic, wintertime wave activity. It is concluded that observed multi-year, zonally averaged distributions of CH4 can be used to diagnose major instances of wave-induced transport in the middle atmosphere and to detect changes in the stratospheric BDC.

scholarly journals The Climatology of the Middle Atmosphere in a Vertically Extended Version of the Met Office’s Climate Model. Part I: Mean State

2010 ◽  
Vol 67 (5) ◽  
pp. 1509-1525 ◽  
Author(s):  
S. C. Hardiman ◽  
N. Butchart ◽  
S. M. Osprey ◽  
L. J. Gray ◽  
A. C. Bushell ◽  
...  
Keyword(s):  
Zonal Wind ◽  
Annual Cycle ◽  
Radiative Forcing ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
Wave Drag ◽  
Reanalysis Data ◽  
Horizontal Resolution ◽  
Quasi Biennial Oscillation

Abstract The climatology of a stratosphere-resolving version of the Met Office’s climate model is studied and validated against ECMWF reanalysis data. Ensemble integrations are carried out at two different horizontal resolutions. Along with a realistic climatology and annual cycle in zonal mean zonal wind and temperature, several physical effects are noted in the model. The time of final warming of the winter polar vortex is found to descend monotonically in the Southern Hemisphere, as would be expected for purely radiative forcing. In the Northern Hemisphere, however, the time of final warming is driven largely by dynamical effects in the lower stratosphere and radiative effects in the upper stratosphere, leading to the earliest transition to westward winds being seen in the midstratosphere. A realistic annual cycle in stratospheric water vapor concentrations—the tropical “tape recorder”—is captured. Tropical variability in the zonal mean zonal wind is found to be in better agreement with the reanalysis for the model run at higher horizontal resolution because the simulated quasi-biennial oscillation has a more realistic amplitude. Unexpectedly, variability in the extratropics becomes less realistic under increased resolution because of reduced resolved wave drag and increased orographic gravity wave drag. Overall, the differences in climatology between the simulations at high and moderate horizontal resolution are found to be small.

scholarly journals Persistence and photochemical decay of springtime total ozone anomalies in the Canadian Middle Atmosphere Model

2007 ◽  
Vol 7 (2) ◽  
pp. 485-493 ◽  
Author(s):  
S. Tegtmeier ◽  
T. G. Shepherd
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Total Ozone ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Correlation Coefficients ◽  
Polar Regions ◽  
Vertical Diffusion ◽  
Ozone Loss ◽  
Atmosphere Model

Abstract. The persistence and decay of springtime total ozone anomalies over the entire extratropics (midlatitudes plus polar regions) is analysed using results from the Canadian Middle Atmosphere Model (CMAM), a comprehensive chemistry-climate model. As in the observations, interannual anomalies established through winter and spring persist with very high correlation coefficients (above 0.8) through summer until early autumn, while decaying in amplitude as a result of photochemical relaxation in the quiescent summertime stratosphere. The persistence and decay of the ozone anomalies in CMAM agrees extremely well with observations, even in the southern hemisphere when the model is run without heterogeneous chemistry (in which case there is no ozone hole and the seasonal cycle of ozone is quite different from observations). However in a version of CMAM with strong vertical diffusion, the northern hemisphere anomalies decay far too rapidly compared to observations. This shows that ozone anomaly persistence and decay does not depend on how the springtime anomalies are created or on their magnitude, but reflects the transport and photochemical decay in the model. The seasonality of the long-term trends over the entire extratropics is found to be explained by the persistence of the interannual anomalies, as in the observations, demonstrating that summertime ozone trends reflect winter/spring trends rather than any change in summertime ozone chemistry. However this mechanism fails in the northern hemisphere midlatitudes because of the relatively large impact, compared to observations, of the CMAM polar anomalies. As in the southern hemisphere, the influence of polar ozone loss in CMAM increases the midlatitude summertime loss, leading to a relatively weak seasonal dependence of ozone loss in the Northern Hemisphere compared to the observations.

scholarly journals On the evaluation of the phase relation between temperature and wind tides based on ground-based measurements and reanalysis data in the middle atmosphere

2019 ◽  
Author(s):  
Kathrin Baumgarten ◽  
Gunter Stober
Keyword(s):  
Zonal Wind ◽  
Phase Relation ◽  
Middle Atmosphere ◽  
Meridional Wind ◽  
Reanalysis Data ◽  
Global Perspective ◽  
Spatial And Temporal Scales ◽  
Tidal Waves ◽  
Additional Information ◽  
Routine Basis

Abstract. The variability of the middle atmosphere is driven by a variety of waves covering different spatial and temporal scales. We are diagnosing the variability of the thermal tides due to changes in the background wind by an adaptive spectral filter, which takes the intermittency of tides into account. We apply this diagnostic to temperature observations from a daylight-capable lidar at mid-latitudes (54° N, 12° E) as well as to reanalysis data of horizontal winds from MERRA-2. These reanalysis data provide additional wind information in the altitude range between 30 and 70 km at the location of the lidar as well as on a global perspective. Using the global data gives information of the tidal modes seen at one location. A comparison of the temperature and wind information affirms whether there is a fixed phase relation of the tidal waves in the temperature and the wind data. We found that in general the local tidal signatures are dominated by migrating tidal modes and the signature is weaker in temperatures than in winds. While the meridional wind tide is leading the zonal wind tide by 90°, the phase relation between the temperature and the wind tide is more complex. At certain altitudes the temperature tide follows the zonal wind tide. This knowledge helps to improve the interpretation of the seasonal variation of tides from different observables especially when only data from single locations are used. The findings provide additional information about the phase stability of tidal waves and the results clearly show the importance of a measurement acquisition on a routine basis with high temporal and spatial resolution.

scholarly journals On the evaluation of the phase relation between temperature and wind tides based on ground-based measurements and reanalysis data in the middle atmosphere

2019 ◽  
Vol 37 (4) ◽  
pp. 581-602 ◽  
Author(s):  
Kathrin Baumgarten ◽  
Gunter Stober
Keyword(s):  
Zonal Wind ◽  
Phase Relation ◽  
Middle Atmosphere ◽  
Meridional Wind ◽  
Global Scale ◽  
Reanalysis Data ◽  
Spatial And Temporal Scales ◽  
Tidal Waves ◽  
Additional Information ◽  
Routine Basis

Abstract. The variability in the middle atmosphere is driven by a variety of waves covering different spatial and temporal scales. We diagnose the variability in the thermal tides due to changes in the background wind by an adaptive spectral filter, which takes the intermittency of tides into account. We apply this diagnostic to temperature observations from daylight-capable lidar at midlatitudes (54∘ N, 12∘ E) as well as to reanalysis data of horizontal winds from Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). These reanalysis data provide additional wind information in the altitude range between 30 and 70 km at the location of the lidar as well as on a global scale. Using the global data gives information on the tidal modes seen at one location. A comparison of the temperature and wind information affirms whether there is a fixed phase relation of the tidal waves in the temperature and the wind data. We found that in general the local tidal signatures are dominated by migrating tidal modes, and the signature is weaker in temperatures than in winds. While the meridional wind tide leads the zonal wind tide by 90∘, the phase relation between the temperature and the wind tide is more complex. At certain altitudes the temperature tide follows the zonal wind tide. This knowledge helps in improving the interpretation of the seasonal variation in tides from different observables, especially when only data from single locations are used. The findings provide additional information about the phase stability of tidal waves, and the results clearly show the importance of a measurement acquisition on a routine basis with high temporal and spatial resolution.

Alpha-Effect, Current and Kinetic Helicities for Magnetically Driven Turbulence, and Solar Dynamo

2000 ◽  
Vol 179 ◽  
pp. 387-388
Author(s):  
Gaetano Belvedere ◽  
V. V. Pipin ◽  
G. Rüdiger
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Convection Zone ◽  
Solar Surface ◽  
Momentum Transport ◽  
Angular Momentum Transport ◽  
Magnetic Buoyancy ◽  
Alpha Effect ◽  
Current Helicity

Extended AbstractRecent numerical simulations lead to the result that turbulence is much more magnetically driven than believed. In particular the role ofmagnetic buoyancyappears quite important for the generation ofα-effect and angular momentum transport (Brandenburg & Schmitt 1998). We present results obtained for a turbulence field driven by a (given) Lorentz force in a non-stratified but rotating convection zone. The main result confirms the numerical findings of Brandenburg & Schmitt that in the northern hemisphere theα-effect and the kinetic helicityℋkin= 〈u′ · rotu′〉 are positive (and negative in the northern hemisphere), this being just opposite to what occurs for the current helicityℋcurr= 〈j′ ·B′〉, which is negative in the northern hemisphere (and positive in the southern hemisphere). There has been an increasing number of papers presenting observations of current helicity at the solar surface, all showing that it isnegativein the northern hemisphere and positive in the southern hemisphere (see Rüdigeret al. 2000, also for a review).

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