scholarly journals Eddy Momentum, Heat, and Moisture Transports During the Boreal Winter: Three Reanalysis Data Comparison

Atmosphere ◽  
2016 ◽  
Vol 26 (4) ◽  
pp. 649-663
Author(s):  
Hyejin Moon ◽  
Kyung-Ja Ha
Keyword(s):  
Reanalysis Data ◽  
Boreal Winter ◽  
Data Comparison ◽  
Heat And Moisture ◽  
Moisture Transports

scholarly journals The Climatology of Brewer-Dobson Circulation and the Contribution of Gravity Waves

2018 ◽  
Author(s):  
Kaoru Sato ◽  
Soichiro Hirano
Keyword(s):  
Gravity Waves ◽  
Mass Flux ◽  
Lower Stratosphere ◽  
Reanalysis Data ◽  
Boreal Winter ◽  
Potential Contribution ◽  
Flux Divergence ◽  
Mean Circulation ◽  
Residual Mean Circulation ◽  
Mean State

Abstract. The climatology of residual mean circulation, which is a main component of Brewer-Dobson circulation, and the potential contribution of gravity waves (GWs) are examined for the annual mean state and for each season based on the transformed-Eulerian mean zonal momentum equation using modern four reanalysis data, which allows us to examine the whole stratosphere. First, the potential contribution of Rossby waves (RWs) to residual mean circulation is estimated from Eliassen-Palm flux divergence. The rest of residual-mean circulation, from which the potential RW contribution and zonal mean zonal wind tendency are subtracted, is regarded as the potential GW contribution. These potential wave contributions are exact contributions for the annual mean state and give good approximates for solstitial seasons. The GWs contribute to drive not only the summer hemispheric part of the winter deep branch and low-latitude part of shallow branches, as indicated by previous studies, but also cause a higher-latitude extension of the deep circulation in all seasons except for summer. This GW contribution is essential to determine the location of the turn-around latitude. The autumn circulation is stronger and wider than that of spring in the equinoctial seasons, regardless of almost symmetric RW and GW contributions around the equator. This asymmetry is attributable to the existence of the spring-to-autumn pole circulation corresponding to the angular momentum transport associated with seasonal variation due to the radiative process. The potential GW contribution is larger in September-to-November than in March-to-May in both hemispheres. The upward mass flux is maximized in the boreal winter in the lower stratosphere, while it exhibits semi-annual variation in the upper stratosphere. The GW contribution to the annual mean upward mass flux is in a range of 10–30 %, depending on the reanalysis data. The boreal winter maximum in the lower stratosphere is attributable to stronger RW activity in both hemispheres than in the austral winter.

scholarly journals Observational Evidence of Frontal-Scale Atmospheric Responses to Kuroshio Extension Variability

2015 ◽  
Vol 28 (23) ◽  
pp. 9459-9472 ◽  
Author(s):  
Yi-Hui Wang ◽  
W. Timothy Liu
Keyword(s):  
Kuroshio Extension ◽  
Linear Regression Analysis ◽  
Surface Wind ◽  
Reanalysis Data ◽  
Satellite Observations ◽  
Climate Index ◽  
Boreal Winter ◽  
Atmospheric Response ◽  
Free Atmosphere ◽  
Low Frequencies

Abstract This study investigates the regional atmospheric response to the Kuroshio Extension (KE) using a combination of multiple satellite observations and reanalysis data from boreal winter over a period of at least a decade. The goal is to understand the relationship between KE variations and atmospheric responses at low frequencies. A climate index is used to measure the interannual to decadal KE variability, which leaves remarkable imprints on the mesoscale sea surface temperature (SST). Clear spatial coherence between the SST signals and frontal-scale atmospheric variables, including surface wind convergence, vertical velocity, precipitation, and clouds, is identified by linear regression analysis. Consistent with previous studies, the penetrating effect of the KE variability on the free atmosphere is found. The westward tilt of the atmospheric response above the KE near 500 hPa is revealed. The difference in the associations of frontal-scale air temperature and geopotential height with the KE variability between the satellite observations and the reanalysis data suggests an imperfect interpretation of frontal-scale oceanic forcing on the overlying atmosphere in the reanalysis assimilation system.

Variations of Northern Hemisphere Storm Track and Extratropical Cyclone Activity Associated with the Madden–Julian Oscillation

2017 ◽  
Vol 30 (13) ◽  
pp. 4799-4818 ◽  
Author(s):  
Yanjuan Guo ◽  
Toshiaki Shinoda ◽  
Jialin Lin ◽  
Edmund K. M. Chang
Keyword(s):  
Storm Track ◽  
Meridional Wind ◽  
Reanalysis Data ◽  
Boreal Winter ◽  
Madden Julian Oscillation ◽  
Mean Flow ◽  
Cyclone Activity ◽  
Intraseasonal Variations ◽  
The Pacific ◽  
Cyclone Frequency

This study investigates the intraseasonal variations of the Northern Hemispheric storm track associated with the Madden–Julian oscillation (MJO) during the extended boreal winter (November–April) using 36 yr (1979–2014) of reanalysis data from ERA-Interim. Two methods have been used to diagnose storm-track variations. In the first method, the storm track is quantified by the temporal-filtered variance of 250-hPa meridional wind (vv250) or mean sea level pressure (pp). The intraseasonal anomalies of vv250 composited for eight MJO phases are characterized by a zonal band of strong positive (or negative) anomalies meandering from the Pacific all the way across North America and the Atlantic into northern Europe, with weaker anomalies of opposite sign at one or both flanks. The results based on pp are consistent with those based on vv250 except for larger zonal variations, which may be induced by surface topography. In the second method, an objective cyclone-tracking scheme has been used to track the extratropical cyclones that compose the storm track. The MJO-composite anomalies of the “accumulated” cyclone activity, a quantity that includes contributions from both the cyclone frequency and cyclone mean intensity, are very similar to those based on pp. Further analysis demonstrates that major contribution comes from variations in the cyclone frequency. Further analysis suggests that the intraseasonal variations of the storm track can be primarily attributed to the variations of the mean flow that responds to the anomalous MJO convections in the tropics, with possible contribution also from the moisture variations.

scholarly journals Decadal changes of wintertime poleward heat and moisture transport associated with the amplified Arctic warming

2021 ◽  
Author(s):  
Xiaozhuo Sang ◽  
Xiu-Qun Yang ◽  
Lingfeng Tao ◽  
Jiabei Fang ◽  
Xuguang Sun
Keyword(s):  
Heat Transport ◽  
Moisture Transport ◽  
Stationary Wave ◽  
The Arctic ◽  
Stationary Waves ◽  
High Latitudes ◽  
Arctic Warming ◽  
Poleward Heat Transport ◽  
Heat And Moisture ◽  
Moisture Transports

Abstract The Arctic warming, especially during winter, has been almost twice as large as the global average since the late 1990s, which is known as the Arctic amplification. Yet linkage between the amplified Arctic warming and the midlatitude change is still under debate. This study examines the decadal changes of wintertime poleward heat and moisture transports between two 18-yr epochs (1999–2016 and 1981–1998) with five atmospheric reanalyses. It is found that the wintertime Arctic warming induces an amplification of the high latitude stationary wave component of zonal wavenumber one but a weakening of the wavenumber two. These stationary wave changes enhance poleward heat and moisture transports, which are conducive to further Arctic warming and moistening, acting as a positive feedback onto the Arctic warming. Meanwhile, the Arctic warming reduces atmospheric baroclinicity and thus weakens synoptic eddy activities in the high latitudes. The decreased transient eddy activities reduce poleward heat and moisture transports, which decrease the Arctic temperature and moisture, acting as a negative feedback onto the Arctic warming. The total poleward heat transport contributes little to the Arctic warming, since the increased poleward heat transport by stationary waves is nearly canceled by the decreased transport by transient eddies. However, the total poleward moisture transport increases over most areas of the high latitudes that is dominated by the increased transport by stationary waves, which provides a significant net positive feedback onto the Arctic warming and moistening. Such a poleward moisture transport feedback may be particularly crucial to the amplified Arctic warming during winter when the ice-albedo feedback vanishes.

scholarly journals Coupled Interannual Variability of the Hadley and Ferrel Cells

2018 ◽  
Vol 31 (12) ◽  
pp. 4757-4773 ◽  
Author(s):  
Pablo Zurita-Gotor ◽  
Pablo Álvarez-Zapatero
Keyword(s):  
Angular Momentum ◽  
Meridional Circulation ◽  
Reanalysis Data ◽  
Hadley Cell ◽  
Boreal Winter ◽  
Austral Winter ◽  
Momentum Fluxes ◽  
Mean Meridional Circulation ◽  
Eddy Fluxes ◽  
The Mean

This work investigates the covariability in the strength of the Hadley and Ferrel cells on interannual time scales using reanalysis data. A significant correlation is found in both hemispheres only during boreal winter. For other seasons, only the outermost (subtropical) part of the Hadley cell is correlated with changes in the extratropical eddy momentum fluxes, as the eddies are unable to penetrate into the deep tropics. During boreal winter, the northern Hadley cell variability is driven by extratropical planetary momentum fluxes, but the mean meridional circulation response is primarily found below the level of maximum climatological outflow. Instead, at upper levels, changes in the zonal wind dominate the response to the anomalous eddy forcing. During austral winter, the southern Hadley cell is shielded from the extratropical eddy fluxes and its variability displays some of the characteristics of the angular momentum–conserving solution.

The quantification of development processes of explosive cyclones over Northwestern Pacific and Atlantic in boreal winter

2020 ◽  
Author(s):  
Joonsuk Kang ◽  
Seok-Woo Son
Keyword(s):  
Potential Vorticity ◽  
Geopotential Height ◽  
Reanalysis Data ◽  
Northwestern Pacific ◽  
Boreal Winter ◽  
Mean Flow ◽  
Explosive Cyclones ◽  
Development Processes ◽  
Zonal Advection ◽  
Negative Factors

<p>A method utilizing a prognostic potential vorticity (PV) inversion is designed and applied to quantify the processes that contribute to the explosive cyclone (EC) development over Northwestern Pacific and Atlantic in boreal winter. The ECs deepening in the two remarked regions are identified and tracked, by using the automated tracking method on ERA-Interim reanalysis data over the period of 1979–2017. The quantification process first involves time differentiation of linearized potential vorticity (PV), which results in a linear function of geopotential height tendency. It is then equated with the PV tendency equation that consists of mean and transient advection terms to represent dynamical processes that contribute to EC development. The quantification, finally, is performed through the inversion of PV tendency budgets, which yields corresponding geopotential height tendency. The results indicate that EC development is primarily caused by zonal advection of PV anomalies by mean flow (~65%) and diabatic production of PV (~40%), with some negative factors in both regions. The former contributes more for ECs deepening over Northwestern Atlantic (~71%) than Northwestern Pacific (~60%), whereas the latter contributes to a similar extent.</p>

scholarly journals Contributions of Different Combinations of the IPO and AMO to Recent Changes in Winter East Asian Jets

2019 ◽  
Vol 32 (5) ◽  
pp. 1607-1626 ◽  
Author(s):  
Danqing Huang ◽  
Aiguo Dai ◽  
Ben Yang ◽  
Peiwen Yan ◽  
Jian Zhu ◽  
...  
Keyword(s):  
Potential Energy ◽  
East Asian ◽  
Atlantic Multidecadal Oscillation ◽  
Atmospheric Model ◽  
Polar Front ◽  
Reanalysis Data ◽  
Boreal Winter ◽  
Model Simulations ◽  
Available Potential Energy ◽  
Two Jets

Abstract Recent concurrent shifts of the East Asian polar-front jet (EAPJ) and the East Asian subtropical jet (EASJ) in the boreal winter have raised concerns, since they could result in severe weather events over East Asia. However, the possible mechanisms are not fully understood. In this study, the roles of the interdecadal Pacific oscillation (IPO) and the Atlantic multidecadal oscillation (AMO) are investigated by analyzing reanalysis data and model simulations. Results show that combinations of opposite phases of the IPO and AMO can result in significant shifts of the two jets during 1920–2014. This relationship is particularly evident during 1999–2014 and 1979–98 in the reanalysis data. A combination of a negative phase of the IPO (−IPO) and a positive phase of the AMO (+AMO) since the late 1990s has enhanced the meridional temperature gradient and the Eady growth rate and thus westerlies over the region between the two jets, but weakened them to the south and north of the region, thereby contributing to the equatorward and poleward shifts of the EAPJ and EASJ, respectively. Atmospheric model simulations are further used to investigate the relative contribution of −IPO and +AMO to the jet shifts. The model simulations show that the combination of −IPO and +AMO favors the recent jet changes more than the individual −IPO or +AMO. Under a concurrent −IPO and +AMO, the meridional eddy transport of zonal momentum and sensitive heat strengthens, and more mean available potential energy converts to the eddy available potential energy over the region between the two jets, which enhances westerly winds there.

Amazon Coastal Squall Lines. Part II: Heat and Moisture Transports

1994 ◽  
Vol 122 (4) ◽  
pp. 623-635 ◽  
Author(s):  
Steven Greco ◽  
John Scala ◽  
Jeffrey Halverson ◽  
Harold L. Massie ◽  
Wei-Kuo Tao ◽  
...  
Keyword(s):  
Squall Lines ◽  
Heat And Moisture ◽  
Moisture Transports

scholarly journals On the Extratropical Influence of Variations of the Upper-Tropospheric Equatorial Zonal-Mean Zonal Wind during Boreal Winter

2014 ◽  
Vol 28 (1) ◽  
pp. 168-185 ◽  
Author(s):  
Gereon Gollan ◽  
Richard J. Greatbatch
Keyword(s):  
Time Series ◽  
North Atlantic ◽  
Zonal Wind ◽  
North Pacific ◽  
Wave Train ◽  
Reanalysis Data ◽  
Boreal Winter ◽  
Quasi Biennial Oscillation ◽  
The North ◽  
The North Atlantic

Abstract Variations in the global tropospheric zonal-mean zonal wind [U] during boreal winter are investigated using rotated empirical orthogonal functions applied to monthly means. The first two modes correspond to the northern and southern annular mode and modes 3 and 4 represent variability in the tropics. One is related to El Niño–Southern Oscillation and the other has variability that is highly correlated with the time series of [U] at 150 hPa between 5°N and 5°S [U150]E and is related to activity of the Madden–Julian oscillation. The extratropical response to [U150]E is investigated using linear regressions of 500-hPa geopotential height onto the [U150]E time series. Use is made of reanalysis data and of the ensemble mean output from a relaxation experiment using the European Centre for Medium-Range Weather Forecasts model in which the tropical atmosphere is relaxed toward reanalysis data. The regression analysis reveals that a shift of the Aleutian low and a wave train across the North Atlantic are associated with [U150]E. It is found that the subtropical waveguides and the link between the North Pacific and North Atlantic are stronger during the easterly phase of [U150]E. The wave train over the North Atlantic is associated with Rossby wave sources over the subtropical North Pacific and North America. Finally, it is shown that a linear combination of both [U150]E and the quasi-biennial oscillation in the lower stratosphere can explain the circulation anomalies of the anomalously cold European winter of 1962/63 when both were in an extreme easterly phase.

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