scholarly journals Annular versus Nonannular Variability of the Northern Hemisphere Atmospheric Circulation

2008 ◽  
Vol 21 (13) ◽  
pp. 3180-3190 ◽  
Author(s):  
J. M. Castanheira ◽  
M. L. R. Liberato ◽  
L. de la Torre ◽  
H-F. Graf ◽  
A. Rocha
Keyword(s):  
Northern Hemisphere ◽  
Geopotential Height ◽  
Normal Modes ◽  
Principal Component ◽  
Reanalysis Data ◽  
Residual Variability ◽  
Middle Latitudes ◽  
Symmetric Component ◽  
Tropospheric Circulation ◽  
Highly Correlated

Abstract The annular variability of the northern winter extratropical circulation is reassessed based on reanalysis data that are dynamically filtered by normal modes. One-half of the variability of the monthly averaged barotropic zonally symmetric circulation of the Northern Hemisphere is statistically distinct from the remaining variability and is represented by its leading empirical orthogonal function (EOF) alone. The daily time series of the circulation anomalies projected onto the leading EOF is highly correlated (r ≥ 0.7) with the lower-stratospheric northern annular mode (NAM) indices showing that annular variability extends from the stratosphere deep into the troposphere. However, the geopotential and wind anomalies associated with the leading principal component (PC1) of the barotropic zonally symmetric circulation are displaced northward relative to the zonal mean anomalies associated with the PC1 of the geopotential height variability at single-isobaric tropospheric levels. The regression pattern of the 500-hPa geopotential height (Z500) onto the lower-stratospheric NAM also shows zonally symmetric components displaced northward with respect to those of the leading EOF of the Z500 field. A principal component analysis (PCA) of the residual variability of the Z500 field remaining after the substraction of the Z500 regressed onto the lower-stratospheric NAM index also reveals a pattern with a zonally symmetric component at midlatitudes. However, this zonally symmetric component appears as the second EOF of the residual variability and is the imprint of two independent dipoles over the Pacific and Atlantic Oceans. Results show that a zonally symmetric component of the middle- and lower-tropospheric circulation variability exists at high latitudes. At the middle latitudes, the zonally symmetric component, if any exists, is artificially overemphasized by the PCA on single-isobaric tropospheric levels.

Detecting regimes of the mid-latitude atmospheric circulation by nonlinear data decomposition

2020 ◽  
Author(s):  
Dmitry Mukhin ◽  
Abdel Hannachi
Keyword(s):  
Atmospheric Circulation ◽  
Northern Hemisphere ◽  
Large Scale ◽  
Decadal Variability ◽  
Principal Component ◽  
Reanalysis Data ◽  
Kernel Principal Component Analysis ◽  
Middle Latitudes ◽  
External Forcings

<p>We suggest a method for nonlinear analysis of atmospheric circulation regimes in the middle latitudes. The method is based on the kernel principal component analysis allowing to separate principal modes of dynamics entangled in data. We propose a new kernel function accounting specifics of large-scale wave patterns in the mid-latitude atmosphere. First, capabilities of the method are shown by the analysis of the 3-layer quasi-geostrophic model of the Northern hemisphere atmosphere: a statistically significant set of modes can be detected by the method from relatively short (several thousand days) time series. Next, we consider reanalysis data of wintertime geopotential height anomalies over the Northern hemisphere from 1950 to the present. The principal components obtained uncover several recurrent and persistent wave structures which are associated with different weather regimes. We find that there is a pronounced inter-annual and decadal variability in the dominance of different modes in different years. Possible climatic and external forcings which impact such variability as well as long-term predictability of anomalous weather seasons based on the obtained components are discussed.</p>

scholarly journals Characterizing quasi-biweekly variability of the Asian monsoon anticyclone using potential vorticity and large-scale geopotential height field

2020 ◽  
Vol 20 (22) ◽  
pp. 13857-13876
Author(s):  
Arata Amemiya ◽  
Kaoru Sato
Keyword(s):  
Potential Vorticity ◽  
Geopotential Height ◽  
Large Scale ◽  
Asian Monsoon ◽  
Reanalysis Data ◽  
Longitudinal Distribution ◽  
Middle Latitudes ◽  
Subseasonal Variability ◽  
Westward Movement ◽  
Isentropic Surface

Abstract. The spatial pattern of subseasonal variability of the Asian monsoon anticyclone is analyzed using long-term reanalysis data, focusing on the large-scale longitudinal movement. The air inside the anticyclone is quantified by a thickness-weighted low-PV (potential vorticity) area on an isentropic surface. It is shown that the longitudinal movement of the air inside the Asian monsoon anticyclone has a timescale of 1 to 2 weeks, which is shorter than the monthly dominant timescale of the variability in the anticyclone intensity. The movement of the anticyclonic air is suggested to be largely controlled by passive advection. The typical time evolution of the variability pattern, explained by two leading empirical orthogonal function (EOF) components of 100 hPa geopotential height, shows large-scale geopotential anomalies moving westward spanning from low to middle latitudes. This corresponds well with the rapid westward movement of low-PV air known as “eddy shedding” and following the eastward retreat of the anticyclonic air. The two EOF components can also explain the bimodal longitudinal distribution of geopotential maximum location.

scholarly journals Are the Northern Hemisphere Winter Storm Tracks Significantly Correlated?

2004 ◽  
Vol 17 (21) ◽  
pp. 4230-4244 ◽  
Author(s):  
Edmund K. M. Chang
Keyword(s):  
Northern Hemisphere ◽  
Storm Track ◽  
Reanalysis Data ◽  
Storm Tracks ◽  
The Pacific ◽  
Aircraft Observations ◽  
Highly Correlated ◽  
Hemisphere Winter ◽  
Aircraft Data ◽  
Northern Hemisphere Winter

Abstract In this study, the correlation between the Northern Hemisphere winter Pacific and Atlantic storm tracks is examined using the NCEP–NCAR reanalysis and the 40-yr ECMWF Re-Analysis (ERA-40), as well as unassimilated aircraft observations. By examining month-to-month variability in the 250-hPa meridional velocity variance, the correlation between the two storm track peaks is found to be as high as 0.5 during the winters between 1975/76 and 1998/99. Here, it is shown that the correlation between the two storm tracks can be clearly detected from the aircraft data. Further analyses of the reanalysis data show that the correlation can also be seen in other eddy variance and covariance statistics, including the poleward heat flux at the 700-hPa level. The correlation between the two storm tracks, as seen in both reanalysis datasets, is shown to be much weaker during the period 1957/58–1971/72, suggesting a possible regime transition from largely uncorrelated storm tracks to highly correlated storm tracks during the 1970s. However, during this earlier period, the number of aircraft observations is insufficient to verify the low correlation seen in the reanalyses. Thus, low biases in the reanalyses during the earlier period cannot be ruled out. An ensemble of four GCM simulations performed using the GFDL GCM forced by global observed SST variations between 1950 and 1995 has also been examined. The correlation between the two storm tracks in the GCM simulations is much lower (0.18) than that observed, even if the analysis is restricted to the GCM simulations from the period 1975/76–1994/95. A Monte Carlo test shows that the observed correlation and the GCM correlation are statistically distinct at the 1% level. Correlations between the Southern Hemisphere summer Pacific and Atlantic storm tracks have also been examined based on the reanalyses datasets. The results suggest that the amplitude of the SH summer Pacific and Atlantic storm tracks are not significantly correlated, showing that seeding of the Atlantic storm track by the Pacific storm track does not necessarily lead to significant correlations between the two storm tracks.

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 Northern Hemisphere Modes of Variability and the Timing of Spring in Western North America

2011 ◽  
Vol 24 (15) ◽  
pp. 4003-4014 ◽  
Author(s):  
Toby R. Ault ◽  
Alison K. Macalady ◽  
Gregory T. Pederson ◽  
Julio L. Betancourt ◽  
Mark D. Schwartz
Keyword(s):  
North America ◽  
Northern Hemisphere ◽  
Principal Component ◽  
Reanalysis Data ◽  
Onset Date ◽  
Western North America ◽  
Spatial And Temporal Patterns ◽  
Modes Of Variability ◽  
Index Model ◽  
Maximum Temperatures

Abstract Spatial and temporal patterns of variability in spring onset are identified across western North America using a spring index (SI) model based on weather station minimum and maximum temperatures (Tmin and Tmax, respectively). Principal component analysis shows that two significant and independent patterns explain roughly half of the total variance in the timing of spring onset from 1920 to 2005. However, these patterns of spring onset do not appear to be linear responses to the primary modes of variability in the Northern Hemisphere: the Pacific–North American pattern (PNA) and the northern annular mode (NAM). Instead, over the period when reanalysis data and the spring index model overlap (1950–2005), the patterns of spring onset are local responses to the state of both the PNA and NAM, which together modulate the onset date of spring by 10–20 days on interannual time scales. They do so by controlling the number and intensity of warm days. There is also a regionwide trend in spring advancement of about −1.5 days decade−1 from 1950 to 2005. Trends in the NAM and PNA can only explain about one-third (−0.5 day decade−1) of this trend.

scholarly journals Suitability Analysis of 17 Probiotic Type Strains of Lactic Acid Bacteria as Starter for Kimchi Fermentation

Foods ◽  
2021 ◽  
Vol 10 (6) ◽  
pp. 1435
Author(s):  
Hee Seo ◽  
Jae-Han Bae ◽  
Gayun Kim ◽  
Seul-Ah Kim ◽  
Byung Hee Ryu ◽  
...  
Keyword(s):  
Lactic Acid ◽  
Lactic Acid Bacteria ◽  
Growth Rates ◽  
Principal Component ◽  
Fermented Foods ◽  
Suitability Analysis ◽  
Moderate Growth ◽  
Health Promoting ◽  
Highly Correlated ◽  
Type Strains

The use of probiotic starters can improve the sensory and health-promoting properties of fermented foods. This study aimed to evaluate the suitability of probiotic lactic acid bacteria (LAB) as a starter for kimchi fermentation. Seventeen probiotic type strains were tested for their growth rates, volatile aroma compounds, metabolites, and sensory characteristics of kimchi, and their characteristics were compared to those of Leuconostoc (Le.) mesenteroides DRC 1506, a commercial kimchi starter. Among the tested strains, Limosilactobacillus fermentum, Limosilactobacillus reuteri, Lacticaseibacillus rhamnosus, Lacticaseibacillus paracasei, and Ligilactobacillus salivarius exhibited high or moderate growth rates in simulated kimchi juice (SKJ) at 37 °C and 15 °C. When these five strains were inoculated in kimchi and metabolite profiles were analyzed during fermentation using GC/MS and 1H-NMR, data from the principal component analysis (PCA) showed that L. fermentum and L. reuteri were highly correlated with Le. mesenteroides in concentrations of sugar, mannitol, lactate, acetate, and total volatile compounds. Sensory test results also indicated that these three strains showed similar sensory preferences. In conclusion, L. fermentum and L. reuteri can be considered potential candidates as probiotic starters or cocultures to develop health-promoting kimchi products.

scholarly journals Probabilistic Forecasting of the 500 hPa Geopotential Height over the Northern Hemisphere Using TIGGE Multi-model Ensemble Forecasts

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 253
Author(s):  
Luying Ji ◽  
Qixiang Luo ◽  
Yan Ji ◽  
Xiefei Zhi
Keyword(s):  
Northern Hemisphere ◽  
Geopotential Height ◽  
Prediction Skill ◽  
Ensemble Prediction ◽  
Lead Times ◽  
Height Distribution ◽  
Height Field ◽  
Probabilistic Forecasting ◽  
Ensemble Forecasts ◽  
Geopotential Height Field

Bayesian model averaging (BMA) and ensemble model output statistics (EMOS) were used to improve the prediction skill of the 500 hPa geopotential height field over the northern hemisphere with lead times of 1–7 days based on ensemble forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF), National Centers for Environmental Prediction (NCEP), and UK Met Office (UKMO) ensemble prediction systems. The performance of BMA and EMOS were compared with each other and with the raw ensembles and climatological forecasts from the perspective of both deterministic and probabilistic forecasting. The results show that the deterministic forecasts of the 500 hPa geopotential height distribution obtained from BMA and EMOS are more similar to the observed distribution than the raw ensembles, especially for the prediction of the western Pacific subtropical high. BMA and EMOS provide a better calibrated and sharper probability density function than the raw ensembles. They are also superior to the raw ensembles and climatological forecasts according to the Brier score and the Brier skill score. Comparisons between BMA and EMOS show that EMOS performs slightly better for lead times of 1–4 days, whereas BMA performs better for longer lead times. In general, BMA and EMOS both improve the prediction skill of the 500 hPa geopotential height field.

scholarly journals Southern Hemisphere atmospheric blocking diagnostic by ECMWF and NCEP/NCAR data

2012 ◽  
Vol 27 (3) ◽  
pp. 263-271 ◽  
Author(s):  
Monica Cristina Damião Mendes ◽  
Iracema F. A. Cavalcanti ◽  
Dirceu Luis Herdies
Keyword(s):  
Atlantic Ocean ◽  
Southern Hemisphere ◽  
Geopotential Height ◽  
Seasonal Cycle ◽  
South Pacific ◽  
Reanalysis Data ◽  
Data Sets ◽  
Atmospheric Blocking ◽  
Assimilation Scheme

An assessment of blocking episodes over the Southern Hemisphere, selected from the Era-40 and NCEP/NCAR reanalysis are presented in this study. Blocking can be defined by an objective index based on two 500 hPa geopotential height meridional gradients. The seasonal cycle and preferential areas of occurrence are well reproduced by the two data sets. In both reanalysis used in this study, South Pacific and Oceania were the preferred regions for blocking occurrence, followed by the Atlantic Ocean. However the results revealed differences in frequencies of occurrences, which may be related to the choice of assimilation scheme employed to produce the reanalysis data sets. It is important to note that the ERA 40 and NCEP/NCAR reanalysis were produced using consistent models and assimilation schemes throughout the whole reanalyzed period, which are different for each set.

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