scholarly journals Indices of the Hadley circulation strength and associated circulation trends

2021 ◽  
Author(s):  
Matic Pikovnik ◽  
Žiga Zaplotnik ◽  
Lina Boljka ◽  
Nedjeljka Žagar
Keyword(s):  
Total Energy ◽  
Stream Function ◽  
Hadley Circulation ◽  
Hadley Cell ◽  
Positive Trend ◽  
Function Decomposition ◽  
Mode Function ◽  
Long Term Trends ◽  
Mean Circulation

Abstract. This study compares the trends of Hadley cell (HC) strength using different HC measures applied to the ECMWF ERA5 and ERA-Interim reanalyses in the period 1979–2018. The HC strength is commonly evaluated by indices derived from the mass-weighted zonal-mean stream function. Other measures include the velocity potential and the vertical velocity. Six known measures of the HC strength are complemented by a measure of the average HC strength, obtained by averaging the stream function in the latitude-pressure (φ-p) plane, and by the total energy of unbalanced zonal-mean circulation in the normal-mode function decomposition. It is shown that measures of the HC strength, which rely on point values in the φ-p plane, produce unreliable long-term trends of both the northern and southern HCs, especially in ERA-Interim; magnitudes and even the signs of trends depend on the choice of HC strength measure. The two new measures alleviate the vertical and meridional inhomogeneities of the trends in the HC strength. In both reanalyses, there is a positive trend in the total energy of zonal-mean unbalanced circulation. The average HC strength measure also shows a positive trend in ERA5 in both hemispheres, while the trend in ERA-Interim is insignificant.

Comparison of the Long-Term Trends of the Largest Waves in the Ice-Free Arctic Waters From Different Reanalysis Products

2018 ◽  
Author(s):  
Takuji Waseda ◽  
Takehiko Nose ◽  
Adrean Webb
Keyword(s):  
Arctic Ocean ◽  
The Arctic ◽  
Extreme Value Analysis ◽  
Positive Trend ◽  
Value Analysis ◽  
The Arctic Ocean ◽  
Ship Route ◽  
Long Term Trends ◽  
Horizontal Grid

The long-term trends of the expected largest waves in the ice-free Arctic waters from Laptev to Beaufort Seas was studied analyzing the ERA-interim reanalysis from 1979 to 2016. The analysis showed that the positive trend is largest in October and increased almost 70 cm in 38 years. For ships navigating the Northern Ship Route, it is important to know what the possible largest waves to expect during its cruise. In view of conducting the extreme value analysis, the uncertainty of the largest wave needs to be validated. However, the observation in the Arctic Ocean is limited. We, therefore, rely on the reanalysis wave products in the Arctic Ocean, whose uncertainty is yet to be determined. ERA-Interim and ERA-5 are compared in the Laptev, the East Siberian, Chukchi and Beaufort Seas. The comparison is relevant as the two products differ in its horizontal grid resolution and availability of the satellite altimeter significant wave height data assimilation. During 2010–2016 when the ERA5 is available, only a small difference from ERA-Interim was detected in the mean. However, the expected largest waves in the domain tended to be large for the ERA-5, 8% normalized bias. The tendency was quite similar with a high correlation of 0.98.

scholarly journals West African Summer Monsoon Precipitation Variability as Represented by Reanalysis Datasets

Climate ◽  
2020 ◽  
Vol 8 (10) ◽  
pp. 111
Author(s):  
Kwesi Akumenyi Quagraine ◽  
Francis Nkrumah ◽  
Cornelia Klein ◽  
Nana Ama Browne Klutse ◽  
Kwesi Twentwewa Quagraine
Keyword(s):  
Summer Monsoon ◽  
Southern Oscillation ◽  
West African Monsoon ◽  
West African ◽  
Positive Trend ◽  
In Situ Data ◽  
Dry Conditions ◽  
Long Term Trends

Focusing on West Africa, a region riddled with in situ data scarcity, we evaluate the summer monsoon monthly rainfall characteristics of five global reanalysis datasets: ERA5, ERA-Interim, JRA-55, MERRA2, and NCEP-R2. Their performance in reproducing the West African monsoon (WAM) climatology, interannual variability, and long-term trends for the main monsoon months are compared to gauge-only and satellite products. We further examine their ability to reproduce teleconnections between sea surface temperatures and monsoon rainfall. All reanalyses are able to represent the average rainfall patterns and seasonal cycle; however, regional biases can be marked. ERA5, ERA-Interim, and NCEP-R2 underestimate rainfall over areas of peak rainfall, with ERA5 showing the strongest underestimation, particularly over the Guinea Highlands. The meridional northward extent of the monsoon rainband is well captured by JRA-55 and MERRA2 but is too narrow in ERA-Interim, for which rainfall stays close to the Guinea Coast. Differences in rainband displacement become particularly evident when comparing strong El Niño Southern Oscillation (ENSO) years, where all reanalyses except ERA-Interim reproduce wetter Sahelian conditions for La Niña, while overestimating dry conditions at the coast except for NCEP-R2. Precipitation trends are not coherent across reanalyses and magnitudes are generally overestimated compared to observations, with only JRA-55 and NCEP-R2 displaying the expected positive trend in the Sahel. ERA5 generally outperforms ERA-Interim, highlighting clear improvements over its predecessor. Ultimately, we find the strengths of reanalyses to strongly vary across the region.

A Closer Comparison of Early and Late-Winter Atmospheric Trends in the Northern Hemisphere

2005 ◽  
Vol 18 (16) ◽  
pp. 3204-3216 ◽  
Author(s):  
Yongyun Hu ◽  
Ka Kit Tung ◽  
Jiping Liu
Keyword(s):  
Northern Hemisphere ◽  
General Circulation ◽  
Polar Vortex ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Reanalysis Data ◽  
Hadley Cell ◽  
The Arctic ◽  
Late Winter ◽  
Positive Trend

Abstract Decadal trends are compared in various fields between Northern Hemisphere early winter, November–December (ND), and late-winter, February–March (FM), months using reanalysis data. It is found that in the extratropics and polar region the decadal trends display nearly opposite tendencies between ND and FM during the period from 1979 to 2003. Dynamical trends in late winter (FM) reveal that the polar vortex has become stronger and much colder and wave fluxes from the troposphere to the stratosphere are weaker, consistent with the positive trend of the Arctic Oscillation (AO) as found in earlier studies, while trends in ND appear to resemble a trend toward the low-index polarity of the AO. In the Tropics, the Hadley circulation shows significant intensification in both ND and FM, with stronger intensification in FM. Unlike the Hadley cell, the Ferrel cell shows opposite trends between ND and FM, with weakening in ND and strengthening in FM. Comparison of the observational results with general circulation model simulations is also discussed.

scholarly journals Impact of Fake Below-Ground Meridional Wind on Hadley Circulation: Climatology, Interannual Variability, and Long-Term Trends

Atmosphere ◽  
2020 ◽  
Vol 11 (5) ◽  
pp. 446
Author(s):  
Jianbo Cheng ◽  
Zhihang Xu ◽  
Xiaoya Hou
Keyword(s):  
Interannual Variability ◽  
Hadley Circulation ◽  
Absolute Magnitude ◽  
Meridional Wind ◽  
Reanalysis Data ◽  
Computing Methods ◽  
Boreal Summer ◽  
Below Ground ◽  
Long Term Trends

The fake below-ground meridional wind (FBGMW) exists in reanalysis products which is not present in the real atmosphere and should be removed before calculating the mass stream function (MSF). In this study, the impacts of FBGMW on Hadley circulation (HC) in terms of climatology, interannual variability, and long-term trends were investigated using five reanalysis data sets based on three different computing methods. Generally, the impacts of FBGMW on the HC are most notable, although the absolute magnitude of the FBGMW is rather small. The key finding of this study is that the FBGMW has vital influences on the Northern Hemisphere (NH) HC during boreal summer. This is because the NH HC during boreal summer is very weak; the errors of the MSF caused by not considering FBGMW have more obvious influences on the NH HC during boreal summer than that in other months. The previous analysis without considering FBGMW led to overestimation of the poleward expansion of the NH HC during boreal summer, and the long-term trends of the HC should be more accurately estimated after considering the FBGMW. This finding suggests that the previous studies related to the NH HC during boreal summer without considering FBGMW should be reconsidered.

scholarly journals The Interannual Relationship between the Latitude of the Eddy-Driven Jet and the Edge of the Hadley Cell

2011 ◽  
Vol 24 (2) ◽  
pp. 563-568 ◽  
Author(s):  
Sarah M. Kang ◽  
Lorenzo M. Polvani
Keyword(s):  
Coupled Model ◽  
Austral Summer ◽  
Hadley Cell ◽  
Model Intercomparison ◽  
Phase 3 ◽  
Long Term Trends ◽  
Intercomparison Project ◽  
Highly Correlated ◽  
Universal Ratio

Abstract A strong correlation between the latitudes of the eddy-driven jet and of the Hadley cell edge, on interannual time scales, is found to exist during austral summer, in both the NCEP–NCAR reanalysis and the models participating in the Coupled Model Intercomparison Project, phase 3 (CMIP3). In addition, a universal ratio close to 1:2 characterizes the robust connection between these two latitudes on a year-to-year basis: for a 2° shift of the eddy-driven jet, the edge of the Hadley cell shifts by 1°. This 1:2 interannual ratio remains the same in response to climate change, even though the values of the two latitudes increase. The corresponding trends are also highly correlated; in the CMIP3 scenario integrations, however, no universal ratio appears to exist connecting these long-term trends. In austral winter and in the Northern Hemisphere, no strong interannual correlations are found.

scholarly journals Statistics of long-term ionospheric measurements

2012 ◽  
Vol 10 ◽  
pp. 255-258 ◽  
Author(s):  
T. Damboldt ◽  
P. Suessmann
Keyword(s):  
Solar Activity ◽  
Solar Minimum ◽  
Marked Decrease ◽  
Lower Thermosphere ◽  
Neutral Density ◽  
Positive Trend ◽  
Long Term Trends ◽  
Dominant Influence ◽  
Trend Reversal

Abstract. It is shown that after elimination of the dominant influence of solar activity, the height hmF2 of the maximum ionisation of the ionosphere (which is inversely linearly related to M(3000)F2 as described for example by the Shimazaki formula) shows a marked decrease during the recent solar minimum (2005 to 2009) of about 20 km. This is in accordance with results of studies of the decreased neutral density of the lower thermosphere and the density decrease at about 400 km during the unusual recent solar minimum. It is also shown that there is a trend reversal in the height of the ionosphere hmF2 in about 1963/1964 with a negative trend from 1942 to 1963 and a positive trend from 1964 to 2005. This is in contrast to the results reported in most other publications of ionospheric long-term trends. There is no significant trend in foF2 and, particularly, none of the effects described above for hmF2 could be found in foF2.

Statistical analysis of long-term trends in UK effective rainfall: implications for deep-seated landsliding

2020 ◽  
Vol 53 (4) ◽  
pp. 587-597
Author(s):  
E.M. Lee
Keyword(s):  
Time Series ◽  
Statistical Test ◽  
Positive Trend ◽  
Effective Rainfall ◽  
Significant Spatial Variation ◽  
Long Term Trends ◽  
Temperature Records ◽  
Parametric Statistical Test ◽  
The Uk

Rainfall and its impact on the water content of a slope are known to be important controls on landslide activity in the UK. This paper presents an analysis of long-term monthly rainfall and temperature records from selected stations throughout the UK, including the application of a non-parametric statistical test to evaluate the significance of any trends in these time series. The results indicate that there is significant spatial variation in the long-term trends. A positive trend of increasing effective rainfall (precipitation minus evapotranspiration) is present at some (but not all) Scottish stations (Eskdalemuir, Lerwick, Paisley, Stornoway and Tiree), but is not present across the rest of the UK.

scholarly journals Trends in the characteristics of the annual and semiannual variations observed in the radio wave absorption in the lower ionosphere

1999 ◽  
Vol 17 (10) ◽  
pp. 1336-1343 ◽  
Author(s):  
J. Laštovička ◽  
D. Pancheva
Keyword(s):  
Radio Wave ◽  
Lower Thermosphere ◽  
Lower Ionosphere ◽  
Positive Trend ◽  
Continuous Increase ◽  
Wave Absorption ◽  
Yearly Average ◽  
Radio Wave Absorption ◽  
Long Term Trends

Abstract. The continuous increase in concentration of greenhouse gases in the atmosphere is expected to cool higher levels of the atmosphere. There is some direct and indirect experimental evidence of long-term trends in temperature and other parameters in the mesosphere and lower thermosphere (MLT). Here we look for long-term trends in the annual and semiannual variations of the radio wave absorption in the lower ionosphere, which corresponds to the MLT region heights. Data from central and southeastern Europe are used. A consistent tendency to a positive trend in the amplitude of the semiannual wave appears to be observed. The reality of a similar tendency in the amplitude of the annual wave is questionable in the sense that the trend in the amplitude of the annual wave is probably induced by the trend in the yearly average values of absorption. The phases of both the annual and semiannual waves display a forward tendency, i.e. shift to an earlier time in the year. A tentative interpretation of these results in terms of changes of the seasonal variation of temperature and wind at MLT heights does not contradict the trends observed in those parameters.Key words. Ionosphere (ionosphere – atmosphere interactions; mid-latitude ionosphere) · Meteorology and atmospheric dynamics (middle atmosphere dynamics)

Sign in / Sign up

Export Citation Format

Share Document