<p>The Earth's climate system has undergone significant changes over the past decades, driven primarily by anthropogenic greenhouse gas emissions. These changes have affected various climatic elements, including the direction and speed of mid-latitudes (MLs) westerlies in the Northern Hemisphere (NH), which are crucial to the transfer of matter and energy across the Earth's surface. Examining the spatiotemporal variations in the westerlies is essential for improving our understanding of climate change mechanisms and their implications. Accordingly, this study examined the prolonged variations in MLs westerlies characteristics within the Northern Hemisphere (NH) from 1959 to 2021. Wind data at specific atmospheric pressure levels (PLs) (ranging from 800 to 500 hPa) were extracted from the European Center for Medium-Range Weather Forecasts (ECMWF) version ERA5 (ECMWF Reanalysis version 5) database. Through statistical techniques, the trends and attributes pertaining to shifts in the speed and direction of the westerlies were investigated. The findings demonstrated that the predominant intensity of the average upward trends in the directional component of westerlies at MLs was approximately less than <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11600_2024_1525_Article_IEq1.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="16" /> </InlineMediaObject> <EquationSource Format="TEX">${1}^{^\circ }$</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow> <mn>1</mn> </mrow> <mrow /> <mmultiscripts> <mrow /> <mrow /> <mo>∘</mo> </mmultiscripts> </mmultiscripts> </math></EquationSource> </InlineEquation> per annum. In contrast, the prevailing intensity of the increasing trends in the velocity of westerlies, particularly over the North Atlantic Ocean, surpasses an average of <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11600_2024_1525_Article_IEq2.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="50" /> </InlineMediaObject> <EquationSource Format="TEX">${0.03}^{\text{m}/\text{s}}$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mn>0.03</mn> </mrow> <mrow> <mtext>m</mtext> <mo stretchy="false">/</mo> <mtext>s</mtext> </mrow> </msup> </math></EquationSource> </InlineEquation> per year. Conversely, the intensity of the downward trends in the velocity of westerlies in the southern regions of the North Atlantic Ocean and the Mediterranean Sea is significantly less than -<InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11600_2024_1525_Article_IEq2.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="50" /> </InlineMediaObject> <EquationSource Format="TEX">${0.03}^{\text{m}/\text{s}}$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mn>0.03</mn> </mrow> <mrow> <mtext>m</mtext> <mo stretchy="false">/</mo> <mtext>s</mtext> </mrow> </msup> </math></EquationSource> </InlineEquation> per year. An increasing trend in the westerlies direction was noted across longitudes ranging from <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11600_2024_1525_Article_IEq4.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="32" /> </InlineMediaObject> <EquationSource Format="TEX">${180}^{^\circ }$</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow> <mn>180</mn> </mrow> <mrow /> <mmultiscripts> <mrow /> <mrow /> <mo>∘</mo> </mmultiscripts> </mmultiscripts> </math></EquationSource> </InlineEquation> to <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11600_2024_1525_Article_IEq5.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="32" /> </InlineMediaObject> <EquationSource Format="TEX">${270}^{^\circ }$</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow> <mn>270</mn> </mrow> <mrow /> <mmultiscripts> <mrow /> <mrow /> <mo>∘</mo> </mmultiscripts> </mmultiscripts> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11600_2024_1525_Article_IEq5.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="32" /> </InlineMediaObject> <EquationSource Format="TEX">${270}^{^\circ }$</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow> <mn>270</mn> </mrow> <mrow /> <mmultiscripts> <mrow /> <mrow /> <mo>∘</mo> </mmultiscripts> </mmultiscripts> </math></EquationSource> </InlineEquation> to<InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11600_2024_1525_Article_IEq7.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="32" /> </InlineMediaObject> <EquationSource Format="TEX">${360}^{^\circ }$</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mrow> <mn>360</mn> </mrow> <mrow /> <mmultiscripts> <mrow /> <mrow /> <mo>∘</mo> </mmultiscripts> </mmultiscripts> </math></EquationSource> </InlineEquation>, indicating a transition toward zonal and meridional patterns, particularly evident in regions such as the Northern Atlantic and Pacific Oceans, North Africa, the Mediterranean Sea, and the Eurasia. Furthermore, trends and shifts in direction and speed increased from 800 to 500 hPa. Generally, in the regions of the North Atlantic Ocean and the Mediterranean Sea at the PLs of 500, 550, and 600 hPa, with notable breakpoints occurring more than 30 times in regions such as the North Atlantic Ocean and parts of the northern regions of East Asia, these changes began in the early 1970s, with a pronounced retreat occurring primarily after the 1990s and continuing beyond 2010.</p>

Long-term changes in the speed and direction of westerlies in the mid-latitudes of the Northern Hemisphere (MLNH)

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发表日期：

2025年1月23日

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Hossein Asakereh,
Arman Jahedi

摘要

The Earth's climate system has undergone significant changes over the past decades, driven primarily by anthropogenic greenhouse gas emissions. These changes have affected various climatic elements, including the direction and speed of mid-latitudes (MLs) westerlies in the Northern Hemisphere (NH), which are crucial to the transfer of matter and energy across the Earth's surface. Examining the spatiotemporal variations in the westerlies is essential for improving our understanding of climate change mechanisms and their implications. Accordingly, this study examined the prolonged variations in MLs westerlies characteristics within the Northern Hemisphere (NH) from 1959 to 2021. Wind data at specific atmospheric pressure levels (PLs) (ranging from 800 to 500 hPa) were extracted from the European Center for Medium-Range Weather Forecasts (ECMWF) version ERA5 (ECMWF Reanalysis version 5) database. Through statistical techniques, the trends and attributes pertaining to shifts in the speed and direction of the westerlies were investigated. The findings demonstrated that the predominant intensity of the average upward trends in the directional component of westerlies at MLs was approximately less than ${1}^{^\circ }$ $1^{^{\circ}}$ per annum. In contrast, the prevailing intensity of the increasing trends in the velocity of westerlies, particularly over the North Atlantic Ocean, surpasses an average of ${0.03}^{\text{m}/\text{s}}$ ${0.03}^{m / s}$ per year. Conversely, the intensity of the downward trends in the velocity of westerlies in the southern regions of the North Atlantic Ocean and the Mediterranean Sea is significantly less than - ${0.03}^{\text{m}/\text{s}}$ ${0.03}^{m / s}$ per year. An increasing trend in the westerlies direction was noted across longitudes ranging from ${180}^{^\circ }$ $180^{^{\circ}}$ to ${270}^{^\circ }$ $270^{^{\circ}}$ and ${270}^{^\circ }$ $270^{^{\circ}}$ to ${360}^{^\circ }$ $360^{^{\circ}}$ , indicating a transition toward zonal and meridional patterns, particularly evident in regions such as the Northern Atlantic and Pacific Oceans, North Africa, the Mediterranean Sea, and the Eurasia. Furthermore, trends and shifts in direction and speed increased from 800 to 500 hPa. Generally, in the regions of the North Atlantic Ocean and the Mediterranean Sea at the PLs of 500, 550, and 600 hPa, with notable breakpoints occurring more than 30 times in regions such as the North Atlantic Ocean and parts of the northern regions of East Asia, these changes began in the early 1970s, with a pronounced retreat occurring primarily after the 1990s and continuing beyond 2010.