<p>The properties of kinetic Alfvén waves (KAWs) are investigated in the negative positive ion electron (NPIE) plasma of Titan’s ionosphere. The concentrations of positive and negative ions in dayside and nightside regions of this ionosphere are different, whereas the magnitude of the ambient magnetic field also varies. The plasma data indicate the possibility for the existence of very low frequency and long wavelength kinetic Alfvén waves (KAWs) in this environment. The frequencies and wavelengths of these waves are estimated considering only the two kinds of positive <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10509_2025_4461_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="70" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>H</mi> <mi>C</mi> <mi>N</mi> <msup> <mi>H</mi> <mo>+</mo> </msup> </math></EquationSource> <EquationSource Format="TEX">$HCNH^{+}$</EquationSource> </InlineEquation> and negative <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10509_2025_4461_Article_IEq2.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="41" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>C</mi> <msup> <mi>N</mi> <mo>−</mo> </msup> </math></EquationSource> <EquationSource Format="TEX">$CN^{-}$</EquationSource> </InlineEquation> ions, which have dominant concentrations. Extremely small magnetic field <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10509_2025_4461_Article_IEq3.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="103" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mo stretchy="false">∣</mo> <msub> <mi>B</mi> <mn>0</mn> </msub> <mo stretchy="false">∣</mo> <mo>≃</mo> <mn>0.0002</mn> </math></EquationSource> <EquationSource Format="TEX">$\mid B_{0} \mid \simeq 0.0002$</EquationSource> </InlineEquation> <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10509_2025_4461_Article_IEq4.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>G</mi> </math></EquationSource> <EquationSource Format="TEX">$G$</EquationSource> </InlineEquation> can sustain KAWs with extremely small frequencies of the order of <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10509_2025_4461_Article_IEq5.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="100" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mo>≃</mo> <mn>0.004</mn> <mtext> rad</mtext> <mo stretchy="false">/</mo> <mtext>s</mtext> </math></EquationSource> <EquationSource Format="TEX">$\simeq 0.004\text{ rad}/\text{s}$</EquationSource> </InlineEquation> and very long wavelengths of the order of a thousand kilometres along field lines while the Titan is about a million kilometres away from Saturn’s surface. It is pointed out that the weakly nonlinear KAWs can also give rise to electromagnetic solitary waves similar to the Earth’s upper ionosphere. The formation of solitary structures by the nonlinear KAWs is also investigated using the appropriate normalization of spatial coordinates in parallel and perpendicular directions with respect to the ambient magnetic field. The almost stationary electromagnetic pulses may appear in Titan’s ionosphere moving at very small speeds.</p>

Properties of kinetic Alfvén waves (KAWs) in negative-positive ion plasma of Titan’s ionosphere

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发表日期：

2025年8月6日

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Shanza Arooj,
Shaukat Ali Shan,
Hamid Saleem

摘要

The properties of kinetic Alfvén waves (KAWs) are investigated in the negative positive ion electron (NPIE) plasma of Titan’s ionosphere. The concentrations of positive and negative ions in dayside and nightside regions of this ionosphere are different, whereas the magnitude of the ambient magnetic field also varies. The plasma data indicate the possibility for the existence of very low frequency and long wavelength kinetic Alfvén waves (KAWs) in this environment. The frequencies and wavelengths of these waves are estimated considering only the two kinds of positive $H C N H^{+}$ $HCNH^{+}$ and negative $C N^{-}$ $CN^{-}$ ions, which have dominant concentrations. Extremely small magnetic field $∣ B_{0} ∣ ≃ 0.0002$ $\mid B_{0} \mid \simeq 0.0002$ $G$ $G$ can sustain KAWs with extremely small frequencies of the order of $≃ 0.004 rad / s$ $\simeq 0.004\text{ rad}/\text{s}$ and very long wavelengths of the order of a thousand kilometres along field lines while the Titan is about a million kilometres away from Saturn’s surface. It is pointed out that the weakly nonlinear KAWs can also give rise to electromagnetic solitary waves similar to the Earth’s upper ionosphere. The formation of solitary structures by the nonlinear KAWs is also investigated using the appropriate normalization of spatial coordinates in parallel and perpendicular directions with respect to the ambient magnetic field. The almost stationary electromagnetic pulses may appear in Titan’s ionosphere moving at very small speeds.