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<title>Reversals and excursions of the geodynamo | Astronomy &amp; Geophysics | Oxford Academic</title>
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<div class="volume trailing-comma">Volume 40</div>
<div class=issue>Issue 6</div>
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December 1999 </div>
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Reversals and excursions of the geodynamo
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<button type=button class="linked-name js-linked-name-trigger btn-as-link">J J Love</button><span class=delimiter></span>
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<div class=ww-citation-primary><em>Astronomy &amp; Geophysics</em>, Volume 40, Issue 6, December 1999, Pages 6.146.19, <a href=https://doi.org/10.1093/astrog/40.6.6.14 data-google-interstitial=false>https://doi.org/10.1093/astrog/40.6.6.14</a></div>
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<div class=citation-date>01 December 1999</div>
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<h2 class=authorNotes-section-title id=authorNotesSectionTitle scrollto-destination=authorNotesSectionTitle>Author notes</h2>
<div content-id class=footnote><span class=fn><div class=footnote-content><p class=footnote-compatibility>Many of the issues presented here were addressed in detail at a recent Royal Society Discussion Meeting held in London (7 and 8 July 1999) and organized by Profs David Gubbins, Dennis Kent, and Carlo Laj.</p></div></span></div>
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<div class="__db_score __db_score_normal">5</div>
<div class="__db_label sf-hidden">CITATIONS</div>
<img src="data:image/png;base64,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
</div>
</div></a></span>
</div>
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<div class="contentmet-views contentmet-badges-wrap js-contentmet-views">
<h3 class=contentmet-text>Views</h3>
<div class="contentmet-item circle-text circle-text-views">
<div class=contentmet-number>414</div>
</div>
</div>
<div class="contentmet-item contentmet-badges-wrap">
<h3 class=contentmet-text>Altmetric</h3>
<div class="contentmet-item contentmet-altmetric">
<div class="widget widget-AltmetricLink widget-instance-ArticleLevelMetrics_AltmetricLinkSummary">
<div id=altmetricEmbedId runat=server class=altmetric-embed data-badge-type=donut data-hide-no-mentions=false data-doi=10.1093/astrog/40.6.6.14 data-uuid=1ec35868-b950-ce5c-5b60-5874952790dc><a href="https://www.altmetric.com/details.php?domain=academic.oup.com&amp;doi=10.1093%2Fastrog%2F40.6.6.14" target=_self style=cursor:pointer;display:inline-block;background-image:url(data:image/png;base64,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<span class=contentmet-more-info>More metrics information</span>
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<div class="artmet-modal js-artmet-modal sf-hidden" id=MetricsModal>
<div class="artmet-modal-contents js-metric-modal-contents at-alm-modal-contents sf-hidden">
<div class="artmet-full-wrap clearfix js-metric-full-wrap hide sf-hidden">
<div class="artmet-stats-wrap clearfix sf-hidden">
<div class="artmet-item artmet-citations sf-hidden">
<div class="artmet-badges-wrap artmet-dimensions sf-hidden">
<div class="widget widget-DimensionsBadge widget-instance-ArticleLevelMetrics_DimensionsBadgeDetails sf-hidden">
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<div class="artmet-item artmet-altmetric js-show-if-unknown sf-hidden">
<div class="artmet-badges-wrap js-artmet-badges sf-hidden">
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<div class="widget widget-Alerts widget-instance-Article_RightRailB0Article_RightRail_Alerts">
<div class=alertsWidget>
<h3>Email alerts</h3>
<div class="userAlert alertType-1">
<a class=js-user-alert role=button data-userloggedin=False data-alerttype=1 data-google-interstitial=false>Article activity alert</a>
</div>
<div class="userAlert alertType-3">
<a class=js-user-alert role=button data-userloggedin=False data-alerttype=3 data-google-interstitial=false>Advance article alerts</a>
</div>
<div class="userAlert alertType-5">
<a class=js-user-alert role=button data-userloggedin=False data-alerttype=5 data-google-interstitial=false>New issue alert</a>
</div>
<div class="userAlert alertType-MarketingLink">
<a class=js-user-alert role=button data-userloggedin=False data-additionalurl=/my-account/communication-preferences data-google-interstitial=false>Receive exclusive offers and updates from Oxford Academic</a>
</div>
<div class="userAlertSignUpModal reveal-modal small sf-hidden" data-reveal>
</div>
</div>
</div>
<div class="widget widget-TrendMD widget-instance-Article_RightRailB0trendmd">
<div id=trendmd-suggestions></div>
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<div class="widget widget-AstrophysicsDataSystem widget-instance-Article_RightRailB0Article_RightRail_AstrophysicsDataSystem">
<h3>Astrophysics Data System</h3>
<a href=http://adsabs.harvard.edu/doi/10.1093/astrog/40.6.6.14 target data-google-interstitial=false>ADS Abstract</a>
</div>
<div class="widget widget-ArticleCitedBy widget-instance-Article_RightRailB0Article_RightRail_ArticleCitedBy">
<div class="rail-widget_wrap vt-articles-cited-by">
<h3 class=article-cited-title>Citing articles via</h3>
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