用自监督学习发现太阳风双重起源,突破传统聚类的几何限制。
Discovering Dual-Origin Slow Wind from Solar Orbiter with Self-Supervised Contrastive Learning

- 基于Transformer和对比学习构建自监督聚类框架Solar-CDC
- 在3万+观测数据上实现0.869的轮廓系数,显著超越传统方法
- 无需输入电荷态信息也能复现已知分类,揭示日冕洞边界源区
慢太阳风是否源自单一日冕源或两个不同通道,是日地物理中的核心未解之谜。解决该问题需对抵达速度相近但重离子成分不同的两类群体进行无监督分离。本文提出Solar-CDC,一种基于Transformer编码器的自监督对比深度聚类框架,通过三元组边界损失优化嵌入空间,并利用k-means动态更新伪标签。理论上证明,t-SNE、UMAP等保持邻域结构的方法存在根本性局限:保留邻接图将使跨簇切分比例不变,保留1-ε比例链接最多使该比例移动ε,且两者均与目标维度无关。引入边界目标可重构图结构,使切分比例趋近于零。实验上,在30,602条Solar Orbiter观测数据中,30种降维与聚类组合最高轮廓系数仅0.454,而Solar-CDC达0.869。仅突破几何约束不足以保证物理合理性:TriMap虽也优化三元组并达0.824,但其聚类在已知成分分类上表现低于随机。Solar-CDC则恢复出平均电荷态比为0.080、0.160、0.400的三类,中间组位于与日冕洞边界相关的窗口内。即使完全不提供电荷态比作为输入,模型仍能复现该分类体系。因此,Solar-CDC将自监督表示学习与日冕源诊断相连接。关键在于,只有当学习损失由动态更新的物理可解释聚类驱动时,才能恢复真实物理群体。
原文摘要 · Abstract (English)
Whether the slow solar wind originates from one coronal source or two distinct channels remains a central open question in heliophysics. Resolving this requires unsupervised separation of two populations that arrive at nearly the same bulk speed and differ mainly in heavy-ion composition. We present Solar-CDC, a self-supervised contrastive deep clustering (CDC) framework that maps plasma observables to a latent space via a Transformer encoder, optimizes a triplet margin loss, and updates pseudo-labels via $k$-means. Theoretically, we prove that neighborhood-preserving embeddings such as t-SNE and UMAP are fundamentally constrained. Preserving the neighbor graph leaves the cross-cluster cut fraction unchanged, and preserving all but a fraction $\varepsilon$ of its links moves that fraction by at most $\varepsilon$. Neither bound depends on the target dimension. A margin objective rewrites the graph and drives the cut fraction to zero. Empirically, on 30,602 Solar Orbiter observations, thirty combinations of dimensionality reduction and clustering peak at a silhouette of $0.454$, whereas Solar-CDC reaches $0.869$. Escaping the geometric bound alone does not guarantee physical validity: TriMap also optimizes triplets and reaches $0.824$, yet its clusters score below chance against the published composition taxonomy. Solar-CDC instead recovers clusters with mean charge-state ratios of $0.080$, $0.160$, and $0.400$, placing the intermediate population inside the window associated with coronal-hole boundaries. Even when the defining charge-state ratio is withheld from the inputs entirely, the model still recovers the taxonomy defined on it. Solar-CDC thus connects self-supervised representation learning to coronal source diagnostics. Importantly, a learning loss recovers physical populations only when driven by dynamically updated physically-aware clusters rather than distances.
Thank you to arXiv for use of its open access interoperability. PaperDance 不是 arXiv 官方产品;中文卡片由大模型生成,请以原文为准。