On 17 September 2013, Claudia Stoian asked on the sys-func and sysfling email lists:
What do you think about the following clauses, are they adverbial or non-defining relative clauses?Every night, at exactly 21:53, the Chief Yeoman Warder of the Tower emerges from the Byward Tower wearing his long red coat and Tudor bonnet and carrying a candle lantern and the Queen's Keys.
The clauses in yellow (wearing... and carrying...) are not relative clauses, but rather present participle clauses (one of the three infinitive clause types)
I have never liked the label "adverbial" used in traditional grammar: clauses are not adverbs. "Adverbial" (or adverb-like) is a holdover from grammars which only had one label for each item, (its class), while good grammars label items by both function (what it does in larger units) and structural class (what shape of unit it is). Because we have two kinds of label, rather than talk of adverbial clauses, we can talk of clauses functioning as Adjunct (or as Circumstance, pick your layer).
I would say these clauses are Circumstances, my best guess would be Manner (how did he emerge?) but I am not sure of that.
On The SFL model, Adjuncts and circumstances are functional elements of the clause. Clauses do not function as Adjuncts or circumstances unless they are embedded in a ranking clause. In the example above, the clauses in question are ranking clauses within a clause complex — see analysis here — and so do not function as Adjunct or circumstance.