This is a time for “I statements” to avoid triggering defensiveness on his part. If you are not familiar with this technique, there are lots of resources online. The essence is to create statements that focus on your feelings, the event, the impact, and what you would prefer instead.
For example, you might say, “I feel anxious when you fire questions at me with no context. As a result, I’m less productive and it takes longer to provide the information you need. I would like it if you would give me advance warning to prepare.”
When this goes well, it opens the other person’s eyes to the effect of their behavior. As an optimist, I believe that most people don’t intend to be jerks and will try to do better. You can then develop a shared strategy for interacting constructively.
At the same time, if they are impulsive by nature and are being reactive to their senior leaders, they may have trouble forming a new habit.
That’s where we come back to your personal buffering.
First you need to understand your own triggers. Are your interactions with him more fraught than with other people you engage with? Then keep in mind that your old reactions may no longer be serving you well.
Buffer inwardly. Visualize a shield of some sort that keeps his emotions off you, even as you’re interacting. Use your breath to stay centered.
Buffer externally. When he raises issues out of the blue, take charge. Get him focused, be able to take notes, and remind him of your communication agreement.
Be persistent and advocate for your needs, while being a cooperative partner and colleague.