A Tropical Zodiac Question

[R. Eugene Laughlin]

I have a question for the astrologers in the room, specifically those working the Western Tropical Zodiac with some knowledge of its roots.

The Signs of the Zodiac typically subsume two fundamental qualities: Elemental and Modal. Each Sign can be understood as a unique combination of those two qualities: 4 Elements X 3 Modes = 12 Signs. The assignments of Elemental and Modal qualities are the result of their respective processional orders. For the Modes, the order is Cardinal, Fixed, and Mutable, starting on at the Spring Equinox, which marks the first day of Aries. For the Elements, the order is Fire, Earth, Air, and Water, also starting at the Spring Equinox, so...

Aries = Cardinal Fire
Taurus = Fixed Earth
Gemini = Mutable Air
Cancer = Cardinal Water
Leo = Fixed Fire
Virgo = Mutable Earth
Libra = Cardinal Air
Scorpio = Fixed Water
Sagittarius = Mutable Fire
Capricorn = Cardinal Earth
Aquarius = Fixed Air
Pisces = Mutable Water

The Modal processional order makes sense to me as having its derivation rooted in the natural seasonal cycle on Earth, when the Zodiac commences from the first day of Aries, which is the first day of Spring (the Spring Equinox). That alignment renders three Signs per Season, as follows:

The Cardinal Signs are the relevant season in ascent. The Fixed Signs each are the relevant season at its peak, and the Mutable Signs are the relevant season in decline and transition into the next season. I get that. Indeed, my Pagan heart loves it.

I wonder if anyone here has any insight into the Elemental processional order: Fire, Earth, Air, Water? Is that order derived from a natural cycle too? Is it derived from something else? The order is clearly traditional, but why? What's it about?