#2894 "Dumoine Gravity Waves on Gravity Waves"

2894 "Dumoine Gravity Waves on Gravity Waves"
Oils on canvas panel 8 X 10 (inches).
Started 8:45 am Saturday, August 3rd, 2024
from very near N46.467042 W77.767350.

It was time to retreat from the strong August sunshine and heat. I paddled upstream to the Dumoine Campsite and set up my easel in the shade on terra firma. I stood at the sandy slope beside the gnarled roots I had painted in #2882 "Dumoine Shore Twisted Roots" on Thursday, August 1st. The trees that surround the large fire pit provided the shadows and shelter that I needed. I had painted from the canoe for more than two hours and standing on the shoreline with my field easel was a welcomed change. 

The low horizon reveals that the focus of this painting is the weather - surprise, surprise. There were two trains of gravity waves in that sky that caught my interest. There were also gravity waves on the flatwater of the Dumoine that reflected the sky.  The morning light coloured the clouds and I wanted to capture those hues before they disappeared with higher sun angles. 

The larger bands of altocumulus clouds were evenly spaced with relatively smooth and straight edges. These gravity waves were aligned perpendicular to the southeasterly flow at cloud level. The flow followed a wave pattern upward into the cloudy crests and then downward into the trough below the lifted condensation level for that portion of the atmosphere. The stable layer sponsoring these waves was the warm frontal surface of the air mass. The amplitude and wavelength of the gravity waves are explained in the above inset overlaying the actual skyscape that I painted. 

These clouds are so common that the patterns and the science of their creation are typically underappreciated. The large size of these gravity waves prompted comparison with larger swells with longer wavelengths like those witnessed on the ocean. The energy that created those atmospheric swells was considerable and some distance away. An animation of the wind flow plays in my mind's eye whenever I see them. A similar process plays out on the surface of a lake with waves and wind. 

More subtle gravity waves were embedded on top of the larger waves. They are represented by the black waves in the inset above and the blue squiggles superimposed on the actual sky photo. These smaller-scale gravity waves revealed a wind component from the southwest. These winds would have been in the airmass above the warm frontal surface. Those winds veered in direction above the frontal surface.  Winds that veer with height are characteristic of warm air advection. 

Classic Warm Front Conceptual Model

None of this is going to be on any exam. It is just that I find clouds interesting and they reveal the weather. In this case, the surface front associated with the weather pattern was a hundred kilometres or more to the south and oriented west to east - more or less based on these cloud observations. I recall the surface winds (of the cold conveyor belt) as being light. It was going to be a great day for plein air painting but there would be weather along the warm front probably staying to the south of John's Cabin.

The following conveyor belt conceptual model of a mid-latitude weather system depicts my location and view given the characteristics of the cloud and the wind. 

This is number thirty-one of thirty-five paintings I completed en plein air at CPAWS DRAW 2024. It was a wonderful experience with a terrific group of people. https://cpaws-ov-vo.org/draw-retreat-artists/ A portion of sales from this endeavour will go to support CPAW and keep the 'wild' in the wilderness. 

#2894 "done like dinner" and time to grab another canvas

Note that the gravity waves on the surface of the Dumoine River were swells and perpendicular to the current. Conditions were calm and those bands of reflection on the water's surface were not wind waves. The energy required to generate gravity waves can originate from either fluid at the stable interface that separates them. 

For this and much more art, click on Pixels or go straight to the Collections. Here is the new Wet Paint 2024 Collection. Here is the link to the CPAWS DRAW Collection

Warmest regards and keep your paddle in the water,

Phil Chadwick