Weather in a desert planet

Question

Neviat, it is a desert planet with 81.5% of the Earth's atmospheric pressure and 80% of its gravity, it is generally dry but has many lakes and oases at its poles, the temperature across the latitudes does not change much (at the equator it is close to 70 degrees Celsius, and at the poles it is 30)

Want details? Here's to you: the activity of its tectonic plates is similar to the Earth, but it has giant volcanoes (It's a really big number, about five hundred volcanoes, most of them only erupt for a few dozen years) that reach impressive sizes (12-20 km!), the rotation period of the planet is really long, seven days, its orbit is very circular It takes 4.685 years

Its surface is 35% covered by dunes, and 45% are dry, barren and empty lands, and 10% are mountains of up to a few short kilometers in length, the rest are lakes and oases or rocky bumpy places.

my question is:

What will winds and dust storms be like in general? I mean intensity, speed and so on.

Answer 1

A rotation period of 7 days is an important feature. It would mean any life would have to be specially adapted. This should be quite possible, but would lead to life very different from Earth due to the long nights. Most Earth plants would not survive.

Perhaps more importantly there would be less mixing of air masses at the equator due to the slow rotation rate so probably less cyclonic and anti-cyclonic winds. With so much desert even light winds would continually erode and churn the sand and dunes leading to a lot of fine dust.

So dust storms on the scale seen on Mars. But with 81% of Earth’s atmospheric pressure they could be much thicker than on Mars. And with less wind slower moving. Perhaps like a thick dusty “pea soup” fog or smog wafting around over thousands of square miles.

However small patches of water would be problematic, especially with temperatures of 30-70 degrees C. Vast quantities of water would just evaporate and stay in the air. At 50 degrees every cubic metre of water can hold 130g of water. And a desert planet with a high temperature high humidity atmosphere does not sound likely.

Answer 2

Strong winds from the dark side.

The long day and asymmetric heating would in some ways mimic a tidally locked planet.

How would winds behave on a tidally locked planet?

It would cause ground level winds out of the (colder) dark side, and high altitude winds out of the (warmer) light side.

Rain on the volcano sides.

Giant volcanoes would make rain during the day. Ground level winds coming out of the dark side would bring with them whatever moisture there was. As these winds hit the volcano sides and ascend, the ability of the air to hold water will decrease and that water will fall out as rain on the mountainside. These mountainsides will be the greenest areas on the planet and the lakes will be at the bases of them, capturing the rain. The rainshadow sides of these giant mountains will be bone dry.