Why do these aircraft in long term storage have air and power connections? With the Covid-19 crisis many thousands of passenger aircraft have been put in storage. In this  Bloomberg article from July 2019 shows several aircraft in what appears to be storage with covers on engines and cockpit windows. They also appear to be connected to an electrical supply and the engines to some sort of compressor.
Here is a screen shot of the image: 
And a link to a large size version of the full image.
Another link to a different photo of stored 737MAX with similar connections.
The Airbus website describes requirements for long term storage, but mentions no connections to air or electricity.
Why are these aircraft provided with air and power?
Why do these aircraft in long term storage have air and power connections?

The photo is of 737MAX being stored in July 2019. Back then, airlines might still have hoped that this wouldn't be &quot;long-term storage&quot; at all!
Usually, airplanes being mothballed are stripped of corrosive / humidity-sensitive parts (e.g. the interior) as much as possible, stored in the dry desert, and it is considered acceptable if getting them back out of storage requires weeks if not months of refurbishment.
None of these three things seems to apply here. The photo doesn't look like it was taken in the desert, the airplanes are probably fully intact, and the airlines were hoping that with a simple software patch, they might be able to get them off the ground quickly again.
Therefore, they would have opted to, instead of preparing the airplanes for long-term storage, have them partially powered up, or use external air conditioning units. I would be willing to bet that those exact some planes are stored differently in July of 2020!