posted 01-11-2001 10:09 AM            

The trails were visible from Ramsey NJ, as I boarded a NJ Transit train all the way to Hoboken NJ, (my daily commute into NYC). As I was sitting on the left side of the south bound train I was able to see the trails throughout my entire commute. The trails were directly over my position at the Glen Rock NJ train station.

I observed 4 other Jet aircraft that were flying at lower altitudes then the 2 Jets leaving contrails. Twice, I observed both the "normal" jets and "contrail" jets at the same time and in the same space (albeit different altitudes). In both instances only the higher jets were leaving a trail.

Once my train pulled into the Hoboken Train station I could see the point of origin from the trail as originating from north east of Hoboken, across the Hudson river.
Therefore these trails must have been over northern Manhattan.

posted 01-11-2001 10:39 AM            

quote:

---

My question, besides what the hell is going on, is it possible that if two Jets are flying at the same time in the same atmospheric conditions, but different altitudes, only one would produce a trail?

---

Yes, that is certainly possible.

At different altitudes you will find varying temperatures. The temperature must be below a certain point for a contrail to form, even if the required moisture is present. The higher you go, obviously the colder it gets.

Even at the same altitude in the same atmospheric condition different types of engines can produce different contrailing properties due to the production of different amounts of moisture, however the differences shouldn't be radical (i.e. no trail at all vs. trails that last for hours). Also the same aircraft could appear to produce different trails, if, for example, one was increasing power, while the other was closer to gliding. This difference has been proposed as the reason for the differences seen in the photo below, however it is certainly debateable.

For how long can you remember seeing highly persistent trails (if that is actually what you are seeing) in your area?

posted 01-11-2001 11:48 AM            

"Moving up the focal length ladder, the 100mm can give you both macro and a very slight compression of perspective. 100mm and longer lenses also give you the capability to isolate objects in your composition. Landscape and scenic photography with lenses of 200mm and up will produce an effect called compression of apparent perspective. Compression of apparent perspective means that the scene becomes flattened and objects in the foreground seem to be closer than they actually are to objects in the background. This compression of the scene is not a normal perception of the human eye and can be used to advantage to produce some very dramatic looking images."