Howard, this is a banding problem. Here is a quote from Nikontech website.
"Patterns of vertical lines, sometimes referred to as banding, are a digital imaging artifact.
Lines can be vertical or horizontal, depending on the orientation of the camera at the time that an affected image was captured. Banding can become visible only in specific shooting conditions that include particular combinations of high contrast scene content, lighting, camera settings, substantial enlargement and the shooting environment.
Banding can be further described as long banding or short banding. Long banding will generally appear throughout an image. Short banding will not appear throughout an image. Commonly, if certain variables coincide, short banding can appear most prominently at intersections of extreme contrast and when an image is enlarged substantially. Appearance of short banding may typically be a pattern of physically short lines and will usually not affect the vast majority of images.
It is important to note that banding will generally be greatly exaggerated when an image is enlarged and viewed on a computer monitor. A useful printed image, even when enlarged to a size that relates to a substantially enlarged monitor image, will not exhibit the same banding (or for that matter, many other artifacts) that may be visible on a monitor. Therefore, artifacts that may be visible on a monitor often have very little practical correlation to the realistic use of an image file (e.g., an image viewed on a monitor in its entirety and enlarged prints)."
Nikons answer to the problem is to replace the 'memory compression'.
Jarrell