tag:blogger.com,1999:blog-5337555368793819627.post5390045819829562162..comments2023-06-07T09:04:36.390-04:00Comments on More Grumbine Science: FeedbackRobert Grumbinehttp://www.blogger.com/profile/10783453972811796911noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-5337555368793819627.post-8975469058801305842009-04-16T11:26:00.000-04:002009-04-16T11:26:00.000-04:00I'm looking for good examples of showing feedb...I'm looking for good examples of showing feedbacks graphically, in consistent ways, for the general audience. Do you have any good examples?<br /><br />(I am convinced that the usual description of positive & negative feedbacks, in words, just doesn't communicate strongly enough to many people.)John Masheyhttps://www.blogger.com/profile/17786354229618237133noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-91074028676643363042009-04-03T02:35:00.000-04:002009-04-03T02:35:00.000-04:00One of the best examples of biological feedback cy...One of the best examples of biological feedback cycles is the snowshoe hare/lynx cycle. The cycles are roughly 10 years long, have been well studied and are incredibly interesting... at least for those of us interested in population ecology.<BR/><BR/>@ Ian<BR/><BR/>Lindzen's ideas are not new, but so far there isn't much support for themScruffy Danhttps://www.blogger.com/profile/09576996151807188873noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-47684215967664579662009-04-02T14:12:00.000-04:002009-04-02T14:12:00.000-04:00Very odd. I started in electrical engineering and...Very odd. I started in electrical engineering and was used to that culture's notion of what feedback was before I ever started looking in to the climate literature. When I did start, I never had any difficulties with climatological usages.<BR/><BR/>In positive feedback, for electrical engineers, it's simply that the signal (sound from the speakers) is fed back in to the system (microphone) directly. In my climate example, it's temperature increase being fed back in.<BR/><BR/>Electrical engineers' negative feedback is that you feed back the signal inverted. Instead of feeding back a +1 volt, you pass back a -1 volt. I can't offhand think of any climate components that would carry out a negative feedback in this sense.<BR/><BR/>What is really at hand (I did check out Lindzen's note) is not whether the feedback is positive or negative -- in my engineer's sense of the term. <BR/><BR/>The important thing is whether the gain is greater or less than one. The gain is a measure of how big a result you get for how big a kick you give the system. In an audio amplifier, the gain is very much greater than 1. In my climate example, it was 2. Lindzen believes that the gain is more like 0.3 -- still positive, just smaller than the kick provided by greenhouse gas forcing. <BR/><BR/>In the case of the ice-albedo feedback, it is a positive feedback (and with a gain, at least now, that seems to be greater than 1). Whatever kick you give the system gets amplified, in the same direction. If there is more ice, you get colder temperatures, which gives more ice -- change in the same direction as the kick. If there is less ice, you get warmer temperatures, which gives less ice -- again, same direction as the kick.<BR/><BR/>For the predator-prey situation, we have a negative feedback process. More sharks means fewer fish, means fewer sharks. Or more fish means more sharks, which gives fewer fish. After 1 cycle, the sign of the kick gets changed.<BR/><BR/>I don't know what the problem is over there. But this usage is perfectly common in either climate or electrical engineering.Robert Grumbinehttps://www.blogger.com/profile/10783453972811796911noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-48628744136721680842009-04-02T12:38:00.000-04:002009-04-02T12:38:00.000-04:00Nice examples - the predator-prey example gives a ...Nice examples - the predator-prey example gives a clear picture of cycling within constraints.<BR/><BR/>On the topic of feedback, there's lots of current blog discussion on negative climate feedbacks in particular (all prompted by a Dick Lindzen post on Watts Up). A few posters on Watts Up seem confused by the terms *negative* and *positive* feedbacks in climate science, which are apparently different from their favored use of the terms in an engineering field. Specifically, rather than thinking of a positive feedback as one that intensifies or amplifies a forcing (whether cooling or warming), some commenters think that positive feedback should refer to warming only. Do you have any insight into why this difference in the use of *negative* and *positive* exists to describe feedbacks?Iannoreply@blogger.com