...come into it?However, I suggest two means by which one can personally use remote sensing to actually idenitfy the aircraft you see in real time. By doing so, you can determine and record the actual aircrat seen. The first method is by using internet based live flight tracking such as Flightaware.com. It uses FAA generated data. The second method is using a telescope to zoom in and even photograph the aircraft's unique tail number.
Very few people believe that ordinary commercial flights are spraying anything. The logistics and secrecy involved make it rather unlikely, so generally most chemtrail believers are under the impression that military or other non-commercial flights are spraying. Simply identifying the flights seen takes most of the mystery out of chemtrails. Even if you insist that commercial flights are spraying, having their identity and destination would allow you to follow up on that belief.
I have written more on this in detail:
Please come back and let us know of your progress.
70% RH is pretty rare at 30000ft and above where I come from and where aircraft fly; if you're seeing a lot of 'persistent contrails' you might ask why and investigate for yourself.
The 70% is a rule of thumb. The numbers behind formation and persistence of contrails are actually a little complicated, as there are several variables involved. There's the temperature, pressure and relative humidity (RH) of the air, and the temperature, pressure, speed, and humidity of the exhaust gas.
How would you define "pretty rare"? Once a month? Once a week? 10% of days? 20% of days?
Ross did not count the pressure and speed of the exhaust gas, which is fine because they really only affect the mixing a bit. It does have an effect, but not a huge one, so can safely be ignored. I probably should not even have mentioned them - I was just thinking of all possible variables. I should debunk myself
If we are going down the road of all possible variable, you'd probably want to add the amount of incident sunlight (only really relevant if it's non-persistent, and then not much), and availability of condensation nuclei (not much, as there's plenty in the exhaust)
Contrails, as I said, are surprisingly complex.
I'd suggest checking out radiosonde data in a google search and going to the Uni of Wyoming for those in the US. There you can get two radiosonde readings a day from numerous stations and they will give you an idea. Have a look every day for a month if you really want to know. Log it - percentage? My guess (for altitudes between 30 and 40 thousand feet) would be 5 percent of days. Why don't you do the experiment? Publish the figures every day. Show me to be wrong
Fair enough. But, and I think I responded to Ross before on this 'five variables' thing: There are an indefinable number of variables can be derived from these 'five' - don't you agree?
I have said before that they (contrails) are hard to understand; prediction methods are unreliable; we don't know that much etc. Is this common ground? we appear to agree on something!
I was not addressing you. I have asked you about that information several times with no response. After you read and understand it, we can discuss it, but if you cannot grasp the concept, it is probably not relevant to you.So where does:
come into it?
lee said:The truth is this: 70% RH is pretty rare at 30000ft and above where I come from and where aircraft fly; if you're seeing a lot of 'persistent contrails' you might ask why and investigate for yourself.
Dr. Ulrich Schumann said:As shown by Figure 5, more than 40 % of all data collected during a measurement campaign over
the North Atlantic [43, 44] were taken in ice-supersaturated regions. Measurements on modern airliners
 indicated that such aircraft fly in ice-supersaturated air masses about 15 % of the flight time.
Figure 5. Relative humidity with respect to liquid water versus ambient temperature. The thin full
curve denotes the relative humidity for ice saturation. The dashed line denotes liquid saturation. The
symbols denote measured data for cases exceeding ice saturation as derived from a frostpoint hygrometer
(Ovarlez et al. ) and temperature sensors (extended from Schumann et al. ). The pair
of curves with various line notations represent the relative humidity for constant water vapour content
at various temperatures.
Ice-supersaturated air masses form in regions with rising air motion and are partially filled with cirrus
clouds . Regions with ice supersaturation have been found with horizontal extensions of the
order 150 km  and vertical extensions of about 500m in the mean . Supersaturation is also
observed at least occasionally in the lower stratosphere up to the hygropause in the polar winter and
also, rarely [47, 54], in the lower stratosphere at mid-latitudes and in the tropics up to a about one
kilometre above the local tropopause [55, 56].
The area size of the regions with ice-supersaturated air masses defines the potential contrail cover
which would appear if aircraft were to fly everywhere and at all times. Global distribution maps of ice
supersaturated regions have been produced from satellite data  and from analysis of meteorological
data . Such analysis suggest that the global average contrail cover (partially overlapping with
cirrus clouds) could approach 16 % . Over Europe the potential contrail cover reaches 12 %,
which is consistent with estimates derived from satellite observations of the size of regions with clusters
of persistent contrails  and by in situ humidity measurements [42, 53].
If these numbers were realised it would mean a very large change in high cloudiness. For comparison, the
mean high cloud(cirrus) cover at northern mid-latitudes is about 20 - 30 % according to different
observations [59, 60]. Subvisible clouds with optical depths below about 0.03 are even more abundant .
Gierens etal. said:Abstract. In order to determine typical sizes of ice-supersaturated regions (ISSRs) in the upper troposphere and lowermost stratosphere we set up the frequency distribution of path lengths flown by MOZAIC aircraft within ISSRs. The mean path length is about 150 km with a standard deviation of 250 km. We analyse the influence of a selection bias (viz. that large ISSRs are more often crossed by aircraft than small ones) on the obtained path length statistics and derive a mathemat-ical equation that relates the path length distribution to the underlying size distribution of ISSRs, assuming that they have circular shape. We solve the equation (by trial and error) and test the result using numerical simulations. Surprisingly, we find that there may be many more very small ISSRs than apparent from the data such that the true mean diameter of the ISSRs may be of the order a few kilometres only. The relevance of the result is discussed and dedicated research flights to measure the true extension of ISSRs are recommended
Concerning the extent of ice supersaturated regions, researchers took measurements on ordinary commercial airliners flying their normal routes. They found some huge areas of ice supersaturation, and some perplexing data they had a lot of trouble analyzing, mainly because the flights were not dedicated to the research. For that reason, their conclusions were tempered with some qualifications.
...in order to determine typical sizes of ice-supersaturated regions (ISSRs) in the upper troposphere and lowermost stratosphere
Commercial aircraft don't fly in the stratosphere which begins at approx 60,000ft - so irrelevant - the upper troposphere is what? alt 12000m - 14000m or 39600ft - 46000ft - the lowest being right at the cusp of commercial traffic limits. What good is that?
The key word there being "about", as the height of the stratosphere varies with location (being lower closer to the poles) and season. See:The stratosphere is situated between about 10 km (6 mi) [32,800 feet] and 50 km (30 mi) altitude above the surface at moderate latitudes, while at the poles it starts at about 8 km (5 mi) [26,246 feet] altitude.
Commercial airliners typically cruise at altitudes of 9–12 km (30,000–39,000 ft) in temperate latitudes (in the lower reaches of the stratosphere). They do this to optimize fuel burn, mostly thanks to the low temperatures encountered near the tropopause and the low air density that reduces parasitic drag on the airframe. It also allows them to stay above any hard weather (extreme turbulence).
The boundary between the troposphere and the stratosphere is called the "tropopause", located at an altitude of around 5 miles [26,400 feet] in the winter, to around 8 miles high in the summer [42,240], and as high as 11 or 12 miles in the deep tropics.
I would appreciate that very much. By the way, I notice that the ERA-Interim page has a message saying, "This server is been replaced by a more powerful system that can be found at http://apps.ecmwf.int/datasets/. Please start using this new system, as this server will be discontinued in the near future."Because a lot of chemtrail believers say that "Those lines in the sky are chemtrails: relative humidity is too low for contrail persistence. Radiosonde data proves it", I'd like to offer a way for debunking these claims. Weather sondes are affected by dry bias or even stop working at high altitudes: https://www.metabunk.org/threads/ac...midity-soundings-for-contrail-prediction.758/, so satellite info should be used. There are some model reanalyses: NCEP (GFS), ERA-Interim. The second one should be used for obtaining precious data. It is rather difficult to visualize it. I ask all the debunkers: should I describe the way to do it? It will take me a long time to write the post.
There might be some confusion between types of contrails. Aerodynamic contrails require plenty of atmospheric humidity, where engine exhaust contrails can form in the absence of atmospheric RH because the required moisture is produced in abundance by the combustion of jet fuel.
The chart shows that at greater humidity contrails will form over a wider range of temperatures and pressures.
The 100% humidity line marks the edge of an area representing the conditions in which contrails will form at 100% RH, this area is to the left of the line (lower temperatures) and includes the area demarcated by the 0% RH line which is labelled "always contrails" and the central stripe labelled "maybe contrails."
As an example, at 100% RH, 300hPa and -44 degrees you will get contrails because the coordinate (-44 degrees, 300hPa) is to the left of the 100% RH line. That same point on the chart is to the right of the 0% RH line so contrails would not form at 300hPa and -44 degrees at 0% RH the conditions being too warm.
http://science-edu.larc.nasa.gov/contrail-edu/resources-activities-appleman_student.phpB. Using the graph: The two most important lines on the chart are the 0 percent relative humidity line and the 100 percent relative humidity line. If the atmosphere were colder than the temperature indicated by the 0% line, a contrail would form even if the relative humidity of the atmosphere were zero. By itself, the airplane will supply enough moisture to make the contrail, and no moisture is necessary from the atmosphere to form the cloud. According to the chart, contrails will always form when the temperature profile is to the left of the 0% line. If the atmosphere were warmer than the temperature indicated by the 100% line, a contrail could not form even if the relative humidity of the atmosphere were 100 percent. The combined moisture from the jet exhaust and the atmosphere will never be enough for the mixture to produce a cloud. Temperature profiles to the right of the 100% line will never form a contrail. For temperatures between the 0% and 100% lines, the possibility of a contrail forming will depend on the atmospheric moisture, represented on the chart as relative humidity. A contrail may or may not form when the temperature is between the 0% and 100% lines.
Contrails can form at any level of RH, if it's cold enough. But if it's lower than a certain value, then they will not persist.
The 70% is a rule of thumb number for contrail persistence, and the real number varies with pressure (i.e. altitude). The numbers behind formation and persistence of contrails are actually a little complicated, as there are several variables involved. There's the temperature, pressure and relative humidity (RH) of the air, and the temperature, pressure, speed, and humidity of the exhaust gas.
For a contrail to persist, the relative humidity with respect to ice (RHI) needs to be above 100%. Note the RH is not the same as RHI. It differs in the same way that dew point differs from frost point. It's also not a simple matter to convert from one to another, as they derive for different complex equations (polynomials), even the approximations of which (such as Goff-Gratch) are overly complex, so conversion is done with tables, or computers.
This link will give a taste of the complexity. Note that the equations given at the bottom of the page are approximations.
Anyway, that's just to explain why there's not a precise figure. 70% is ABOUT the RH where RHI is above 100% in average contrail condition.
To answer your question: no, persistent contrail do not need higher humidity. If the RHI is above 100% (approximately 70% RH), then a contrail will persist. Contrails will fade away if the humidity is below this level. The dryer the air, the quicker they will fade away.
I just tracked a Hong Kong Airline on 9/1/16 close to 11:30am near Noosa making a rare (I have only seen 2 -3 of these in the last 2years, there could be way more I don't see) non-persistent contrail. I looked up the Appleman chart and the weather conditions it was -52.7C @ 200hPa & 6% humidity (if I haven't made any errors which is so easy to do). And it sits in just the right place for contrail formation I think.
# convert RHw to RHi, as per # http://www.esrl.noaa.gov/psd/people/ola.persson/polar_studies/refereed/Ice_sat_2000JC000411.pdf # But see http://cires.colorado.edu/~voemel/vp.html # ta = temperature of atmosphere, in Celsius # p = pressure in hPa (hectopascals), which are the same as mb (millibars) # note this is defined as accurate from -0C to -50C, but it's unclear how inaccurate it is # at temperatures below -50C def rhw2rhi(rh, ta, p) e_sat_w_Ta = (1.0007 + 0.00000346 * p)*6.1121*Math.exp((17.966*ta)/(247.15+ta)); e_sat_i_Ta = (1.0003 + 0.00000418 * p)*6.1115*Math.exp((22.452*ta)/(272.55+ta)); return rh * (e_sat_w_Ta/e_sat_i_Ta); end
If I read your info correctly, the flight in question was HX16 from Gold Coast to Cairns (Airbus A330-343) that passed over Noosa Heads at 40,000 ft. This is higher than 200 hPa, so temperature could be even lower than -53°C. Perhaps, it was just cold enough for the formation of a short contrail even in dry ambient air. In a more humid air, the contrail would last longer and be longer as well. Other conditions being equal, for RHi below 100%, there would be a correlations between relative humidity and the contrail length/duration. Non-persistent contrails can be quite long. A one minute contrail will extend for nine miles behind the plane that flies with the speed of one mile in about seven seconds.I just tracked a Hong Kong Airline on 9/1/16 close to 11:30am near Noosa making a rare (I have only seen 2 -3 of these in the last 2years, there could be way more I don't see) non-persistent contrail. I looked up the Appleman chart and the weather conditions it was -52.7C @ 200hPa & 6% humidity (if I haven't made any errors which is so easy to do). And it sits in just the right place for contrail formation I think. Being non-persistent the RHi must be less than 100%?
I've munged up a calculator, details here:Something I think might be useful it to write a web calculator that calculates this, something that can be extended to draw graphs etc.