Hailstorms and tornadoes are more common during the weekday due to human created aerosols.
By Dr. Roger Pielke Sr.
New Paper “Why Do Tornados And Hail Storms Rest On Weekends” By Rosenfeld and Bell 2011
There is a new paper which further documents the diversity of human climate forcings that is presented in
Pielke Sr., R., K. Beven, G. Brasseur, J. Calvert, M. Chahine, R. Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W. Krajewski, E. Philip Krider, W. K.M. Lau, J. McDonnell, W. Rossow, J. Schaake, J. Smith, S. Sorooshian, and E. Wood, 2009: Climate change: The need to consider human forcings besides greenhouse gases. Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American Geophysical Union
and in the American Meteorological Society statement on
Inadvertent Weather Modification (Adopted by the AMS Council on 2 November 2010)
The new paper is
Rosenfeld, D., and T. L. Bell (2011), Why do tornados and hail storms rest on weekends?, J. Geophys. Res., doi:10.1029/2011JD016214, in press.
The abstract reads [highlights added]
“This study shows for the first time statistical evidence that when anthropogenic aerosols over the eastern USA during summertime are at their weekly mid-week peak, tornado and hailstorm activity there is also near its weekly maximum. The weekly cycle in summertime storm activity for 1995-2009 was found to be statistically significant and unlikely to be due to natural variability. It correlates well with previously observed weekly cycles of other measures of storm activity. The pattern of variability supports the hypothesis that air pollution aerosols invigorate deep convective clouds in a moist, unstable atmosphere, to the extent of inducing production of large hailstones and tornados. This is caused by the effect of aerosols on cloud-drop nucleation, making cloud drops smaller and hydrometeors larger. According to simulations the larger ice hydrometeors contribute to more hail. The reduced evaporation from the larger hydrometeors produces weaker cold pools. Simulations have shown that too cold and fast-expanding pools inhibit the formation of tornados. The statistical observations suggest that this might be the mechanism by which the weekly modulation in pollution aerosols is causing the weekly cycle in severe convective storms during summer over the eastern USA.”
Excerpts from the paper read
“The results are in agreement with our previous reports of similar weekly cycles in the rainfall [Bell et al., 2008] and lightning [Bell et al., 2009a] over the USA. The cycle was ascribed there to aerosols invigorating deep convective clouds in a warm, moist atmosphere. It is therefore not too surprising to find that the invigorated clouds also produce more hail and tornados.”
“This study has shown a clear correspondence between the weekly cycle of anthropogenic aerosols and the occurrences of severe convective storms, which is highly unlikely to be a result of natural variability. The observed associations cannot serve as proof for causality. However, the results are consistent with the hypothesis that air pollution aerosols invigorate deep convective clouds in moist and unstable atmosphere, and the possibility that they can even induce the storms to produce large hail and tornados. This is also consistent with the hypothesis that the severe storms are better organized and violent because aerosols increase the hydrometeor size, decreasing their evaporation and so weakening the negative buoyancy of the downdrafts, thereby preventing the gust front from outrunning and undercutting the updraft in the feeder clouds. Anthropogenic emissions have caused large enhancements of aerosol loads even over the remote continents, with typical enhancements of 50–300% over remote regions of Asia, North America, and South America (Wilson et al., 2001; Chin et al., 2004; Park et al., 2006; Stier et al., 2006).Regarding this increase, it is worth pointing out that if a roughly 10% weekly variation in pollution levels is resulting in a similar change in severe storm activity, then the “background” aerosol level, which is elevated with respect to the pre-industrial level even during weekends, is also likely to be changing the storm frequency that we experience today.”
I lived in the California Bay Area and have long noted that in summer the weekends are almost always cooler and windier than the middle of the week. I suspect that this corresponds with the development of a updraft around Sacramento that pulls cooler air, and offshore fog, in through the Bay Area (you can watch it coming over the hills). It would make sense that the updraft may be the result of a short term forcing from the weekday traffic in Sacramento. There does not seem to be any correspondence to the bloviating in the legislature.
Heavy industry like oil refineries, power stations etc work 7 days. It must be those office workers who are to blame.
The observed associations cannot serve as proof for causality.
That’s a beautiful sentence. I wish more people would use it.
Not all aerosols peak during the week. It appears that elemental (also called black) carbon, mainly from diesels, is at its lowest concentrations on Sunday and Monday in rural middle America. Natural dusts are also lower on Sundays and Mondays — perhaps also due to less driving, less stirring up of dust? Nitrates (mainly but not exclusively a vehicular emission) exhibit the same weekly cycle. Surprisingly, power plant particle emissions do not, although sulfur dioxide levels (a gas) are lower on weekends. See this link:
http://www.atmos-chem-phys.org/8/2729/2008/acp-8-2729-2008.pdf
Here are parts of the Abstract:
“Data from the Interagency Monitoring of Protected Visual Environments (IMPROVE) network of aerosol samplers and NOAA monitoring sites are examined for weekly cycles. At remote and rural sites, fine particle elemental carbon, crustal elements, and coarse particle mass had pronounced (up to 20%) weekly cycles with minima on Sunday or Monday. Fine particle organic carbon and mass had smaller amplitude cycles, also with Sunday or Monday minima. There was no statistically significant weekly cycle in fine particle sulfate despite a 5 to 15% weekly cycle in power plant SO2 emissions. Although results for nitrate may be more susceptible to sampling artifacts, nitrate also showed a pronounced weekly cycle with an amplitude similar to elemental carbon…[snip]…These results support a large role of diesel emissions in elemental carbon aerosol over the entire United States and suggest that a large fraction of the airborne soil dust is anthropogenic. They also suggest that studies of weekly cycles in temperature, cloudiness, precipitation, or other meteorological variables should look for causes more in light-absorbing particles and possible ice nucleation by dust rather than sulfate or total aerosol.
How about electromagnetic “pollution”? Take a look at http://broadcast.homestead.com .
Back O/T: Are the human-induced storms located near the centers of aerosol pollution?
Global Atmosphere Watch (GAW)
“Note that also mineral aerosol components (Ca2+, Mg2+ and
Na+) show this weekly periodicity although they are typically
not attributed to human activities.”
http://goldschmidt.info/2009/abstracts/finalPDFs/A383.pdf
So if there is a natural weekly cycle for mineral aerosol components why does a weekly cycle of other aerosols have to be induced from human activity?
To John W: The only explanation I can see for a weekly cycle in which mineral aerosol components drop is that with less traffic on weekends, less road dust is put into the air. Your citation comes to very similar conclusions as mine (above) does:
http://www.atmos-chem-phys.org/8/2729/2008/acp-8-2729-2008.pdf
in that they both find traffic aerosols lower on weekends than weekdays.
Here’s a similar “study” from 2008 (details available)
http://earth.huji.ac.il/data/pics/Bell_JGR08.pdf
From their summary:
“3) there is a strong tendency for this weekly variation
to show up in afternoon data in most (but not all) summers;”
and
“5) the effect, which clearly must be anthropogenic,
extends over the nearby Atlantic, and is almost as strong
there, but is reversed in sign;”
They’re not looking for a natural cause, it simply must be anthropogenic even though it doesn’t show up every summer and the effect reverses over the Atlantic. Ignore what doesn’t fit!
If air pollution was worse prior to this time, were the storms worse as well? It’s too bad we don’t have a clean, natural period with plenty of data to compare to now. I’m sure human aerosols have some kind of effect, much more so than any trace gas.
http://earth.huji.ac.il/data/pics/Bell_JGR08.pdf
“To look for signs of the influence of weekly variations
in human activity on precipitation, averages for each
day of the week based on 8 years (1998–2005) of data”
Spring Equinox
1998 – 2005
Monday 1 13%
Tuesday 1 13%
Wednesday 1 13%
Thursday 0 0%
Friday 2 25%
Saturday 1 13%
Sunday 2 25%
http://www.timeanddate.com/calendar/seasons.html
Anthropogenic suppression of spring equinox!
AusieDan said:
“I was under the impression that the level of storms has fallen over the last 50 years, relative to the previous 50 years.
Am I mistaken?”
Tornadoes F3 and stronger have actually shown a slight long term decline during the 20th century.
It appears to me the most likely explanation is global warming, affecting the Arctic more than other regions of the world. This reduces the north-south temperature gradient in North America, where most of the world’s tornadoes form. This temperature gradient powers the wind sheer that major tornadoes need to form.
Although I see existence of AGW, I am seeing its magnitude being about 40-50% of that proposed by most proponents of existence of AGW.
As for effects of weekly cycle of aerosols on overall storm trends – this could very easily
be very minor. The article bringing this up shows this effect in summertime in the highly populated eastern USA, while the worst of severe thunderstorm and tornado activity is in springtime in central and south-central USA. In other regions and at other times of the year, this effect may not be significant. And, the major historic tornado outbreaks occurred when large weather systems favorable to their formation existed – likely independently from air pollution.
If it were, there would be little or none at all!