An observational Study of the “Interstate 5” Dust Storm Case

Abstract

On 29 November 1991 a series of collisions involving 164 vehicles occurred on Interstate 5 in the San Joaquin Valley in California in a dust storm that reduced the visibility to near zero. The accompanying high surface winds are hypothesized to result from intense upper-tropospheric downward motion that led to the formation of a strong upper front and tropopause fold and that transported high momentum air downward to midlevels where boundary layer processes could then mix it to the surface. The objectives of the research presented in this paper are to document the event, to provide support for the hypothesis that both upper-level and boundary layer processes were important, and to determine the structure of the mesoscale circulations in this case for future use in evaluating the navy's mesoscale data assimilation system.The strong upper-level descent present in this case is consistent with what one would expect for jet streak and frontal circulations in combination with quasigeostrophic processes. During the period examined, upper-level data and analyses portray a strong upper-tropospheric jet streak with maximum winds initially in excess of 85 m s -1 (-170 kt) that weakened as it propagated southward around the base of a long-wave trough. The jet streak was accompanied by a strong upper front and tropopause fold, both of which imply intense downward motion. The vertical motion field near the time of the accidents had two maxima-one that was associated with a combination of quasigeostrophic forcing and terrain-induced descent in the lee of the Sierra and one that was associated with the descending branch of the secondary circulation in the jet streak exit region and the cold advection by both the geostrophic wind and the ageostrophic wind in the upper front. The 700-hPa wind speed maximum over and west of the San Joaquin Valley overlapped with the latter maximum, supporting the hypothesized role of downward momentum transport. Given the significant 700-hPa wind speeds over the San Joaquin Valley during daytime hours on the day of the collisions, boundary layer mixing associated with solar heating of the earth's surface was then able to generate high surface winds. Once the high surface winds began, a dust storm was inevitable, since winter rains had not yet started and soil conditions were drier than usual in this sixth consecutive drought year. Surface observations from a variety of sources depict blowing dust and high surface winds at numerous locations in the San Joaquin Valley, the Mojave and other desert sites, and in the Los Angeles Basin and other south coast sites. High surface winds and low visibilities began in the late morning at desert and valley sites and lasted until just after sunset, consistent with the hypothesized heating-induced mixing. The 0000 UTC soundings in California portrayed an adiabatic layer from the surface to at least 750 hPa, also supporting the existence of mixing. On the other hand, the high winds in the Los Angeles Basin began near sunset in the wake of a propagating me...

Numerical simulation of "an American haboob"

“…More information on density currents can be found in Knippertz et al (2007), Emmel et al (2010), Knippertz and Todd (2012). Pauley et al (1996) described a dust storm on 29 November 1991 that caused a pileup on Interstate 5 in California, US, involving 164 vehicles. They reported that dust uptake came from surrounding agricultural areas that were left unplanted after being plowed, before the rainy season began; disturbing a soil surface makes it more susceptible to dust generation (Gillete et al, 1980).…”

“…They reported that dust uptake came from surrounding agricultural areas that were left unplanted after being plowed, before the rainy season began; disturbing a soil surface makes it more susceptible to dust generation (Gillete et al, 1980). Pauley et al (1996) also noted that in these agricultural regions dust is present often enough that the US Environmental Protection Agency (EPA) is proposing sanctions for San Joaquin Valley growers for not attending the standard for PM 10 (particulate matter of 10 micrometers or less). It should also be noted that drought conditions had prevailed in that area for 6 years.…”

Visibility monitoring using conventional roadside cameras – Emerging applications

“…Dust storms potentially reduce the visibility to zero and cause dramatic pile-ups. These phenomena are likely to occur in dry agricultural areas subject to land erosion, like the I-5 in California's San Joaquin Valley in 1991 (164 vehicles involved, 151 injured, 17 dead) (Pauley et al, 1996) or the A19 Mecklenburg-Vorpommern in Germany in 2011 (82 vehicles involved, 100 injured, 8 dead) (Hunfeld et al, 2011). Smoke caused by factories or fires in the vicinity of highways is also a dramatic source of reduction of the visibility (AbdelAty et al, 2011).…”

Climatic analyses on increasing dust storm frequency in the springs of 2000 and 2001 in Inner Mongolia

“…Meanwhile, there have been parallel studies outside of China on this subject. Examples include: Chung et al (2003), who studied dust storms and associated dust fall observed in Chongju-Chongwon, Korea, during 1997Korea, during -2000Lee et al (2003), who studied the long-range transport of Asian dust from dust storms and its impact on Japan; McTainsh et al (1998), who made an analysis of the effects from climatic changes on dust storms in the dry and semi-dry regions of Australia; and Pauley et al (1996), who diagnosed and analysed five dust storm events in the San Joaquin valley, California, USA.…”