Environmental Engineering Reference
In-Depth Information
throughout this region; however, we did not find temperature to add explanatory
power to our statistical model based on the wind field. This is because tempe-
rature is largely a function of marine penetration through the complex Central
California terrain. The degree of marine penetration is already reflected in the
wind field, and thus temperature offers little additional information. We have not
explored clustering of (scalar) temperature because the algorithm utilized has
been tailored for (two-dimensional) wind fields.
Christian Reuten:
When you talked about the influence of up- and down-slope
flows, did you mean slope flows or valley flows?
Answer:
Both slope flows and valley flows impact ozone levels throughout the
Central California valleys. Strong up/down valley flows tend to ventilate the
region. Weaker valley flows indicate near-calm and stable conditions that set
the stage for ozone exceedances. Under such conditions, the localized slope
flows have important influences on ozone source-receptor relationships. Over-
night downslope (drainage) flows especially impact fresh emissions during the
morning hours. Certain downslope flow features appear to trigger ozone exceed-
ances under near-calm, stable, subsiding conditions.
Chip Levy:
Will you not consider inter-annual variability of the met triggers you
have identified (i.e. ENSO type as well as climate change)?
Answer:
In this study, we focused on a 15-year period to obtain representative
meteorological patterns impacting ozone levels. Certain patterns were associated
with conducive conditions under which ozone exceedances become likely.
Year-to-year variability in the frequency of such conducive conditions largely
determines how many exceedances occur in a given year. We attempted to
relate the frequency of conducive conditions with traditional indices for inter-
annual variability such as El Nino-Southern Oscillation Index (ENSO) and the
Pacific/North American teleconnection pattern (PNA). We found no simple
relationship between such indices and the frequency of conducive conditions
indicated by the clustering. A follow-up study of the inter-annual variability is
indeed being considered. Our method requires extremely high quality data
which are difficult to obtain prior to our 15-year study period. We do not
believe that a 15-year study period is sufficient to observe climate change
trends. Rather, we would consider the climate stable during this 15-year period
to assay the degree of natural year-to-year variability in planetary flow patterns.
Such a study would provide a baseline for examining future trends due to
climate change.
