Daily Archives: February 24, 2014

Mid-February Wind Review

Greetings from Bodega Head! Today will be a short post. We are still anticipating quite a storm to arrive later in the week, and today should be our last day in the bright sunshine, northerly afternoon winds and relatively high pressure until the beginning of next week.

In anticipation, some of the crew got out for some R&R yesterday afternoon. After so much time in the coastal grassland, its easy to forget that whole communities of giants live just minutes away:


BBACPAX at the Armstrong Redwoods State Nature Reserve.

Local Conditions:


Timeseries of local weather conditions at the Bodega Marine Reserve. Credit: DRI-WRCC.

We have had southeasterly winds for most of the morning, leading to elevated accumulation mode particle counts at the trailer (3000 particles per cc) and few course mode particles. Unlike over the weekend, we did not see any NOx, or CO spikes from the campground to our East.  We are nearing the common time for the sea-breeze to come onshore. This has happened between 10 am and 11 am PST every morning during episodes of high pressure, and we are preparing to sample elevated coarse mode (primarily sea salt) aerosols throughout this afternoon. This may be the last day we see a diurnal shift in ambient aerosol conditions for quite some time. The animation I have linked below shows the high-resolution MM5 forecast 10 m winds from this morning through late Tuesday.

MM5 surface wind loop Credit: DRI-CEFA.

As time passes, the elongated clockwise wind pattern offshore dissipates in favor of strengthening southerlies at the coast, followed by strong southerlies throughout the domain and eventually, it is possible that we get a coastal jet windward of the Sonoma County coastal range. There are also some slight hints that we may see Petaluma Gap Flow – something we will be watching with great interest.

Review of wind conditions for the first half of our study:

We are approaching the halfway point of BBACPAX, and with a prolonged period of stormy weather approaching I thought it prudent to review the primary flow regimes of the past 13 days here at the site.

In this post, I presented an analysis of the typical quiescent day here at BML. The flow we were seeing at our sampling site was dominated by a diurnal cycle related to the large-scale northerlies plus the sea-breeze circulation. For the most part, we saw strong (20 kts or more) Northwesterlies in the late afternoon hours, light south-southeast winds in the early morning, and transition periods in-between.

A wind-rose diagram of the data from the nearby DRI-WRCC station shows these preferred flow regimes very clearly:


Wind Rose generated from 10-m tower anemometer at the DRI-WRCC Bodega Marine Reserve site. Credit: WRI-WRCC.

This data has been compiled from the period Feb 12 – Feb 24, 2014. This period included one 24-30 hour period of large-scale southerlies associated with a landfalling pacific wintertime cyclone (PWC), but for the most part it was dominated by high pressure and quiescent conditions.

It is interesting to compare the Bodega Marine Reserve wind rose to that from an inland site:


The wind data in this rose comes from the Blue Oak Ranch Reserve site of the same network. The site is located windward of the Central CA coastal range but inland. Instead of two primary flow regimes here, we see simply one prevailing wind flow direction, WSW.

The diurnal flow reversal we experienced during our first two weeks at Bodega Marine Lab had a profound effect on the aerosol number, size and chemistry we observed. That data is being analyzed now, and I hope to include some relevant blog posts about aerosol and trace gas concentration (with cool figures!) soon.

Next chance for rain:

We are still watching the storm which should arrive Wednesday. Ill post tomorrow about our chances to see unique flow features such as the Coastal Jet and Petaluma Gap Flow.