After the Storm

Greetings from Bodega Head!

Skies have been mostly overcast the last several days, however plenty of color can be found nearby if you know where to look!


Anenomes in a tide pool near Mussel Point, Bodega Marine Reserve, CA.

We are expecting a quiet weather day today, with overcast skies and maybe passing drizzle as the storm which soaked much of CA the last 3 days has stalled and continues to dissipate near the Central coast. The OPC surface analysis:


Surface analysis for the Northeast Pacific Valid at 12 UTC on March 2, 2014. Credit: NOAA-OPC.

A broad area of low pressure is in control over the Northern Pacific. This will continue over the next several days. However, as we will see in coming posts, the storms which come eastward toward the Pacific coast are not expected to intensify or dig south, due to a bland zonal upper level pattern.

Local Conditions:

It has been a couple days since I posted a weather update from BBACPAX, so I will review what happened here for the past 2 days.

We picked up an additional inch of rain here on Friday evening and early morning Saturday. Most of this came near a mesoscale front which passed us at 3 am PST on Friday.


Surface met variables at BML for the 48 hours ending at 00 UTC on March 1, 2014. Credit: NOAA-HMT.

The rain early Friday morning and late Friday night pushed our 3-day rain total to about 3.25 inches. Through most of yesterday, pressures rose and winds shifted from Easterly to Westerly and Northerly, then Southerly as of this morning. The strongest sustained winds we have measured at the site during BBACPAX, 31 knots, occurred mid-morning yesterday:


Surface met variables at BML for the 48 hours ending at 17 UTC on March 2, 2014. Credit: NOAA-HMT.

New Particle Formation?

During the strong Easterly flow period yesterday, the sun came out, visibility was extremely good and we had very low particulate mass. However, total particle counts peaked over 20,000 per cc. There was a single size mode measured by SMPS near 30 nm, but larger particles were nearly non-existent. We also noticed a slow increase then decrease in the SO2 concentration. Taken together, these measurements after a major rain storm are indicative of a new particle formation (NPF) event. During NPF, organic gases (VOC) participate in heterogeneous reactions and condense to form secondary organic particles in the Aitken size mode. NPF must occur in the absence of larger organic aerosols, as the pre-existing larger particles will grow at the expense of the VOC gas before it can nucleate. Thus, NPF is often observed after rain has scavenged existing particles from the planetary boundary layer.   Trajectories over BML also passed over the Central Valley and North Bay Area, which are places that could provide the VOC and oxidizers necessary for the reactions. It is yet unsure whether NPF occurred locally or whether it occurred upstream of our location and the Aitken mode particles were simply transported here. We will have more analysis of the chemical data associated with this event soon!

Local aerosol transport:

Pressures are increasing at BML as a high pressure center builds to our southeast. As this continues, winds will turn ever more Westerly. However, late tomorrow, we expect a weak surface low pressure system to traverse the northwest corner of California. As a result, the transport source regions we are exposed to here at BML will perform a slow walk from South of Point Reyes, to Southwest of us over the open water, and return to our south once more. I have included a back trajectory analysis from the North American Model forecast below:


Forecast back trajectories from BML for the next 24 hours based on NAM 4 km forecast. Credit: NOAA-HYSPLIT.

We are interested in characterizing the ice nuclei activity of naturally emitted marine biological aerosols and measuring their chemical mixing state in-line using our CFDC-pCVI-ATOFMS system. We prefer West to Southwest trajectories in order to perform this analysis, since the source regions associated with W or SW trajectories are over the open ocean and therefore less likely to experience shipping traffic or continental air influences. Because of these trajectories, we have identified this afternoon and tomorrow morning as targets for CFDC-pCVI-ATOFMS measurements.

Outlook and long-range aerosol transport:

As the surface low approaches and trajectories (and onshore winds) return to southerly tomorrow evening, we may see some rain. Most of this rain will occur in the late evening near 6 – 8 pm:


3-hr precipitation forecast from MM5 4km valid at 1900 PST on March 3, 2014.

GEOS-5 also expects us to see an increase in dust AOT over CA during this same period.


Dust AOT forecast by GEOS-5 valid at 1900 PST on March 3, 2014. Credit: NASA-GMAO.

It is uncertain whether cloud tops will be high enough to intercept this next dust plume, as both the surface system associated with the rain, and the large scale trough associated with the dust are fairly weak. We will have to watch the S-Band radars at CZC and STR, our ATOFMS LVN and our precipitation samples to learn whether dust participates in the precipitation forming process for this small storm.

Next chance for rain:

After Monday night, the next storm system to impact our area will arrive late Wednesday to early Thursday. We will examine that system in the next weather post.



One response to “After the Storm

  1. Pingback: The Surprise AR | ATOFMS Field Notebook

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