Category Archives: past projects

Coastal-Urban Microclimates (2010-2012)

Weather and wind forecasting typically relies upon low-resolution computer simulations, with no more detail than a 12-kilometer grid.  Also, these model simulations virtually never incorporate urban features such as pavement and skylines.  As a result, they cannot accurately predict how temperature varies over city neighborhoods during a heat wave, nor can they always tell what direction wind will be blowing an atmospheric contaminant.  In the end, weather forecasters do an amazing job with mediocre weather models by using their long-term knowledge of what works for various situations and locations.

Air temperature measurements at 1:15 AM during a recent heat wave.  The 240 weather stations demonstrate how some neighborhoods around New York City were as much as 15 degrees warmer than rural areas.  Data credits given below.

Sometimes this isn’t good enough, so a goal of a research collaboration between our research group and collaborators at the Naval Research Laboratory and City College of New York was to push the boundaries of dealing with these shortcomings in atmospheric prediction.  Our research aimed to help improve prediction capabilities for weather and atmospheric transport, as well as the scientific understanding of urban weather features such as the urban heat island, which often keeps temperatures 10-15 degrees (F) warmer than rural areas at night, as shown above.  The influence of the ocean and sea breezes on weather is also captured much better by COAMPS than by most weather models.  Previous results and publications from similar research are summarized on Julie Pullen’s webpage.

We worked with the Navy’s Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS) computer model, and using grids as high as 333 meters resolution.  For checking the model results with actual weather observations, we used the usual airport and city weather stations, maintained by NOAA, but also hundreds of civilian-run weather stations — all these are conveniently merged in City College’s NYC Met Net.

A student publication resulting from this research is:

Meir, T., Orton, P.M., Pullen, J., Holt, T., Thompson, W.T., Arend, M.F., 2013. Forecasting the New York City urban heat island and sea breeze during extreme heat events. Weather and Forecasting.  doi: 10.1175/WAF-D-13-00012.1.  webPDF

 

[Temperature figure data credits:  NOAA (NOS-PORTS, NWS-ASOS, NWS-HADS, Urbanet), Rutgers NJ Weather and Climate Network, APRSWXNET, AWS Convergence Technologies, Inc. (WeatherBug), and Weatherflow, via Mark Arend (NYCMetNet).]

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Did the Oil Spill Stop Hurricanes?

It has been known for centuries that oil reduces the ability for wind to create sea surface waves. Benjamin Franklin famously hid oil in the bottom of his cane, so he could shake it over a pond like a sorcerer, and stop the wind’s creation of ripples. More recently, scientists have demonstrated the mechanism that is at work – oil films reduce water’s surface tension, reducing the air-to-water flux of momentum, also known as wind stress.  Studies have even shown that natural oil slicks above seafloor seeps in many parts of the world are visible from space due to their effects on sea surface roughness.

credit: Washington Post

The widespread and persistent surface oil on the Gulf of Mexico caused by the 2010 oil spill provided an unprecedented opportunity last summer to explore the effect of oils on atmosphere-ocean exchanges of momentum, as well as heat and gases.  I wrote a proposal with Wade McGillis (Columbia University) that was funded by the National Science Foundation.  The plan was to quantify these effects using an anchored catamaran on the Alabama continental shelf, as well as large-scale mapping aboard a ship with air-sea flux measurements.

The research also has many applications related to understanding the Gulf oil spill and its consequences, because modified air-sea exchanges of heat, moisture and momentum could impact oil spill transport, atmospheric delivery of moisture to the Southeastern United States, and transfer of heat from the ocean to the atmosphere, an important factor during hurricane season.  The hurricane season was quiet in the Gulf, and it is possible that the oil films left over from the spill reduced the availability of the ocean’s heat and moisture for growing tropical storms.

The mooring study was conducted from July 30 through August 10, examining the water column heat budget and air-sea heat and CO2 fluxes. The study included one hydrographic profile mooring, vessel-based measurements, and a moored catamaran with measurements of oxygen, chlorophyll, turbidity, atmosphere and water pCO2, air-sea fluxes of CO2, heat, momentum, and moisture using the gradient flux (atmospheric profile) technique (McGillis et al. 2001), and net shortwave and longwave radiation.

The oil spill was capped right before we began the field work, so — fortunately for those who live in and around the Gulf — we never got the opportunity to study how oils affected the air-sea fluxes.  And there is only so much you can do with three months of post-doc funding, so deeper analysis of our field data will require additional funding.  In retrospect, it was an amazing adventure and great experience for Wade, four undergraduate students, and myself, learning how to make automated field measurements of the coastal ocean heat budget.

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