Principal Investigators:

Goal:

Develop a regional (and coastal) meteorological evaluation database for WRF and explore the development of Planetary Boundary Layer (PBL) mixing depth during sea breeze conditions.

Discussion:

The mixed layer height is a key atmospheric parameter for all models intended to predict conditions at the surface, and especially for atmospheric dispersion and air quality models since the PBL height controls the depth of the atmosphere over which emissions will be diluted. Mixed layer heights exhibit strong diurnal patterns. Development of the mixed layer is influenced by many factors -- local topographical features, surface type, synoptic conditions, cloud cover, etc. In situations like that considered here, the inland transport of marine air may significantly affect the temporal and spatial development of the mixed layer.

The objective of this study is to characterize the temporal and spatial development of the mixed layer under influence of a marine sea breeze. The intent is to build on previous meteorological research conducted by Jackson State University as outlined in "Study of Meso-Scale Coastal Circulations in Mississippi Gulf Coast with Mesonet Observations and Modeling, Chaila, et al.". The focus of the study will be the last two weeks of June, 2009 (June 15 - June 30, 2009)

Experimental Plan:

Based on data extracted from the Harrison High School weather station, the study would be scheduled for the last two weeks of June, 2009. As shown in Figure 1, for winds greater than 2.0 m/s, wind directions are fairly well established from 180-190 degrees. Restricting wind speed to greater than 3.0 m/s, as shown in Figure 2, tends to highlight the southerly wind direction component anticipated for a well-established sea breeze circulation penetrating inland to the Harrison station. Consistent conditions for strong southerly winds were observed only for the month of June. Selecting the last two weeks of June optimizes the probability of observing sea breeze conditions as well as facilitating participation of students from Jackson State University.

The study will take advantage of the existing two inland coastal atmospheric turbulence monitoring stations located at Harrison Central High School and West Wortham Elementary School as well as the off-shore turbulence station anticipated for installation on Ship Island this winter. An additional surface weather station is proposed to be temporarily located at either Stone High School or Stone Middle School, Wiggins, MS. This would provide four surface turbulence monitoring stations in direct line with any developed sea breeze circulation.

In addition to the surface turbulence monitoring stations, ARL proposes to deploy two portable rawinsonde upper air measurement systems. Two options exist for locating the rawinsonde systems. Option one, the preferred case, assumes obtaining permission for the National Park Service to conducted sounding from Shipp Island. The other upper air system would be located at Harrison Central High School. During sea breeze conditions, this deployment of measurement capability would provide vertical winds and temperature data from an off-shore station as well as vertical measurements through the sea breeze circulation. The second option, which assumes that Shipp Island would not be available as a launch site, would locate rawinsonde measurements at Harrison Central High School and Stone High School, Wiggins, Ms. This option provides vertical soundings within and outside any developed sea breeze. Figure 3 provides a Google Earth map indicating the placement of surface and upper air measurement sites within the study domain.

The rawinsonde measurement goal would be to conduct soundings on four days with an optional fifth day available if conditions permit. Coincident rawinsonde sounding would be conducted every two hours, beginning at 8:00 am until 4:00 pm providing a detailed description of the regional upper air patterns. Two crews of at least two researchers would be required for each rawinsonde observation site. Crews would consist of at least one NOAA/ARL/ATDD engineer and one research staff member from Jackson State University. If available, additional support from JSU would facilitate balloon launches. For option 1, rawinsonde crews would be based in Gulf Port. For option 2, crews would be located in Gulf Port and Wiggins. Based on ATDD standard operating procedures, rawinsonde profiles will be automatically transmitted to an established ARL/ATDD FTP Web based site. JSU and NOAA researchers will be able to download observational data from this location. Meteorological data collected at the existing Harrison High School and West Wortham Elementary School stations plus data collected from the proposed Shipp Island and Wiggins location would also be available from the same ATDD ftp web site.

Measurement Approach:

Surface turbulence measurements

The joint study will make use of existing ARL/JSU monitoring stations located at Harrison Central High school (30.515017N 89.102709W) and West Wortham Elementary School (30.56678N 89.180794W). The study anticipate the installation of an additional monitoring station on Shipp Island(30.223005N 89.901765W). To supplement the surface turbulence network, a temporary monitoring station would be installed at Stone Elementary School (30.843565N 89.110185W), Wiggins, MS. This will provide a line of turbulence monitoring stations beginning 15 km off-shore with Shipp Island to 50 km inland at Wiggins, MS. Depending on availability of instrumentation, two additional temporary stations are proposed. While specific locations have not been establish, locations for the supplemental stations are suggested (1) in proximity to the GulfPort -Biloxi Airport and (2) McHenry, MS.

Surface measurements will consist of

• wind speed/ direction from RM Young propeller anemometer
• temperature
• relative humidity
• u,v,w wind component from RM Young sonic anemometer
• velocity covariance, heat flux
• solar radiation

Sensor data will be acquired using Campbell Scientific dataloggers with 1 and 15 minute averages and statistics computed for each variable. Acquired data will be retrieved by cell modem and stored at ATDD. Acquired data will be made available on ATDD ftp site.

Upper air measurements

The joint study will employ two NOAA/ATDD portable rawinsonde systems to acquire vertical profiles of wind speed, wind direction, temperature and pressure. ATDD's portable systems are GRAW model GS-H mobile rawinsonde systems. These consist of a laptop computer, handheld 400 MHz receiver and model DFM-06 microprocessor controlled programmable radiosonde. To provide sufficient frequency separation, one radiosonde system will operate at 401.5 MHz while the other will operate at 404.5Mhz. Radiosonde operations will follow standard National Weather Service procedures. As outlined in the discussion of the plan, proposed launch stations include:

• Ship Island
• Harrison Central High School
• Stone Elementary School, Wiggins , MS.

Proposed rawinsonde launch times are

• 0800
• 1000
• 1200
• 1400
• 1600

Personnel

Two+ NOAA/ATDD field engineers

Two+ JSU students

Data Analysis

Although sea breeze regimes have been the focus of considerable research, the evolution of the PBL in situations considered here remains somewhat obscure. The situation is clearly beyond conventional understanding and simulation, since the circumstances violate the usual time-stationarity and spatial-homogeneity assumptions. Regardless of such complexities, the dynamics of sea breeze circulations is of great interest because a large proportion of the national population lives within reach of the local sea breeze (which can reach as far as 30 km inland, if not sometimes more). Within this framework, ARL and JSU, will conduct a joint effort to analyze acquired meteorological data. The scope of this effort will be defined in subsequent meetings and discussions between JSU and ARL. An outline for the analysis of data obtained as a series of daytime case studies, would include:

A: Radiosonde data

• For each day’s observations, and using the radiosonde observations, assess the time-evolving details of the sea breeze circulation – its depth and velocity normal to the shore.
• Assess the sea breeze along-shore component, so as to quantify the well known helical circulation pattern.
• Relate both of these dynamic features to the external meteorological conditions, as also revealed by the radiosonde data.

B: Surface turbulence data

• Relate changes in measured turbulent kinetic energy (TKE) to the fetch, over the water for a start and subsequently over the land.
• Construct cross-sections (normal to the coast) of sensible heat, latent heat flux, and shear stress, using the ATDD towers as baselines and interpolating using surface temperature.
• Relate the updraft potential resulting from the combined sensible and latent heats to the strength and depth of the sea breeze itself.

C: Integrated analysis

• Using all available data, relate the depth and strength of the sea breeze circulation to (a) the surface fluxes and/or (b) the mesoscale meteorology and (c) JSU WRF forecasts.

D: Mixed layer consequences

• The sea breeze front serves as an atmospheric barrier to on-flowing air. Hence, the data obtained will be used to quantify the change in the depth of the mixed layer occasioned by the sea breeze.

Publications

The prime goal here is to help improve forecasting in areas where there is a high population density. A major step will be in communicating the results to the user community, through formal publications and meeting presentations.

Two joint JSU/ARL formal papers are anticipated, one focusing on the experiment and its data, the other on the relationships between surface flux regimes, mesoscale meteorology, sea breeze characteristics, and PBL depth. A meeting presentation is also anticipated at perhaps the first AMS or AGU meeting following completion of data analysis.

Supplemental Study

ARL/ATDD will take advantage of the ARL/JSU field study to prepare for participation in summer trials during CalNex 2010. ARL/ATTD will take advantage of the proposed temporary observation station at Wiggins, MS to install the additional turbulence and chemical sampling instrumentation proposed for CalNex 2010. This will give ARL/ATDD an opportunity to test communications, integration of high frequency ozone observations and surface flux measurements, and inclusion of filter pack and denuder sampling for sulfur and nitrogen compounds. The enhanced observations will be conducted during the proposed study period.