Wu

Sponsors:National Aeronautics and Space Administration (NASA)Goddard Space Flight Center (GSFC)Goddard Institute for Space Studies (GISS)New York City Research Initiative (NYCRI)United States Department of Education The Alliance for Continuous Innovative Learning Environments in STEM (CILES) CILES Grant #P031C110158CUNY: The City College of New York

The importance of the PBL height makes it very important that independent methods are developed to accurately measure it for future comparison to models. The purpose of this experiment was to analyze methods of determining PBL Height from LIDAR and Microwave Radiometer data.

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Figure 1: The location of the PBL height for a given day.

State of Alaska Department of Environmental Conservation. Division of Air Quality: Particulate Matter-Background Information. http://dec.alaska.gov/air/anpms/pm/pm_bckgrd.htm (Accessed July 11, 2012).

Union of Concerned Scientists. Global Warming: Global Warming Science and Impacts. http://www.ucsusa.org/global_warming/science_and_impacts/science/aerosols-and-global-warming-faq.html (Accessed July 23, 2012).

United States Environmental Protection Agency. Fine Particle (PM2.5) Designations: Basic Information. http://www.epa.gov/airquality/particlepollution/designations/basicinfo.htm (Accessed July 10, 2012).

Figure 1 obtained from: http://upload.wikimedia.org/wikipedia/commons/5/5f/PBLimage.jpgFigure 2 obtained from http://www.arm.gov/instruments/images/mwr.jpgpFigure 3 obtained from http://sky.ccny.cuny.edu/wc/LidarTelescopesm.jpg

Comparing Microwave Radiometer and LIDAR Techniques in Determining Planetary Boundary Layer Height

Michael Hirschberger

Abstract

Planetary Boundary Layer (PBL)

Objective

References

Results

Discussion/Conclusions

Data and Calculations

Aerosols are generally located in the lowest part of the atmosphere, the Planetary Boundary Layer (PBL). The PBL is characterized by strong turbulence and a high degree of mixing, especially when convective heating is dominant and aerosols mix well. Low-lying aerosols exist in the PBL for a few days, while those higher in the PBL can last for a few years. If aerosols are well mixed in the PBL, then the height of the PBL is important in relating fine-mode aerosols (surface PM2.5) to the full column aerosol optical depth (AOD). AOD is a measurement of the amount of extinction (scattering and absorption of sunlight) that is caused by aerosols. AOD is a critical measurement in assessing the impact that aerosols have on climate.

Data was obtained for 11 days from 11/28/11 to 12/13/11 with the exception of 11/29, 12/3, 12/6, 12/7, and 12/10. Relative humidity, ground pressure, and temperature obtained from the radiometer were used to calculate virtual temperature, the temperature at which a quantity of dry air would have a total pressure and density equal to a quantity of moist air.Equations used:

1. Saturated water vapor pressure, esat:

t0=6.11 hpa, a=7.5, b=237.5, T=temperature

2. Water vapor pressure, e:

3. Pressure, p:

4. Mixing Ratio, w:

5.Virtual Temperature, TV:

Virtual temperature was calculated at 30-minute intervals for each day. The gradient of virtual temperature with respect to altitude was then calculated for each interval. The height at which maxima of this gradient occurred was determined to be the PBL height for that interval. The MWR vertical resolution is ~ 50 meters and the retrieval is not so simple so accuracy in the MWR PBL heights is expected to be less than the LIDAR.

Equipment

Microwave Radiometer (MWR): An instrument that measures energy emitted from the atmosphere at many wavelengths in the microwave band (22 – 60 GHz). From these measurements, it is possible to determine the vertical structure of temperature and the amount of water vapor present.

Figure 2: Microwave Radiometer (MWR)

Figure 3:LIDAR

p0=ground pressure, h0=7 km, h=altitude

11 12 13 14 15 16

0.5

1

1.5

2

2.5

3

Local time (hr)

Altitude (

km

)

2011-12-02, Log(e) of Pz2 at 1064-nm

PBL-top

-1

0

1

2

3

Figure 4: MWR 12/02/11Figure 5: LIDAR 12/02/11

11 12 13 14 15 16

0.5

1

1.5

2

2.5

3

3.5

Local time (hr)

Altitude (

km

)

2011-12-08, Log(e) of Pz2 at 1064-nm

-0.5

0

0.5

1

1.5

2

2.5

3PBL-top

11 12 13 14 15 16

0.5

1

1.5

2

2.5

3

Local time (hr)

Altitude (

km

)

2011-12-13, Log(e) of Pz2 at 1064-nm

-0.5

0

0.5

1

1.5

2

2.5

3PBL-top

Figure 8: MWR 12/13/11

Figure 6: MWR 12/08/11

Figure 9: LIDAR 12/13/11

Figure 7: LIDAR 12/08/11

In comparing MWR and LIDAR techniques to determine PBL height, there were generally reasonable correlations between the two. Although correlations could be seen, it is clear that the LIDAR graphs were more detailed because those calculations were performed on 1-min. intervals as opposed to the MWR 30-min. intervals. In addition, the Signal to Noise of LIDAR makes it particularly useful in determining the effective PBL height that the aerosols are trapped in. Both of these tools should be useful in assessing model PBL heights.

Future Work•To compare virtual temperature gradient calculations to those of potential temperature to determine PBL height.•To shorten the interval of the MWR calculations to produce graphs which more closely resemble those of the LIDAR data.•To compare PBL heights from instruments against WRF model outputs.

The height of the planetary boundary layer (PBL) is a critical measurement in assessing atmospheric phenomena that have effects on earth’s climate. In particular, PBL height is important in relating the aerosol optical depth (AOD) to surface PM2.5 (fine-mode aerosols), especially when there is a high degree of aerosol mixing in the PBL. The importance of the PBL height makes it crucial that independent methods are developed to accurately measure it for future comparison to models. This study compared an indirect method of obtaining the PBL height using Microwave Radiometer (MWR) data to a more accurate method that uses data obtained from the Light Detection And Ranging (LIDAR) instrument, which directly measures PBL height. To obtain PBL height from MWR data, calculations were performed to find the virtual temperature gradient. The height at which the maxima of this gradient occurred was determined to be the PBL height for that particular time interval. Our results show generally reasonable correlations between the two methods. The Signal to Noise of LIDAR makes LIDAR particularly useful in determining the effective PBL height that the aerosols are trapped in. Both of these methods should be useful in assessing model PBL heights.

Light Detection and Ranging (LIDAR): An instrument that vertically emits a laser into the atmosphere. From the degree of backscatter that occurs, aerosol levels can be calculated at all heights of the laser’s range.

Mentors: Dr. Barry Gross, Dr. Yonghua Wu

NYCRI Contributor:Michael Hirschberger (UG)