THEORETICAL BACKGROUND | NWP LANDUSE TYPE

1. WRF

WRF is a community model developed by the National Center for Atmospheric Research(NCAR). They have designated our country(Korea) as Savannah (which is wrong). WRF is a non-hydrostatic model that is suitable for simulating microscale and mesoscale meteorological phenomena.

The USGS land cover data set is the most common land cover data used in the WRF model.

2. Sea & Land Breeze

Source of the picture : My Water (http://www.water.or.kr)

The Sea Breeze formation factor in coastal areas is the difference in specific heat. There is a greater impact on Sea Breeze when the altitude and the number of mountains are higher. Because of the Heat Island Effect* in urban region, the temperature difference between land and sea becomes larger. Therefore, the Sea Breeze is stronger and the Land Breeze is weaker in large cities (ex, INCHEON, SEOUL).

* Heat Island Effect :

This refers to the formation of a hot area (Heat Island) in the center of a city where temperatures are higher than those in the suburbs. The formation of Heat Island is caused by the effects of artificial heat or air pollution in urban areas.

(ref. Earth Science Dictionary)

The formation of Sea Breeze (day):

The temperature of the ground, whose specific heat is relatively less than the sea level, rises faster than the sea level. This causes the air on the heated ground to rise due to buoyancy by temperature. Therefore the air above the sea level moves in the direction of the land.

The formation of Land Breeze (night):

At night, the ground is cooled by long wave radiation faster than the sea level, due to smaller specific heat. Therefore the air temperature on the ground is lower than air temperature above the sea level. The density currents caused by temperature difference forms the Land Breeze.

3. LANDUSE Types (USGS)

Land cover represents the actual or physical presence of vegetation (or other materials where vegetation is nonexistent) on the land surface. Land cover is also often described as what can be seen on land viewed from above. It is one means to describe landscape patterns and characteristics that are critical in understanding aspects of the environment, including the availability of and changes in habitat, the potential for dispersion of chemicals and other pollutants, and potential contributors to climate change, such as reflectivity of the land.

(Ref. Report on the Environment, EPA: United States Environmental Protection Agency https://cfpub.epa.gov/roe/indicator_pdf.cfm?i=49 )

4. Variables of LANDUSE Types

ALBD(Albedo) : The albedo is defined as the ratio between the reflected energy and the incident energy over a unit area, from which it can be inferred that there is some similarity between the albedo and the reflectance.

(ref. Chapter 7 - Broadband Albedo,Shunlin Liang, Xiaowen Li, Jindi Wang, Advanced Remote Sensing, Academic Press, 2012, Pages 175-233, https://doi.org/10.1016/B978-0-12-385954-9.00007-1. )

SLMO(Soil Moisture) : Soil moisture is the source of water that evaporates and transpires from the soil and vegetation into the atmosphere, thus affecting the distribution of clouds and precipitation.

(ref. A. Robock, HYDROLOGY, FLOODS AND DROUGHTS | Soil Moisture, Gerald R. North, John Pyle, Fuqing Zhang, Encyclopedia of Atmospheric Sciences (Second Edition), Academic Press, 2015, https://doi.org/10.1016/B978-0-12-382225-3.00169-9.)

SFEM(Surface Emissivity _ Stefan-Boltzmann) : Emissivity of a surface is its effectiveness in emitting energy as thermal radiation. For Earth temperature bodies this radiation is emitted at long wavelengths compared to the sunlight. Thermal radiation or black body radiation is governed by the Stephen-Boltzmann law.

(ref. Land use influence in WRF model. A high resolution mesoscale modeling over Oriental Pyrenees, page 4, Bernat Jim´enez Esteve.)

SFZ0(Surface Roughness) : Roughness length (z0) is a parameter widely used in most of the superficial layer parameterizations. It is associated to the roughness elements at the surface. However it is not a real length, but it is an empirical parameter which depends on the type of land cover.

(ref. Land use influence in WRF model. A high resolution mesoscale modeling over Oriental Pyrenees, page 2, Bernat Jim´enez Esteve.)

5. Surface Roughness

The friction force of the surface is concentrated on the lower part of the atmospheric boundary layer. The dynamic mixing by the surface friction occurs at the ground boundary layer adjacent to the surface, and the wind speed is increased by the algebraic function according to the altitude.

Calculation of surface Roughness Length ( )

1. Using Wind Speed observation

2. Using Geographic Information System data

6. Boundary Layer

Boundary Layer is particularly characterized by well-developed mixing by fractional drag, ‘bubbling-up’ of air parcels. It absorbs the heat from the air parcel through water.

Height of the boundary layer is not constant with time, it depends upon the strength of the surface-generated mixing. Daytime: 1-2 km, Night: 0.1 km

(Because of the vertical convection by temperature difference)

The horizontal distance of the boundary layer is related to the distance which air can travel during heating or cooling portion of the daily cycle.