Identification

Title

Impacts of a revised surface roughness parameterization in the Community Land Model 5.1

Abstract

The roughness of the land surface (z(0)) is a key property, exerting significant influence on the amount of near-surface turbulent activity and consequently the turbulent exchange of energy, water, momentum, and chemical species between the land and the atmosphere. Variations in z(0) are substantial across different types of land cover, ranging from typically less than 1 mm over fresh snow or sand deserts up to more than 1 m over urban areas or forests. In this study, we revise the parameterizations and parameter choices related to z(0) in the Community Land Model 5.1 (CLM), the land component of the Community Earth System Model (CESM). We propose a number modifications for z(0) in CLM, guided by observational data. Most importantly, we find that the observations support an increase in z(0) for all types of forests and a decrease in the momentum z(0) for bare soil, snow, glaciers, and crops. We then assess the effect of those modifications in land-only and land-atmosphere coupled simulations. With the revised parameterizations, diurnal variations of the land surface temperature (LST) are dampened in forested regions and are amplified over warm deserts. These changes mitigate model biases compared to MODerate resolution Imaging Spectroradiometer (MODIS) remote sensing observations. The changes in LST are generally stronger during the day than at night. For example, the LST increases by 5.1 K at 13:30 local solar time but only by 0.6 K at 01:30 during boreal summer across the entire Sahara. The induced changes in the diurnal variability of nearsurface air temperatures are generally of the opposite sign and of smaller magnitude. Near-surface winds accelerate in areas where the momentum z(0) was lowered, such as the Sahara, the Middle East, and Antarctica, and decelerate in regions with forests. Overall, this study finds that the current representation of z(0) in CLM is not in agreement with observational constraints for several types of land cover. The proposed model modifications are shown to considerably alter the simulated climate in terms of temperatures and wind speed at the land surface.

Resource type

document

Resource locator

Unique resource identifier

code

https://n2t.org/ark:/85065/d79g5rfk

codeSpace

Dataset language

eng

Spatial reference system

code identifying the spatial reference system

Classification of spatial data and services

Topic category

geoscientificInformation

Keywords

Keyword set

keyword value

Text

originating controlled vocabulary

title

Resource Type

reference date

date type

publication

effective date

2016-01-01T00:00:00Z

Geographic location

West bounding longitude

East bounding longitude

North bounding latitude

South bounding latitude

Temporal reference

Temporal extent

Begin position

End position

Dataset reference date

date type

publication

effective date

2022-03-21T00:00:00Z

Frequency of update

Quality and validity

Lineage

Conformity

Data format

name of format

version of format

Constraints related to access and use

Constraint set

Use constraints

Limitations on public access

None

Responsible organisations

Responsible party

contact position

OpenSky Support

organisation name

UCAR/NCAR - Library

full postal address

PO Box 3000

Boulder

80307-3000

email address

opensky@ucar.edu

web address

http://opensky.ucar.edu/

name: homepage

responsible party role

pointOfContact

Metadata on metadata

Metadata point of contact