Identification

Title

Effects of convective scale downdrafts on the rainfall simulation in NCAR-CAM3

Abstract

In this work, an attempt is made to systematically evaluate the effect of convective scale downdrafts on the model-simulated rainfall, in both aqua- and actual-planet frameworks, using the NCAR CAM3. From the aqua-planet simulations, it was found that there is a reduction in the total rainfall (TRF) with increase in the intensity of downdrafts, which is primarily attributed to the reduction in the deep convective component (DRF). However, with stronger downdrafts, the shallow convective and the large-scale components (SRF and LRF, respectively) are found to increase. The reduction in DRF is due to the increased evaporation of convective precipitation within the downdrafts. It is found that, with intense downdrafts, there is an increase in relative humidity throughout the troposphere, due to the combined effect of both moisture and temperature. There is an overall increase in specific humidity of the atmosphere with stronger downdrafts, excepting at around the 900-hPa level. In addition, there is a reduction in temperature throughout the troposphere, primarily due to the reduction in the overall temperature tendency due to moist processes and that due to the radiative processes. The changes in the radiative forcing are found to be primarily due to a significant increase in the low cloud fraction with strong downdrafts. In the actual-planet framework, it is seen that, with strong convective downdrafts, there is a reduction in TRF and DRF and a corresponding increase in SRF and LRF, similar to the results obtained from the aqua-planet simulations. The vertical structures of the thermodynamic variables (RH, q, and T) show similar sensitivity to the downdraft intensity as that seen in the aqua-planet framework. Sensitivity of frequency and intensity of model-simulated rainfall to the downdraft intensity was also analyzed, and it was seen that there were significant differences in the frequency distribution of rainfall. It was seen that, with an increase in downdraft intensity, there is an increase in the frequency of light rain (1-10 mm/day) for TRF with a corresponding reduction in all other rainfall bins. A similar behavior was seen for the DRF as well, while the SRF and LRF components showed an increase in rainfall accumulation in all the bins. In addition, the impact of convective downdrafts on the mean spatial pattern of rainfall is also analyzed, for the DJF and JJA periods (boreal winter and summer, respectively). For the DJF period, with strong downdrafts, it was seen that grossly over the whole domain, there were a reduction in DRF and an increase in SRF and LRF. In contrast, during JJA, although a major part of the domain showed a reduction in DRF, there were regions like western Arabian Sea and the Somali coast with increase in DRF with intense downdrafts. The SRF and LRF components, however, show a spatially homogeneous increase over almost the entire domain with increase in downdraft intensity.

Resource type

document

Resource locator

Unique resource identifier

code

http://n2t.net/ark:/85065/d72z167d

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

2012-02-01T00:00:00Z

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