Identification

Title

A stochastic convective approach to account for model uncertainty due to unresolved humidity variability

Abstract

Forecast uncertainty can result from the neglect of humidity variability on spatial scales not resolved by forecast models. To account for this, a stochastic convective scheme for the European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble prediction system is presented that uses the subgrid humidity distributions provided by the cloud scheme. Each member of a forecast ensemble randomly samples this distribution to perturb the convective parcel's initial humidity and/or the humidity of the air entrained during ascent. Accounting for humidity variability with the new scheme has a smaller impact on tropical ensemble spread in the short range compared to the ECMWF operational scheme that represents uncertainty because of parameterization error. Combining the two schemes to account for both parameterization error and subgrid humidity variability simultaneously generally improves the skill of the operational system for most variables in the short to medium range in midlatitudes, while results in the tropics are mixed, with a notable deterioration in medium-range probabilistic skill for temperature and zonal wind. This deterioration is a consequence of the methodology employed. Since the convective scheme is highly nonlinear, providing zero-mean humidity perturbations to the scheme's input profiles does not lead to zero-mean perturbations to the output tendencies. For some parameters, this results in an increased bias of the ensemble mean and a deterioration in probabilistic skill. As future convective schemes are optimized to maximize deterministic forecast skill, the methodology will require modification to ensure zero-mean convective output perturbations.

Resource type

document

Resource locator

Unique resource identifier

code

https://n2t.org/ark:/85065/d7xs5vk9

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

2008-09-16T00:00:00Z

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