Identification

Title

Temperature and pressure dependence of the rain-snow phase transition over land and ocean

Abstract

The phase of precipitation is important for weather forecasts, land hydrology and remote sensing. To quantify the temperature and pressure dependence of snow frequency (F, in %) when precipitation occurs, we have analyzed 3-hourly weather reports of surface air temperature (Ts, °C) and pressure (Ps), and snow and rain occurrences from over 15,000 land stations and available ship observations from 1977 - 2007. It is found that the phase transition occurs over a fairly wide range of temperature from about −2°C to +4°C over (low-elevation) land and −3°C to +6°C over ocean. The F-Ts relationship can be represented by a hyperbolic tangent: F(Ts) = a [tanh (b (Ts - c)) - d], with the slope parameter b close to 0.7 over land and 0.4 over ocean. The pressure-dependence is only secondary and reflected in the parameters. Results show that snow occurs often (F > 50%) for Ts ≤ 1.2°C over land and Ts ≤ 1.9°C over ocean, and are non-negligible (F > 5%) for Ts ≤ 3.8°C over land and Ts ≤ 5.5°C over ocean. This "warm bias" results from the falling of snowflakes into warmer surface layers, which is especially true over ocean. The warm bias is higher when air pressure is below ~750 hPa because snow falls faster in thin air.

Resource type

document

Resource locator

Unique resource identifier

code

https://n2t.org/ark:/85065/d7wh2q52

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

2008-06-17T00:00:00Z

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