Posits as an alternative to floats for weather and climate models

Conference item

Posit numbers, a recently proposed alternative to floating-point numbers, claim to have smaller arithmetic rounding errors in many applications. By studying weather and climate models of low and medium complexity (the Lorenz system and a shallow water model) we present benefits of posits compared to floats at 16 bit. As a standardised posit processor does not exist yet, we emulate posit arithmetic on a conventional CPU. Using a shallow water model, forecasts based on 16-bit posits with 1 or 2 exponent bits are clearly more accurate than half precision floats. We therefore propose 16 bit with 2 exponent bits as a standard posit format, as its wide dynamic range of 32 orders of magnitude provides a great potential for many weather and climate models. Although the focus is on geophysical fluid simulations, the results are also meaningful and promising for reduced precision posit arithmetic in the wider field of computational fluid dynamics.

Authors: Klöwer, M; Düben, P; Palmer, T

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Association for Computing Machinery
• Host title: CoNGA'19 Proceedings of the Conference for Next Generation Arithmetic 2019
• Journal: CoNGA'19 Proceedings of the Conference for Next Generation Arithmetic 2019
• Article number: 2
• Publication date: 2019-03-13
• Acceptance date: 2019-02-04
• Event start date: 2019-03-13
• Event end date: 2019-03-14
• DOI: 10.1145/3316279.3316281
• ISBN: 9781450371391
• Keywords: posits; floating point; weather forecast; computational fluid dynamics; climate projections; reduced precision; computer arithmetic