Evaluating Satellite Sounding Temperature Observations for Cold Air Aloft Detection

Rebekah Esmaili,Chris Barnet,Mark Schoeberl,Nadia Smith

doi:10.3390/atmos11121360

Abstract

Cold Air Aloft (CAA) can impact commercial flights when cold air descends below 12,192 m (40,000 ft) and temperatures drop dramatically. A CAA event is identified when air temperature falls below −65 °C, which decreases fuel efficiency and poses a safety hazard. This manuscript assesses the performance of the National Oceanic and Atmospheric Administration Unique Combined Atmospheric Processing System (NUCAPS) in detecting CAA events using sounders on polar-orbiting satellites. We compare NUCAPS air temperature profiles with those from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) for January–March 2018. Of 1311 collocated profiles, 236 detected CAA. Our results showed that NUCAPS correctly detects CAA in 48.1% of profiles, while 17.2% are false positives and 34.7% are false negatives. To identify the reason for these detection states, we used a logistic regression trained on NUCAPS diagnostic parameters. We found that cloud cover can impact the skill even at higher vertical levels. This work indicates that a CAA-specific quality flag is feasible and may be useful to help forecasters to diagnose NUCAPS in real-time. Furthermore, the inclusion of an additional sounder data source (e.g., NOAA-20) may increase CAA forecast accuracy. Cloud scenes change rapidly, so additional observations provide more opportunities for correct detection.

Highlights

Over 14,000 flights crossed into the Arctic Circle since the 2000s
We examined 1311 NUCAPS and COSMIC matchups, of which 236 COSMIC profiles detected Cold Air Aloft (CAA)
NUCAPS has minimal reliance on non-sounder data sources and, as a result, retrievals are independent of Numerical Weather Prediction (NWP) models

Summary

Introduction

A typical flight from New York to Hong Kong can save 16 kL of fuel and 2 h of time [1]. Jet fuel can gel when the aircraft is exposed to air temperatures below 208 K (−65 ◦ C) for extended periods of time, which typically reduces fuel efficiency and could, in theory, cause crashes. The tropopause height is lowest near the poles, so cold air can descend below 12 km (~40,000 ft) and into the cruising altitudes of polar crossing flights (Figure 1a) [2]. These events, known as Cold Air Aloft (CAA), are a particular aviation concern during the boreal winter

Results

Discussion

Conclusion