Preprints
https://doi.org/10.5194/egusphere-2022-755
https://doi.org/10.5194/egusphere-2022-755
 
25 Aug 2022
25 Aug 2022
Status: this preprint is open for discussion.

How adequately are elevated moist layers represented in reanalysis and satellite observations?

Marc Prange1,2, Stefan A. Buehler1, and Manfred Brath1 Marc Prange et al.
  • 1Universität Hamburg, Meteorologisches Institut, Bundesstraße 55, 20146 Hamburg, Germany
  • 2International Max Planck Research School on Earth System Modelling (IMPRS-ESM), Bundesstraße 53, 20146 Hamburg, Germany

Abstract. We assess the representation of Elevated Moist Layers (EMLs) in ERA5 reanalysis, the IASI L2 retrieval Climate Data Record (CDR) and the AIRS-based CLIMCAPS-Aqua L2 retrieval. EMLs are free tropospheric moisture anomalies that typically occur in the vicinity of deep convection in the tropics. EMLs significantly effect the spatial structure of radiative heating, which is considered a key driver for meso-scale dynamics, in particular convective aggregation. To our knowledge, the representation of EMLs in the mentioned data products have not been explicitly studied, a gap we address in this work. We assess the different datasets' capability of capturing EMLs by collocating them with 2146 radiosondes launched from Manus Island within the Western Pacific warmpool, a region where EMLs occur particularly often. We identify and characterise moisture anomalies in the collocated datasets in terms of moisture anomaly strength, vertical thickness and altitude. By comparing the distributions of these characteristics, we deduce what specific EML characteristics the datasets are capturing well and what they are missing. Distributions of ERA5 moisture anomaly characteristics match those of the radiosonde dataset quite well and remaining biases can be removed by applying a 1 km moving average to the radiosonde profiles. We conclude that ERA5 is a suitable reference dataset for investigating EMLs. We find that the IASI L2 CDR is subject to stronger smoothing than ERA5 with moisture anomalies being on average 13 % weaker and 28 % thicker than collocated ERA5 anomalies. The CLIMCAPS L2 product shows significant biases in its mean vertical humidity structure compared to the three other investigated datasets. These biases manifest as an underestimation of mean moist layer height of about 1.3 km compared to the three other datasets, a general mid-tropospheric moist bias and an upper tropospheric dry bias. Biases found in the all-sky scenes do not change significantly when limiting the analysis to clear-sky scenes. We calculate radiatively driven vertical velocities derived from longwave heating rates to estimate the dynamical effect of the moist layers. Moist-layer-associated vertical velocity values derived from GRUAN soundings range between 2 to 3 hPa hour-1 while mean meso-scale pressure velocities from the EUREC4A field campaign range between 1 to 2 hPa hour-1, highlighting the dynamical significance of EMLs. Subtle differences in the representation of moisture and temperature structures in ERA5 and the satellite datasets create large relative errors in ωrad on the order of 40–80 % with reference to GRUAN, indicating limited usefulness of these datasets to assess the dynamical impact of EMLs.

Marc Prange et al.

Status: open (until 06 Oct 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-755', Nadia Smith, 20 Sep 2022 reply
    • AC1: 'Reply on RC1', Marc Prange, 04 Oct 2022 reply

Marc Prange et al.

Data sets

Supplementary data for "How adequately are elevated moist layers represented in reanalysis and satellite observations?" Marc Prange, Stefan A. Buehler, Manfred Brath https://doi.org/10.5281/zenodo.6940500

Marc Prange et al.

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Short summary
We investigate the representation of elevated moist layers (EMLs) in two satellite retrieval products and ERA5 reanalysis. EMLs occur in the vicinity of tropical convective storms and are thought to have an impact on their evolution through radiative heating. We provide a first dedicated assessment of EMLs in long-term data products in terms of moist layer strength, vertical thickness and altitude by comparing to collocated radiosondes over the Western Pacific, a region where EMLs often occur.