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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 17 Dec 2018

Research article | 17 Dec 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Characteristics of the tropical tropopause inversion layer using high-resolution temperature profiles retrieved from COSMIC GNSS Radio Occultation

Noersomadi Noersomadi1,2, Toshitaka Tsuda1, and Masatomo Fujiwara3 Noersomadi Noersomadi et al.
  • 1Research Institute for Sustainable Humanosphere (RISH), Kyoto University, Uji, 611-0011, Japan
  • 2National Institute of Aeronautics and Space (LAPAN), Bandung, 40173, Indonesia
  • 3Faculty of Environmental Earth Science, Hokkaido University, Sapporo, 060-0810, Japan

Abstract. Using COSMIC GNSS Radio Occultation (RO) observations from January 2007 to December 2016, we retrieved temperature profiles with 0.1 km vertical resolution in the upper troposphere and lower stratosphere (UTLS). We investigated the global distribution of static stability (N2) and the characteristics of the tropopause inversion layer (TIL) in the tropics, where a large change in temperature gradient occurs associated with sharp variations of N2. We show the variations of the mean N2 profiles in conventional height coordinates as well as in coordinates relative to both the Lapse Rate Tropopause (LRT) and the Cold Point Tropopause (CPT). When the N2 profiles are averaged relative to CPT height, there is a very thin (< 1 km) layer with average maximum N2 in the range 11.0–12.0 × 10−4 s−2. The mean and standard deviation of the tropopause sharpness (S-ab), defined as the difference between the maximum N2 (maxN2) and minimum N2 (minN2) within ±1 km of the CPT, is (10.5 ± 3.7) × 10−4 s−2. About 70 % of the values of TIL thickness (dH), which is the thickness of the layer over which N2 ≥ 0.8maxN2, were in the range 0.4 ± 0.04 km.

We focused on the variation of S-ab in two longitude regions, 90°–150° E (Maritime Continent; MC) and 170°–230° E (Pacific Ocean; PO), with different land–sea distribution. Seasonal variations of S-ab and dH were related to the deep convective activity represented by low Outgoing Longwave Radiation (OLR) during the Australian and Asian monsoons. The S-ab anomaly (S-ab*) was out-of-phase with the OLR anomaly in both the MC and PO. The correlation between S-ab* over the MC and PO and the sea surface temperature (SST) Niño 3.4 index was −0.66 and +0.88, respectively. This means that during La Niña (SST Nino 3.4 < −0.5 K) in the MC, and El Niño (SST Nino 3.4 > +0.5 K) in the PO, warmer SSTs in the MC and PO produce more active deep convection that tends to force the air upward to the tropopause layer and increase the temperature gradient there. The intra-seasonal variation in S-ab* during slow and fast episodes of the Madden–Julian Oscillation (MJO) demonstrates that eastward propagation of positive S-ab* is associated with organized deep convection. This suggests that convective activity in the tropics is a major control on variations in tropopause sharpness at intra-seasonal to interannual time-scales.

Noersomadi Noersomadi et al.
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Status: final response (author comments only)
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Noersomadi Noersomadi et al.
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Short summary
Characteristics of static stability (N2) in the tropical tropopause are analyzed using 0.1 km vertical resolution temperature profiles retrieved from COSMIC GNSS-RO. We define the tropopause inversion layer (TIL) by the sharp increase in N2 across the cold point tropopause (CPT) and the thickness of the enhanced peak in N2 just above CPT. We investigated the TIL at the intra-seasonal to inter annual time scales above the Maritime Continent and Pacific Ocean with different land-sea distribution.
Characteristics of static stability (N2) in the tropical tropopause are analyzed using 0.1 km...