Combining geometrical optics (GO) and wave optics (WO), the COSMIC data analysis and archive center (CDAAC) retrieved two sets of dry atmosphere temperatures (T) from COSMIC GPS radio occultation (GPS-RO), which are called atmPrf2010 and atmPrf2013. In atmPrf2010, the sewing height between WO and GO varies between 10 and 20 km, but is fixed at 20 km for atmPrf2013. The height resolution of the atmPrf2010 depends on the sewing height, while the T profiles by atmPrf2013 are smoothed over 500 m. We also derived T by applying WO throughout the troposphere and the stratosphere up to a 30-km altitude, which is called rishfsi2013. The three retrievals have different characteristics in the height resolution around the tropopause. Therefore, we aim to examine a possible discrepancy in the statistical results of the cold-point tropopause (CPT) and the lapse rate tropopause (LRT) among the three datasets, conducting their inter-comparisons as well as the comparison between GPS-RO and the simultaneous radiosonde dataset. We investigate the T variations in the upper troposphere and lower stratosphere (UTLS) over the tropics from October 1, 2011, to March 31, 2012, when radiosonde soundings were conducted as the CINDY-DYNAMO 2011 campaign. The mean T profiles are consistent between atmPrf2010 and atmPrf2013, but rishfsi2013 results are colder (warmer) than the CDAAC retrievals below (above) the tropopause. The mean T difference between atmPrf2013 and atmPrf2010 is 0.17 K at the cold-point tropopause (CPT) and −0.38 K at the lapse rate tropopause (LRT). On the other hand, rishfsi2013 shows a colder T at CPT by −0.77 and −0.59 K relative to atmPrf2013 and atmPrf2010, respectively, and the warmer T by 0.60 and 0.20 Kd at LRT. During CINDY-DYNAMO, we found 134 radiosonde soundings that coincide with GPS-RO within ±3 h and are collocated within 200 km from GPS-RO. The mean T difference at CPT from the radiosondes is 0.32, 0.49 and −0.24 K for atmPrf2010, atmPrf2013 and rishfsi2013, respectively. Both atmPrf2013 and atmPrf2010 have a positive bias at CPT, while rishfsi2013 has a negative one. Similar comparisons at LRT are −0.45, −0.69 and −0.41 K, respectively, showing a negative bias for all GPS-RO retrievals. The results show that rishfsi2013 is consistent with the retrievals at CDAAC and the radiosondes. Due to its good height resolution, rishfsi2013 is useful for studies on mesoscale T perturbations in the UTLS.

We present new insights into post-sunrise ionospheric irregularities in Southeast Asia during the intense geomagnetic storm of 19–20 April 2024. By utilizing Total Electron Content (TEC) and Rate of TEC Change Index (ROTI) maps, along with ionosondes, we identified the emergence of post-sunset Equatorial Plasma Bubbles (EPBs)—plasma depletion structures and irregularities—in western Southeast Asia on 19 April. These EPBs moved eastward, and the irregularities dissipated before midnight after the EPBs covered approximately 10° of longitude. Interestingly, plasma density depletion structures persisted and turned westward after midnight until post-sunrise the following day. Concurrently, an increase in F-region height from midnight to sunrise, possibly induced by the storm’s electric field, facilitated the regeneration of irregularities in the residual plasma depletions during the post-sunrise period. The significant increase in F-region height was particularly pronounced in western Southeast Asia. As a result, post-sunrise irregularities expanded their latitudinal structure while propagating westward. These findings suggest that areas with decayed plasma depletion structures from post-sunset EPBs that last past midnight could be sites for creating post-sunrise irregularities during geomagnetic storms. The storm-induced electric fields produce EPBs and ionospheric irregularities at longitudes where the surviving plasma depletion structures of post-sunset EPBs are present.

The radio acoustic sounding system (RASS) with the equatorial atmosphere radar (EAR) at Koto Tabang, Indonesia was adapted to test the effects of the acoustic source location and acoustic frequency range on the continuous measurement of height profiles of temperature in the tropical troposphere. We installed the acoustic transmitting system by using six high-power horn speakers and four subwoofers. We developed a three-dimensional ray-tracing method of acoustic waves to predict the shape of acoustic wavefronts, accounting for the effects of the background winds on acoustic wave propagation. Then, we selected the appropriate antenna beam directions for EAR that satisfy the Bragg condition between the radar and acoustic wave propagation vectors. We carried out eight campaign observations in 2016, testing the performance of EAR–RASS. We found that the location and acoustic frequency range affected the RASS echoes. We also tested the compensation method of the background wind velocity with EAR to obtain the true sound speed. We intensively analyzed the RASS results from August 29 to September 3, 2016, when radiosondes were launched 12 times from the EAR site. We successfully retrieved the temperature profiles from RASS from 2 to 6–14 km with time and height resolutions of about 10 min and 150 m, respectively. Some temperature profiles were obtained up to about the tropopause at 17 km, although the observation period was short. During the RASS campaign, we detected a few interesting events regarding temperature variations as well as large perturbations in the three components of wind velocity.

Using COSMIC GPS Radio Occultation (RO) observations from January 2007 to December 2016, we retrieved temperature profiles with the height resolution of about 0.1 km in the upper troposphere and lower stratosphere (UTLS). We investigated the distribution of static stability (N²) and the zonal structure of the tropopause inversion layer (TIL) in the tropics, where a large change in the temperature gradient occurs associated with sharp variations in N². We show the variations in the mean N² profiles in coordinates relative to the cold-point tropopause (CPT). A very thin (<1 km) layer is found with average maximum N² in the range of 11.0–$\mathrm{12.0}\times {\mathrm{10}}^{-\mathrm{4}}$ s⁻². The mean and standard deviation of TIL sharpness, defined as the difference between the maximum N² (max⁡N²) and minimum N² (min⁡N²) within ±1 km of the CPT, is $(\mathrm{10.5}\pm \mathrm{3.7})\times {\mathrm{10}}^{-\mathrm{4}}$ s⁻². The max⁡N² is typically located within 0.5 km above CPT. We focused on the variation in TIL sharpness in two longitude regions, 90–150^∘ E (Maritime Continent; MC) and 170–230^∘ E (Pacific Ocean; PO), with different land–sea distribution. Seasonal variations in TIL sharpness and thickness were related to the deep convective activity represented by low outgoing longwave radiation (OLR) during the Australian and Asian monsoons. The deviation from the mean sharpness (sharpness anomaly) was out of phase with the OLR anomaly in both the MC and PO. The correlation between the sharpness anomaly over the MC and PO and the sea surface temperature (SST) Niño 3.4 index was −0.66 and +0.88, respectively. During La Niña (SST Niño 3.4 $<-\mathrm{0.5}$ K) in the MC and El Niño (SST Niño 3.4 $>+\mathrm{0.5}$ 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 intraseasonal variation in sharpness anomaly during slow and fast episodes of the Madden–Julian Oscillation (MJO) demonstrates that eastward propagation of the positive sharpness anomaly is associated with organized deep convection. Deep convection during MJO will tend to decrease N² below CPT and increase N² above CPT, thus enlarging the TIL sharpness. Convective activity in the tropics is a major control on variations in tropopause sharpness at intraseasonal to interannual timescales.

This research aims to investigate the dynamic of static stability (N2), potential energy of gravity waves (Ep), and vortex in the stratospheric northern hemisphere during 2012-2013 winter using temperature (T) and zonal wind (u) data from NCEP-DOE Reanalysis II. The results showed two occurrences of decreasing N2 ascociated with reversal of u in the first and third week of December 2012 were believed as a trigger of Sudden Stratospheric Warmings (SSW) on January 7, 2013. There was a flow from the polar to the tropics region during the SSW event. It caused the tropopause folding in the sub-tropic region indicated by the distribution of Ep on January 24, 2013. This tropopause folding triggered the convective activity over the Indonesian continents as shown by the negative OLR anomaly from 22 to 26 January 2013. The impact of SSW event in the northern hemisphere to the convective activity was 20%. This results showed the interaction between stratosphere and troposphere and also the teleconnection between the polar and the tropics. ABSTRAKPenelitian ini bertujuan menyelidiki dinamika stabilitas statis (N2), energi potensial gelombang gravitas (Ep), dan pusaran angin di lapisan stratosfer Belahan Bumi Utara (BBU) selama musim dingin 2012-2013 menggunakan data temperatur (T) dan komponen angin zonal (u) dari NCEP-DOE Reanalysis II. Hasil riset menunjukkan bahwa dua kejadian penurunan N2 pada pekan awal dan ketiga bulan Desember 2012 diyakini sebagai pemicu kejadian Sudden Stratosphere Warmings (SSW) tanggal 7 Januari 2013. Pada saat terjadi SSW terdapat aliran dari kutub menuju tropis. Aliran ini mengakibatkan terjadinya pelipatan lapisan tropopause di wilayah sub-tropis yang terlihat pada distribusi Ep tanggal 24 Januari 2013. Pelipatan lapisan tropopause ini kemudian memicu aktivitas konvektif di atas wilayah Indonesia yang ditandai oleh anomali OLR negatif antara tanggal 22-26 Januari 2013. Dampak kejadian SSW di BBU terhadap aktivitas konvektif di atas wilayah kepulauan Indonesia sebesar 20%. Hasil ini membuktikan interaksi antara lapisan stratosfer dan troposfer serta telekoneksi wilayah kutub dan tropis.