Tropical Cold-Point Tropopause: Climatology, Seasonal Cycle, and Intraseasonal Variability Derived from COSMIC GPS Radio Occultation Measurements

Abstract The finescale structure of the tropical cold-point tropopause (CPT) is examined using high-resolution temperature profiles derived from Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) global positioning system (GPS) radio occultation measurements for 4 yr from September 2006 to August 2010. The climatology, seasonal cycle, and intraseasonal variability are analyzed for three CPT properties: temperature (T-CPT), pressure (P-CPT), and sharpness (S-CPT). Their relationships with tropospheric and stratospheric processes are also discussed. The climatological P-CPT is largely homogeneous in the deep tropics, whereas T-CPT and S-CPT exhibit local minima and maxima, respectively, at the equator in the vicinity of deep convection regions. All three CPT properties, however, show coherent seasonal cycle in the tropics; the CPT is colder, higher (lower in pressure), and sharper during boreal winter than during boreal summer. This seasonality is consistent with the seasonal cycle of tropical upwelling, which is largely driven by stratospheric and near-tropopause processes, although the amplitude of the seasonal cycle of T-CPT and S-CPT is modulated by tropospheric circulations. On intraseasonal time scales, P-CPT and T-CPT exhibit homogeneous variability in the deep tropics, whereas S-CPT shows pronounced local variability and seasonality. The wavenumber–frequency spectra reveal that intraseasonal variability of CPT properties is primarily controlled by Kelvin waves, with a nonnegligible contribution by Madden–Julian oscillation convection. The Kelvin waves, which are excited by deep convection but often propagate along the equator freely, explain the homogeneous P-CPT and T-CPT variabilities. On the other hand, the vertically tilted dipole of temperature anomalies, which is associated with convectively coupled equatorial waves, determines the local structure and seasonality of S-CPT variability.

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Tropical Intraseasonal Variability in the MRI-20km60L AGCM*

Journal of Climate ◽

10.1175/2008jcli2406.1 ◽

2009 ◽

Vol 22 (8) ◽

pp. 2006-2022 ◽

Cited By ~ 20

Author(s):

Ping Liu ◽

Yoshiyuki Kajikawa ◽

Bin Wang ◽

Akio Kitoh ◽

Tetsuzo Yasunari ◽

...

Keyword(s):

Intraseasonal Variability ◽

Power Spectra ◽

Cumulus Parameterization ◽

Boreal Summer ◽

Boreal Winter ◽

Loose Coupling ◽

Low Level ◽

Mature Phase ◽

The Mean ◽

Ceof Analysis

Abstract This study documents the detailed characteristics of the tropical intraseasonal variability (TISV) in the MRI-20km60L AGCM that uses a variant of the Arakawa–Schubert cumulus parameterization. Mean states, power spectra, propagation features, leading EOF modes, horizontal and vertical structures, and seasonality associated with the TISV are analyzed. Results show that the model reproduces the mean states in winds realistically and in convection comparable to that of the observations. However, the simulated TISV is less realistic. It shows low amplitudes in convection and low-level winds in the 30–60-day band. Filtered anomalies have standing structures. Power spectra and lag correlation of the signals do not propagate dominantly either in the eastward direction during boreal winter or in the northward direction during boreal summer. A combined EOF (CEOF) analysis shows that winds and convection have a loose coupling that cannot sustain the simulated TISV as realistically as that observed. In the composited mature phase of the simulated MJO, the low-level convergence does not lead convection clearly so that the moisture anomalies do not tilt westward in the vertical, indicating that the low-level convergence does not favor the eastward propagation. The less realistic TISV suggests that the representation of cumulus convection needs to be improved in this model.

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Influence of ENSO and MJO on the zonal structure of tropical tropopause inversion layer using high-resolution temperature profiles retrieved from COSMIC GPS Radio Occultation

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-6985-2019 ◽

2019 ◽

Vol 19 (10) ◽

pp. 6985-7000

Author(s):

◽

Toshitaka Tsuda ◽

Masatomo Fujiwara

Keyword(s):

Temperature Gradient ◽

Radio Occultation ◽

Deep Convection ◽

Inversion Layer ◽

Temperature Profiles ◽

Convective Activity ◽

Zonal Structure ◽

Gps Radio Occultation ◽

The Mean ◽

The Tropics

Abstract. 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 11.0–12.0×10-4 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 (10.5±3.7)×10-4 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 <-0.5 K) in the MC and El Niño (SST Niño 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 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.

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Diurnal Cycles of Synthetic Microwave Sounding Lower-Stratospheric Temperatures from Radio Occultation Observations, Reanalysis, and Model Simulations

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-21-0071.1 ◽

2021 ◽

Author(s):

Aodhan J Sweeney ◽

Qiang Fu

Keyword(s):

Diurnal Cycle ◽

Radio Occultation ◽

Lower Stratosphere ◽

Deep Convection ◽

Winter Season ◽

Boreal Winter ◽

Diurnal Cycles ◽

Stratospheric Temperature ◽

Diurnal Range ◽

Microwave Sounding

AbstractAn observationally-based global climatology of the temperature diurnal cycle in the lower stratosphere is derived from eleven different satellites with Global Positioning System-Radio Occultation (GPS-RO) measurements from 2006-2020. Methods used in our analysis allow for accurate characterization of global stratospheric temperature diurnal cycles, even in the high latitudes where the diurnal signal is small but longer timescale variability is large. A climatology of the synthetic Microwave Sounding Unit (MSU) and Advanced MSU (AMSU) Temperature in the Lower Stratosphere (TLS) is presented to assess the accuracy of diurnal cycle climatologies for the MSU and AMSU TLS observations, which have traditionally been generated by model data. The TLS diurnal temperature ranges are typically less than 0.4 K in all latitude bands and seasons investigated. It is shown that the diurnal range (maximum minus minimum temperature) of TLS is largest over southern hemisphere tropical land in the boreal winter season, indicating the important role of deep convection. The range, phase, and seasonality of the TLS diurnal cycle are generally well captured by the WACCM6 simulation and ERA5 reanalysis. We also present an observationally-based diurnal cycle climatology of temperature profiles from 300-10 hPa for various latitude bands and seasons and compare the ERA5 reanalysis with the observations.

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Association of Convection with the 5-Day Rossby–Haurwitz Wave

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-14-0316.1 ◽

2015 ◽

Vol 72 (9) ◽

pp. 3309-3321 ◽

Cited By ~ 4

Author(s):

Malcolm J. King ◽

Matthew C. Wheeler ◽

Todd P. Lane

Keyword(s):

Large Scale ◽

Southern Oscillation ◽

Tropical Convection ◽

Marshall Islands ◽

Eastern Pacific ◽

Boreal Summer ◽

Boreal Winter ◽

Tropical Andes ◽

Quasi Biennial Oscillation ◽

Frequency Spectra

Abstract The seasonality, regionality, and nature of the association between tropical convection and the 5-day wavenumber-1 Rossby–Haurwitz wave are examined. Spectral coherences between daily outgoing longwave radiation (OLR), a proxy for convection, and 850-hPa zonal wind over the period January 1979–February 2013 are compared for different seasons and for phases of El Niño–Southern Oscillation (ENSO) and the quasi-biennial oscillation (QBO). Increased coherence, indicating a stronger association, occurs in boreal spring and autumn, with slightly reduced coherence in boreal summer and significantly reduced coherence in boreal winter. The regionality of the association is examined using lagged-regression techniques. Significant local signals in tropical convection are found over West Africa, the tropical Andes, the eastern Pacific Ocean, and the Marshall Islands. The relative phasing between the 5-day wave wind and OLR signals is in quadrature in Africa and the Marshall Islands, in phase with easterlies over the Andes, and out of phase with easterlies over the eastern Pacific. Frequency spectra of precipitation averaged over the identified local regions reveal spectral peaks in the 4–6-day range. The phasing between the large-scale wind and local convection signals suggests that the 5-day wave is actively modulating the convection around the Americas.

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Tropospheric methane in the tropics – first year from IASI hyperspectral infrared observations

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-6337-2009 ◽

2009 ◽

Vol 9 (17) ◽

pp. 6337-6350 ◽

Cited By ~ 83

Author(s):

C. Crevoisier ◽

D. Nobileau ◽

A. M. Fiore ◽

R. Armante ◽

A. Chédin ◽

...

Keyword(s):

Seasonal Cycle ◽

Atmospheric Transport ◽

Deep Convection ◽

High Spectral Resolution ◽

Boreal Winter ◽

Monsoon Period ◽

Transport Pathways ◽

Geographical Patterns ◽

Methane Distribution ◽

The Tropics

Abstract. Simultaneous observations from the Infrared Atmospheric Sounding Interferometer (IASI) and from the Advanced Microwave Sounding Unit (AMSU), launched together onboard the European MetOp platform in October 2006, are used to retrieve a mid-to-upper tropospheric content of methane (CH4) in clear-sky conditions, in the tropics, over sea, for the first 16 months of operation of MetOp (July 2007–October 2008). With its high spectral resolution, IASI provides nine channels in the 7.7 μm band highly sensitive to CH4 with reduced sensitivities to other atmospheric variables. These channels, sensitive to both CH4 and temperature, are used in conjunction with AMSU channels, only sensitive to temperature, to decorrelate both signals through a non-linear inference scheme based on neural networks. A key point of this approach is that no use is made of prior information in terms of methane seasonality, trend, or geographical patterns. The precision of the retrieval is estimated to be about 16 ppbv (~0.9%). Features of the retrieved methane space-time distribution include: (1) a strong seasonal cycle of 30 ppbv in the northern tropics with a maximum in January–March and a minimum in July–September, and a flat seasonal cycle in the southern tropics, in agreement with in-situ measurements; (2) a latitudinal decrease of 30 ppbv from 20° N to 20° S, in boreal spring and summer, lower than what is observed at the surface but in excellent agreement with tropospheric aircraft measurements; (3) geographical patterns in good agreement with simulations from the atmospheric transport and chemistry model MOZART-2, but with a higher variability and a higher concentration in boreal winter; (4) signatures of CH4 emissions transported to the middle troposphere such as a large plume of elevated tropospheric methane south of the Asian continent, which might be due to Asian emissions from rice paddies uplifted by deep convection during the monsoon period and then transported towards Indonesia. In addition to bringing a greatly improved view of methane distribution, these results from IASI should provide a means to observe and understand atmospheric transport pathways of methane from the surface to the upper troposphere.

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Comparison of Seasonal foEs and fbEs Occurrence Rates Derived from Global Digisonde Measurements

Atmosphere ◽

10.3390/atmos12121558 ◽

2021 ◽

Vol 12 (12) ◽

pp. 1558

Author(s):

Dawn K. Merriman ◽

Omar A. Nava ◽

Eugene V. Dao ◽

Daniel J. Emmons

Keyword(s):

Southern Hemisphere ◽

Lower Limit ◽

Northern Hemisphere ◽

Radio Occultation ◽

Austral Summer ◽

Peak Frequency ◽

Boreal Summer ◽

Gps Radio Occultation ◽

Drastic Decrease ◽

Sporadic E

A global climatology of sporadic-E occurrence rates (ORs) based on ionosonde measurements is presented for the peak blanketing frequency, fbEs, and the ordinary mode peak frequency of the layer, foEs. ORs are calculated for a variety of sporadic-E frequency thresholds: no lower limit, 3, 5, and 7 MHz. Seasonal rates are calculated from 64 Digisonde sites during the period 2006–2020 using ionograms either manually or automatically scaled with ARTIST-5. Both foEs and fbEs ORs peak in the Northern Hemisphere during the boreal summer, with a decrease by roughly a factor of 2–3 in fbEs rates relative to foEs rates without a lower threshold on the sporadic-E intensity. This ratio of foEs to fbEs OR increases with increasing sporadic-E intensity, up to a factor of 5 for the 7 MHz threshold. An asymmetry is observed with the Southern Hemisphere peaks during the austral summer, with slightly lower rates compared with the Northern Hemisphere during the boreal summer. A drastic decrease in ORs is observed for the higher intensity thresholds, such that the fbEs occurrence rates for 7 MHz are nearly zero during most locations and seasons. These updated occurrence rates can be used for future statistical comparisons with GPS radio occultation-based sporadic-E occurrence rates.

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Association of Tropical Cirrus in the 10–15-km Layer with Deep Convective Sources: An Observational Study Combining Millimeter Radar Data and Satellite-Derived Trajectories

Journal of the Atmospheric Sciences ◽

10.1175/jas3627.1 ◽

2006 ◽

Vol 63 (2) ◽

pp. 480-503 ◽

Cited By ~ 55

Author(s):

Gerald G. Mace ◽

Min Deng ◽

Brian Soden ◽

Ed Zipser

Keyword(s):

Deep Convection ◽

Source Region ◽

Winter Monsoon ◽

Boreal Summer ◽

Doppler Velocity ◽

Boreal Winter ◽

Radar Observations ◽

Back Trajectories ◽

Cloud Radar ◽

Cloud Properties

Abstract In this paper, millimeter cloud radar (MMCR) and Geosynchronous Meteorological Satellite (GMS) data are combined to study the properties of tropical cirrus that are common in the 10–15-km layer of the tropical troposphere in the western Pacific. Millimeter cloud radar observations collected by the Atmospheric Radiation Measurement program on the islands of Manus and Nauru in the western and central equatorial Pacific during a 12-month period spanning 1999 and 2000 show differences in cirrus properties: over Manus, where clouds above 7 km are observed 48% of the time, the cirrus are thicker and warmer on average and the radar reflectivity and Doppler velocity are larger; over Nauru clouds above 7 km are observed 23% of time. To explain the differences in cloud properties, the relationship between tropical cirrus and deep convection is examined by combining the radar observations with GMS satellite-derived back trajectories. Using a data record of 1 yr, it is found that 47% of the cirrus observed over Manus can be traced to a deep convective source within the past 12 h while just 16% of the cirrus observed over Nauru appear to have a convective source within the previous 12 h. Of the cirrus that can be traced to deep convection, the evolution of the radar-observed cloud properties is examined as a function of apparent cloud age. The radar Doppler moments and ice water path of the observed cirrus at both sites generally decrease as the cirrus age increase. At Manus, it is found that cirrus during boreal winter typically advect over the site from the southeast from convection associated with the winter monsoon, while during boreal summer, the trajectories are mainly from the northeast. The properties of these two populations of cirrus are found to be different, with the winter cirrus having higher concentrations of smaller particles. Examining statistics of the regional convection using Tropical Rainfall Measuring Mission (TRMM), it is found that the properties of the winter monsoon convection in the cirrus source region are consistent with more intense convection compared to the convection in the summer source region.

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The Relationship between ITCZ Location and Cross-Equatorial Atmospheric Heat Transport: From the Seasonal Cycle to the Last Glacial Maximum

Journal of Climate ◽

10.1175/jcli-d-12-00467.1 ◽

2013 ◽

Vol 26 (11) ◽

pp. 3597-3618 ◽

Cited By ~ 194

Author(s):

Aaron Donohoe ◽

John Marshall ◽

David Ferreira ◽

David Mcgee

Keyword(s):

Seasonal Cycle ◽

Climate Models ◽

Regression Coefficient ◽

Boreal Summer ◽

Boreal Winter ◽

Atmospheric Heat Transport ◽

Atmospheric Heat ◽

The Relationship ◽

The Last Glacial Maximum ◽

The Last Glacial

Abstract The authors quantify the relationship between the location of the intertropical convergence zone (ITCZ) and the atmospheric heat transport across the equator (AHTEQ) in climate models and in observations. The observed zonal mean ITCZ location varies from 5.3°S in the boreal winter to 7.2°N in the boreal summer with an annual mean position of 1.65°N while the AHTEQ varies from 2.1 PW northward in the boreal winter to 2.3 PW southward in the boreal summer with an annual mean of 0.1 PW southward. Seasonal variations in the ITCZ location and AHTEQ are highly anticorrelated in the observations and in a suite of state-of-the-art coupled climate models with regression coefficients of −2.7° and −2.4° PW−1 respectively. It is also found that seasonal variations in ITCZ location and AHTEQ are well correlated in a suite of slab ocean aquaplanet simulations with varying ocean mixed layer depths. However, the regression coefficient between ITCZ location and AHTEQ decreases with decreasing mixed layer depth as a consequence of the asymmetry that develops between the winter and summer Hadley cells as the ITCZ moves farther off the equator. The authors go on to analyze the annual mean change in ITCZ location and AHTEQ in an ensemble of climate perturbation experiments including the response to CO2 doubling, simulations of the Last Glacial Maximum, and simulations of the mid-Holocene. The shift in the annual average ITCZ location is also strongly anticorrelated with the change in annual mean AHTEQ with a regression coefficient of −3.2° PW−1, similar to that found over the seasonal cycle.

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Radio occultation bending angle anomalies during tropical cyclones

Atmospheric Measurement Techniques ◽

10.5194/amt-4-1053-2011 ◽

2011 ◽

Vol 4 (6) ◽

pp. 1053-1060 ◽

Cited By ~ 10

Author(s):

R. Biondi ◽

T. Neubert ◽

S. Syndergaard ◽

J. K. Nielsen

Keyword(s):

Radio Occultation ◽

Lower Stratosphere ◽

Time Window ◽

Deep Convection ◽

Atomic Clock ◽

Space Station ◽

Radiation Balance ◽

Bending Angle ◽

Upper Troposphere ◽

Gps Radio Occultation

Abstract. The tropical deep convection affects the radiation balance of the atmosphere changing the water vapor mixing ratio and the temperature of the upper troposphere lower stratosphere. The aim of this work is to better understand these processes and to investigate if severe storms leave a significant signature in radio occultation profiles in the tropical tropopause layer. Using tropical cyclone best track database and data from different GPS radio occultation missions (COSMIC, GRACE, CHAMP, SACC and GPSMET), we selected 1194 profiles in a time window of 3 h and a space window of 300 km from the eye of the cyclone. We show that the bending angle anomaly of a GPS radio occultation signal is typically larger than the climatology in the upper troposphere and lower stratosphere and that a double tropopause during deep convection can easily be detected using this technique. Comparisons with co-located radiosondes, climatology of tropopause altitudes and GOES analyses are also shown to support the hypothesis that the bending angle anomaly can be used as an indicator of convective towers. The results are discussed in connection to the GPS radio occultation receiver which will be part of the Atomic Clock Ensemble in Space (ACES) payload on the International Space Station.

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