Atmospheric diurnal and semi-diurnal variations observed with GPS radio occultation soundings

Abstract. Diurnal and semi-diurnal variations, driven by solar forcing, are two fundamental modes in the Earth's weather and climate system. Radio occultation (RO) measurements from the six COSMIC satellites (Constellation Observing System for Meteorology Ionosphere and Climate) provide rather uniform global coverage with high vertical resolution, all-weather and diurnal sampling capability. This paper analyzes the diurnal and semi-diurnal variations of both temperature and refractivity from two-year (2007–2008) COSMIC RO measurements in the troposphere and stratosphere. The RO observations reveal both propagating and trapped vertical structures of diurnal and semi-diurnal variations, including transition regions near the tropopause where data with high vertical resolution are critical. In the tropics the diurnal amplitude in refractivity decreases with altitude from a local maximum in the planetary boundary layer and reaches the minimum around 14 km and then further increase amplitude in the stratosphere. The upward propagating component of the migrating diurnal tides in the tropics is clearly captured by the GPS RO measurements, which show a downward progression in phase from upper troposphere to the stratopause with a vertical wavelength of about 25 km. Below 500 hPa (~5.5 km), seasonal variations of the peak diurnal amplitude in the tropics follow the solor forcing change in latitude, while at 30 km the seasonal pattern reverses with the diurnal amplitude peaking at the opposite side of the equator relative to the solar forcing. Polar regions shows large diurnal variations in the stratosphere with strong seasonal variations and the cause(s) of these variations require further investigations.

Download Full-text

Atmospheric diurnal variations observed with GPS radio occultation soundings

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-6889-2010 ◽

2010 ◽

Vol 10 (14) ◽

pp. 6889-6899 ◽

Cited By ~ 16

Author(s):

F. Xie ◽

D. L. Wu ◽

C. O. Ao ◽

A. J. Mannucci

Keyword(s):

Radio Occultation ◽

Local Maximum ◽

Diurnal Variations ◽

Vertical Resolution ◽

Tidal Amplitude ◽

Solar Forcing ◽

Summer Hemisphere ◽

High Vertical Resolution ◽

Global Coverage ◽

The Tropics

Abstract. The diurnal variation, driven by solar forcing, is a fundamental mode in the Earth's weather and climate system. Radio occultation (RO) measurements from the six COSMIC satellites (Constellation Observing System for Meteorology, Ionosphere and Climate) provide nearly uniform global coverage with high vertical resolution, all-weather and diurnal sampling capability. This paper analyzes the diurnal variations of temperature and refractivity from three-year (2007–2009) COSMIC RO measurements in the troposphere and stratosphere between 30° S and 30° N. The RO observations reveal both propagating and trapped vertical structures of diurnal variations, including transition regions near the tropopause where data with high vertical resolution are critical. In the tropics the diurnal amplitude in refractivity shows the minimum around 14 km and increases to a local maximum around 32 km in the stratosphere. The upward propagating component of the migrating diurnal tides in the tropics is clearly captured by the GPS RO measurements, which show a downward progression in phase from stratopause to the upper troposphere with a vertical wavelength of about 25 km. At ~32 km the seasonal variation of the tidal amplitude maximizes at the opposite side of the equator relative to the solar forcing. The vertical structure of tidal amplitude shows strong seasonal variations and becomes asymmetric along the equator and tilted toward the summer hemisphere in the solstice months. Such asymmetry becomes less prominent in equinox months.

Download Full-text

An assessment of differences in lower stratospheric temperature records from (A)MSU, radiosondes, and GPS radio occultation

Atmospheric Measurement Techniques ◽

10.5194/amt-4-1965-2011 ◽

2011 ◽

Vol 4 (9) ◽

pp. 1965-1977 ◽

Cited By ~ 21

Author(s):

F. Ladstädter ◽

A. K. Steiner ◽

U. Foelsche ◽

L. Haimberger ◽

C. Tavolato ◽

...

Keyword(s):

Time Series ◽

Radio Occultation ◽

Sampling Error ◽

Vertical Resolution ◽

Stratospheric Temperature ◽

Microwave Sounding ◽

The Difference ◽

Temperature Records ◽

Atmospheric Variations ◽

The Tropics

Abstract. Uncertainties for upper-air trend patterns are still substantial. Observations from the radio occultation (RO) technique offer new opportunities to assess the existing observational records there. Long-term time series are available from radiosondes and from the (Advanced) Microwave Sounding Unit (A)MSU. None of them were originally intended to deliver data for climate applications. Demanding intercalibration and homogenization procedures are required to account for changes in instrumentation and observation techniques. In this comparative study three (A)MSU anomaly time series and two homogenized radiosonde records are compared to RO data from the CHAMP, SAC-C, GRACE-A and F3C missions for September 2001 to December 2010. Differences of monthly anomalies are examined to assess the differences in the datasets due to structural uncertainties. The difference of anomalies of the (A)MSU datasets relative to RO shows a statistically significant trend within about (−0.2±0.1) K/10 yr (95% confidence interval) at all latitudes. This signals a systematic deviation of the two datasets over time. The radiosonde network has known deficiencies in its global coverage, with sparse representation of most of the southern hemisphere, the tropics and the oceans. In this study the error that results from sparse sampling is estimated and accounted for by subtracting it from radiosonde and RO datasets. Surprisingly the sampling error correction is also important in the Northern Hemisphere (NH), where the radiosonde network is dense over the continents but does not capture large atmospheric variations in NH winter. Considering the sampling error, the consistency of radiosonde and RO anomalies is improving substantially; the trend in the anomaly differences is generally very small. Regarding (A)MSU, its poor vertical resolution poses another problem by missing important features of the vertical atmospheric structure. This points to the advantage of homogeneously distributed measurements with high vertical resolution.

Download Full-text

Tropospheric dry layers in the tropical western Pacific: comparisons of GPS radio occultation with multiple data sets

Atmospheric Measurement Techniques ◽

10.5194/amt-10-1093-2017 ◽

2017 ◽

Vol 10 (3) ◽

pp. 1093-1110 ◽

Cited By ~ 11

Author(s):

Therese Rieckh ◽

Richard Anthes ◽

William Randel ◽

Shu-Peng Ho ◽

Ulrich Foelsche

Keyword(s):

Radio Occultation ◽

Western Pacific ◽

Radiosonde Data ◽

Data Sets ◽

Vertical Resolution ◽

Gps Radio Occultation ◽

Tropical Western Pacific ◽

Multiple Data ◽

Multiple Data Sets ◽

The Tropics

Abstract. We use GPS radio occultation (RO) data to investigate the structure and temporal behavior of extremely dry, high-ozone tropospheric air in the tropical western Pacific during the 6-week period of the CONTRAST (CONvective TRansport of Active Species in the Tropics) experiment (January and February 2014). Our analyses are aimed at testing whether the RO method is capable of detecting these extremely dry layers and evaluating comparisons with in situ measurements, satellite observations, and model analyses. We use multiple data sources as comparisons, including CONTRAST research aircraft profiles, radiosonde profiles, AIRS (Atmospheric Infrared Sounder) satellite retrievals, and profiles extracted from the ERA (ERA-Interim reanalysis) and the GFS (US National Weather Service Global Forecast System) analyses, as well as MTSAT-2 satellite images. The independent and complementary radiosonde, aircraft, and RO data provide high vertical resolution observations of the dry layers. However, they all have limitations. The coverage of the radiosonde data is limited by having only a single station in this oceanic region; the aircraft data are limited in their temporal and spatial coverage; and the RO data are limited in their number and horizontal resolution over this period. However, nearby observations from the three types of data are highly consistent with each other and with the lower-vertical-resolution AIRS profiles. They are also consistent with the ERA and GFS data. We show that the RO data, used here for the first time to study this phenomenon, contribute significant information on the water vapor content and are capable of detecting layers in the tropics and subtropics with extremely low humidity (less than 10 %), independent of the retrieval used to extract moisture information. Our results also verify the quality of the ERA and GFS data sets, giving confidence to the reanalyses and their use in diagnosing the full four-dimensional structure of the dry layers.

Download Full-text

Global distribution of vertical wavenumber spectra in the lower stratosphere observed using high-vertical-resolution temperature profiles from COSMIC GPS radio occultation

Annales Geophysicae ◽

10.5194/angeo-34-203-2016 ◽

2016 ◽

Vol 34 (2) ◽

pp. 203-213 ◽

Cited By ~ 2

Author(s):

◽

T. Tsuda

Keyword(s):

Annual Cycle ◽

Radio Occultation ◽

Time Lag ◽

Tropical Region ◽

Vertical Resolution ◽

Spectral Parameters ◽

Height Range ◽

Gps Radio Occultation ◽

Mountainous Regions ◽

High Vertical Resolution

Abstract. We retrieved temperature (T) profiles with a high vertical resolution using the full spectrum inversion (FSI) method from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) GPS radio occultation (GPS-RO) data from January 2007 to December 2009. We studied the characteristics of temperature perturbations in the stratosphere at 20–27 km altitude. This height range does not include a sharp jump in the background Brunt–Väisälä frequency squared (N2) near the tropopause, and it was reasonably stable regardless of season and latitude. We analyzed the vertical wavenumber spectra of gravity waves (GWs) with vertical wavelengths ranging from 0.5 to 3.5 km, and we integrated the (total) potential energy EpT. Another integration of the spectra from 0.5 to 1.75 km was defined as EpS for short vertical wavelength GWs, which was not studied with the conventional geometrical optics (GO) retrievals. We also estimated the logarithmic spectral slope (p) for the saturated portion of spectra with a linear regression fitting from 0.5 to 1.75 km.Latitude and time variations in the spectral parameters were investigated in two longitudinal regions: (a) 90–150° E, where the topography was more complicated, and (b) 170–230° E, which is dominated by oceans. We compared EpT, EpS, and p, with the mean zonal winds (U) and outgoing longwave radiation (OLR). We also show a ratio of EpS to EpT and discuss the generation source of EpS. EpT and p clearly showed an annual cycle, with their maximum values in winter at 30–50° N in region (a), and 50–70° N in region (b), which was related to the topography. At 30–50° N in region (b), EpT and p exhibited some irregular variations in addition to an annual cycle. In the Southern Hemisphere, we also found an annual oscillation in EpT and p, but it showed a time lag of about 2 months relative to U. Characteristics of EpTand p in the tropical region seem to be related to convective activity. The ratio of EpT to the theoretical model value, assuming saturated GWs, became larger in the equatorial region and over mountainous regions.

Download Full-text

Atmospheric QBO and ENSO indices with high vertical resolution from GNSS radio occultation temperature measurements

10.5194/amt-2017-226-rc4 ◽

2017 ◽

Author(s):

Anonymous

Keyword(s):

Radio Occultation ◽

Temperature Measurements ◽

Vertical Resolution ◽

High Vertical Resolution ◽

Enso Indices

Download Full-text

Diurnal variations of cloud and relative humidity profiles across the tropics

Scientific Reports ◽

10.1038/s41598-019-52437-6 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 5

Author(s):

H. Chepfer ◽

H. Brogniez ◽

V. Noel

Keyword(s):

Water Vapor ◽

Relative Humidity ◽

Diurnal Variations ◽

Lower Atmosphere ◽

Positive Anomaly ◽

Solar Forcing ◽

Early Afternoon ◽

Thin Cloud ◽

The Tropics ◽

Humidity Profiles

Abstract Even though the diurnal cycle of solar forcing on the climate system is well defined, the diurnal evolutions of water vapor and clouds induced by the solar forcing are not yet established across the tropics. Here we combine recent satellite observations of clouds profiles and relative humidity profiles to document the diurnal variations of the water vapor and clouds vertical distributions over all the tropics in June-July-August. While the daily mean water vapor and cloud profiles are different between land and ocean, their diurnal variations with respect to their daily means exhibit similar features. Relative humidity profiles and optically thin cloud fraction profiles vary together which maximize during night-time in the entire troposphere and a minimize in day-time. The fraction of optically opaque clouds peak in the free troposphere in the early afternoon, transforms into a high altitude positive anomaly of optically thin clouds from nightfall to sunrise. In addition, land regions exhibit a daily low thin cloud positive anomaly, while oceanic regions exposed to subsidence air motions exhibit positive anomalies of opaque clouds in the lower atmosphere during the second half of the night, which grow until sunrise.

Download Full-text

Atmospheric QBO and ENSO indices with high vertical resolution from GNSS radio occultation temperature measurements

10.5194/amt-2017-226 ◽

2017 ◽

Author(s):

Hallgeir Wilhelmsen ◽

Florian Ladstädter ◽

Barbara Scherllin-Pirscher ◽

Andrea K. Steiner

Keyword(s):

Radio Occultation ◽

Temperature Variability ◽

Temperature Measurements ◽

Time Lags ◽

Vertical Resolution ◽

Eof Analysis ◽

Atmospheric Variability ◽

Climate Trend ◽

High Vertical Resolution ◽

Altitude Level

Abstract. We provide atmospheric temperature variability indices for the tropical troposphere and stratosphere based on Global Navigation Satellite System (GNSS) Radio Occultation (RO) temperature measurements. By exploiting the high vertical resolution and the uniform distribution of the GNSS RO temperature soundings we introduce two approaches, both based on an empirical orthogonal function (EOF) analysis. The first method utilizes the whole vertical and horizontal RO temperature field from 30° S to 30° N and from 2 km to 35 km altitude. The resulting indices, the leading principle components, resemble the well-known patterns of the Quasi-Biennial Oscillation (QBO) and the El Niño-Southern Oscillation (ENSO) in the tropics. They provide some information on the vertical structure, however, they are not vertically resolved. The second method applies the EOF analysis on each altitude level separately and the resulting indices contain information on the horizontal variability at each densely available altitude level. They capture more variability than the indices from the first method and present a mixture of all variability modes contributing at the respective altitude level, including the QBO and ENSO. Compared to commonly used variability indices from QBO winds or ENSO sea surface temperature, these new indices cover the vertical details of the atmospheric variability. Using them as proxies for temperature variability is also of advantage because there is no further need to account for response time lags. Atmospheric variability indices as novel products from RO are expected to be of high benefit for studies on atmospheric dynamics and variability, for climate trend analysis, as well as for climate model evaluation.

Download Full-text

Atmospheric QBO and ENSO indices with high vertical resolution from GNSS radio occultation temperature measurements

Atmospheric Measurement Techniques ◽

10.5194/amt-11-1333-2018 ◽

2018 ◽

Vol 11 (3) ◽

pp. 1333-1346 ◽

Cited By ~ 8

Author(s):

Hallgeir Wilhelmsen ◽

Florian Ladstädter ◽

Barbara Scherllin-Pirscher ◽

Andrea K. Steiner

Keyword(s):

Radio Occultation ◽

Temperature Variability ◽

Temperature Measurements ◽

Time Lags ◽

Vertical Resolution ◽

Eof Analysis ◽

Atmospheric Variability ◽

Climate Trend ◽

High Vertical Resolution ◽

Altitude Level

Abstract. We provide atmospheric temperature variability indices for the tropical troposphere and stratosphere based on global navigation satellite system (GNSS) radio occultation (RO) temperature measurements. By exploiting the high vertical resolution and the uniform distribution of the GNSS RO temperature soundings we introduce two approaches, both based on an empirical orthogonal function (EOF) analysis. The first method utilizes the whole vertical and horizontal RO temperature field from 30∘ S to 30∘ N and from 2 to 35 km altitude. The resulting indices, the leading principal components, resemble the well-known patterns of the Quasi-Biennial Oscillation (QBO) and the El Niño–Southern Oscillation (ENSO) in the tropics. They provide some information on the vertical structure; however, they are not vertically resolved. The second method applies the EOF analysis on each altitude level separately and the resulting indices contain information on the horizontal variability at each densely available altitude level. They capture more variability than the indices from the first method and present a mixture of all variability modes contributing at the respective altitude level, including the QBO and ENSO. Compared to commonly used variability indices from QBO winds or ENSO sea surface temperature, these new indices cover the vertical details of the atmospheric variability. Using them as proxies for temperature variability is also of advantage because there is no further need to account for response time lags. Atmospheric variability indices as novel products from RO are expected to be of great benefit for studies on atmospheric dynamics and variability, for climate trend analysis, as well as for climate model evaluation.

Download Full-text

Tropospheric dry layers in the TropicalWestern Pacific: Comparisons of GPS radio occultation with multiple data sets

10.5194/amt-2016-258 ◽

2016 ◽

Cited By ~ 1

Author(s):

Therese Rieckh ◽

Richard Anthes ◽

William Randel ◽

Shu-Peng Ho ◽

Ulrich Foelsche

Keyword(s):

Radio Occultation ◽

Radiosonde Data ◽

Vertical Resolution ◽

Significant Information ◽

Data Set ◽

Gps Radio Occultation ◽

Multiple Data ◽

Single Station ◽

Multiple Data Sets ◽

The Tropics

Abstract. We use GPS Radio Occultation (RO) data to investigate the structure and temporal behavior of extremely dry, high-ozone tropospheric air in the Tropical Western Pacific during the six-week period of the CONTRAST (CONvective TRansport of Active Species in the Tropics) experiment (January and February 2014). Our analyses are aimed at testing if the RO method is capable of detecting these extremely dry layers, and evaluating comparisons with in situ measurements, satellite observations, and model analyses. We use multiple data sources as comparisons, including CONTRAST research aircraft profiles, radiosonde profiles, AIRS (Atmospheric Infrared Sounder) satellite retrievals, and profiles extracted from the ERA (ERA-Interim Reanalysis) and the GFS (US National Weather Service Global Forecast System) analyses, as well as MTSAT-2 satellite images. The independent and complementary radiosonde, aircraft, and RO data provide high vertical resolution observations of the dry layers. However, they all have limitations. The coverage of the radiosonde data is limited by having only a single station in this oceanic region; the aircraft data are limited in their temporal and spatial coverage; and the RO data are limited in their number and horizontal resolution over this period. However, nearby observations from the three types of data are highly consistent with each other and with the lower-vertical resolution AIRS profiles. They are also consistent with the ERA and GFS data. We show that the RO data, used here for the first time to study this phenomenon, contribute significant information on the water vapor content and are capable of detecting layers in the tropics and subtropics with extremely low humidity (less than 10 %), independent of the retrieval used to extract moisture information. Our results also verify the quality of the ERA data set, giving confidence to the reanalysis and its use in diagnosing the full four-dimensional structure of the dry layers.

Download Full-text