Project Managers Data Quality Report



Static pressure is available using two different systems: Research and Avionics.


Research static pressure is measured with a Paroscientific (MODEL 1000) with a stated accuracy of 0.01% of full scale. This measurement is output in the netCDF files as:



static pressure as measured using the fuselage holes


same as PSF. Used to choose reference variable if more than one instrument provides measurement of the same parameter


static pressure corrected for airflow effects (pcor)


same as PSFC. Used to choose reference variable if more than one instrument provides measurement of the same parameter


Use PSXC for the normal measure of pressure (e.g., in equation of state or hydrostatic equation).


Avionics static pressure is recorded from the GV avionics. This is slower than the Paroscientific measurement, but it has been corrected for airflow effects and it is certified for 'Reduced vertical separation minimum' (RVSM) through the calculation of pressure altitude.  RAF has no documentation on how Gulfstream and Honeywell corrected this pressure measurement, but the measurement has passed very strict FAA certification requirements.



Avionics static pressure



Temperature was measured using five different sensors on the GV:

Two heated dual element Harco sensors were used to measure the total temperature. These sensors are characterized by a moderate response rate but are unaffected by icing. A fifth measurement of temperature (slow and with some delay) was provided by the GV avionics instrumentation.

The Harco measurements were logged using analog channels, subject to a three stage calibration (sensor head bath calibration, A/D board calibration, final engineering calibration) and are affected by a variable recovery factor. The recovery factor is a function of altitude and mach number, and RAF is currently fine tuning the correction algorithms for the recovery factor.  A/D corrections are analog board specific and are logged in the project calibration files and accompanying RAF project hardware documentation.

There are currently complications of A/D calibrations and instability of the thermal environment of the GV DSM and amplifiers used to collect temperature data. A comparison with multiple radiosondes led RAF to believe that the avionics temperature is the most accurate measurement at this time. ATX was set to AT_A for this project.


Total air temperature from the heated HARCO sensor # 1 right


Total air temperature from the heated HARCO sensor # 2 right


Total air temperature from the heated HARCO sensor # 1 left


Total air temperature from the heated HARCO sensor # 2 left


Total air temperature from the avionics system


Ambient air temperature from the Rosemount system


Ambient temperature from the heated HARCO sensor # 1 right


Ambient temperature from the heated HARCO sensor # 2 right


Ambient temperature from the heated HARCO sensor # 1 left


Ambient temperature from the heated HARCO sensor # 2 left


Ambient temperature from the avionics system


Ambient temperature reference. This is usually the same as ATHR2 but can be replaced by another sensor output if ATHR2 experiences a problem on a particular flight. In such case a flight-by-flight report will note the change.


RAF recommends using ATX for the temperature in thermodynamic equations, etc.


Dewpoint temperature and vapor density:

Humidity was measured using two Buck Research 1011C cooled-mirror hygrometers that are normally used for measuring tropospheric humidity.  They have a sandwich of three Peltier elements to cool the mirror, and in comparison to earlier generations of cooled-mirror hygrometers, they have a much-improved capability to measure at low temperatures.  These sensors are assumed to measure dewpoint above 0°C and frostpoint below 0°C.  The instrument has a quoted accuracy of 0.1 °C over the -75 to +50 °C; however, based on examination of the measurements RAF is not comfortable with accuracies better 0.5 °C for dewpoint and 1 °C for frostpoint.  The cooled-mirror sensors have a slow response, in particular at lower temperatures, and this may give considerable differences between the measurements from the two units or when comparing with faster instruments.  Their cooling rates depend in part on the airflow through the sensor, and this may depend on the angle of the external stub relative to the airflow.  The angle may differ between the two sensors, and this may contribute to response-time differences between the sensors.  At very low temperatures the sensors may jump ("rail") to even lower temperatures; these data were removed from the dataset and replaced with a NAN.  The water vapor concentration derived from the chilled mirror sensors is used in other calculations (e.g., true airspeed). However, the impact of these out of bounds conditions on derived calculations that depend on humidity correction is very small at extremely low dew points, so omitting the dewpoint data below -72C has nearly no impact on the other variables.

The chilled mirror sensors are subject to flooding on rapid descents of the aircraft into the humid boundary layer. This results in temporary loss of the instruments ability to measure the dewpoint, which may last from 3 to 15 minutes, depending on conditions. This problem can also be seen in the form of "ringing", or a decaying sinusoidal oscillation of the signal, that appears after altitude changes, for example those following a period of cold soaking at high altitudes. During these periods it is advised to compare the data from both chilled mirrors and choose the one that recovers faster.


VCSEL Hygrometer was deployed for measuring atmospheric water vapor content throughout the troposphere and lower stratosphere using high sensitivity optical absorption methods, using a new, near-infrared, vertical cavity surface emitting laser (VCSEL) at 1854 nm. In conjunction with a compact, multipass, open air cell and digital signal processor (DSP) electronics, this sensor consumes very low power (< 5 W), is lightweight (< 2 kg excluding the inlet housing), and occupies only the space within an aperture plate. The use of the 1854 nm VCSEL allows for a limit of detection of <1 ppmv, a precision of 3% or 0.05 ppmv max, and a minimum sampling frequency of up to 25 Hz.



Dewpoint/frostpoint for left fuselage cooled-mirror sensor


Dewpoint for left cooled-mirror sensor


Dewpoint/frostpoint for right cooled-mirror sensor


Dewpoint for right cooled-mirror sensor


Reference dewpoint, from either right or left cooled-mirror sensor. Typically, DPLC was a better performing sensor and was used for DPXC. If DPRC was used, a note will be made in the flight specific discussion below.


Mixing ratio (g/kg) based on DPXC


VCSEL Moisture Number Density


Dewpoint calculated from the VCSEL H2O mixing ratio and ATX.


RAF recommends using DPXC as a slow 'tropospheric' variable, and DP_VXL or CONC_H2O_VXL as a fast-response variable.


Attack and Sideslip:

Measurements of attack and sideslip were done using the 5-hole nose cone pressure sensors, ADIFR and BDIFR.  Although sampled at 50 sps, internal filtering in the Mensor pressure sensors (model 6100) limits usefulness of high-rate analysis to about 5 Hz.


Vertical differential pressure


Attack angle. Determined from the vertical differential pressure of the radome gust probe.


Horizontal differential pressure


Sideslip angle. Determined from the horizontal differential pressure of the radome gust probe.

Both AKRD and SSLIP were calibrated using in-flight maneuvers.

Note that icing may affect the radome holes. In case the vertical differential pressure sensor holes are iced over, ADIFR is unavailable, consequently rendering the research airspeed measurement invalid. In such cases the avionics airspeed measurement was substituted and a note made in the flight specific section. On several HIPPO flights once the radome was affected by icing, it only recovered after another icing/thawing episode on the subsequent dip.


True airspeed:

True airspeed was also measured primarily using a Mensor 6100 sensor, thus limiting the effective response to 5 Hz.

The radome pitot tube system uses the center hole of the 5-hole nose cone in conjunction with the research static pressure ports on the fuselage aft of the entrance door.  A standard avionics pitot tube is also mounted on the fuselage aft of the radome, and this system is also referenced to the fuselage static ports aft of the main entrance door.  It was found during empirical analysis that the fuselage pitot system gave more consistent results in reverse-heading maneuvers; it is suspected that this is due to random pressure changes at the radome center hole as has been suggested by modeling.  The fuselage system is used for the calculation of the aircraft true airspeed, as well as for attack and sideslip angles.  True airspeed is also recorded from the aircraft avionics system, but this system is considered of slower response.  Measurements using the radome and fuselage pitot systems were corrected using in-flight maneuvers.



True airspeed using the radome system


True airspeed from the fuselage pitot system


True airspeed using the fuselage pitot system and adding humidity corrections to the calculations; this is mainly of benefit in tropical low-altitude flight


True airspeed from the avionics system


Reference true air speed. This is normally equal to TASF but TASR or TAS_A may be substituted in cases where TASF is compromised for any reason. This would be noted in the individual flight reports.

RAF recommends using TASX as the aircraft true air speed.


Position and ground speed:

The measurement of aircraft position (latitude, longitude and geometric altitude) and aircraft velocities relative to the ground are done using several sensors onboard the GV.


Novatel Omnistar-enabled GPS (Reference):  These data are sampled at 10 sps and averaged to 1 sps.  Omnistar-corrected measurements are available in real-time but accuracy may vary depending on the location. Generally, Omnistar-corrected position is accurate within 15 cm vertically and 10 cm horizontally, which was proven by comparing against a differential GPS measurements.  The values from this sensor start with a "G"; e.g.:


Latitude (recommended for general use)


Longitude (recommended for general use)


Geometric altitude (recommended for general use)


Ground speed


Ground speed in north direction


Ground speed in east direction


Quality factor of the Novatel GPS. Five is the highest quality with Omnistar HP correction, 6 cm horizontal, 12 cm vertical specified accuracy. Two is the lower quality Omnistar VBS corrected data with a sub 1 m specified accuracy, this level is usually seen on the edge of the Omnistar HP coverage area; One is the lowest quality, GPS-only position with a 10-15 m specified accuracy. Nine is a WAAS-augmented GPS with a 8 m accuracy. All estimates are based on a 99% confidence limit.


Reference altitude. This value is recommended for use for most applications. It is usually equal to GGALT. In rare cases where GGALT data were interrupted, the value will be substituted by the best available alternative such as GGALT_GMN, GGALTC or in the worst case, PALT.

These are good values to use for cases where the highest real-time accuracy is needed.  These variables are subsequently used to constrain the INS drift for the calculations of the GV winds; more about this below.


A secondary Garmin GPS system provided redundant position measurements that should be used during periods of noisy or missing Novatel Omnistar-corrected GPS data. The Garmin data are not corrected and the accuracy is within 10 meters. These variables have the same naming convention as the reference GPS above with a suffix _GMN.

During HIPPO-3 the aircraft data system experienced several crashes, causing a complete loss of position data. These intervals have been filled in using linear interpolation and noted in individual flight reports below. The interpolation is reasonably accurate because a) the aircraft remained on a predictable course during the outages and b) altitude change patterns were very predictable.


Honeywell inertial reference system 1 and 2:  The GV is equipped with three inertial systems.  Data from the first two of these are logged on the main aircraft data logger, with subscripts the latter having variable names with suffix "_IRS2".  The advantage of the IRS values is that they typically have very high sample rates and very little noise from measurement to measurement.  However, since they are based on accelerometers and gyroscopes, their values may drift with time.  The drift is corrected for by filtering the INS positions towards the GPS positions with a long time-constant filter; the filtered values have a "C" added to the end.



latitude from IRS 1, no GPS filtering


latitude from IRS 1, filtered towards GPS values


latitude from IRS 2, no GPS filtering


longitude from IRS 1, no GPS filtering


longitude from IRS 1, filtered towards GPS values


longitude from IRS 2, no GPS filtering


ground speed from IRS 1, no GPS filtering


ground speed from IRS 2, no GPS filtering


The choice of variables for position analysis depends on the type of analysis; in general the Novatel Omnistart GPS is sufficiently accurate.

Please note that when the GPS position is lost due to an ADS crash, IRS data are also lost. When the system later recovers, LATC, LONC and ALTC show deviations at the edges of the data gap. This is an artifact of the filtering algorithm and should be ignored.


Not all INS variables are output in the final data set, including IRS2. If you require more detailed INS data please contact RAF.


  • Attitude angles:

    Aircraft attitude angles are measured by the two Honeywell IRS units.


Pitch of the aircraft


Pitch of the aircraft from the second IRS


Roll of the aircraft


Roll of the aircraft from the second IRS


True heading of the aircraft


True heading of the aircraft from the second IRS

The values of pitch angle (PITCH) have been corrected using in-flight measurements to give approximately the same values as the aircraft attack angle (AKRD) for long, straight and level parts of flights; this correction is performed to give a near-zero mean updraft (WIC) over extended flight legs.  The variation from flight to flight of this offset is caused by small differences in the pre-flight alignment of the inertial navigation system.  No alignment correction has been applied to PITCH_IRS2.

  • Wind speeds:

    Wind speeds are derived from the 5-hole radome gust probe combined with other pressure, temperature and inertial measurements supported by GPS data. The use of the Mensor 6100 pressure sensors for ADIFR, BDIFR and radome dynamic pressure (QCF) results in the following limitations on the wind data: pressure measurements were sampled at 50 sps and thus resulting in power spectra to 25 Hz.  Examination of power spectra and specifications from Mensor indicate that the sensors have internal filters with a -3dB (half-power) cutoff at 12 Hz, resulting in a noticeable roll-off in the spectra beginning approximately at 6 to 7 Hz.  Users of wind data should be aware that contributions to covariances and dissipation calculations will be affected at and above these frequencies.

The following lists the most commonly used wind variables:


Wind vector, east component


Wind vector, east component, GPS corrected for INS drift


Wind vector, north component


Wind vector, north component, GPS corrected



Wind vector, longitudinal component


Wind vector, longitudinal component, GPS corrected


Wind vector, lateral component


Wind vector, lateral component, GPS corrected



Wind vector, vertical gust component


Wind vector, vertical gust component, GPS corrected



Wind speed, horizontal component


Wind speed, horizontal component, GPS corrected


Horizontal wind direction


Horizontal wind direction, GPS corrected

RAF recommends using the GPS corrected wind components, i.e., the variables ending in "C". Uncorrected wind variables may not be included in the final data release.

Liquid water content:

A PMS-King type liquid water content sensor was installed on the GV. The corrected liquid water content obtained from relating the power consumption (required to maintain a constant temperature) to liquid water content, taking into account the effect of convective heat losses.



Liquid water content derived from PLWC, g/m3


Raw dissipated power, watt

Note that the King probe is not optimized for the GV airspeeds. Changes in the airspeed and related heat transfer are not currently well quantified in the processing code and may result in the fluctuations in the PLWCC baseline. For estimating the liquid water content please use the signal height above the baseline, which may be smaller than the total signal magnitude.


Icing rate indicator

Rosemount Model 871FA Icing Rate Detector - Right Wing pylon Access Plate (RICE). The instrument reports a sharp spike when icing is detected, often coincident with a diversion between QCR and QCF, indicative of the radome tip icing.


The Microwave Temperature Profiler (MTP) was deployed. The MTP is a passive microwave radiometer, which measures the natural thermal emission from oxygen molecules in the earth-s atmosphere for a selection of elevation angles between zenith and nadir by scanning through an arc in the flight direction. The MTP observing frequencies are located on oxygen absorption lines at 56.363, 57.612 and 58.363 GHz. The measured brightness temperatures versus elevation angle are converted to air temperature versus altitude using a quasi-Bayesian statistical retrieval procedure. An altitude temperature profile (ATP) is produced in this manner every 18 seconds along the flight track. Temperature accuracy is approximately 1 K within 3 km of flight altitude, and < 2K within 6 km of flight altitude. Vertical resolution is approximately 150 meters at flight level, and approximately half the distance from the aircraft away from flight level. Data are provided in the form of altitude temperature profiles and color-coded temperature "curtains", and may be converted to isentropic cross sections.


CDP (Cloud Droplet Probe)

The CDP is a commercial instrument from Droplet Measuring Technologies (DMT). It measures the intensity of forward light scattering (4 - 12°) to determine the sizes of individual cloud droplets. An internal multi-channel analyzer assigns individual particles to bins, and the data interface outputs a histogram of particle size and concentration. On the NSF/NCAR C­‑130 and HIAPER, the CDP is mounted in a PMS canister. Variables output by the CDP instrument have _LWI suffix.


size range

2 - 50 µm diameter

concentration range

0 - 5,000 cm-3

number of size bins

10, 20, 30, or 40

sample area

200µm x 1.5mm

volume sample rate

30 cm3/s at airspeed 100 m/s

airspeed range

10 - 200 m/s

data interface

serial RS-232 or RS-422

data rate

10 histograms per second

more information:


2D-C imaging aerosol spectrometer

Ultra-High Sensitivity Aerosol Spectrometer - UHSAS

The UHSAS is a single-particle light scattering instrument. It uses a CW high energy laser diode, wide angle collection optics centered at 90°, and four stages of amplification to size aerosol particles according to their scattered light. It assigns bins to individual particles and outputs a histogram of particle size and concentration. The RAF version of this instrument has been highly modified from the commercially-available lab bench version.  It uses volume flow controllers to keep the flow constant over a wide range of operating pressures and temperatures. The probe mounts in a PMS canister. The variables output by UHSAS have the suffix _RWO.


The probe did not operate properly during the project due to multiple hardware maladjustments that were rectified after the project by the manufacturer. The size distribution and concentration data are inaccurate but the latter can be used for qualitative identification of presence of aerosols.


size range

75 - 1000 nm diameter

concentration range

0 - 18,000 cm-3

number of size bins


volume sample rate

1 cm3/s

data interface

serial RS-232

data rate

10 histograms per second


more information:


Data logging and averaging:

Analog data were logged at 500 sps and averaged to 1 sps. Serial data (e.g., RS-232), ARINC data (IRS units), etc. were recorded at the instrument-specific output rate.

The recordings listed for a given second contains measurements logged at e.g., 12:00:00.000 and until 12:00:01.  The value of "Time" corresponding to this interval is given a 12:00:00 in the released data set.

All measurements are "time-tagged" at the time of logging.  Subsequently these measurements are interpolated onto a regular grid and averaged.

RAF staff have reviewed the data set for instrumentation problems.  When an instrument has been found to be malfunctioning, specific time intervals are noted.  In those instances the bad data intervals have been filled in the netCDF data files with the missing data code of -32767.  In some cases a system may be out for an entire flight.








Polynomial coefficients





























































































The following table identifies the sensors serial numbers and calibrations that were used on the GV for HIPPO Global Phase 1:


Calibration data are not provided for temperatures because of the continuing work on A/D correction integration that affects calibration coefficients.

Data Quality Control



  • Vertical wind speed (WIC) data are reliable only during straight and level flight. Expect deviations whenever the aircraft is not in straight and level flight. For HIPPO there was very little straight and level flight and effort was made to tune the WIC processing to obtain good vertical wind in climbs and descents but deviations can still be seen.
  • DPRS, DPLS, DPRC, DPLC: dewpointers tend to overshoot and oscillate after rapid temperature increase on aircraft descents. Using best judgment, these overshoots are removed from DPXC, which is the recommended reference dewpoint variable, but are left in DPLC, which is the source variable for DPXC, for comparison. The operating range for both DPLC and DPRC is down to approximately -70C and values below that should not be used for quantitative analyses. DP_VXL (dewpoint measurement produced by VCSEL hygrometer) is not affected by rapid  temperature changes and should be used whenever the DPXC is missing, and for any kind of high resolution analyses.
  • Icing was a frequent occurrence during HIPPO-2. To detect icing conditions look for the onset of a difference between QCR and QCF in addition to spiking signals in PLWCC and RICE. The radome tip dynamic pressure sensor hole (the QCR variable) ices over very quickly in icing conditions, resulting in the lag in response or constant pressure reading. These data are not representative of flight conditions (refer to QCF instead) but are useful for identifying periods of icing early, so they were left in the dataset. Variables dependent on the QCR (for example TASR) will also be unusable during radome icing.
  • Sometimes the icing extended enough to reach the vertical differential pressure sensor holes on the radome (ADIFR). This measurement is critical for determining the true air speed (TASR and TASF) and when the radome holes freeze over, TASF (which is the source for the reference airspeed, TASX) becomes unavailable. In such cases TAS_A, the avionics true airspeed, was substituted into TASX to allow continuous record of particle and other data that rely upon TASX. In addition, ADIFR is the only measurement of the angle of attack and is directly used in the 3D wind calculations, so when this variable is lost the wind data are also irrecoverably lost.
  • PLWCC processing: the background output of the King hot wire probe is loosely coupled to zero using a sliding window average. Once a cloud is encountered the coupling unlatches and the liquid water content is calculated using the last background value as a reference. This sometimes results in artifacts if the baseline continues to drift as a function of airspeed. This is an algorithm flaw that will be addressed in the future through refinements in the PLWCC airspeed parameterization. Since the airspeed affects the baseline of the signal, please use the signal height above the baseline, which may be smaller than the total signal magnitude, for estimating the liquid water content.
  • 2D-C probe located on LWO has demonstrated elongated cloud droplet shapes once the droplets reach about 1 mm in diameter. The cause for this may be related to the air compression and flow artifacts near the leading edge of the wing and tip of the PMS can. This requires further investigation and more cloud data. Please keep in mind that elliptical shapes of the particles can lead to overestimation of the liquid water content derived from the 2D probe data.
  • UHSAS probe did respond to aerosol particles but had multiple hardware issues and misalignment of optical components that were identified after inspecting the data closely after the project. The issues were acknowledged and corrected by the manufacturer. Unfortunately, the size distribution and concentration data are both inaccurate and not recoverable. The concentration data are left in the final dataset only as a qualitative measure of the periods when the aircraft encountered increased aerosol concentrations.
  • Aircraft Data System (ADS) started experiencing a hardware issue believed to be caused by vibration on the aircraft. The issue manifested itself in loss of the screen image, subsequently disabling the onboard technician from monitoring the data. This on occasion resulted in the loss of one of the dewpointer data feeds when the instrument was flooded undetected on a dip and did not recover. The issue was rectified before RF07 by re-seating the CPUs on the main server's motherboard.



Flight specific notes:



RF01: No issues other than those common for all flights. Minor satcom losses, see technician notes.


RF02: No issues other than those common for all flights.


RF03: Icing of the radome encountered from 23:07 to 00:39. Only QCR was affected; ADIFR worked properly. No water vapor data on the last high ascent; depointers and VCSEL all lost signal below -75C frostpoint.


RF04: ADS screen froze at take-off, the technician could not monitor data properly. Very sparse data from the dewpointers; VCSEL worked well the entire flight. Use VCSEL data for all humidity reference for this flight.


RF05: ADS screen froze at take-off, the technician could not monitor data properly. ADIFR malfunctioned from 20:43 to 21:10 with no apparent icing; to recover the data continuously, TAS_A was used for the reference airspeed for this flight. Despite repeated cycling, the dewpointers did not work most of the flight. VCSEL worked well. Use VCSEL data for all humidity reference for this flight.


RF06: ADS system actually completely locked up at take-off and had to be restarted. At 21:25 data recording has resumed and ADS worked well for the rest of the flight. Error codes were recorded off of the main server. The right dewpointer went out of balance several times; use DPL and VCSEL for humidity data.


RF07: ADS system was repaired before this flight and did not exhibit any more abnormal behavior. No issues other than those common for all flights.


RF08: ADIFR signal was lost from 23:36 to 02:15 and did not recover despite rebooting the DSM; other nose DSM logged variables were not affected. ADIFR recovered on its own at 02:15 TAS_A is used for the reference airspeed on this flight. VCSEL and DPR did not work on this flight; VCSEL was apparently affected by microbial/fungus growth on mirrors in Honiara and DPR suffered an internal mechanical failure.


RF09: Nose DSM had intermittent issues at 22:05-22:08 and at 22:53, 23:01; no TAS substitutions were made due to the briefness of the outages.


RF10: Apparent partial icing or water ingestion of the QCR hole from 23:30 to 01:58. airspeed was not affected. Other parameters nominal.


RF11: Ice covered QCR on climb out and remained from 18:51 to 21:07. Airspeed was not affected.



April 7, 2011 Update


Changes to the HIPPO-2 production data, v. 2


WP3 is obsolete and removed from the data file.

TVIR, virtual temperature, is added to the data file.

Calculations for the dew point from the chilled mirror sensors (DPRC, DPLC, DPXC); THETA, THETAV, PALT are updated based on commonly accepted published algorithms. This change is insignificant and is mainly for data traceability purposes.

Specific details are below:


Variables renamed to properly and consistently reflect probe position on the GV:

  • All aerosol and cloud data previously referenced as xxx_LOI are now referenced as xxx_LWI
  • All aerosol and cloud data previously referenced as xxx_LCO are now referenced as xxx_LWO

UHSAS data are no longer included in the data set per community request. The data were not accurate and only could be used for qualitative assessment of presence of aerosols.

WP3 retirement: The IRS provides VSPD which is better (but needs some investigation to understand how it is processed and filtered). WP3 last appeared in the VOCALS and PLOWS datasets but was not used for the calculation of either WI or WIC in VOCALS and, while it was used to calculate WI in PLOWS, investigators were advised to use WIC instead (which depends on VSPD).

TVIR: The virtual temperature is the temperature of a dry-air parcel that would have the same density as the actual moist-air parcel.

DPxx: switch from Goff-Gratch formula to the Murphy-Koop algorithm.

THETA: Calculations based on Bolton (1980) are replaced with more accurate ones from Davies-Jones (2009); variable definition is changed to a more specific " pseudo-adiabatic equivalent potential temperature".

THETAE: abrupt deviations from other THETA variables are caused by the incomplete removal of the problematic dewpointer data from DPXC. Ignore these parts of the data.

PALT: use the International Standard Atmosphere or the equivalent U.S. Standard Atmosphere. The effects of the change are small but not entirely negligible, and this change makes the measurement consistent with the adopted standards for aviation. The differences are as follows:

  1. 1. The change in the constant for the low-altitude branch, to 44330.77 m, causes about a 5 m maximum change in results, with the maximum at 11000 m.
  1. 2. The change in the exponents for the low-altitude branch, to 0.1902632, causes at most a change of about 1 m in the results.
  1. 3. The change in the high-altitude branch increases with altitude, but at 120 mb (about 15 km) the change is about +5 m.

2D processing: improved algorithm is now in place, refer to: Sid2h Processing Software for details.

Feb 22, 2013 Update

December 18, 2012

HIPPO Global Data Change Notification

Dates affected: all phases, HIPPO-1 through HIPPO-5

Contact: P. Romashkin

Data affected: WI, WIC

Impact: Minimal

Description: An inconsistency in the processing of WI and WIC was discovered in which the two variables were calculated using a different vertical velocity for the different HIPPO deployments, leading essentially to a naming inconsistency. Serendipitously, another the inconsistency in the ASCII data tables for H-1 and 2 vs. H-3, H-4 and H-5 resulted in the correctly calculated data being available to the investigators: in H-1 and H-2, WI was included in the data, which was calculated using the more accurate vertical velocity; in H-3, H-4 and H-5 WIC was included, which was also calculated using the more accurate vertical velocity. At this time all five projects were re-processed to make the WI and WIC consistent across all five deployments. WIC is recommended for use and is calculated using the more accurate GPS-corrected vertical velocity VSPD_G.

This change is not expected to noticeably impact existing research because for the deployments 1 and 2 the WIC released at this time and recommended for future use is insignificantly different from the WI released previously.